%0 Artikel %@ 2296-7745 %A van Oostende, M. %A Hieronymi, M. %A Krasemann, H. %A Baschek, B. %D 2023 %J Frontiers in Marine Science %N 2685 %P 1052166 %R doi:10.3389/fmars.2023.1052166 %T Global ocean colour trends in biogeochemical provinces %U https://dx.doi.org/10.3389/fmars.2023.1052166 %X Satellite-derived ocean colour data provide continuous, daily measurements of global waters and are an essential tool for monitoring these waters in a changing climate. Merging observations from different satellite sensors is necessary for long-term and continuous climate research because the lifetime of these sensors is limited. A key issue in deriving long-term trends from merged ocean colour data is the inconsistency between the spatiotemporal coverage of the different sensor datasets that can lead to spurious multi-year fluctuations or trends in the time series. This study used the merged ocean colour satellite dataset produced by the Ocean Colour Climate Change Initiative (OC-CCI version 6.0) to infer global and local trends in optically active constituents. We applied a novel correction method to the OC-CCI dataset that results in a spatiotemporally consistent dataset, allowing the examination of long-term trends of optically active constituents with greater accuracy. We included sea surface temperature, salinity, and several climate oscillations in our analysis to gain insight into the underlying processes of derived trends. Our results indicate a significant increase in chlorophyll-a concentration in the polar waters, a decrease in chlorophyll-a concentration in some equatorial waters, and point to ocean darkening, predominantly in the polar waters, due to an increase in non-phytoplankton absorption. This study contributes to broader knowledge of global trends of optically active constituents and their relation to a changing environment. %0 Artikel %@ 1942-2466 %A Calil, P. %D 2023 %J Journal of Advances in Modeling Earth Systems : JAMES %N 2512 %P e2022MS003158 %R doi:10.1029/2022MS003158 %T High-Resolution, Basin-Scale Simulations Reveal the Impact of Intermediate Zonal Jets on the Atlantic Oxygen Minimum Zones %U https://dx.doi.org/10.1029/2022MS003158 2 %X Eastward zonal jets at intermediate depths of 300–800 m connect the oxygen-rich western boundary of the Atlantic basin with the oxygen minimum zones (OMZs) on the eastern boundary. They are not well represented in climate models because the low horizontal resolution of these models yields excessive viscosity. We use two physical-biogeochemical model configurations of the Tropical Atlantic to show that the increase in resolution results in more robust intermediate zonal jets and a better representation of the OMZs. The OMZ structure is distorted at low-resolution as surface, westward jets advect low-oxygen waters from the eastern boundary much further west than in the climatology. The emergence of robust eastward jets in the high-resolution run alleviate this problem and reproduce the Atlantic OMZs more accurately. The asymmetry between westward and eastward jets occurs because the former are associated with homogenous potential vorticity regions originating in the eastern boundary while the latter are associated with potential vorticity gradients. Intermediate, eastward jets constrain the westward expansion of the OMZs by supplying oxygen to their western edge. Within the OMZs, higher resolution allows a better representation of the boundary current system and eddying processes at depth which redistribute of low oxygen values from the productive eastern boundary. Basin-scale, high-resolution simulations reproduce more accurately the transfer of energy across scales that results in robust zonal jets as well as their impact on the ocean biogeochemistry. Accurate model predictions provide a pathway to disentangle natural and anthropogenic causes of ocean deoxygenation. %0 Artikel %@ 0022-0981 %A Farrell, E. %A Beermann, J. %A Neumann, A. %A Wrede, A. %D 2023 %J Journal of Experimental Marine Biology and Ecology %N 1185 %P 151837 %R doi:10.1016/j.jembe.2022.151837 %T The interplay of temperature and algal enrichment intensifies bioturbation of the intertidal amphipod Corophium volutator %U https://dx.doi.org/10.1016/j.jembe.2022.151837 %X Bioturbation is a central transport process for ecosystem functioning, especially in large soft sediment habitats like the Wadden Sea. The amphipod C. volutator is a dominant bioturbator in the Wadden Sea, due to its great abundance and almost continuous particle movement. Expedition or loss of its bioturbation activity could thus hold ramifications for ecosystem functioning within sediments, like carbon sequestration and nutrient recycling. Here we test the effect that temperature and organic enrichment have on the bioturbation of C. volutator; two prevalent abiotic factors in the Corophiid's habitat that have fluctuated over recent decades, and are expected to change in the future. In-situ experiments were conducted under 8 and 15 °C, with varying levels (0 g, 0.1 g, and 0.2 g) of powdered Ulva compressa enriching cores containing C. volutator. We found a significant interaction effect of temperature and organic enrichment on the bioturbation rate of the amphipod, with bioturbation only increasing with added organic enrichment at 15 °C. Further, a threshold within our experiments was also reached under 15 °C, where the amphipod ceased to expedite bioturbation under higher organic enrichment. This upper limit on this dominant bioturbation imposed with organic enrichment emphasizes the sensitivity of C. volutator. Our findings reveal bioturbation can be limited by temperature in colder months, and opposingly, limited by organic enrichment under warmer conditions. In future Wadden Sea scenarios where temperature is predicted to be warmer and winters milder, enhanced bioturbation activity by C. volutator could prove crucial in continued ecosystem functions. %0 Artikel %@ 0048-9697 %A Carlson, D. %A Vivó-Pons, A. %A Treier, U. %A Mätzler, E. %A Meire, L. %A Sejr, M. %A Krause-Jensen, D. %D 2023 %J Science of the Total Environment %N 1562 %P 161213 %R doi:10.1016/j.scitotenv.2022.161213 %T Mapping intertidal macrophytes in fjords in Southwest Greenland using Sentinel-2 imagery %U https://dx.doi.org/10.1016/j.scitotenv.2022.161213 %X Changes in the distribution of coastal macrophytes in Greenland, and elsewhere in the Arctic are difficult to quantify as the region remains challenging to access and monitor. Satellite imagery, in particular Sentinel-2 (S2), may enable large-scale monitoring of coastal areas in Greenland but its use is impacted by the optically complex environments and the scarcity of supporting data in the region. Additionally, the canopies of the dominant macrophyte species in Greenland do not extend to the sea surface, limiting the use of indices that exploit the reflection of near-infrared radiation by vegetation due to its absorption by seawater. Three hypotheses are tested: I) 10-m S2 imagery and commonly used detection methods can identify intertidal macrophytes that are exposed at low tide in an optically complex fjord system in Greenland impacted by marine and land terminating glaciers; II) detached and floating macrophytes accumulate in patches that are sufficiently large to be detected by 10-m S2 images; III) iceberg scour and/or turbid meltwater runoff shape the spatial distribution of intertidal macroalgae in fjord systems with marine-terminating glaciers. The NDVI produced the best results in optically complex fjord systems in Greenland. 12 km2 of exposed intertidal macrophytes were identified in the study area at low tide. Floating mats of macrophytes ranged in area from 400 m2 to 326,800 m2 and were most common at the mouth of the fjord. Icebergs and turbidity appear to play a role in structuring the distribution of intertidal macrophytes and the retreat of marine terminating glaciers could allow macrophytes cover to expand. The challenges and solutions presented here apply to most fjords in Greenland and, therefore, the methodology may be extended to produce a Greenland-wide estimate of intertidal macrophytes. %0 Artikel %@ 2041-1723 %A Lehmann, N. %A Stacke, T. %A Lehmann, S. %A Lantuit, H. %A Gosse, J. %A Mears, C. %A Hartmann, J. %A Thomas, H. %D 2023 %J Nature Communications %N 2484 %P 1648 %R doi:10.1038/s41467-023-37165-w %T Alkalinity responses to climate warming destabilise the Earth´s thermostat %U https://dx.doi.org/10.1038/s41467-023-37165-w %X Alkalinity generation from rock weathering modulates Earth’s climate at geological time scales. Although lithology is thought to dominantly control alkalinity generation globally, the role of other first-order controls appears elusive. Particularly challenging remains the discrimination of climatic and erosional influences. Based on global observations, here we uncover the role of erosion rate in governing riverine alkalinity, accompanied by areal proportion of carbonate, mean annual temperature, catchment area, and soil regolith thickness. We show that the weathering flux to the ocean will be significantly altered by climate warming as early as 2100, by up to 68% depending on the environmental conditions, constituting a sudden feedback of ocean CO2 sequestration to climate. Interestingly, warming under a low-emissions scenario will reduce terrestrial alkalinity flux from mid-latitudes (–1.6 t(bicarbonate) a−1 km−2) until the end of the century, resulting in a reduction in CO2 sequestration, but an increase (+0.5 t(bicarbonate) a−1 km−2) from mid-latitudes is likely under a high-emissions scenario, yielding an additional CO2 sink. %0 Artikel %@ 0079-6611 %A Koziorowska-Makuch, K. %A Szymczycha, B. %A Thomas, H. %A Kulinski, K. %D 2023 %J Progress in Oceanography %N 1956 %P 102977 %R doi:10.1016/j.pocean.2023.102977 %T The marine carbonate system variability in high meltwater season (Spitsbergen Fjords, Svalbard) %U https://dx.doi.org/10.1016/j.pocean.2023.102977 %X The spatial variability in hydrography (salinity and temperature) and carbonate chemistry (alkalinity - AT, total inorganic carbon concentration - CT, pH, CO2 partial pressure - pCO2, and the saturation state of aragonite - ΩAr) in high meltwater season (summer) was investigated in four Spitsbergen fjords - Krossfjorden, Kongsfjorden, Isfjorden, and Hornsund. It was found that the differences in hydrology entail spatial changes in the CO2 system structure. AT decline with decreasing salinity was evident, hence it is clear that freshwater input generally has a diluting effect and lowers AT in the surface waters of the Spitsbergen fjords. Significant surface water AT variability (1889–2261 µmol kg−1) reveals the complexity of the fjords’ systems with multiple freshwater sources having different alkalinity end-member characteristics and identifies the mean AT freshwater end-member of 595 ± 84 µmol kg−1 for the entire region. The effect of AT fluxes from sediments on the bottom water was rather insignificant, despite high AT values (2288–2666 μmol kg−1) observed in the pore waters. Low pCO2 results in surface water (200–295 μatm) points to intensive biological production, which can strongly affect the CT values, however, is less important for shaping alkalinity. It has also been shown that the freshening of the surface water in the fjords reduces significantly ΩAr (an increase in freshwater fraction contribution by 1% causes a decrease in ΩAr by 0.022). Although during the polar day, due to low pCO2, ΩAr values are still rather far from 1 (they ranged from 1.4 to 2.5), during polar night, when pCO2 values are much higher, ΩAr may drop markedly. This study highlights that the use of salinity to estimate the potential alkalinity can carry a high uncertainty, while good recognition of the surface water AT variability and its freshwater end-members is key to predict marine CO2 system changes along with the ongoing freshening of fjords waters due to climate warming. %0 Artikel %@ 0029-8018 %A Deschner, S. %A Kock, T. %A Schelwat, H. %A Baschek, B. %D 2023 %J Ocean Engineering %N 1349 %P 113201 %R doi:10.1016/j.oceaneng.2022.113201 %T Submerged marine towed instrument array: A theoretical investigation using Lagrange mechanics %U https://dx.doi.org/10.1016/j.oceaneng.2022.113201 %X Towed instrument arrays (TIA) measure physical data in the ocean surface boundary layer (OSBL). The TIA consists of probes mounted on a cable and towed behind a vessel. The comparably low interpolation errors of the two-dimensional results vastly enrich research on ocean energy dissipation. Here, we develop a new theoretical framework considering the mounted probes and their effects on the dynamics of the TIA in analogy to multiple pendulums on a moving suspension point. The dynamics are induced by external velocity-dependent drag- and coordinate-dependent depressor forces. We show that our method of including nonlinear drag forces is consistent and that our discrete approach is capable of computing continuous solutions in the limit . Hence, the proposed method unifies earlier approaches and is tested against several analytical and known numerical solutions. The phase space for the case is similar to that of a damped harmonic oscillator. A typical timescale estimates the equilibrium state of the dynamical system. We provide evidence of our method by comparing the results with real measurement data. Based on the theoretical investigations, test cases, and the comparison with real data, our method is a powerful tool, suitable for campaign planning, instrument design, and post-processing purposes. %0 Artikel %@ 0048-9697 %A Gjerluff Ager, T. %A Krause-Jensen, D. %A Olesen, B. %A Carlson, D. %A Hylstofte Sichlau Winding, M. %A Sejr, M. %D 2023 %J Science of the Total Environment %N 1562 %P 162224 %R doi:10.1016/j.scitotenv.2023.162224 %T Macroalgal habitats support a sustained flux of floating biomass but limited carbon export beyond a Greenland fjord %U https://dx.doi.org/10.1016/j.scitotenv.2023.162224 %X Despite growing attention on the contribution of macroalgae to carbon cycling and sequestration (blue carbon), more observational data is needed to constrain current estimates. In this study, we estimate the floating macroalgal carbon flux within and beyond a large sub-Arctic fjord system, Nuup Kangerlua, Greenland, which could potentially reach carbon sinks. Our study estimates 1) the fjord-scale area with macroalgal coverage and barrens caused by sea urchin grazing, 2) the floating macroalgal biomass in the fjord, and 3) the annual export flux of floating macroalgae out of the fjord system. ROV surveys documented that macroalgal habitats cover 32 % of the seafloor within the photic zone (0-30 m) with an average coverage of 39.6, 22, and 7.2 % in the depth intervals 0–10, 10–20, and 20-30 m, respectively. 15 % of the area suitable for macroalgae was denuded by sea urchin grazing. Floating macroalgae were common with an average biomass of 55 kg wet weight km−2. Densities and species composition varied seasonally with the highest levels after storms. The floating biomass was composed of intertidal macroalgal species (58 %) (Fucus vesiculosus, Fucus distichus, and Ascophyllum nodosum) and kelps (42 %) (Saccharina longicruris, S. latissima, and Alaria esculenta). We deployed surface GPS drifters to simulate floating macroalgal trajectories and velocity. Data indicated that 80 % of the floating biomass is retained in the fjord where its fate in relation to long-term sequestration is unknown. Export beyond the fjord was limited and indicated an annual floating macroalgal export beyond the fjord of only 6.92 t C yr−1, which is equal to ~0.02 % of the annual net primary production. Our findings suggest that floating macroalgae support a limited blue carbon potential beyond this fjord and that future research should focus on the fate of retained floating macroalgae and subsurface export to resolve the connectivity between macroalgal habitats and long-term carbon sinks. %0 Artikel %@ 0048-9697 %A Fettweis, M. %A Riethmüller, R. %A Van der Zande, D. %A Desmit, X. %D 2023 %J Science of the Total Environment %N 1562 %P 162273 %R doi:10.1016/j.scitotenv.2023.162273 %T Sample based water quality monitoring of coastal seas: How significant is the information loss in patchy time series compared to continuous ones? %U https://dx.doi.org/10.1016/j.scitotenv.2023.162273 %X The high temporal and spatial variability of tidal dominated coastal areas poses a challenge for characterising water quality. Water quality monitoring relies often on information collected by water sampling from a vessel or by satellites, and covers limited time periods and therefore limited tidal and meteorological conditions. To assess the loss of information from discrete sampling, continuous time series of one year (suspended particulate matter (SPM) concentration, SPM flux and Chlorophyll a (Chl) concentration) were used. Eight different schemes of sampling into these time series were applied that are typical for many monitoring programs. They differ in the time between sampling events (synodic or half-synodic) and the duration of the sampling (tidal cycle, half a tidal cycle, one or more samples). The information loss was quantified by applying a bootstrap method to calculate the mean and standard deviation over the considered period. These were then compared with the true mean calculated from the continuous series. The probability to match the true mean within a certain margin depends on the sampling period and the season, but it is always low, especially if the allowed uncertainty is stringent (e.g., ±2.5 % about the true mean). For the SPM concentration this probability is lower than 10 % and for Chl concentration lower than 20 %. Similarly, conclusions arise for the detection of trends in a 20 year time series of SPM concentration with an artificial yearly increase of 0.5 %. None of the sampling schemes was able to assess statistical significant interannual trends with probabilities above 60 %. Further, the significant trends overestimated the increase by a factor 2 to 8. Here, present modus operandi is thus inadequate for basic trend detection, but may be acceptable for the more marine, lower turbid areas where higher probabilities were obtained in this study. %0 Artikel %@ 0012-8252 %A Brewin, R.J.W. %A Sathyendranath, S. %A Kulk, G. %A Rio, M.-H. %A Concha, J.A. %A Bell, T.G. %A Bracher, A. %A Fichot, C. %A Frölicher, T.L. %A Galí, M. %A Hansell, D. A. %A Kostadinov, T.S. %A Mitchell, C. %A Neeley, A.R. %A Organelli, E. %A Richardson, K. %A Rousseaux, C. %A Shen, F. %A Stramski, D. %A Tzortziou, M. %A Watson, A.J. %A Addey, C.I. %A Bellacicco, M. %A Bouman, H. %A Carroll, D. %A Cetinić, I. %A Dall’Olmo, G. %A Frouin, R. %A Hauck, J. %A Hieronymi, M. %A Hu, C. %A Ibello, V. %A Jönsson, B. %A Kong, C.E. %A Kovač, Ž. %A Laine, M. %A Lauderdale, J. %A Lavender, S. %A Livanou, E. %A Llort, J. %A Lorinczi, L. %A Nowicki, M. %A Pradisty, N.A. %A Psarra, S. %A Raitsos, D.E. %A Ruescas, A.B. %A Russell, J.L. %A Salisbury, J. %A Sanders, R. %A Shutler, J.D. %A Sun, X. %A Taboada, F.G. %A Tilstone, G. %A Wei, X. %A Woolf, D.K. %D 2023 %J Earth-Science Reviews %N 2468 %P 104386 %R doi:10.1016/j.earscirev.2023.104386 %T Ocean carbon from space: current status and priorities for the next decade %U https://dx.doi.org/10.1016/j.earscirev.2023.104386 %X The ocean plays a central role in modulating the Earth’s carbon cycle. Monitoring how the ocean carbon cycle is changing is fundamental to managing climate change. Satellite remote sensing is currently our best tool for viewing the ocean surface globally and systematically, at high spatial and temporal resolutions, and the past few decades have seen an exponential growth in studies utilising satellite data for ocean carbon research. Satellite-based observations must be combined with in situ observations and models, to obtain a comprehensive view of ocean carbon pools and fluxes. To help prioritise future research in this area, a workshop was organised that assembled leading experts working on the topic, from around the world, including remote-sensing scientists, field scientists and modellers, with the goal to articulate a collective view of the current status of ocean carbon research, identify gaps in knowledge, and formulate a scientific roadmap for the next decade, with an emphasis on evaluating where satellite remote sensing may contribute. A total of 449 scientists and stakeholders participated (with balanced gender representation), from North and South America, Europe, Asia, Africa, and Oceania. Sessions targeted both inorganic and organic pools of carbon in the ocean, in both dissolved and particulate form, as well as major fluxes of carbon between reservoirs (e.g., primary production) and at interfaces (e.g., air-sea and land–ocean). Extreme events, blue carbon and carbon budgeting were also key topics discussed. Emerging priorities identified include: expanding the networks and quality of in situ observations; improved satellite retrievals; improved uncertainty quantification; improved understanding of vertical distributions; integration with models; improved techniques to bridge spatial and temporal scales of the different data sources; and improved fundamental understanding of the ocean carbon cycle, and of the interactions among pools of carbon and light. We also report on priorities for the specific pools and fluxes studied, and highlight issues and concerns that arose during discussions, such as the need to consider the environmental impact of satellites or space activities; the role satellites can play in monitoring ocean carbon dioxide removal approaches; economic valuation of the satellite based information; to consider how satellites can contribute to monitoring cycles of other important climatically-relevant compounds and elements; to promote diversity and inclusivity in ocean carbon research; to bring together communities working on different aspects of planetary carbon; maximising use of international bodies; to follow an open science approach; to explore new and innovative ways to remotely monitor ocean carbon; and to harness quantum computing. Overall, this paper provides a comprehensive scientific roadmap for the next decade on how satellite remote sensing could help monitor the ocean carbon cycle, and its links to the other domains, such as terrestrial and atmosphere. %0 Artikel %@ 2296-7745 %A El Kassar, J. %A Juhls, B. %A Hieronymi, M. %A Preusker, R. %A Morgenstern, A. %A Fischer, J. %A Overduin, P.P. %D 2023 %J Frontiers in Marine Science %N 2685 %P 1082109 %R doi:10.3389/fmars.2023.1082109 %T Optical remote sensing (Sentinel 3 OLCI) used to monitor dissolved organic carbon in the Lena River, Russia %U https://dx.doi.org/10.3389/fmars.2023.1082109 %X In the past decades the Arctic has experienced stronger temperature increases than any other region globally. Shifts in hydrological regimes and accelerated permafrost thawing have been observed and are likely to increase mobilization of organic carbon and its transport through rivers into the Arctic Ocean. In order to better quantify changes to the carbon cycle, Arctic rivers such as the Lena River in Siberia need to be monitored closely. Since 2018, a sampling program provides frequent in situ observations of dissolved organic carbon (DOC) and colored dissolved organic matter (CDOM) of the Lena River. Here, we utilize this ground truth dataset and aim to test the potential of frequent satellite observations to spatially and temporally complement and expand these observations. We explored all available overpasses (~3250) of the Ocean and Land Colour Instrument (OLCI) on Sentinel-3 within the ice-free periods (May – October) for four years (2018 to 2021) to develop a new retrieval scheme to derive concentrations of DOC. OLCI observations with a spatial resolution of ~300 m were corrected for atmospheric effects using the Polymer algorithm. The results of this study show that using this new retrieval, remotely sensed DOC concentrations agree well with in situ DOC concentrations (MAPD=10.89%, RMSE=1.55 mg L−1, r²=0.92, n=489). The high revisit frequency and wide swath of OLCI allow it to capture the entire range of DOC concentrations and their seasonal variability. Estimated satellite-derived DOC export fluxes integrated over the ice-free periods of 2018 to 2021 show a high interannual variability and agree well with flux estimates from in situ data (RMSD=0.186 Tg C, MAPD=4.05%). In addition, 10-day OLCI composites covering the entire Lena River catchment revealed increasing DOC concentration and local sources of DOC along the Lena from south to north. We conclude that moderate resolution satellite imagers such as OLCI are very capable of observing DOC concentrations in large/wide rivers such as the Lena River despite the relatively coarse spatial resolution. The global coverage of remote sensing offers the expansion to more rivers in order to improve our understanding of the land-ocean carbon fluxes in a changing climate. %0 Artikel %@ 1866-3508 %A Rick, J.J. %A Scharfe, M. %A Romanova, T. %A van Beusekom, J.E.E. %A Asmus, R. %A Asmus, H. %A Mielck, F. %A Kamp, A. %A Sieger, R. %A Wiltshire, K.H. %D 2023 %J Earth System Science Data %N 2511 %P 1037 - 1057 %R doi:10.5194/essd-15-1037-2023 %T An evaluation of long-term physical and hydrochemical measurements at the Sylt Roads Marine Observatory (1973–2019), Wadden Sea, North Sea %U https://dx.doi.org/10.5194/essd-15-1037-2023 3 %X he Sylt Roads pelagic time series covers physical and hydrochemical parameters at five neighboring stations in the Sylt–Rømø bight, Wadden Sea, North Sea. Since the beginning of the time series in 1973, sea surface temperature (SST), salinity, ammonium, nitrite, nitrate, and soluble reactive phosphorus (SRP) have been measured twice a week. The other parameters were introduced later (dissolved silicate (Si) since 1974, pH since 1979, dissolved organic nitrogen (DON) since 1996, dissolved organic phosphorus (DOP) since 2001, chlorophyll a since 1979, and suspended particulate matter (SPM) since 1975), and in the case of dissolved oxygen, were already discontinued (1979–1983). In the years 1977, 1978, and 1983, no sampling took place. Since the start of the continuous sampling in 1984, the sea surface temperature in the bight has risen by +1.11 ∘C, with the highest increases during the autumn months, while the pH and salinity decreased by 0.23 and 0.33 units, respectively. Summer and autumn salinities are generally significantly elevated compared to spring and winter conditions. Dissolved nutrients (ammonium, nitrite, nitrate, and SRP) have displayed periods of intense eutrophication (1973–1998) and de-eutrophication since 1999. Silicate has shown significantly higher winter levels since 1999. Interestingly, phytoplankton parameters did not mirror these large changes in nutrient concentrations, as a seasonal comparison of the two eutrophication periods showed no significant differences with regard to chlorophyll a. This phenomenon might be triggered by an important switch in nutrient limitation during the time series. With regard to nutrients, the phytoplankton was probably primarily limited by silicate until 1998, while, since 1999, the SRP limitation has become increasingly important. All data are available in Rick et al. (2017b–e, 2020a–o) from https://doi.org/10.1594/PANGAEA.150032, https://doi.org/10.1594/PANGAEA.873549, https://doi.org/10.1594/PANGAEA.873545, https://doi.org/10.1594/PANGAEA.873547, https://doi.org/10.1594/PANGAEA.918018, https://doi.org/10.1594/PANGAEA.918032, https://doi.org/10.1594/PANGAEA.918027, https://doi.org/10.1594/PANGAEA.918023, https://doi.org/10.1594/PANGAEA.918033, https://doi.org/10.1594/PANGAEA.918028, https://doi.org/10.1594/PANGAEA.918024, https://doi.org/10.1594/PANGAEA.918034, https://doi.org/10.1594/PANGAEA.918029, https://doi.org/10.1594/PANGAEA.918025, https://doi.org/10.1594/PANGAEA.918035, https://doi.org/10.1594/PANGAEA.918030, https://doi.org/10.1594/PANGAEA.918026, https://doi.org/10.1594/PANGAEA.918036, and https://doi.org/10.1594/PANGAEA.918031. %0 Artikel %@ 1094-4087 %A Röttgers, R. %A Hieronymi, M. %D 2023 %J Optics express %N 2231 %P 10512 - 10524 %R doi:10.1364/OE.482395 %T Transfer model to determine the above-water remote-sensing reflectance from the underwater remote-sensing ratio %U https://dx.doi.org/10.1364/OE.482395 6 %X Remote-sensing reflectance, Rrs(λ, θ, Δϕ, θs), contains the spectral color information of the water body below the sea surface and is a fundamental parameter to derive satellite ocean color products such as chlorophyll-a, diffuse light attenuation, or inherent optical properties. Water reflectance, i.e., spectral upwelling radiance, normalized by the downwelling irradiance, can be measured under- or above-water. Several models to extrapolate this ratio from underwater “remote-sensing ratio”, rrs(λ), to the above-water Rrs, have been proposed in previous studies, in which the spectral dependency of water refractive index and off-nadir viewing directions have not been considered in detail. Based on measured inherent optical properties of natural waters and radiative transfer simulations, this study proposes a new transfer model to spectrally determine Rrs from rrs for different sun-viewing geometries and environmental conditions. It is shown that, compared to previous models, ignoring spectral dependency leads to a bias of ∼2.4% at shorter wavelengths (∼400 nm), which is avoidable. If nadir-viewing models are used, the typical 40°-off nadir viewing geometry will introduce a difference of ∼5% in Rrs estimation. When the solar zenith angle is higher than 60°, these differences of Rrs have implications for the downstream retrievals of ocean color products, e.g., > 8% difference for phytoplankton absorption at 440 nm and >4% difference for backward particle scattering at 440 nm by the quasi-analytical algorithm (QAA). These findings demonstrate that the proposed rrs-to-Rrs model is applicable to a wide range of measurement conditions and provides more accurate estimates of Rrs than previous models. %0 Artikel %@ 2169-9275 %A Lazaneo, C. %A Calil, P. %A Tandon, A. %A da Silveira, I. %D 2022 %J Journal of Geophysical Research : Oceans %N 2698 %P e2020JC017099 %R doi:10.1029/2020JC017099 %T Submesoscale Coherent Vortices in the South Atlantic Ocean: A Pathway for Energy Dissipation %U https://dx.doi.org/10.1029/2020JC017099 2 %X Mesoscale eddies propagate westward across the South Atlantic basin. As they reach the westernmost part of the basin, at approximately 20°S, they interact with a quasi-zonal seamount chain, the Vitória-Trindade Ridge (VTR). The interactions with the local topography lead to submesoscales instabilities, which ignite the formation of submesoscale coherent vortices (SCVs) such as those described in the present study for the first time in the VTR region. Here, using high-resolution hydrographic and microstructure measurements, we describe the dynamics of two adjacent SCVs wandering through the ridge. We find that the anticyclonic SCVs are characterized by a low potential vorticity and angular momentum signature, and are therefore prone to both centrifugal and symmetric instabilities. This dynamic regime suggests small-scale turbulence is actively cascading energy down to dissipation, diagnosed from turbulent kinetic energy dissipation estimates within one of the SCVs through microstructure measurements. The energy dissipation levels observed within the SCV are two orders of magnitude larger than in surrounding waters. The thermohaline signatures of each SCV reveal homogenized waters in their cores but with small thermohaline anomalies when compared to surrounding waters, suggesting a remote generation site. Here, we argue that such vortices are essential agents for energy dissipation in the ocean. We speculate that the observed SCVs were formed due to mesoscale eddy-topography interaction along the VTR and advected by the meandering South Equatorial Current to the location of field observations. %0 Artikel %@ 1726-4170 %A Schulz, G. %A Sanders, T. %A van Beusekom, J. E. E. %A Voynova, Y. G. %A Schöl, A. %A Dähnke, K %D 2022 %J Biogeosciences %N 2118 %P 2007 - 2024 %R doi:10.5194/bg-19-2007-2022 %T Suspended particulate matter drives the spatial segregation of nitrogen turnover along the hyper-turbid Ems estuary %U https://dx.doi.org/10.5194/bg-19-2007-2022 7 %X Estuaries are nutrient filters and change riverine nutrient loads before they reach coastal oceans. Their morphology have been extensively changed by anthropogenic activities like draining, deepening and dredging to meet economic and social demand, causing significant regime changes like tidal amplifications and in some cases to hyper-turbid conditions. Furthermore, increased nutrient loads, especially nitrogen, mainly by agriculture cause coastal eutrophication. Estuaries can either act as a sink or as a source of nitrate, depending on environmental and geomorphological conditions. These factors vary along an estuary, and change nitrogen turnover in the system. Here, we investigate the factors controlling nitrogen turnover in the hyper-turbid Ems estuary (Northern Germany), which has been strongly impacted by human activities. During two research cruises in August 2014 and June 2020, we measured water column properties, dissolved inorganic nitrogen, dual stable isotopes of nitrate and dissolved nitrous oxide concentration along the estuary. We found that three distinct biogeochemical zones exist along the estuary. A strong fractionation (∼26 ‰) of nitrate stable isotopes points towards nitrate removal via water column denitrification in the hyper-turbid tidal river, driven by anoxic conditions in deeper water layers. In the middle reaches of the estuary nitrification gains importance, turning this section into a net nitrate source. The outer reaches are dominated by mixing, with nitrate uptake in 2020. %0 Artikel %@ 1726-4170 %A Haugk, C. %A Jongejans, L. L. %A Mangelsdorf, K. %A Fuchs, M. %A Ogneva, O. %A Palmtag, J. %A Mollenhauer, G. %A Mann, P. J. %A Overduin, P. P. %A Grosse, G. %A Sanders, T. %A Tuerena, R. E. %A Schirrmeister, L. %A Wetterich, S. %A Kizyakov, A. %A Karger, C. %A Strauss, J. %D 2022 %J Biogeosciences %N 2118 %P 2079 - 2094 %R doi:10.5194/bg-19-2079-2022 %T Organic matter characteristics of a rapidly eroding permafrost cliff in NE Siberia (Lena Delta, Laptev Sea region) %U https://dx.doi.org/10.5194/bg-19-2079-2022 7 %X Organic carbon (OC) stored in Arctic permafrost represents one of Earth's largest and most vulnerable terrestrial carbon pools. Amplified climate warming across the Arctic results in widespread permafrost thaw. Permafrost deposits exposed at river cliffs and coasts are particularly susceptible to thawing processes. Accelerating erosion of terrestrial permafrost along shorelines leads to increased transfer of organic matter (OM) to nearshore waters. However, the amount of terrestrial permafrost carbon and nitrogen as well as the OM quality in these deposits is still poorly quantified. We define the OM quality as the intrinsic potential for further transformation, decomposition and mineralisation. Here, we characterise the sources and the quality of OM supplied to the Lena River at a rapidly eroding permafrost river shoreline cliff in the eastern part of the delta (Sobo-Sise Island). Our multi-proxy approach captures bulk elemental, molecular geochemical and carbon isotopic analyses of Late Pleistocene Yedoma permafrost and Holocene cover deposits, discontinuously spanning the last ∼52 kyr. We showed that the ancient permafrost exposed in the Sobo-Sise cliff has a high organic carbon content (mean of about 5 wt %). The oldest sediments stem from Marine Isotope Stage (MIS) 3 interstadial deposits (dated to 52 to 28 cal ka BP) and are overlaid by last glacial MIS 2 (dated to 28 to 15 cal ka BP) and Holocene MIS 1 (dated to 7–0 cal ka BP) deposits. The relatively high average chain length (ACL) index of n-alkanes along the cliff profile indicates a predominant contribution of vascular plants to the OM composition. The elevated ratio of iso- and anteiso-branched fatty acids (FAs) relative to mid- and long-chain (C ≥ 20) n-FAs in the interstadial MIS 3 and the interglacial MIS 1 deposits suggests stronger microbial activity and consequently higher input of bacterial biomass during these climatically warmer periods. The overall high carbon preference index (CPI) and higher plant fatty acid (HPFA) values as well as high ratios point to a good quality of the preserved OM and thus to a high potential of the OM for decomposition upon thaw. A decrease in HPFA values downwards along the profile probably indicates stronger OM decomposition in the oldest (MIS 3) deposits of the cliff. The characterisation of OM from eroding permafrost leads to a better assessment of the greenhouse gas potential of the OC released into river and nearshore waters in the future. %0 Artikel %@ 1812-0784 %A Petit, T. %A Hamre, B. %A Sandven, H. %A Röttgers, R. %A Kowalczuk, P. %A Zablocka, M. %A Granskog, M. %D 2022 %J Ocean Science %N 2310 %P 455 - 468 %R doi:10.5194/os-18-455-2022 %T Inherent optical properties of dissolved and particulate matter in an Arctic fjord (Storfjorden, Svalbard) in early summer %U https://dx.doi.org/10.5194/os-18-455-2022 2 %X There have been considerable efforts to understand the hydrography of Storfjorden (Svalbard). A recurring winter polynya with large sea ice production makes it an important region of dense water formation at the scale of the Arctic Ocean. In addition, this fjord is seasonally influenced by freshwater inputs from sea ice melt and the surrounding islands of the Svalbard archipelago, which impacts the hydrography. However, the understanding of factors controlling the optical properties of the waters in Storfjorden are lacking and are crucial for the development of more accurate regional bio-optical models. Here, we present results from the first detailed optical field survey of Storfjorden conducted in early summer of 2020. Our observations are based on spectrometric analysis of water samples and in situ vertical profiles with an absorption and attenuation meter, a fluorometer, and a conductivity, temperature, and depth (CTD) sensor. In addition to the expected seasonal contribution from phytoplankton, we find that in early summer waters in Storfjorden are optically complex with a significant contribution from coloured dissolved organic matter (CDOM, 33 %–64 % of the non-water absorption at 443 nm) despite relatively low CDOM concentrations and in the nearshore or near the seabed from non-algal particles (up to 61 % of the non-water absorption at 550 nm). In surface waters, the spatial variability of light attenuation was mainly controlled by inorganic suspended matter originating from river runoff. A distinct subsurface maximum of light attenuation was largely driven by a subsurface phytoplankton bloom, controlled by stratification resulting from sea ice melt. Lastly, the cold dense bottom waters of Storfjorden from winter sea ice production periodically overflows the sill at the mouth of the fjord and can thus reach the Fram Strait. It contained elevated levels of both non-algal particles and dissolved organic matter, which are likely caused by the dense flows of the nepheloid layer interacting with the sea bed. %0 Artikel %@ 2169-9275 %A Whitmore, L. M. %A Shiller, A. M. %A Horner, T. J. %A Xiang, Y. %A Auro, M. %A Bauch, D. %A Dehairs, F. %A Lam, P. %A Li, J. %A Maldonado, M. %A Mears, C. %A Newton, R. %A Pasqualini, A. %A Planquette, H. %A Rember, R. %A Thomas, H. %D 2022 %J Journal of Geophysical Research : Oceans %N 2698 %P e2021JC017417 %R doi:10.1029/2021JC017417 %T Strong Margin Influence on the Arctic Ocean Barium Cycle Revealed by Pan-Arctic Synthesis %U https://dx.doi.org/10.1029/2021JC017417 4 %X Early studies revealed relationships between barium (Ba), particulate organic carbon and silicate, suggesting applications for Ba as a paleoproductivity tracer and as a tracer of modern ocean circulation. But, what controls the distribution of barium (Ba) in the oceans? Here, we investigated the Arctic Ocean Ba cycle through a one-of-a-kind data set containing dissolved (dBa), particulate (pBa), and stable isotope Ba ratio (δ138Ba) data from four Arctic GEOTRACES expeditions conducted in 2015. We hypothesized that margins would be a substantial source of Ba to the Arctic Ocean water column. The dBa, pBa, and δ138Ba distributions all suggest significant modification of inflowing Pacific seawater over the shelves, and the dBa mass balance implies that ∼50% of the dBa inventory (upper 500 m of the Arctic water column) was supplied by nonconservative inputs. Calculated areal dBa fluxes are up to 10 μmol m−2 day−1 on the margin, which is comparable to fluxes described in other regions. Applying this approach to dBa data from the 1994 Arctic Ocean Survey yields similar results. The Canadian Arctic Archipelago did not appear to have a similar margin source; rather, the dBa distribution in this section is consistent with mixing of Arctic Ocean-derived waters and Baffin Bay-derived waters. Although we lack enough information to identify the specifics of the shelf sediment Ba source, we suspect that a sedimentary remineralization and terrigenous sources (e.g., submarine groundwater discharge or fluvial particles) are contributors. %0 Artikel %@ 0043-1354 %A Liu, J. %A Wang, R. %A Li, Y. %A Zheng, Q. %A Jiao, F. %A He, C. %A Shi, Q. %A Xu, Y. %A Zhang, R. %A Thomas, H. %A Batt, J. %A Hill, P. %A Lewis, M. %A Maclntyre, H. %A Lu, L. %A Zhang, Q. %A Tu, Q. %A Shi, T. %A Chen, F. %A Jiao, N. %D 2022 %J Water Research %N 1591 %P 118281 %R doi:10.1016/j.watres.2022.118281 %T Metagenomic evidence for the microbial transformation of carboxyl-rich alicyclic molecules: A long-term macrocosm experiment %U https://dx.doi.org/10.1016/j.watres.2022.118281 %X Carboxyl-rich alicyclic molecules (CRAMs) widely exist in the ocean and constitute the central part of the refractory dissolved organic matter (RDOM) pool. Although a consensus has been reached that microbial activity forms CRAMs, the detailed molecular mechanisms remain largely unexplored. To better understand the underlying genetic mechanisms driving the microbial transformation of CRAM, a long-term macrocosm experiment spanning 220 days was conducted in the Aquatron Tower Tank at Dalhousie University, Halifax, Canada, with the supply of diatom-derived DOM as a carbon source. The DOM composition, community structure, and metabolic pathways were characterised using multi-omics approaches. The addition of diatom lysate introduced a mass of labile DOM into the incubation seawater, which led to a low degradation index (IDEG) and refractory molecular lability boundary (RMLB) on days 1 and 18. The molecular compositions of the DOM molecules in the later incubation period (from day 120 to day 220) were more similar in composition to those on day 0, suggesting a rapid turnover of phytoplankton debris by microbial communities. Taxonomically, while Alpha proteobacteria dominated during the entire incubation period, Gamma proteobacteria became more sensitive and abundant than the other bacterial groups on days 1 and 18. Recalcitrant measurements such as IDEG and RMLB were closely related to the DOM molecules, bacterial community, and Kyoto encyclopaedia of Genes and Genomes (KEGG) modules, suggesting close associations between RDOM accumulation and microbial metabolism. KEGG modules that showed strong positive correlation with CRAMs were identified using a microbial ecological network approach. The identified KEGG modules produced the substrates, such as the acetyl-CoA or 3‑hydroxy-3-methylglutaryl-CoA, which could participate in the mevalonate pathway to generate the precursor of CRAM analogues, isopentenyl-PP, suggesting a potential generation pathway of CRAM analogues in bacteria and archaea. This study revealed the potential genetic and molecular processes involved in the microbial origin of CRAM analogues, and thus indicated a vital ecological role of bacteria and archaea in RDOM production. This study also offered new perspectives on the carbon sequestration in the ocean. %0 Artikel %@ 0886-6236 %A Carroll, D. %A Menemenlis, D. %A Dutkiewicz, S. %A Lauderdale, J. %A Adkins, J. %A Bowman, K. %A Brix, H. %A Fenty, I. %A Gierach, M. %A Hill, C. %A Jahn, O. %A Landschützer, P. %A Manizza, M. %A Mazloff, M. %A Miller, C. %A Schimel, D. %A Verdy, A. %A Whitt, D. %A Zhang, H. %D 2022 %J Global Biogeochemical Cycles %N 2144 %P e2021GB007162 %R doi:10.1029/2021GB007162 %T Attribution of Space-Time Variability in Global-Ocean Dissolved Inorganic Carbon %U https://dx.doi.org/10.1029/2021GB007162 3 %X The inventory and variability of oceanic dissolved inorganic carbon (DIC) is driven by the interplay of physical, chemical, and biological processes. Quantifying the spatiotemporal variability of these drivers is crucial for a mechanistic understanding of the ocean carbon sink and its future trajectory. Here, we use the Estimating the Circulation and Climate of the Ocean-Darwin ocean biogeochemistry state estimate to generate a global-ocean, data-constrained DIC budget and investigate how spatial and seasonal-to-interannual variability in three-dimensional circulation, air-sea CO2 flux, and biological processes have modulated the ocean sink for 1995–2018. Our results demonstrate substantial compensation between budget terms, resulting in distinct upper-ocean carbon regimes. For example, boundary current regions have strong contributions from vertical diffusion while equatorial regions exhibit compensation between upwelling and biological processes. When integrated across the full ocean depth, the 24-year DIC mass increase of 64 Pg C (2.7 Pg C year−1) primarily tracks the anthropogenic CO2 growth rate, with biological processes providing a small contribution of 2% (1.4 Pg C). In the upper 100 m, which stores roughly 13% (8.1 Pg C) of the global increase, we find that circulation provides the largest DIC gain (6.3 Pg C year−1) and biological processes are the largest loss (8.6 Pg C year−1). Interannual variability is dominated by vertical advection in equatorial regions, with the 1997–1998 El Niño-Southern Oscillation causing the largest year-to-year change in upper-ocean DIC (2.1 Pg C). Our results provide a novel, data-constrained framework for an improved mechanistic understanding of natural and anthropogenic perturbations to the ocean sink. %0 Artikel %@ 1461-0248 %A Maasri, A. %A Jähnig, S.C. %A Adamescu, M.C. %A Adrian, R. %A Baigun, C. %A Baird, D.J. %A Batista-Morales, A. %A Bonada, N. %A Brown, L.E. %A Cai, Q. %A Campos-Silva, J.V. %A Clausnitzer, V. %A Contreras-MacBeath, T. %A Cooke, S.J. %A Datry, T. %A Delacámara, G. %A De Meester, L. %A Dijkstra, K.-D.B. %A Do, V.T. %A Domisch, S. %A Dudgeon, D. %A Erös, T. %A Freitag, H. %A Freyhof, J. %A Friedrich, J. %A Friedrichs-Manthey, M. %A Geist, J. %A Gessner, M.O. %A Goethals, P. %A Gollock, M. %A Gordon, C. %A Grossart, H.-P. %A Gulemvuga, G. %A Gutiérrez-Fonseca, P.E. %A Haase, P. %A Hering, D. %A Hahn, H.J. %A Hawkins, C.P. %A He, F. %A Heino, J. %A Hermoso, V. %A Hogan, Z. %A Hölker, F. %A Jeschke, J.M. %A Jiang, M. %A Johnson, R.K. %A Kalinkat, G. %A Karimov, B.K. %A Kasangaki, A. %A Kimirei, I.A. %A Kohlmann, B. %A Kuemmerlen, M. %A Kuiper, J.J. %A Kupilas, B. %A Langhans, S.D. %A Lansdown, R. %A Leese, F. %A Magbanua, F.S. %A Matsuzaki, S.-I.S. %A Monaghan, M.T. %A Mumladze, L. %A Muzon, J. %A Mvogo Ndongo, P.A. %A Nejstgaard, J.C. %A Nikitina, O. %A Ochs, C. %A Odume, O. %A Opperman, J.J. %A Patricio, H. %A Pauls, S. %A Raghavan, R. %A Ramírez, A. %A Rashni, B. %A Ross-Gillespie, V. %A Samways, M.J. %A Schäfer, R.B. %A Schmidt-Kloiber, A. %A Seehausen, O. %A Shah, D.N. %A Sharma, S. %A Soininen, J. %A Sommerwerk, N. %A Stockwell, J.D. %A Suhling, F. %A Tachamo Shah, R.D. %A Tharme, R.E. %A Thorp, J.H. %A Tickner, D. %A Tockner, K. %A Tonkin, J.D. %A Valle, M. %A Vitule, J. %A Volk, M. %A Wang, D. %A Wolter, C. %A Worischka, S. %D 2022 %J Ecology Letters %N 2851 %P 255 - 263 %R doi:10.1111/ele.13931 %T A global agenda for advancing freshwater biodiversity research %U https://dx.doi.org/10.1111/ele.13931 2 %X Global freshwater biodiversity is declining dramatically, and meeting the challenges of this crisis requires bold goals and the mobilisation of substantial resources. While the reasons are varied, investments in both research and conservation of freshwater biodiversity lag far behind those in the terrestrial and marine realms. Inspired by a global consultation, we identify 15 pressing priority needs, grouped into five research areas, in an effort to support informed stewardship of freshwater biodiversity. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated actions towards its sustainable management and conservation. %0 Artikel %@ 0024-3590 %A Grigoratou, M. %A Montes, E. %A Richardson, A.J. %A Everett, J.D. %A Acevedo-Trejos, E. %A Anderson, C. %A Chen, B. %A Guy-Haim, T. %A Hinners, J. %A Lindemann, C. %A Garcia, T.M. %A Möller, K.O. %A Monteiro, F.M. %A Neeley, A.R. %A O'Brien, T.D. %A Palacz, A.P. %A Poulton, A.J. %A Prowe, A.E.F. %A Rodríguez-Santiago, Á.E. %A Rousseaux, C.S. %A Runge, J. %A Saad, J.F. %A Santi, I. %A Stern, R. %A Soccodato, A. %A Våge, S. %A Vogt, M. %A Zervoudaki, S. %A Muller-Karger, F.E. %D 2022 %J Limnology and Oceanography %N 1281 %P 22 - 26 %R doi:10.1002/lob.10479 %T The Marine Biodiversity Observation Network Plankton Workshops: Plankton Ecosystem Function, Biodiversity, and Forecasting - Research Requirements and Applications %U https://dx.doi.org/10.1002/lob.10479 1 %X Plankton is a massive and phylogenetically diverse group of thousands of prokaryotes, protists (unicellular eukaryotic organisms), and metazoans (multicellular eukaryotic organisms; Fig. 1). Plankton functional diversity is at the core of various ecological processes, including productivity, carbon cycling and sequestration, nutrient cycling (Falkowski 2012), interspecies interactions, and food web dynamics and structure (D'Alelio et al. 2016). Through these functions, plankton play a critical role in the health of the coastal and open ocean and provide essential ecosystem services. Yet, at present, our understanding of plankton dynamics is insufficient to project how climate change and other human-driven impacts affect the functional diversity of plankton. That limits our ability to predict how critical ecosystem services will change in the future and develop strategies to adapt to these changes. %0 Artikel %@ 0301-4797 %A Li, Y. %A Bi, S. %A Xu, J. %A Guo, F. %A Lyu, H. %A Dong, X. %A Cai, X. %D 2022 %J Journal of Environmental Management %N 2070 %P 114734 %R doi:10.1016/j.jenvman.2022.114734 %T Utilization of GOCI data to evaluate the diurnal vertical migration of Microcystis aeruginosa and the underlying driving factors %U https://dx.doi.org/10.1016/j.jenvman.2022.114734 %X Cyanobacterial blooms are one of the most severe ecological problems affecting lakes. The vertical migration of cyanobacteria in the water column increases the uncertainty in the formation and disappearance of blooms, which may be closely associated with light, temperature, and wind speed. However, it is difficult to quantitatively evaluate the influencing factors of cyanobacteria vertical movement in natural environment compared to the laboratory experimental environment. Besides, both field survey and laboratory experiment method have the difficulties in determining the diurnal vertical migration of cyanobacteria at the synoptic lake scale. In this study, based on the diurnal dynamics of cyanobacterial bloom intensity (CBI) observed by the Geostationary Ocean Color Imager (GOCI) from 2011 to 2019, the daily variations, floating rate, and sinking rate of Microcystis aeruginosa were calculated in the natural environment. Then, the effects of light, temperature, and wind speed on the vertical migration of M. aeruginosa were analysed from the perspectives of day, night, and season. The results are as follows: the records of three typical patterns of diurnal CBI exhibited strong seasonal variability from the 9-year statistics; at night, the buoyancy recovery rate of cyanobacterial colonies increased with temperature, so that at temperature >15 °C and wind speed <3 m s−1, CBI reached the maximum of the whole day at 08:16; the sinking rate of M. aeruginosa was positively correlated with the cumulated light energy at both synoptic and pixel scale; the upward migration speed of M. aeruginosa was positively correlated with the maximum wind speed of the day before cyanobacterial bloom. Therefore, the severer cyanobacterial blooms were often observed by satellite images after strong winds. The analysis of diurnal variation, floating rate, and sinking rate of M. aeruginosa will expand our knowledge for further understanding the formation mechanism of cyanobacterial blooms and for improving the accuracy of model simulation to predict the hourly changes in cyanobacterial blooms in Lake Taihu. %0 Artikel %@ 1470-160X %A Wang, H. %A Li, Y. %A Zeng, S. %A Cai, X. %A Bi, S. %A Liu, H. %A Mu, M. %A Dong, X. %A Li, J. %A Xu, J. %A Lyu, H. %A Zhu, Y. %A Zhang, Y. %D 2022 %J Ecological Indicators %N 2373 %P 108607 %R doi:10.1016/j.ecolind.2022.108607 %T Recognition of aquatic vegetation above water using shortwave infrared baseline and phenological features %U https://dx.doi.org/10.1016/j.ecolind.2022.108607 %X Accurate monitoring of emergent aquatic vegetation (EAV) and floating-leave aquatic vegetation (FAV), is vital because vegetation provides a critical habitat for aquatic animals and plays a critical role in protecting biodiversity. However, owing to the interference of water spectrum signals, it is difficult to extract the emerging aquatic vegetation information from remote sensing images, especially to distinguish between EAV and FAV. This study first proposed an enhanced aquatic vegetation index based on the difference in two short-wave infrared (SWIR) bands to extract the aquatic vegetation above the water surface, and then, the EAV and FAV were further distinguished coupled with the phenological characteristics, subsequently, a case study of Taihu Lake for accurately extracting seasonal and annual distributions. The results demonstrate that the proposed aquatic vegetation index is highly sensitive to EAV and FAV, and can further distinguish EAV from them coupled with phenological difference. Additionally, the dramatic changes in EAV and FAV in time and space indicated that human purse seine culture has had a great influence on the succession of aquatic vegetation, which may lead to the deterioration of the water ecology environment. Using the SWIR bands coupled with phenological difference is a promising method for recognizing aquatic vegetation above the water surface owing that it can weaken and eliminate the impact of algal bloom at the same time. %0 Artikel %@ 1099-4300 %A Albert, C. %A Callies, U. %A von Toussaint, U. %D 2022 %J Entropy %N 3005 %P 231 %R doi:10.3390/e24020231 %T A Bayesian Approach to the Estimation of Parameters and Their Interdependencies in Environmental Modeling %U https://dx.doi.org/10.3390/e24020231 2 %X We present a case study for Bayesian analysis and proper representation of distributions and dependence among parameters when calibrating process-oriented environmental models. A simple water quality model for the Elbe River (Germany) is referred to as an example, but the approach is applicable to a wide range of environmental models with time-series output. Model parameters are estimated by Bayesian inference via Markov Chain Monte Carlo (MCMC) sampling. While the best-fit solution matches usual least-squares model calibration (with a penalty term for excessive parameter values), the Bayesian approach has the advantage of yielding a joint probability distribution for parameters. This posterior distribution encompasses all possible parameter combinations that produce a simulation output that fits observed data within measurement and modeling uncertainty. Bayesian inference further permits the introduction of prior knowledge, e.g., positivity of certain parameters. The estimated distribution shows to which extent model parameters are controlled by observations through the process of inference, highlighting issues that cannot be settled unless more information becomes available. An interactive interface enables tracking for how ranges of parameter values that are consistent with observations change during the process of a step-by-step assignment of fixed parameter values. Based on an initial analysis of the posterior via an undirected Gaussian graphical model, a directed Bayesian network (BN) is constructed. The BN transparently conveys information on the interdependence of parameters after calibration. Finally, a strategy to reduce the number of expensive model runs in MCMC sampling for the presented purpose is introduced based on a newly developed variant of delayed acceptance sampling with a Gaussian process surrogate and linear dimensionality reduction to support function-valued outputs. %0 Artikel %@ 0044-7447 %A Townhill, B.L. %A Reppas-Chrysovitsinos, E. %A Sühring, R. %A Halsall, C.J. %A Mengo, E. %A Sanders, T. %A Dähnke, K. %A Crabeck, O. %A Kaiser, J. %A Birchenough, S.N.R. %D 2022 %J Ambio %N 1025 %P 471 - 483 %R doi:10.1007/s13280-021-01657-0 %T Pollution in the Arctic Ocean: An overview of multiple pressures and implications for ecosystem services %U https://dx.doi.org/10.1007/s13280-021-01657-0 2 %X The Arctic is undergoing unprecedented change. Observations and models demonstrate significant perturbations to the physical and biological systems. Arctic species and ecosystems, particularly in the marine environment, are subject to a wide range of pressures from human activities, including exposure to a complex mixture of pollutants, climate change and fishing activity. These pressures affect the ecosystem services that the Arctic provides. Current international policies are attempting to support sustainable exploitation of Arctic resources with a view to balancing human wellbeing and environmental protection. However, assessments of the potential combined impacts of human activities are limited by data, particularly related to pollutants, a limited understanding of physical and biological processes, and single policies that are limited to ecosystem-level actions. This manuscript considers how, when combined, a suite of existing tools can be used to assess the impacts of pollutants in combination with other anthropogenic pressures on Arctic ecosystems, and on the services that these ecosystems provide. Recommendations are made for the advancement of targeted Arctic research to inform environmental practices and regulatory decisions. %0 Artikel %@ 2296-7745 %A Detoni, A. %A Subramanian, A. %A Haley, S. %A Dyhrman, S. %A Calil, P. %D 2022 %J Frontiers in Marine Science %N 2685 %P 856643 %R doi:10.3389/fmars.2022.856643 %T Cyanobacterial Diazotroph Distributions in the Western South Atlantic %U https://dx.doi.org/10.3389/fmars.2022.856643 %X Inputs of new nitrogen by cyanobacterial diazotrophs are critical to ocean ecosystem structure and function. Relative to other ocean regions, there is a lack of data on the distribution of these microbes in the western South Atlantic. Here, the abundance of six diazotroph phylotypes: Trichodesmium, Crocosphaera, UCYN-A, Richelia associated with Rhizosolenia (Het-1) or Hemiaulus (Het-2), and Calothrix associated with Chaetoceros (Het-3) was measured by quantitative PCR (qPCR) of the nifH gene along a transect extending from the shelf-break to the open ocean along the Vitória-Trindade seamount chain (1200 km). Using nifH gene copies as a proxy for phylotype abundance, Crocosphaera signals were the most abundant, with a broad distribution throughout the study region. Trichodesmium signals were the second most abundant, with the greatest numbers confined to the warmer waters closer to the coast, and a significant positive correlation with temperature. The average signals for the host-associated diazotrophs (UCYN-A, Het-1, and Het-2) were consistently lower than for the other phylotypes. These findings expand measurements of cyanobacterial diazotroph distribution in the western South Atlantic, and provide a new resource to enhance modeling studies focused on patterns of nitrogen fixation in the global ocean. %0 Artikel %@ 0044-7447 %A Tuerena, R.E. %A Mahaffey, C. %A Henley, S.F. %A de la Vega, C. %A Norman, L. %A Brand, T. %A Sanders, T. %A Debyser, M. %A Dähnke, K. %A Braun, J. %A März, C. %D 2022 %J Ambio %N 1025 %P 355 - 369 %R doi:10.1007/s13280-021-01673-0 %T Nutrient pathways and their susceptibility to past and future change in the Eurasian Arctic Ocean %U https://dx.doi.org/10.1007/s13280-021-01673-0 2 %X Climate change is altering nutrient cycling within the Arctic Ocean, having knock-on effects to Arctic ecosystems. Primary production in the Arctic is principally nitrogen-limited, particularly in the western Pacific-dominated regions where denitrification exacerbates nitrogen loss. The nutrient status of the eastern Eurasian Arctic remains under debate. In the Barents Sea, primary production has increased by 88% since 1998. To support this rapid increase in productivity, either the standing stock of nutrients has been depleted, or the external nutrient supply has increased. Atlantic water inflow, enhanced mixing, benthic nitrogen cycling, and land–ocean interaction have the potential to alter the nutrient supply through addition, dilution or removal. Here we use new datasets from the Changing Arctic Ocean program alongside historical datasets to assess how nitrate and phosphate concentrations may be changing in response to these processes. We highlight how nutrient dynamics may continue to change, why this is important for regional and international policy-making and suggest relevant research priorities for the future. %0 Artikel %@ 0044-7447 %A Sanders, T. %A Fiencke, C. %A Fuchs, M. %A Haugk, C. %A Juhls, B. %A Mollenhauer, G. %A Ogneva, O. %A Overduin, P. %A Palmtag, J. %A Povazhniy, V. %A Strauss, J. %A Tuerena, R. %A Zell, N. %A Dähnke, K. %D 2022 %J Ambio %N 1025 %P 423 - 438 %R doi:10.1007/s13280-021-01665-0 %T Seasonal nitrogen fluxes of the Lena River Delta %U https://dx.doi.org/10.1007/s13280-021-01665-0 2 %X The Arctic is nutrient limited, particularly by nitrogen, and is impacted by anthropogenic global warming which occurs approximately twice as fast compared to the global average. Arctic warming intensifies thawing of permafrost-affected soils releasing their large organic nitrogen reservoir. This organic nitrogen reaches hydrological systems, is remineralized to reactive inorganic nitrogen, and is transported to the Arctic Ocean via large rivers. We estimate the load of nitrogen supplied from terrestrial sources into the Arctic Ocean by sampling in the Lena River and its Delta. We took water samples along one of the major deltaic channels in winter and summer in 2019 and sampling station in the central delta over a one-year cycle. Additionally, we investigate the potential release of reactive nitrogen, including nitrous oxide from soils in the Delta. We found that the Lena transported nitrogen as dissolved organic nitrogen to the coastal Arctic Ocean and that eroded soils are sources of reactive inorganic nitrogen such as ammonium and nitrate. The Lena and the Deltaic region apparently are considerable sources of nitrogen to nearshore coastal zone. The potential higher availability of inorganic nitrogen might be a source to enhance nitrous oxide emissions from terrestrial and aquatic sources to the atmosphere. %0 Artikel %@ 0043-1354 %A Shi, W. %A Zhu, L. %A Van Dam, B. %A Smyth, A.R. %A Deng, J. %A Zhou, J. %A Pan, G. %A Yi, Q. %A Yu, J. %A Qin, B. %D 2022 %J Water Research %N 1591 %P 117887 %R doi:10.1016/j.watres.2021.117887 %T Wind induced algal migration manipulates sediment denitrification N-loss patterns in shallow Taihu Lake, China %U https://dx.doi.org/10.1016/j.watres.2021.117887 %X Driven by winds, the distribution of algae is often noticeably patchy at kilometer scales in shallow lakes. The decomposition of the settled algal biomass may affect nitrogen (N) biogeochemical cycles and thereby N loss in sediments. In this study, we investigated sediment denitrification N-loss patterns along algal migration pathway in Taihu Lake, a shallow and eutrophic lake in China, and found that wind-induced algal migration in the overlying water manipulated the temporal and spatial patterns of denitrification N-loss in sediments. A N loss hotspot in sediments was created in the algae concentrated zone, where N loss was, however, temporarily inhibited during algal bloom seasons and generally exhibited a negative relationship with algal biomass. In the zone where algae have left, sediment N loss rate was relatively low and positively correlated with algal biomass. The decay of algal biomass generated organic carbon and created anoxia, favoring denitrification, while excessive algal biomass could deplete oxygen and inhibit nitrification, causing nitrate limitation for denitrification. Piecewise linear regression analysis indicated that algal biomass of Chl-a > 73.0 μg/L in the overlying water could inhibit denitrification N-loss in sediments. This study adds to our understanding of N biogeochemical cycles in shallow eutrophic lakes. %0 Artikel %@ 1380-6165 %A Spieckermann, M. %A Gröngröft, A. %A Karrasch, M. %A Neumann, A. %A Eschenbach, A. %D 2022 %J Aquatic Geochemistry %N 3032 %P 1 - 25 %R doi:10.1007/s10498-021-09401-6 %T Oxygen Consumption of Resuspended Sediments of the Upper Elbe Estuary: Process Identification and Prognosis %U https://dx.doi.org/10.1007/s10498-021-09401-6 %X The resuspension of sediment leads to an increased release of nutrients and organic substances into the overlying water column, which can have a negative effect on the oxygen budget. Especially in the warmer months with a lower oxygen saturation and higher biological activity, the oxygen content can reach critical thresholds in estuaries like the upper Elbe estuary. Many studies have dealt with the nutrient fluxes that occur during a resuspension event. However, the sediment properties that influence the oxygen consumption potential (OCP) and the different biochemical processes have not been examined in detail. To fill this gap, we investigated the biogeochemical composition, texture, and OCP of sediments at 21 locations as well as the temporal variability within one location for a period of 2 years (monthly sampling) in the upper Elbe estuary. The OCP of sediments during a seven-day resuspension event can be described by the processes of sulphate formation, nitrification, and mineralisation. Chlorophyll, total nitrogen (Ntotal), and total organic carbon showed the highest correlations with the OCP. Based on these correlations, we developed a prognosis model to calculate the OCP for the upper Elbe estuary with a single sediment parameter (Ntotal). The model is well suited to calculate the oxygen consumption of resuspended sediments in the Hamburg port area during the relevant warmer months and shows a normalised root mean squared error of < 0.11 ± 0.13. Thus, the effect of maintenance measures such as water injection dredging and ship-induced wave on the oxygen budget of the water can be calculated. %0 Artikel %@ 2296-7745 %A Tian, S. %A Gaye, B. %A Tang, J. %A Luo, Y. %A Lahajnar, N. %A Dähnke, K. %A Sanders, T. %A Xiong, T. %A Zhai, W. %A Emeis, K.-C. %D 2022 %J Frontiers in Marine Science %N 2685 %P 834953 %R doi:10.3389/fmars.2022.834953 %T Nitrate Regeneration and Loss in the Central Yellow Sea Bottom Water Revealed by Nitrogen Isotopes %U https://dx.doi.org/10.3389/fmars.2022.834953 %X The Yellow Sea (YS) is an epicontinental sea framed by the densely populated mainland of China and the Korean peninsula. Human activities over the last decades resulted in heavily increasing discharge of reactive nitrogen into the YS, which created numerous ecological problems. To elucidate the role of central YS in the cycling of reactive nitrogen, specifically the Yellow Sea Cold Water Mass (YSCWM), we determined nutrient concentrations, dual stable isotopes of nitrate (δ15N-NO−3 and δ18O-NO−3), and stable isotopes of particulate and sedimentary nitrogen in spring and summer, i.e., in biologically inactive and active periods. The nitrate concentration in spring was higher than that in summer in the northern part of the YSCWM, Nitrate increased in the southern part accompanied by a decrease in δ15N-NO−3 and δ18O-NO−3, which are indicative of nitrification that was a significant source of recycled nitrate in the south part of YSCWM. To quantify this regenerated nitrate, we use a mixing model with end members of preformed nitrate in spring and regenerated nitrate in summer, both with their distinct dual isotope values. The results suggest that only 35% nitrate was a residual of nitrate preformed in spring and 65% in summer in the southern branch of YSCWM was regenerated. The northern part of YSCWM has low concentrations of dissolved inorganic nitrogen, mainly because of denitrification in sediments. In contrast, the southern pool of YSCWM is a growing reservoir of regenerated terrestrial reactive nitrogen, the addition of which compensates the removal by co-occurring sediment denitrification. In consequence, the southern branch of YSCWM is facing a higher ecological risk than the northern branch, when excess reactive nitrogen discharge from Changjiang River continues at present levels or even increases. %0 Artikel %@ 0269-7491 %A Logemann, A. %A Reininghaus, M. %A Schmidt, M. %A Ebeling, A. %A Zimmermann, T. %A Wolschke, H. %A Friedrich, J. %A Brockmeyer, B. %A Pröfrock, D. %A Witt, G. %D 2022 %J Environmental Pollution %N 2052 %P 119040 %R doi:10.1016/j.envpol.2022.119040 %T Assessing the chemical anthropocene – Development of the legacy pollution fingerprint in the North Sea during the last century %U https://dx.doi.org/10.1016/j.envpol.2022.119040 %X The North Sea and its coastal zones are heavily impacted by anthropogenic activities, which has resulted in significant chemical pollution ever since the beginning of the industrialization in Europe during the 19th century. In order to assess the chemical Anthropocene, natural archives, such as sediment cores, can serve as a valuable data source to reconstruct historical emission trends and to verify the effectiveness of changing environmental legislation. In this study, we investigated 90 contaminants covering inorganic and organic pollutant groups analyzed in a set of sediment cores taken in the North Seas' main sedimentation area (Skagerrak). We thereby develop a chemical pollution fingerprint that records the constant input of pollutants over time and illustrates their continued great relevance for the present. Additionally, samples were radiometrically dated and PAH and PCB levels in porewater were determined using equilibrium passive sampling. Furthermore, we elucidated the origin of lead (Pb) contamination utilizing non-traditional stable isotopic analysis. Our results reveal three main findings: 1. for all organic contaminant groups covered (PAHs, OCPs, PCBs, PBDEs and PFASs) as well as the elements lead (Pb) and titanium (Ti), determined concentrations decreased towards more recent deposited sediment. These decreasing trends could be linked to the time of introductions of restrictions and bans and therefor our results confirm, amongst possible other factors, the effectiveness of environmental legislation by revealing a successive change in contamination levels over the decades. 2. concentration trends for ΣPAH and ΣPCB measured in porewater correspond well with the ones found in sediment which suggests that this method can be a useful expansion to traditional bulk sediment analysis to determine the biologically available pollutant fraction. 3. Arsenic (As) concentrations were higher in younger sediment layers, potentially caused by emissions of corroded warfare material disposed in the study area after WW II. %0 Artikel %@ 2296-7745 %A Macovei, V. %A Callies, U. %A Calil, P. %A Voynova, Y. %D 2022 %J Frontiers in Marine Science %N 2685 %P 827075 %R doi:10.3389/fmars.2022.827075 %T Mesoscale Advective and Biological Processes Alter Carbon Uptake Capacity in a Shelf Sea %U https://dx.doi.org/10.3389/fmars.2022.827075 %X Marine uptake of carbon dioxide reduces the accumulation of carbon dioxide in the atmosphere. Continental shelf seas are essential for carbon uptake from the atmosphere, but are also highly variable environments, for which uncertainties of carbon budget estimates are large. Recent studies indicate that their carbon sink capacity is weakening. A way to reduce the uncertainty of carbon budgets is to increase our observational capacity, for example through FerryBox installations on Ships-of-Opportunity. Here, we compare FerryBox observations in the North Sea for the fall seasons of 2019 and 2020. We show that short-lived mesoscale events can be characterized when the sampling resolution is adequately high, and that these events cause changes in essential environmental variables on the same magnitude as seasonal cycles. Whether advective or biological in origin, these events rapidly lowered seawater pCO2 by 8–10% and influenced the carbon uptake capacity. We demonstrate the importance of resolving and integrating the variability of these smaller features in regional carbon budget assessments and advocate for the tuning of models in order to capture this small-scale variability. %0 Artikel %@ 0078-3234 %A Callies, U. %A von Storch, H. %D 2022 %J Oceanologia %N 1754 %P 410-422 %R doi:10.1016/j.oceano.2022.11.004 %T Extreme separations of bottle posts in the southern Baltic Sea –tentative interpretation of an experiment-of-opportunity %U https://dx.doi.org/10.1016/j.oceano.2022.11.004 2 %X During an experiment-of-opportunity in July 2019, 27 drift bottles were released in the southern Baltic Sea. Ten of these bottles were found and reported at locations that were surprisingly widespread. In this study, we explore the chances to reproduce these findings with a numerical drift model. While trajectories may be considered as completely deterministic, in practice their prediction as well as reconstruction has a strong stochastic component, because of ubiquitous gradients on even the smallest scales. We illustrate different aspects of uncertainty including specification of leeway, random dispersion, and stretching along Lagrangian coherent structures. By and large, the results of numerical ensemble simulations seem to be in reasonable agreement with the observational evidence available. Some drift bottle findings suggest a bias in simulations, but without knowing the drift bottles’ full drift paths, a basis for more detailed model tuning is missing. %0 Artikel %@ 2052-4463 %A Teschke, K. %A Kraan, C. %A Kloss, P. %A Andresen, H. %A Beermann, J. %A Fiorentino, D. %A Gusky, M. %A Hansen, M.L.S. %A Konijnenberg, R. %A Koppe, R. %A Pehlke, H. %A Piepenburg, D. %A Sabbagh, T. %A Wrede, A. %A Brey, T. %A Dannheim, J. %D 2022 %J Scientific Data %N 2569 %P 483 %R doi:10.1038/s41597-022-01590-1 %T CRITTERBASE, a science-driven data warehouse for marine biota %U https://dx.doi.org/10.1038/s41597-022-01590-1 1 %X Data on marine biota exist in many formats and sources, such as published literature, data repositories, and unpublished material. Due to this heterogeneity, information is difficult to find, access and combine, severely impeding its reuse for further scientific analysis and its long-term availability for future generations. To address this challenge, we present CRITTERBASE, a publicly accessible data warehouse and interactive portal that currently hosts quality-controlled and taxonomically standardized presence/absence, abundance, and biomass data for 18,644 samples and 3,664 benthic taxa (2,824 of which at species level). These samples were collected by grabs, underwater imaging or trawls in Arctic, North Sea and Antarctic regions between the years 1800 and 2014. Data were collated from literature, unpublished data, own research and online repositories. All metadata and links to primary sources are included. We envision CRITTERBASE becoming a valuable and continuously expanding tool for a wide range of usages, such as studies of spatio-temporal biodiversity patterns, impacts and risks of climate change or the evidence-based design of marine protection policies. %0 Artikel %@ 0269-7491 %A Wang, S. %A Wrede, A. %A Tremblay, N. %A Beermann, J. %D 2022 %J Environmental Pollution %N 2052 %P 119899 %R doi:10.1016/j.envpol.2022.119899 %T Low-frequency noise pollution impairs burrowing activities of marine benthic invertebrates %U https://dx.doi.org/10.1016/j.envpol.2022.119899 %X Sounds from human activities such as shipping and seismic surveys have been progressively invading natural soundscapes and pervading oceanic ambient sounds for decades. Benthic invertebrates are important ecosystem engineers that continually rework the sediment they live in. Here, we tested how low-frequency noise (LFN), a significant component of noise pollution, affects the sediment reworking activities of selected macrobenthic invertebrates. In a controlled laboratory setup, the effects of acute LFN exposure on the behavior of three abundant bioturbators on the North Atlantic coasts were explored for the first time by tracking their sediment reworking and bioirrigation activities in noisy and control environments via luminophore and sodium bromide (NaBr) tracers, respectively. The amphipod crustacean Corophium volutator was negatively affected by LFN, exhibiting lower bioturbation rates and shallower luminophore burial depths compared to controls. The effect of LFN on the polychaete Arenicola marina and the bivalve Limecola balthica remained inconclusive, although A. marina displayed greater variability in bioirrigation rates when exposed to LFN. Furthermore, a potential stress response was observed in L. balthica that could reduce bioturbation potential. Benthic macroinvertebrates may be in jeopardy along with the crucial ecosystem-maintaining services they provide. More research is urgently needed to understand, predict, and manage the impacts of anthropogenic noise pollution on marine fauna and their associated ecosystems. %0 Artikel %@ 1866-3508 %A Fuchs, M. %A Palmtag, J. %A Juhls, B. %A Overduin, P. P. %A Grosse, G. %A Abdelwahab, A. %A Bedington, M. %A Sanders, T. %A Ogneva, O. %A Fedorova, I. V. %A Zimov, N. S. %A Mann, P. J. %A Strauss, J. %D 2022 %J Earth System Science Data %N 2511 %P 2279 - 2301 %R doi:10.5194/essd-14-2279-2022 %T High-resolution bathymetry models for the Lena Delta and Kolyma Gulf coastal zones %U https://dx.doi.org/10.5194/essd-14-2279-2022 5 %X Arctic river deltas and deltaic near-shore zones represent important land–ocean transition zones influencing sediment dynamics and nutrient fluxes from permafrost-affected terrestrial ecosystems into the coastal Arctic Ocean. To accurately model fluvial carbon and freshwater export from rapidly changing river catchments as well as assess impacts of future change on the Arctic shelf and coastal ecosystems, we need to understand the sea floor characteristics and topographic variety of the coastal zones. To date, digital bathymetrical data from the poorly accessible, shallow, and large areas of the eastern Siberian Arctic shelves are sparse. We have digitized bathymetrical information for nearly 75 000 locations from large-scale (1:25 000–1:500 000) current and historical nautical maps of the Lena Delta and the Kolyma Gulf region in northeastern Siberia. We present the first detailed and seamless digital models of coastal zone bathymetry for both delta and gulf regions in 50 and 200 m spatial resolution. We validated the resulting bathymetry layers using a combination of our own water depth measurements and a collection of available depth measurements, which showed a strong correlation (r>0.9). Our bathymetrical models will serve as an input for a high-resolution coupled hydrodynamic–ecosystem model to better quantify fluvial and coastal carbon fluxes to the Arctic Ocean, but they may be useful for a range of other studies related to Arctic delta and near-shore dynamics such as modeling of submarine permafrost, near-shore sea ice, or shelf sediment transport. The new digital high-resolution bathymetry products are available on the PANGAEA data set repository for the Lena Delta (https://doi.org/10.1594/PANGAEA.934045; Fuchs et al., 2021a) and Kolyma Gulf region (https://doi.org/10.1594/PANGAEA.934049; Fuchs et al., 2021b), respectively. Likewise, the depth validation data are available on PANGAEA as well (https://doi.org/10.1594/PANGAEA.933187; Fuchs et al., 2021c). %0 Artikel %@ 2095-9273 %A Zhang, C. %A Shi, T. %A Liu, J. %A He, Z. %A Thomas, H. %A Dong, H. %A Rinkevich, B. %A Wang, Y. %A Hyun, J.-H. %A Weinbauer, M. %A López-Abbate, C. %A Tu, Q. %A Xie, S. %A Yamashita, Y. %A Tishchenko, P. %A Chen, Q. %A Zhang, R. %A Jiao, N. %D 2022 %J Science Bulletin %N 3115 %P 2564 - 2573 %R doi:10.1016/j.scib.2022.11.016 %T Eco-engineering approaches for ocean negative carbon emission %U https://dx.doi.org/10.1016/j.scib.2022.11.016 24 %X The goal of achieving carbon neutrality in the next 30–40 years is approaching worldwide consensus and requires coordinated efforts to combat the increasing threat of climate change. Two main sets of actions have been proposed to address this grand goal. One is to reduce anthropogenic CO2 emissions to the atmosphere, and the other is to increase carbon sinks or negative emissions, i.e., removing CO2 from the atmosphere. Here we advocate eco-engineering approaches for ocean negative carbon emission (ONCE), aiming to enhance carbon sinks in the marine environment. An international program is being established to promote coordinated efforts in developing ONCE-relevant strategies and methodologies, taking into consideration ecological/biogeochemical processes and mechanisms related to different forms of carbon (inorganic/organic, biotic/abiotic, particulate/dissolved) for sequestration. We focus on marine ecosystem-based approaches and pay special attention to mechanisms that require transformative research, including those elucidating interactions between the biological pump (BP), the microbial carbon pump (MCP), and microbially induced carbonate precipitation (MICP). Eutrophic estuaries, hypoxic and anoxic waters, coral reef ecosystems, as well as aquaculture areas are particularly considered in the context of efforts to increase their capacity as carbon sinks. ONCE approaches are thus expected to be beneficial for both carbon sequestration and alleviation of environmental stresses. %0 Artikel %@ %A Asatryan, G. %A Harbott, M. %A Todorović, S. %A Kaplan, J. %A Lazarus, D. %A Lee, C. %A Parmesan, C. %A Renaudie, J. %A Thomas, H. %A Wu, H. %A Richards, C. %D 2022 %J Frontiers for Young Minds %N 2906 %P 703195 %R doi:10.3389/frym.2022.703195 %T How Do Organisms Affect and Respond to Climate Change? %U https://dx.doi.org/10.3389/frym.2022.703195 %X Life on Earth is diverse at many levels, meaning there is a lot of variety within species and there are many different kinds of species. This biodiversity provides many of the resources that humans need and enhances our quality of life. All of Earth’s organisms are affected by Earth’s climate, but they also influence Earth’s climate. In this article, we show how research on plants, animals, and microbes helps us better understand how living things can both impact and respond to climate change. This research also gives us insight into what the future might be like for life on Earth. Such knowledge will help us to protect our planet—and the living things on it—from the harmful effects of future climate change. %0 Artikel %@ 1726-4170 %A Norbisrath, M. %A Pätsch, J. %A Dähnke, K. %A Sanders, T. %A Schulz, G. %A van Beusekom, J. %A Thomas, H. %D 2022 %J Biogeosciences %N 2118 %P 5151 - 5165 %R doi:10.5194/bg-19-5151-2022 %T Metabolic alkalinity release from large port facilities (Hamburg, Germany) and impact on coastal carbon storage %U https://dx.doi.org/10.5194/bg-19-5151-2022 22 %X Metabolic activities in estuaries, especially these of large rivers, profoundly affect the downstream coastal biogeochemistry. Here, we unravel the impacts of large industrial port facilities, showing that elevated metabolic activity in the Hamburg port (Germany) increases total alkalinity (TA) and dissolved inorganic carbon (DIC) runoff to the North Sea. The imports of particulate inorganic carbon, particulate organic carbon, and particulate organic nitrogen (PIC, POC, and PON) from the upstream Elbe River can fuel up to 90 % of the TA generated in the entire estuary via calcium carbonate (CaCO3) dissolution. The remaining at least 10 % of TA generation can be attributed to anaerobic metabolic processes such as denitrification of remineralized PON or other pathways. The Elbe Estuary as a whole adds approximately 15 % to the overall DIC and TA runoff. Both the magnitude and partitioning among these processes appear to be sensitive to climatic and anthropogenic changes. Thus, with increased TA loads, the coastal ocean (in particular) would act as a stronger CO2 sink, resulting in changes to the overall coastal system's capacity to store CO2. %0 Artikel %@ 0025-326X %A von der Au, M. %A Zimmermann, T. %A Kleeberg, U. %A von Tümpling, W. %A Pröfrock, D. %D 2022 %J Marine Pollution Bulletin %N 1292 %P 114208 %R doi:10.1016/j.marpolbul.2022.114208 %T Characteristic regional differences in trace element pattern of 2014 German North Sea surface Wadden sediments – A judge and assessment %U https://dx.doi.org/10.1016/j.marpolbul.2022.114208 %X The European Marine Strategy Framework Directive (MSFD) requires good ecological status of the marine environment. This also includes the Wadden Sea located in the southeastern part of the North Sea and its chemical status of sediments. Based on results from campaigns conducted in the 1980s, 32 surface sediment samples were taken in 2014 to check whether the sampling strategy required for characterizing the trace element content in sediments is representative and to determine the degree of pollution and potential changes over the last decades. For this purpose the elemental mass fractions of 42 elements were assessed in the ≤20 μm grain size fraction of the surface sediments. %0 Artikel %@ 2296-7745 %A Waldmann, C. %A Fischer, P. %A Seitz, S. %A Köllner, M. %A Fischer, J. %A Bergenthal, M. %A Brix, H. %A Weinreben, S. %A Huber, R. %D 2022 %J Frontiers in Marine Science %N 2685 %P 1002153 %R doi:10.3389/fmars.2022.1002153 %T A methodology to uncertainty quantification of essential ocean variables %U https://dx.doi.org/10.3389/fmars.2022.1002153 %X The goal of this study is to provide a universally applicable procedure for a systematic evaluation of in situ measured data from single sensors regarding quantifying the uncertainty of the measurement results. As determining uncertainty for an environmental parameter also depends on the parameter itself, the focus here will be set on the variable water temperature in the first place. A separate analysis for salinity and other data will follow in later publications. With this first of a series of planned manuscripts on different parameters, we aim at providing a common understanding of how measurement uncertainty on single sensor measurements can be derived. Using an experimental in situ set-up with 6 different standard CTD sensors of two different brands, we created a four month-long, high-quality data set to be used to develop a reliable method for quantifying measurement uncertainties. Although the CTDs were deployed in a mooring in a coastal environment the described method can be extended to other deployment configurations as well. The described procedures have evolved as a stepwise process that takes the different perspectives of the involved authors into account, as well as the special conditions for environmental measurements, which are collected while the observed volume/area is undergoing a constant change. By sharing the ideas with other stakeholders, the basic concept can be extended to other observing programs and to other essential ocean variables. %0 Artikel %@ 0034-4257 %A Juhls, B. %A Matsuoka, A. %A Lizotte, M. %A Bécu, G. %A Overduin, P.P. %A El Kassar, J. %A Devred, E. %A Doxaran, D. %A Ferland, J. %A Forget, M.H. %A Hilborn, A. %A Hieronymi, M. %A Leymarie, E. %A Maury, J. %A Oziel, L. %A Tisserand, L. %A Anikina, D.O.J. %A Dillon, M. %A Babin, M. %D 2022 %J Remote Sensing of Environment %N 2073 %P 113327 %R doi:10.1016/j.rse.2022.113327 %T Seasonal dynamics of dissolved organic matter in the Mackenzie Delta, Canadian Arctic waters: Implications for ocean colour remote sensing %U https://dx.doi.org/10.1016/j.rse.2022.113327 %X Increasing air temperatures and associated permafrost thaw in Arctic river watersheds, such as the Mackenzie River catchment, are directly affecting the aquatic environment. As a consequence, the quantity and the quality of dissolved organic carbon (DOC) that is transported via the Mackenzie River into the Arctic Ocean is expected to change. Particularly in these remote permafrost regions of the Arctic, monitoring of terrigenous organic carbon fluxes is insufficient and knowledge of distribution and fate of organic carbon when released to the coastal waters is remarkably lacking. Despite its poorly evaluated performance in Arctic coastal waters, Satellite Ocean Colour Remote Sensing (SOCRS) remains a powerful tool to complement monitoring of land-ocean DOC fluxes, detect their trends, and help in understanding their propagation in the Arctic Ocean. In this study, we use in situ and SOCRS data to show the strong seasonal dynamics of the Mackenzie River plume and the spatial distribution of associated terrigenous DOC on the Beaufort Sea Shelf for the first time. Using a dataset collected during an extensive field campaign in 2019, the performance of three commonly-used atmospheric correction (AC) algorithms and two available colored dissolved organic matter (CDOM) retrieval algorithms were evaluated using the Ocean and Land Colour Instrument (OLCI). Our results showed that in optically-complex Arctic coastal waters the Polymer AC algorithm performed the best. For the retrieval of CDOM, the gsmA algorithm (Mean Percentage Error (MPE) = 35.7%) showed slightly more consistent results compared to the ONNS algorithm (MPE = 37.9%). By merging our measurements with published datasets, the newly-established DOC-CDOM relationship for the Mackenzie-Beaufort Sea region allowed estimations of DOC concentrations from SOCRS across the entire fluvial-marine transition zone with an MPE of 20.5%. Finally, we applied SOCRS with data from the Sentinel-3 OLCI sensor to illustrate the seasonal variation of DOC concentrations in the surface waters of the Beaufort Sea on a large spatial scales and high frequency throughout the entire open water period. Highest DOC concentrations and largest lateral extent of the plume were observed in spring right after the Mackenzie River ice break-up indicating that the freshet was the main driver of plume propagation and DOC distribution on the shelf. Satellite-derived images of surface water DOC concentration placed the in situ observations into a larger temporal and spatial context and revealed a strong seasonal variability in transport pathways of DOC in the Mackenzie- Beaufort Sea region. %0 Artikel %@ 1866-3508 %A Valente, A. %A Sathyendranath, S. %A Brotas, V. %A Groom, S. %A Grant, M. %A Jackson, T. %A Chuprin, A. %A Taberner, M. %A Airs, R. %A Antoine, D. %A Arnone, R. %A Balch, W. M. %A Barker, K. %A Barlow, R. %A Bélanger, S. %A Berthon, J.-F. %A Beşiktepe, Ş. %A Borsheim, Y. %A Bracher, A. %A Brando, V. %A Brewin, R. J. W. %A Canuti, E. %A Chavez, F. P. %A Cianca, A. %A Claustre, H. %A Clementson, L. %A Crout, R. %A Ferreira, A. %A Freeman, S. %A Frouin, R. %A García-Soto, C. %A Gibb, S. W. %A Goericke, R. %A Gould, R. %A Guillocheau, N. %A Hooker, S. B. %A Hu, C. %A Kahru, M. %A Kampel, M. %A Klein, H. %A Kratzer, S. %A Kudela, R. %A Ledesma, J. %A Lohrenz, S. %A Loisel, H. %A Mannino, A. %A Martinez-Vicente, V. %A Matrai, P. %A McKee, D. %A Mitchell, B. G. %A Moisan, T. %A Montes, E. %A Muller-Karger, F. %A Neeley, A. %A Novak, M. %A O'Dowd, L. %A Ondrusek, M. %A Platt, T. %A Poulton, A. J. %A Repecaud, M. %A Röttgers, R. %A Schroeder, T. %A Smyth, T. %A Smythe-Wright, D. %A Sosik, H. M. %A Thomas, C. %A Thomas, R. %A Tilstone, G. %A Tracana, A. %A Twardowski, M. %A Vellucci, V. %A Voss, K. %A Werdell, J. %A Wernand, M. %A Wojtasiewicz, B. %A Wright, S. %A Zibordi, G. %D 2022 %J Earth System Science Data %N 2511 %P 5737 - 5770 %R doi:10.5194/essd-14-5737-2022 %T A compilation of global bio-optical in situ data for ocean colour satellite applications – version three %U https://dx.doi.org/10.5194/essd-14-5737-2022 12 %X A global in situ data set for validation of ocean colour products from the ESA Ocean Colour Climate Change Initiative (OC-CCI) is presented. This version of the compilation, starting in 1997, now extends to 2021, which is important for the validation of the most recent satellite optical sensors such as Sentinel 3B OLCI and NOAA-20 VIIRS. The data set comprises in situ observations of the following variables: spectral remote-sensing reflectance, concentration of chlorophyll-a, spectral inherent optical properties, spectral diffuse attenuation coefficient, and total suspended matter. Data were obtained from multi-project archives acquired via open internet services or from individual projects acquired directly from data providers. Methodologies were implemented for homogenization, quality control, and merging of all data. Minimal changes were made on the original data, other than conversion to a standard format, elimination of some points, after quality control and averaging of observations that were close in time and space. The result is a merged table available in text format. Overall, the size of the data set grew with 148 432 rows, with each row representing a unique station in space and time (cf. 136 250 rows in previous version; Valente et al., 2019). Observations of remote-sensing reflectance increased to 68 641 (cf. 59 781 in previous version; Valente et al., 2019). There was also a near tenfold increase in chlorophyll data since 2016. Metadata of each in situ measurement (original source, cruise or experiment, principal investigator) are included in the final table. By making the metadata available, provenance is better documented and it is also possible to analyse each set of data separately. The compiled data are available at https://doi.org/10.1594/PANGAEA.941318 (Valente et al., 2022). %0 Artikel %@ 2041-1723 %A Strauss, J. %A Biasi, C. %A Sanders, T. %A Abbott, B.W. %A von Deimling, T.S. %A Voigt, C. %A Winkel, M. %A Marushchak, M.E. %A Kou, D. %A Fuchs, M. %A Horn, M.A. %A Jongejans, L.L. %A Liebner, S. %A Nitzbon, J. %A Schirrmeister, L. %A Walter Anthony, K. %A Yang, Y. %A Zubrzycki, S. %A Laboor, S. %A Treat, C. %A Grosse, G. %D 2022 %J Nature Communications %N 2484 %P 6074 %R doi:10.1038/s41467-022-33794-9 %T A globally relevant stock of soil nitrogen in the Yedoma permafrost domain %U https://dx.doi.org/10.1038/s41467-022-33794-9 1 %X Nitrogen regulates multiple aspects of the permafrost climate feedback, including plant growth, organic matter decomposition, and the production of the potent greenhouse gas nitrous oxide. Despite its importance, current estimates of permafrost nitrogen are highly uncertain. Here, we compiled a dataset of >2000 samples to quantify nitrogen stocks in the Yedoma domain, a region with organic-rich permafrost that contains ~25% of all permafrost carbon. We estimate that the Yedoma domain contains 41.2 gigatons of nitrogen down to ~20 metre for the deepest unit, which increases the previous estimate for the entire permafrost zone by ~46%. Approximately 90% of this nitrogen (37 gigatons) is stored in permafrost and therefore currently immobile and frozen. Here, we show that of this amount, ¾ is stored >3 metre depth, but if partially mobilised by thaw, this large nitrogen pool could have continental-scale consequences for soil and aquatic biogeochemistry and global-scale consequences for the permafrost feedback. %0 Artikel %@ 1718-3200 %A Carlson, D. %A Pett, P. %A Peissel, N. %A Bonnardeaux, C. %A Suaria, G. %D 2022 %J The Journal of Ocean Technology %N 3102 %P 30 - 36 %T Sailing into an Uncertain Future - Connecting Sailors and Scientists to Monitor the Pulse of the Changing Arctic %U 3 %X The number of sailing yachts that are venturing into Arctic waters has increased in the past decade. As a result, the sailing community has the potential to transform observational studies in the region. Longterm, cross-border engagement strategies are necessary to transition to a persistent and organized presence of sailing citizen scientists in the Arctic. In addition to tapping the well of citizen science, sailboats can provide scientists with affordable, flexible, and sustainable research platforms. %0 Artikel %@ 2504-3129 %A Fiencke, C. %A Marushchak, M. %A Sanders, T. %A Wegner, R. %A Beer, C. %D 2022 %J Nitrogen %N 3100 %P 458 - 501 %R doi:10.3390/nitrogen3030031 %T Microbiogeochemical Traits to Identify Nitrogen Hotspots in Permafrost Regions %U https://dx.doi.org/10.3390/nitrogen3030031 3 %X Permafrost-affected tundra soils are large carbon (C) and nitrogen (N) reservoirs. However, N is largely bound in soil organic matter (SOM), and ecosystems generally have low N availability. Therefore, microbial induced N-cycling processes and N losses were considered negligible. Recent studies show that microbial N processing rates, inorganic N availability, and lateral N losses from thawing permafrost increase when vegetation cover is disturbed, resulting in reduced N uptake or increased N input from thawing permafrost. In this review, we describe currently known N hotspots, particularly bare patches in permafrost peatland or permafrost soils affected by thermokarst, and their microbiogeochemical characteristics, and present evidence for previously unrecorded N hotspots in the tundra. We summarize the current understanding of microbial N cycling processes that promote the release of the potent greenhouse gas (GHG) nitrous oxide (N2O) and the translocation of inorganic N from terrestrial into aquatic ecosystems. We suggest that certain soil characteristics and microbial traits can be used as indicators of N availability and N losses. Identifying N hotspots in permafrost soils is key to assessing the potential for N release from permafrost-affected soils under global warming, as well as the impact of increased N availability on emissions of carbon-containing GHGs. %0 Artikel %@ 1726-4170 %A Van Dam, B. %A Lehmann, N. %A Zeller, M. %A Neumann, A. %A Pröfrock, D. %A Lipka, M. %A Thomas, H. %A Böttcher, M. %D 2022 %J Biogeosciences %N 2118 %P 3775 - 3789 %R doi:10.5194/bg-19-3775-2022 %T Benthic alkalinity fluxes from coastal sediments of the Baltic and North seas: comparing approaches and identifying knowledge gaps %U https://dx.doi.org/10.5194/bg-19-3775-2022 16 %X Benthic alkalinity production is often suggested as a major driver of net carbon sequestration in continental shelf ecosystems. However, information on and direct measurements of benthic alkalinity fluxes are limited and are especially challenging when biological and dynamic physical forcing causes surficial sediments to be vigorously irrigated. To address this shortcoming, we quantified net sediment–water exchange of alkalinity using a suite of complementary methods, including (1) 224Ra budgeting, (2) incubations with 224Ra and Br− as tracers, and (3) numerical modeling of porewater profiles. We choose a set of sites in the shallow southern North Sea and western Baltic Sea, allowing us to incorporate frequently occurring sediment classes ranging from coarse sands to muds and sediment–water interfaces ranging from biologically irrigated and advective to diffusive into the investigations. Sediment–water irrigation rates in the southern North Sea were approximately twice as high as previously estimated for the region, in part due to measured porewater 224Ra activities higher than previously assumed. Net alkalinity fluxes in the Baltic Sea were relatively low, ranging from an uptake of −35 to a release of 53 , and in the North Sea they were from 1 to 34 . Lower-than-expected apparent nitrate consumption (potential denitrification), across all sites, is one explanation for our small net alkalinity fluxes measured. Carbonate mineral dissolution and potentially precipitation, as well as sulfide re-oxidation, also appear to play important roles in shaping net sediment–water fluxes at locations in the North Sea and Baltic Sea. %0 Artikel %@ 2673-6187 %A van Oostende, M. %A Hieronymi, M. %A Krasemann, H. %A Baschek, B. %A Röttgers, R. %D 2022 %J Frontiers in Remote Sensing %N 3088 %P 882418 %R doi:10.3389/frsen.2022.882418 %T Correction of inter-mission inconsistencies in merged ocean colour satellite data %U https://dx.doi.org/10.3389/frsen.2022.882418 %X Consistency in a time series of ocean colour satellite data is essential when determining long-term trends and statistics in Essential Climate Variables. For such a long time series, it is necessary to merge ocean colour data sets from different sensors due to the finite life span of the satellites. Although bias corrections have been performed on merged data set products, significant inconsistencies between missions remain. These inconsistencies appear as sudden steps in the time series of these products when a satellite mission is launched into- or removed from orbit. This inter-mission inconsistency is not caused by poor correction of sensor sensitivities but by differences in the ability of a sensor to observe certain waters. This study, based on a data set compiled by the ‘Ocean Colour Climate Change Initiative’ project (OC-CCI), shows that coastal waters, high latitudes, and areas subject to changing cloud cover are most affected by coverage variability between missions. The “Temporal Gap Detection Method” is introduced, which temporally homogenises the observations per-pixel of the time series and consequently minimises the magnitude of the inter-mission inconsistencies. The method presented is suitable to be transferred to other merged satellite-derived data sets that exhibit inconsistencies due to changes in coverage over time. The results provide insights into the correct interpretation of any merged ocean colour time series. %0 Artikel %@ 2662-4435 %A Marshall, T. %A Granger, J. %A Casciotti, K. %A Dähnke, K. %A Emeis, K. %A Marconi, D. %A McIlvin, M. %A Noble, A. %A Saito, M. %A Sigman, D. %A Fawcett, S. %D 2022 %J Communications Earth & Environment %N 2939 %P 151 %R doi:10.1038/s43247-022-00474-x %T The Angola Gyre is a hotspot of dinitrogen fixation in the South Atlantic Ocean %U https://dx.doi.org/10.1038/s43247-022-00474-x %X Biological dinitrogen fixation is the major source of new nitrogen to marine systems and thus essential to the ocean’s biological pump. Constraining the distribution and global rate of dinitrogen fixation has proven challenging owing largely to uncertainty surrounding the controls thereon. Existing South Atlantic dinitrogen fixation rate estimates vary five-fold, with models attributing most dinitrogen fixation to the western basin. From hydrographic properties and nitrate isotope ratios, we show that the Angola Gyre in the eastern tropical South Atlantic supports the fixation of 1.4–5.4 Tg N.a−1, 28-108% of the existing (highly uncertain) estimates for the basin. Our observations contradict model diagnoses, revealing a substantial input of newly-fixed nitrogen to the tropical eastern basin and no dinitrogen fixation west of 7.5˚W. We propose that dinitrogen fixation in the South Atlantic occurs in hotspots controlled by the overlapping biogeography of excess phosphorus relative to nitrogen and bioavailable iron from margin sediments. Similar conditions may promote dinitrogen fixation in analogous ocean regions. Our analysis suggests that local iron availability causes the phosphorus-driven coupling of oceanic dinitrogen fixation to nitrogen loss to vary on a regional basis. %0 Artikel %@ 1726-4170 %A Tian, S. %A Gaye, B. %A Tang, J. %A Luo, Y. %A Li, W. %A Lahajnar, N. %A Dähnke, K. %A Sanders, T. %A Xiong, T. %A Zhai, W. %A Emeis, K.-C. %D 2022 %J Biogeosciences %N 2118 %P 2397 - 2415 %R doi:10.5194/bg-19-2397-2022 %T A nitrate budget of the Bohai Sea based on an isotope mass balance model %U https://dx.doi.org/10.5194/bg-19-2397-2022 9 %X The Bohai Sea (BHS) is a semi-closed marginal sea impacted by one of the most populated areas of China. The supply of nutrients, markedly that of reactive nitrogen, via fluvial and atmospheric transport has strongly increased in parallel with the growing population. Therefore, it is crucial to quantify the reactive nitrogen input to the BHS and understand the processes and determine the quantities of nitrogen eliminated in and exported from the BHS. The nitrogen budget and in particular the internal sources and sinks of nitrate were constrained by using a mass-based and dual stable isotope approach based on δ15N and δ18O of nitrate (NO). Samples of water, suspended matter, and sediments were taken in the BHS in spring (March and April) and summer (July and August) 2018. The Yellow River (YR) was sampled in May and July to November, and Daliao River, Hai River, Luan River, and Xiaoqing River were sampled in November of 2018. In addition to nutrient, particulate organic carbon, and nitrogen concentrations, the dual isotopes of nitrate (δ15N and δ18O), δ15N of suspended matters, and sediments were determined. Based on the available mass fluxes and isotope data an updated nitrogen budget is proposed. Compared to previous estimates, it is more complete and includes the impact of interior cycling (nitrification) on the nitrate pool. The main nitrate sources are rivers contributing 19.2 %–25.6 % and the combined terrestrial runoff (including submarine fresh groundwater discharge of nitrate) accounting for 27.8 %–37.1 % of the nitrate input to the BHS, while atmospheric input contributes 6.9 %–22.2 % to total nitrate. An unusually active interior nitrogen cycling contributes 40.7 %–65.3 % to total nitrate via nitrification. Nitrogen is mainly trapped in the BHS and mainly removed by sedimentation (70.4 %–77.8 %), and only very little is exported to the Yellow Sea (YS) (only 1.8 %–2.4 %). At present denitrification is active in the sediments and removes 20.4 %–27.2 % of nitrate from the pool. However, a further eutrophication of the BHS could induce water column hypoxia and denitrification, as is increasingly observed in other marginal seas and seasonally off river mouths. %0 Artikel %@ 2296-7745 %A Reeder, C. %A Arevalo-Martinez, D. %A Carreres-Calabuig, J. %A Sanders, T. %A Posth, N. %A Löscher, C. %D 2022 %J Frontiers in Marine Science %N 2685 %P 868261 %R doi:10.3389/fmars.2022.868261 %T High Diazotrophic Diversity but Low N2 Fixation Activity in the Northern Benguela Upwelling System Confirming the Enigma of Nitrogen Fixation in Oxygen Minimum Zone Waters %U https://dx.doi.org/10.3389/fmars.2022.868261 %X Oxygen minimum zones (OMZs) have been suggested as a suitable niche for the oxygen-sensitive process of biological fixation of dinitrogen (N2) gas. However, most N2 fixation rates reported from such waters are low. This low N2 fixation activity has been proposed to result from the unusual community of N2 fixers, in which cyanobacteria were typically underrepresented. The Northern Benguela Upwelling System (North BUS) is part of one of the most productive marine ecosystems and hosts a well-developed OMZ. Although previous observations indicated low to absent N2 fixation rates, the community composition of diazotrophs needed to understand the North BUS has not been described. Here, we present a first detailed analysis of the diazotrophic diversity in the North BUS OMZ and the Angola tropical zone (ATZ), based on genetic data and isotope speciation. Consistent with a previous study, we detected a slight N deficit in the OMZ, but isotope data did not indicate any active or past N2 fixation. The diazotroph community in the North BUS was dominated by non-cyanobacterial microbes clustering with members of gamma-proteobacteria, as is typical for other OMZ regions. However, we found a strikingly high diversity of Cluster III diazotrophs not yet described in other OMZs. In contrast to previous observations, we could also identify cyanobacteria of the clades Trichodesmium sp., UCYN-A and Cyanothece sp., in surface waters connected to or above the OMZ, which were potentially active as shown by the presence of genes and transcripts of the key functional marker gene for N2 fixation, nifH. While the detection of diazotrophs and the absence of active N2 fixation (based on isotopic speciation) are consistent with other OMZ observations, the detected regional variation in the diversity and presence of cyanobacteria indicate that we still are far from understanding the role of diazotrophs in OMZs, which, however, is relevant for understanding the N cycle in OMZ waters, as well for predicting the future development of OMZ biogeochemistry in a changing ocean. %0 Artikel %@ 1726-4170 %A Dähnke, K. %A Sanders, T. %A Voynova, Y. %A Wankel, S. %D 2022 %J Biogeosciences %N 2118 %P 5879 - 5891 %R doi:10.5194/bg-19-5879-2022 %T Nitrogen isotopes reveal a particulate-matter-driven biogeochemical reactor in a temperate estuary %U https://dx.doi.org/10.5194/bg-19-5879-2022 24 %X Estuaries and rivers are important biogeochemical reactors that act to modify the loads and composition of nutrients in the coastal zone. In a case study during July 2013, we sampled an 80 km transect along the Elbe Estuary under low-oxygen conditions. To better elucidate specific mechanisms of estuarine nitrogen processing, we tracked the evolution of the stable isotopic composition of nitrate, nitrite, particulate matter, and ammonium through the water column. This approach allowed assessment of the in situ isotope effects of ammonium and nitrite oxidation and of remineralization at the reach scale. The isotope effects of nitrite oxidation and ammonium oxidation were consistent with pure-culture assessments. We found that the nitrogen budget of the Elbe Estuary is governed by settling, resuspension, and remineralization of particulate matter, and we further used our stable isotope data to evaluate sources and sinks of nitrogen in the Elbe Estuary via an isotope mass-balance approach. We find that the reactivity of particulate matter, through its remineralization in the estuary, is the main control on the isotope dynamics of inorganic nitrogen species. Moreover, while underscoring this role of particulate matter delivery and reactivity, the isotope mass balance also indicated additional sinks of reactive nitrogen, such as possible denitrification of water column nitrate in the intensively dredged and deep Hamburg Harbor region. %0 Artikel %@ 2296-7745 %A Van Dam, B. %A Lopes, C. %A Zeller, M. %A Ribas-Ribas, M. %A Wang, H. %A Thomas, H. %D 2021 %J Frontiers in Marine Science %N 2685 %P 729992 %R doi:10.3389/fmars.2021.729992 %T Overstated Potential for Seagrass Meadows to Mitigate Coastal Ocean Acidification %U https://dx.doi.org/10.3389/fmars.2021.729992 %X %0 Artikel %@ 1726-4170 %A Rutherford, K. %A Fennel, K. %A Atamanchuk, D. %A Wallace, D. %A Thomas, H. %D 2021 %J Biogeosciences %N 2118 %P 6271 - 6286 %R doi:10.5194/bg-18-6271-2021 %T A modelling study of temporal and spatial pCO2 variability on the biologically active and temperature-dominated Scotian Shelf %U https://dx.doi.org/10.5194/bg-18-6271-2021 23 %X Continental shelves are thought to be affected disproportionately by climate change and are a large contributor to global air–sea carbon dioxide (CO2) fluxes. It is often reported that low-latitude shelves tend to act as net sources of CO2, whereas mid- and high-latitude shelves act as net sinks. Here, we combine a high-resolution regional model with surface water time series and repeat transect observations from the Scotian Shelf, a mid-latitude region in the northwest North Atlantic, to determine what processes are driving the temporal and spatial variability of partial pressure of CO2 (pCO2) on a seasonal scale. In contrast to the global trend, the Scotian Shelf acts as a net source. Surface pCO2 undergoes a strong seasonal cycle with an amplitude of ∼ 200–250 µatm. These changes are associated with both a strong biological drawdown of dissolved inorganic carbon (DIC) in spring (corresponding to a decrease in pCO2 of 100–200 µatm) and pronounced effects of temperature, which ranges from 0 ∘C in the winter to near 20 ∘C in the summer, resulting in an increase in pCO2 of ∼ 200–250 µatm. Throughout the summer, events with low surface water pCO2 occur associated with coastal upwelling. This effect of upwelling on pCO2 is also in contrast to the general assumption that upwelling increases surface pCO2 by delivering DIC-enriched water to the surface. Aside from these localized events, pCO2 is relatively uniform across the shelf. Our model agrees with regional observations, reproduces seasonal patterns of pCO2, and simulates annual outgassing of CO2 from the ocean of  mol C m−2 yr−1 for the Scotian Shelf, net uptake of CO2 by the ocean of  mol C m−2 yr−1 for the Gulf of Maine, and uptake by the ocean of  mol C m−2 yr−1 for the Grand Banks. %0 Artikel %@ 0024-3590 %A Neumann, A. %A Beusekom, J. %A Eisele, A. %A Emeis, K. %A Friedrich, J. %A Kröncke, I. %A Logemann, E. %A Meyer, J. %A Naderipour, C. %A Schückel, U. %A Wrede, A. %A Zettler, M. %D 2021 %J Limnology and Oceanography %N 1281 %P 2203 - 2217 %R doi:10.1002/lno.11748 %T Macrofauna as a major driver of bentho-pelagic exchange in the southern North Sea %U https://dx.doi.org/10.1002/lno.11748 6 %X The contribution of sediments to nutrient cycling of the coastal North Sea is strongly controlled by the intensity of fluxes across the sediment water interface. Pore‐water advection is one major exchange mechanism that is well described by models, as it is determined by physical parameters. In contrast, biotransport (i.e., bioirrigation, bioturbation) as the other major transport mechanism is much more complex. Observational data reflecting biotransport, from the German Bight for example, is scarce. We sampled the major sediment provinces of the German Bight repeatedly over the years from 2013 to 2019. By employing ex situ whole core incubations, we established the seasonal and spatial variability of macrofauna‐sustained benthic fluxes of oxygen and nutrients. A multivariate, partial least squares analysis identified faunal activity, in specifically bioturbation and bioirrigation, alongside temperature, as the most important drivers of oxygen and nutrient fluxes. Their combined effect explained 63% of the observed variability in oxygen fluxes, and 36–48% of variability in nutrient fluxes. Additional 10% of the observed variability of fluxes were explained by sediment type and the availability of plankton biomass. Based on our extrapolation by sediment provinces, we conclude that pore‐water advection and macrofaunal activity contributed equally to the total benthic oxygen uptake in the German Bight. %0 Artikel %@ 0278-4343 %A Lüdmann, T. %A Saitz, M. %A Metzing, J. %A Emeis, K. %D 2021 %J Continental Shelf Research %N 1087 %P 104292 %R doi:10.1016/j.csr.2020.104292 %T Acoustic backscatter analysis of ground-fishing activity in the German North Sea sector %U https://dx.doi.org/10.1016/j.csr.2020.104292 %X The physical impact of demersal fishing was studied in three different areas of the German North Sea sector by use of a multibeam echosounder. The areas represent typical shallow seas siliciclastic habitats in variable distance to the coastline. Their seabed substrate is dominated by coarse silt close to the shore and by fine sand in the most distal area on the Dogger Bank. The study documents the utility of the multibeam as a suitable tool to map large seafloor areas, as well as to quantify and qualify the footprints of the fishing groundgear. Besides the depth and amplitude information, the multibeam data allows the analysis of the incidence angle-dependent variation of the backscatter signal that provides additional information on the seabed impedance, roughness, volume scatter and substrate type. Two main types of destructive seafloor pattern were observed in the three areas. The dominant type are pairs of parallel furrows exhibiting widths of 6–9 m and depths of 2–6 cm and is related to beam trawling. Separation distance of the pair furrows is 16–23 m. The second type are pairs of narrow furrows (3–4 m) with much larger separation distance of 110–120 m. They are attributed to otter board trawling. A comparison of their mechanical ramification shows that the fishing gear incises the seafloor and modifies seafloor structures and properties. Our investigation documents that beam trawling has the greatest physical impact and exhibits the highest furrow density in the three study areas. The created furrows can persist for at least 4 months in a substrate of very fine sand. Depending on the hydrodynamic regime, the furrows can be later refilled by finer sediments, or levelled out by storm wave-induced turbulence reaching the seafloor. The hydrofoils used in otter trawl to spread the net likewise incise the seafloor, but the furrows are much narrower. However, the ground rope of the net towed between the boards scratches the seafloor and levels the microscale topography along track widths of ca. 100 m. %0 Artikel %@ 1812-0784 %A Callies, U. %D 2021 %J Ocean Science %N 2310 %P 527 - 541 %R doi:10.5194/os-17-527-2021 %T Sensitive dependence of trajectories on tracer seeding positions – coherent structures in German Bight backward drift simulations %U https://dx.doi.org/10.5194/os-17-527-2021 2 %X Backward drift simulations can aid the interpretation of in situ monitoring data. Some trajectories, however, are sensitive to even small changes of the tracer release position. A corresponding spread of backward simulations implies convergence in the forward passage of time. Such uncertainty about the probed water body's origin complicates the interpretation of measurements. This study examines surface drift simulations in the German Bight (North Sea). Lines across which drift behaviour changes non-smoothly are obtained as ridges in the fields of the finite-time Lyapunov exponent (FTLE), a parameter used in dynamical systems theory to identify Lagrangian coherent structures (LCS). Results are shown to closely resemble those obtained considering a) two-particle relative dispersion and b) the average divergence of Eulerian velocities that tracers experience. Structures observed in simulated sea surface temperature and salinity further corroborate the FTLE results. %0 Artikel %@ 0043-1354 %A Zagarese, H. %A de los Ángeles González Sagrario, M. %A Wolf-Gladrow, D. %A Nõges, P. %A Nõges, T. %A Kangur, K. %A Matsuzaki, S. %A Kohzu, A. %A Vanni, M. %A Ozkundakci, D. %A Echaniz, S. %A Vignatti, A. %A Grosman, F. %A Sanzano, P. %A Van Dam, B. %A Knoll, L. %D 2021 %J Water Research %N 1591 %P 116715 %R doi:10.1016/j.watres.2020.116715 %T Patterns of CO2 concentration and inorganic carbon limitation of phytoplankton biomass in agriculturally eutrophic lakes %U https://dx.doi.org/10.1016/j.watres.2020.116715 %X Lake eutrophication is a pervasive problem globally, particularly serious in agricultural and densely populated areas. Whenever nutrients nitrogen and phosphorus do not limit phytoplankton growth directly, high growth rates will rapidly lead to biomass increases causing self-shading and light-limitation, and eventually CO2 depletion. The paradigm of phytoplankton limitation by nutrients and light is so pervasively established, that the lack of nutrient limitation is ordinarily interpreted as sufficient evidence for the condition of light limitation, without considering the possibility of limitation by inorganic carbon. Here, we firstly evaluated how frequently CO2 undersaturation occurs in a set of eutrophic lakes in the Pampa plains. Our results confirm that conditions of CO2 undersaturation develop much more frequently (yearly 34%, summer 44%) in these agriculturally impacted lakes than in deep, temperate lakes in forested watersheds. Secondly, we used Generalized Additive Models to fit trends in CO2 concentration considering three drivers: total incident irradiance, chlorophyll a concentration, and lake depth; in eight multi-year datasets from eutrophic lakes from Europe, North and South America, Asia and New Zealand. CO2 depletion was more often observed at high irradiance levels, and shallow water. CO2 depletion also occurred at high chlorophyll concentration. Finally, we identified occurrences of light- and carbon-limitation at the whole-lake scale. The different responses of chlorophyll a and %0 Artikel %@ 1352-2310 %A Vlasenko, A. %A Matthias, V. %A Callies, U. %D 2021 %J Atmospheric Environment %N 1061 %P 118236 %R doi:10.1016/j.atmosenv.2021.118236 %T Simulation of chemical transport model estimates by means of a neural network using meteorological data %U https://dx.doi.org/10.1016/j.atmosenv.2021.118236 %X Chemical substances of either anthropogenic or natural origin affect air quality and, as a consequence, also the health of the population. Therefore, there is a high demand for reliable air quality scenarios that can support possible management decisions. However, generating long term assessments of air quality assuming different emission scenarios is still a great challenge when using detailed atmospheric chemistry models. In this study, we test machine learning technique based on neural networks (NN) to emulate process-oriented modeling outcomes. A successfully calibrated NN might estimate concentrations of chemical substances in the air several orders faster than the original model and with reasonably small errors. We designed a simple recurrent 3-layer NN to reproduce daily mean concentrations of NO2, SO2 and C2H6 over Europe as simulated by the Community Multiscale Air Quality model (CMAQ). The general structure of the NN can be shown to approximate a continuity equation. Inputs of the network are daily mean meteorological state variables, taken from the climate model COSMO-CLM. The proposed NN emulates CMAQ outputs with an error not exceeding the difference between CMAQ and other known chemical transport models. %0 Artikel %@ 0048-9697 %A Weitere, M. %A Altenburger, R. %A Anlanger, C. %A Baborowski, M. %A Bärlund, I. %A Beckers, L.-M. %A Borchardt, D. %A Brack, W. %A Brase, L. %A Busch, W. %A Chatzinotas, A. %A Deutschmann, B. %A Eligehausen, J. %A Frank, K. %A Graeber, D. %A Griebler, C. %A Hagemann, J. %A Herzsprung, P. %A Hollert, H. %A Inostroza, P.A. %A Jäger, C.G. %A Kallies, R. %A Kamjunke, N. %A Karrasch, B. %A Kaschuba, S. %A Kaus, A. %A Klauer, B. %A Knöller, K. %A Koschorreck, M. %A Krauss, M. %A Kunz, J.V. %A Kurz, M.J. %A Liess, M. %A Mages, M. %A Müller, C. %A Muschket, M. %A Musolff, A. %A Norf, H. %A Pöhlein, F. %A Reiber, L. %A Risse-Buhl, U. %A Schramm, K.-W. %A Schmitt-Jansen, M. %A Schmitz, M. %A Strachauer, U. %A von Tümpling, W. %A Weber, N. %A Wild, R. %A Wolf, C. %A Brauns, M. %D 2021 %J Science of the Total Environment %N 1562 %P 144324 %R doi:10.1016/j.scitotenv.2020.144324 %T Disentangling multiple chemical and non-chemical stressors in a lotic ecosystem using a longitudinal approach %U https://dx.doi.org/10.1016/j.scitotenv.2020.144324 %X Meeting ecological and water quality standards in lotic ecosystems is often failed due to multiple stressors. However, disentangling stressor effects and identifying relevant stressor-effect-relationships in complex environmental settings remain major challenges. By combining state-of-the-art methods from ecotoxicology and aquatic ecosystem analysis, we aimed here to disentangle the effects of multiple chemical and non-chemical stressors along a longitudinal land use gradient in a third-order river in Germany. We distinguished and evaluated four dominant stressor categories along this gradient: (1) Hydromorphological alterations: Flow diversity and substrate diversity correlated with the EU-Water Framework Directive based indicators for the quality element macroinvertebrates, which deteriorated at the transition from near-natural reference sites to urban sites. (2) Elevated nutrient levels and eutrophication: Low to moderate nutrient concentrations together with complete canopy cover at the reference sites correlated with low densities of benthic algae (biofilms). We found no more systematic relation of algal density with nutrient concentrations at the downstream sites, suggesting that limiting concentrations are exceeded already at moderate nutrient concentrations and reduced shading by riparian vegetation. (3) Elevated organic matter levels: Wastewater treatment plants (WWTP) and stormwater drainage systems were the primary sources of bioavailable dissolved organic carbon. Consequently, planktonic bacterial production and especially extracellular enzyme activity increased downstream of those effluents showing local peaks. (4) Micropollutants and toxicity-related stress: WWTPs were the predominant source of toxic stress, resulting in a rapid increase of the toxicity for invertebrates and algae with only one order of magnitude below the acute toxic levels. This toxicity correlates negatively with the contribution of invertebrate species being sensitive towards pesticides (SPEARpesticides index), probably contributing to the loss of biodiversity recorded in response to WWTP effluents. Our longitudinal approach highlights the potential of coordinated community efforts in supplementing established monitoring methods to tackle the complex phenomenon of multiple stress. %0 Artikel %@ 0272-7714 %A Francescangeli, F. %A Milker, Y. %A Bunzel, D. %A Thomas, H. %A Norbisrath, M. %A Schönfeld, J. %A Schmiedl, G. %D 2021 %J Estuarine, Coastal and Shelf Science %N 1123 %P 107198 %R doi:10.1016/j.ecss.2021.107198 %T Recent benthic foraminiferal distribution in the Elbe Estuary (North Sea, Germany): A response to environmental stressors %U https://dx.doi.org/10.1016/j.ecss.2021.107198 %X For the past 200 years, estuarine environments experienced intense and rapid environmental degradations due to human interventions. In addition, Global Changes are modifying the estuarine physiography, leading to a re-structuration of marginal marine benthic communities. The aim of this study is to document, the modern assemblage composition and the species-environment relations of benthic foraminifera upstream the Elbe Estuary (southern North Sea) and to observe what has changed since the first survey in 1981. For this purpose, a surface sampling was carried out from 22 stations along the transitional area of the Elbe Estuary. Living (rose-Bengal stained) and dead foraminiferal assemblages were analysed as well as hydrological and sedimentological parameters (such as salinity, pH, grain-size, and organic matter). Living faunas are characterized by very low densities and largely dominated by Ammonia species. Dead assemblages are more diverse and dominated by Ammonia aomoriensis, Haynesina germanica, and Cribroelphidium selseyense. Salinity and grain-size seem to be the major factors influencing foraminiferal distributions in the transitional area. Under the ongoing climate changes, future strategies will be taken to foster the application of benthic foraminifera as biomonitoring tool in the Elbe Estuary, via this baseline investigation. %0 Artikel %@ 2325-1026 %A Duke, P. %A Else, B. %A Jones, S. %A Marriot, S. %A Ahmed, M. %A Nandan, V. %A Butterworth, B. %A Gonski, S. %A Dewey, R. %A Sastri, A. %A Miller, L. %A Simpson, K. %A Thomas, H. %D 2021 %J Elementa: Science of the Anthropocene %N 2653 %P 00103 %R doi:10.1525/elementa.2021.00103 %T Seasonal marine carbon system processes in an Arctic coastal landfast sea ice environment observed with an innovative underwater sensor platform %U https://dx.doi.org/10.1525/elementa.2021.00103 1 %X Studying carbon dioxide in the ocean helps to understand how the ocean will be impacted by climate change and respond to increasing fossil fuel emissions. The marine carbonate system is not well characterized in the Arctic, where challenging logistics and extreme conditions limit observations of atmospheric CO2 flux and ocean acidification. Here, we present a high-resolution marine carbon system data set covering the complete cycle of sea-ice growth and melt in an Arctic estuary (Nunavut, Canada). This data set was collected through three consecutive yearlong deployments of sensors for pH and partial pressure of CO2 in seawater (pCO2sw) on a cabled underwater observatory. The sensors were remarkably stable compared to discrete samples: While corrections for offsets were required in some instances, we did not observe significant drift over the deployment periods. Our observations revealed a strong seasonality in this marine carbon system. Prior to sea-ice formation, air–sea gas exchange and respiration were the dominant processes, leading to increasing pCO2sw and reduced aragonite saturation state (ΩAr). During sea-ice growth, water column respiration and brine rejection (possibly enriched in dissolved inorganic carbon, relative to alkalinity, due to ikaite precipitation in sea ice) drove pCO2sw to supersaturation and lowered ΩAr to < 1. Shortly after polar sunrise, the ecosystem became net autotrophic, returning pCO2sw to undersaturation. The biological community responsible for this early switch to autotrophy (well before ice algae or phytoplankton blooms) requires further investigation. After sea-ice melt initiated, an under-ice phytoplankton bloom strongly reduced aqueous carbon (chlorophyll-a max of 2.4 µg L–1), returning ΩAr to > 1 after 4.5 months of undersaturation. Based on simple extrapolations of anthropogenic carbon inventories, we suspect that this seasonal undersaturation would not have occurred naturally. At ice breakup, the sensor platform recorded low pCO2sw (230 µatm), suggesting a strong CO2 sink during the open water season. %0 Artikel %@ 1463-5003 %A Vallaeys, V. %A Lambrechts, J. %A Delandmeter, P. %A Pätsch, J. %A Spitzy, A. %A Hanert, E. %A Deleersnijder, E. %D 2021 %J Ocean Modelling %N 2241 %P 101890 %R doi:10.1016/j.ocemod.2021.101890 %T Understanding the circulation in the deep, micro-tidal and strongly stratified Congo River estuary %U https://dx.doi.org/10.1016/j.ocemod.2021.101890 %X The Congo River estuary is characterised by a deep canyon that connects the river to the deep ocean by cutting through the continental shelf. Its estuary is influenced by high river discharge and micro-tidal conditions, with a large depth and limited vertical mixing. This restricts the supply of oxygen from the surface waters to the more saline bottom waters, leading to hypoxic and anoxic zones. We study the dynamics of the Congo River estuary by applying the multi-scale baroclinic coastal ocean model SLIM 3D (www.slim-ocean.be) to this topographically challenging environment. By allowing a high degree of flexibility in the representation of both the complex geometry and the strong stratification, SLIM 3D is able to simulate riverine, tidal and gravitational processes that drive the estuarine circulation. Model results compare favourably with in-situ data in the estuary, suggesting that the exchange flow is correctly simulated. The latter is characterised by a two-layer dynamics. The combination of the large river discharge, the strong stratification and the large depth results in a moderate freshwater Froude number and a very small mixing number. It makes the Congo River an outlier in state-of-the-art estuarine classifications, closer to fjords than salt wedge estuaries. Furthermore, using the age as a diagnosis sheds light on the spatial variability of the estuarine waters ventilation. Local maximum of renewing water age located just below the pycnocline is exceeded by old dense oceanic waters which stagnate at the bottom of the canyon for more than two months due to the small vertical mixing. It helps explain the hypoxic and anoxic conditions observed at the bottom of the submarine canyon. %0 Artikel %@ 2375-2548 %A Jiao, N. %A Liu, J. %A Edwards, B. %A Lv, Z. %A Cai, R. %A Liu, Y. %A Xiao, X. %A Wang, J. %A Jiao, F. %A Wang, R. %A Huang, X. %A Guo, B. %A Sun, J. %A Zhang, R. %A Zhang, Y. %A Tang, K. %A Zheng, Q. %A Azam, F. %A Batt, J. %A Cai, W.-J. %A He, C. %A Herndl, G.J. %A Hill, P. %A Hutchins, D. %A LaRoche, J. %A Lewis, M. %A MacIntyre, H. %A Polimene, L. %A Robinson, C. %A Shi, Q. %A Suttle, C.A. %A Thomas, H. %A Wallace, D. %A Legendre, L. %D 2021 %J Science Advances %N 2650 %P eabc7318 %R doi:10.1126/sciadv.abc7318 %T Correcting a major error in assessing organic carbon pollution in natural waters %U https://dx.doi.org/10.1126/sciadv.abc7318 16 %X Microbial degradation of dissolved organic carbon (DOC) in aquatic environments can cause oxygen depletion, water acidification, and CO2 emissions. These problems are caused by labile DOC (LDOC) and not refractory DOC (RDOC) that resists degradation and is thus a carbon sink. For nearly a century, chemical oxygen demand (COD) has been widely used for assessment of organic pollution in aquatic systems. Here, we show through a multicountry survey and experimental studies that COD is not an appropriate proxy of microbial degradability of organic matter because it oxidizes both LDOC and RDOC, and the latter contributes up to 90% of DOC in high-latitude forested areas. Hence, COD measurements do not provide appropriate scientific information on organic pollution in natural waters and can mislead environmental policies. We propose the replacement of the COD method with an optode-based biological oxygen demand method to accurately and efficiently assess organic pollution in natural aquatic environments. %0 Artikel %@ 1750-5836 %A Omar, A.M. %A García-Ibáñez, M.I. %A Schaap, A. %A Oleynik, A. %A Esposito, M. %A Jeansson, E. %A Loucaides, S. %A Thomas, H. %A Alendal, G. %D 2021 %J International Journal of Greenhouse Gas Control %N 2400 %P 103310 %R doi:10.1016/j.ijggc.2021.103310 %T Detection and quantification of CO2 seepage in seawater using the stoichiometric Cseep method: Results from a recent subsea CO2 release experiment in the North Sea %U https://dx.doi.org/10.1016/j.ijggc.2021.103310 %X Carbon Capture and Storage (CCS) is a potential significant mitigation strategy to combat climate change and ocean acidification. The technology is well understood but its current implementation must be scaled up nearly by a hundredfold to become an effective tool that helps meet mitigation targets. Regulations require monitoring and verification at storage sites, and reliable monitoring strategies for detection and quantification of seepage of the stored carbon need to be developed. The Cseep method was developed for reliable determination of CO2 seepage signal in seawater by estimating and filtering out natural variations in dissolved inorganic carbon (C). In this work, we analysed data from the first-ever subsea CO2 release experiment performed in the north-western North Sea by the EU STEMM−CCS project. We successfully demonstrated the ability of the Cseep method to (i) predict natural C variations around the Goldeneye site over seasonal to interannual time scales; (ii) establish a process-based baseline C concentration with minimal variability; (iii) determine CO2 seepage detection threshold (DT) to reliably differentiate released−CO2 signal from natural variability and quantify released−CO2 dissolved in the sampled seawater. DT values were around 20 % of the natural C variations indicating high sensitivity of the method. Moreover, with the availability of DT value, the identification of released−CO2 required no pre-knowledge of seepage occurrence, but we used additional available information to assess the confidence of the results. Overall, the Cseep method features high sensitivity, automation suitability, and represents a powerful future monitoring tool both for large and confined marine areas. %0 Artikel %@ 0886-6236 %A Van Dam, B. %A Polsenaere, P. %A Barreras-Apodaca, A. %A Lopes, C. %A Sanchez-Mejia, Z. %A Tokoro, T. %A Kuwae, T. %A Gutierrez Loza, L. %A Rutgersson, A. %A Fourqurean, J. %A Thomas, H. %D 2021 %J Global Biogeochemical Cycles %N 2144 %P e2020GB006848 %R doi:10.1029/2020GB006848 %T Global Trends in Air‐Water CO2 Exchange Over Seagrass Meadows Revealed by Atmospheric Eddy Covariance %U https://dx.doi.org/10.1029/2020GB006848 4 %X Coastal vegetated habitats like seagrass meadows can mitigate anthropogenic carbon emissions by sequestering CO2 as “blue carbon” (BC). Already, some coastal ecosystems are actively managed to enhance BC storage, with associated BC stocks included in national greenhouse gas inventories. However, the extent to which BC burial fluxes are enhanced or counteracted by other carbon fluxes, especially air‐water CO2 flux (FCO2) remains poorly understood. In this study, we synthesized all available direct FCO2 measurements over seagrass meadows made using atmospheric Eddy Covariance, across a globally‐representative range of ecotypes. Of the four sites with seasonal data coverage, two were net CO2 sources, with average FCO2 equivalent to 44 ‐ 115% of the global average BC burial rate. At the remaining sites, net CO2 uptake was 101 ‐ 888% of average BC burial. A wavelet coherence analysis demonstrated that FCO2 was most strongly related to physical factors like temperature, wind, and tides. In particular, tidal forcing was a key driver of global‐scale patterns in FCO2, likely due to a combination of lateral carbon exchange, bottom‐driven turbulence, and pore‐water pumping. Lastly, sea‐surface drag coefficients were always greater than prediction for the open ocean, supporting a universal enhancement of gas‐transfer in shallow coastal waters. Our study points to the need for a more comprehensive approach to BC assessments, considering not only organic carbon storage, but also air‐water CO2 exchange, and its complex biogeochemical and physical drivers. %0 Artikel %@ 0013-936X %A Oehler, T. %A Ramasamy, M. %A George, M. %A Babu, S. %A Dähnke, K. %A Ankele, M. %A Böttcher, M. %A Santos, I. %A Moosdorf, N. %D 2021 %J Environmental Science and Technology %N 1114 %P 8432 - 8438 %R doi:10.1021/acs.est.1c00759 %T Tropical Beaches Attenuate Groundwater Nitrogen Pollution Flowing to the Ocean %U https://dx.doi.org/10.1021/acs.est.1c00759 12 %X Tropical urbanized coastal regions are hotspots for the discharge of nutrient-enriched groundwater, which can affect sensitive coastal ecosystems. Here, we investigated how a beach modifies groundwater nutrient loads in southern India (Varkala Beach), using flux measurements and stable isotopes. Fresh groundwater was highly enriched in NO3 from sewage or manure. Submarine groundwater discharge and nearshore groundwater discharge were equally important contributors to coastal NO3 fluxes with 303 mmol NO3 m–1 day–1 in submarine and 334 mmol NO3 m–1 day–1 in nearshore groundwater discharge. However, N/P ratios in nearshore groundwater discharge were up to 3 orders of magnitude greater than that in submarine groundwater, which can promote harmful algae blooms. As groundwater flowed through the beach, N/P ratios decreased toward Redfield ratios due to the removal of 30–50% of NO3 due to denitrification and production of PO4 due to mineralization of organic matter. Overall, tropical beaches can be important natural biogeochemical reactors that attenuate nitrogen pollution and modify N/P ratios in submarine groundwater discharge. %0 Artikel %@ 0171-8630 %A van de Wolfshaar, K. %A Daewel, U. %A Hjøllo, S. %A Troost, T. %A Kreus, M. %A Pätsch, J. %A Ji, R. %A Maar, M. %D 2021 %J Marine Ecology Progress Series %N 1291 %P 79 - 95 %R doi:10.3354/meps13885 %T Sensitivity of the fish community to different prey fields and importance of spatial-seasonal patterns %U https://dx.doi.org/10.3354/meps13885 %X Different fish species and life stages depend not only on food abundance, but also on the size of planktonic prey, and (mis-)matches in time and space with suitable prey may influence the growth and survival of fish during their lifetime. We explored the sensitivity of a fish community to spatial-temporal differences in plankton prey fields. Data from 5 different lower trophic level models in the North Sea (Delft3D-WAQ, ECOHAM, ECOSMO, HBM-ERGOM and NORWECOM) were used to force the food web model OSMOSE which simulates spatially and temporally explicit higher trophic level fish dynamics. The estimated fish biomass levels were clearly and positively linked to zooplankton biomass, and sensitivity studies varying zooplankton biomass revealed that spatial and temporal variation in zooplankton drives the differences in absolute fish biomass. More zooplankton size bins resulted in less fish biomass due to size-based foraging constraints (i.e. a smaller proportion of bins falls within the prey size range of a fish, resulting in a decrease in available food). Nevertheless, we found a consistent response across models in the relative biomass contribution and spatial patterns of selected fish groups, indicating low sensitivity of the composition of the simulated fish community to the zooplankton input. The robustness of the outcome will aid model acceptance and implementation into management action. Relative, not absolute, changes in primary and secondary production may therefore be used to study the effects of management scenarios on fish communities. %0 Artikel %@ 2375-2548 %A Van Dam, B. %A Zeller, M. %A Lopes, C. %A Smyth, A. %A Böttcher, M. %A Osburn, C. %A Zimmerman, T. %A Pröfrock, D. %A Fourqurean, J. %A Thomas, H. %D 2021 %J Science Advances %N 2650 %P eabj1372 %R doi:10.1126/sciadv.abj1372 %T Calcification-driven CO2 emissions exceed “Blue Carbon” sequestration in a carbonate seagrass meadow %U https://dx.doi.org/10.1126/sciadv.abj1372 51 %X Long-term “Blue Carbon” burial in seagrass meadows is complicated by other carbon and alkalinity exchanges that shape net carbon sequestration. We measured a suite of such processes, including denitrification, sulfur, and inorganic carbon cycling, and assessed their impact on air-water CO2 exchange in a typical seagrass meadow underlain by carbonate sediments. Eddy covariance measurements reveal a consistent source of CO2 to the atmosphere at an average rate of 610 ± 990 μmol m−2 hour−1 during our study and 700 ± 660 μmol m−2 hour−1 (6.1 mol m−2 year−1) over an annual cycle. Net alkalinity consumption by ecosystem calcification explains >95% of the observed CO2 emissions, far exceeding organic carbon burial and anaerobic alkalinity generation. We argue that the net carbon sequestration potential of seagrass meadows may be overestimated if calcification-induced CO2 emissions are not accounted for, especially in regions where calcification rates exceed net primary production and burial. %0 Artikel %@ 2296-7745 %A Rixen, T. %A Lahajnar, N. %A Lamont, T. %A Koppelmann, R. %A Martin, B. %A van Beusekom, J. %A Siddiqui, C. %A Pillay, K. %A Meiritz, L. %D 2021 %J Frontiers in Marine Science %N 2685 %P 730591 %R doi:10.3389/fmars.2021.730591 %T Oxygen and Nutrient Trapping in the Southern Benguela Upwelling System %U https://dx.doi.org/10.3389/fmars.2021.730591 %X The Benguela Upwelling System in the southeast Atlantic Ocean is of crucial socio-economic importance due to its high productivity. However, predicting its response to global change and understanding past changes are still great challenges. Here, we compile data obtained from a research cruise and an oceanographic mooring to demonstrate that a topographically steered nutrient trapping zone develops in a narrow belt along the coast during the main upwelling season in austral spring and summer in the southern Benguela Upwelling System. High nutrient concentrations within this zone increase the impact of upwelling on the productivity of the southern Benguela Upwelling System, but the efficient nutrient trapping operates at the expense of decreasing oxygen concentrations. This enhances the probability of anoxic events emerging toward the end of the upwelling season. However, at the end of the upwelling season, the front that separates the coastally trapped waters from open shelf waters weakens or even collapses due to upwelling cessation and the reversing current regime. This, in addition to a stronger vertical mixing caused by winter cooling, fosters the ventilation of the nutrient trapping zone, which reestablishes during the following upwelling season. The postulated intensification of upwelling and changes in the ecosystem structure in response to global warming seem to reduce the nutrient trapping efficiency by increasing offshore advection of surface waters and plankton blooms. The intensified upwelling and resulting lower biological oxygen consumption appears to mask the expected impacts of global warming on the oxygen minimum zone (OMZ) in the southern Benguela Upwelling System. In contrast to other OMZs, including those in northern Benguela Upwelling Systems, the OMZ in the southern Benguela Upwelling System reveals so far no detectable long-term decrease in oxygen. Thus, the nutrient trapping efficiency seems to be a critical feature mitigating global change impacts on the southern Benguela Upwelling System. Since it is topographically steered, regional impacts on the nutrient trapping efficiency appear also to explain varying responses of upwelling systems to global change as the comparison between southern and northern Benguela Upwelling System shows. This emphasizes the need for further and more comparable studies in order to better understand the response of Eastern Boundary Upwelling Systems and their ecosystem services to global change. %0 Artikel %@ 2169-9275 %A Zhang, W. %A Neumann, A. %A Daewel, U. %A Wirtz, K. %A van Beusekom, J. %A Eisele, A. %A Ma, M. %A Schrum, C. %D 2021 %J Journal of Geophysical Research : Oceans %N 2698 %P e2020JC016995 %R doi:10.1029/2020JC016995 %T Quantifying Importance of Macrobenthos for Benthic-Pelagic Coupling in a Temperate Coastal Shelf Sea %U https://dx.doi.org/10.1029/2020JC016995 10 %X Benthic oxygen fluxes consist mostly of advective and diffusive terms. Both terms in the German Bight exhibit a prominent annual cycle but with opposite variation patterns. To understand the driving mechanisms quantitatively, a novel 3-D benthic-pelagic coupled model resolving interactions among macrobenthos, bioturbation, oxygen consumption, and carbon early diagenesis was applied to reconstruct the benthic states. Simulation results show a satisfactory agreement with field data and reveal that the benthic oxygen flux is determined by not only pelagic drivers but also by internal dynamics associated with the interaction between organic carbon and macrobenthos, and bedform morphodynamics. Variation of advective flux, characterized by summer-low and winter-high, is mainly driven by hydrodynamics and bedform morphodynamics, while variation of diffusive flux, featured by summer-high and winter-low, is a compound effect of pelagic and benthic drivers with a dominant control by macrobenthos through bioturbation. The role of bioturbation in benthic oxygen consumption is twofold: (a) on the one hand, it alters the particulate organic carbon (POC) distribution in surface sediments, thereby changing the availability of POC to oxygen consumption; (b) on the other hand, it mixes oxygen down into sediments, thereby facilitating oxygen consumption. Our results indicate that the first role prevails in sandy seafloor characterized by energetic hydrodynamics, while the second role becomes increasingly important along with a weakening of bottom currents. We found that bioturbation contributes up to 87% urn:x-wiley:21699275:media:jgrc24733:jgrc24733-math-0001 4% and 55% urn:x-wiley:21699275:media:jgrc24733:jgrc24733-math-0002 8% of the total benthic oxygen fluxes in muddy seabed and at a regional scale (the German Bight), respectively. %0 Artikel %@ 0012-8252 %A Arlinghaus, P. %A Zhang, W. %A Wrede, A. %A Schrum, C. %A Neumann, A. %D 2021 %J Earth-Science Reviews %N 2468 %P 103803 %R doi:10.1016/j.earscirev.2021.103803 %T Impact of benthos on morphodynamics from a modeling perspective %U https://dx.doi.org/10.1016/j.earscirev.2021.103803 %X Benthic organisms and their bioturbation activities have a profound effect on a multitude of sediment properties. While many studies have already explored benthic impacts at small temporal and spatial scales, little is known on how the small-scale effects accumulate and interactively guide large-scale (km-scale) morphological evolution. Here we firstly summarize the most important processes of benthos affecting sediment stability and then explore existing biomorphodynamic modeling studies both at small- and large-scales. In general, microbenthos (body size <0.1 mm) mainly stabilizes sediments while meio- (0.1–1 mm) and macrobenthos (>1 mm) may stabilize or destabilize sediments. Among all types of sediment, fine-grained fraction (silt and clay) is most sensitive to the impact of benthos. Benthic organisms have the capability to mediate sediment transport and sedimentation patterns beyond their habitats on the long-term and over a large-scale. However, so far, numerical models evaluating benthic impact are limited to explorative studies and have not reached a stage where they can be used for predictive modeling. The barriers hindering a further development of biomorphodynamic models include not only limited understanding of fundamental biological/bio-physical processes affecting morphological development and dynamic feedback loops among them but also a shortage of data for model calibration and confirmation of simulation results. On the other hand, thriving for higher model complexity does not necessarily lead to better performance. Before conducting biomorphodynamic modeling, researchers must figure out which questions can be answered in a meaningful sense with simulation results that can be compared with observations and which level of modeling complexity is sufficient for that purpose. %0 Artikel %@ 0024-3590 %A Van Dam, B. %A Lopes, C. %A Polsenaere, P. %A Price, R. %A Rutgersson, A. %A Fourqurean, J. %D 2021 %J Limnology and Oceanography %N 1281 %P 510 - 527 %R doi:10.1002/lno.11620 %T Water temperature control on CO2 flux and evaporation over a subtropical seagrass meadow revealed by atmospheric eddy covariance %U https://dx.doi.org/10.1002/lno.11620 2 %X Subtropical seagrass meadows play a major role in the coastal carbon cycle, but the nature of air–water CO2 exchanges over these ecosystems is still poorly understood. The complex physical forcing of air–water exchange in coastal waters challenges our ability to quantify bulk exchanges of CO2 and water (evaporation), emphasizing the need for direct measurements. We describe the first direct measurements of evaporation and CO2 flux over a calcifying seagrass meadow near Bob Allen Keys, Florida. Over the 78‐d study, CO2 emissions were 36% greater during the day than at night, and the site was a net CO2 source to the atmosphere of 0.27 ± 0.17 μmol m−2 s−1 (x̅ ± standard deviation). A quarter (23%) of the diurnal variability in CO2 flux was caused by the effect of changing water temperature on gas solubility. Furthermore, evaporation rates were ~ 10 times greater than precipitation, causing a 14% increase in salinity, a potential precursor of seagrass die‐offs. Evaporation rates were not correlated with solar radiation, but instead with air–water temperature gradient and wind shear. We also confirm the role of convective forcing on night‐time enhancement and day‐time suppression of gas transfer. At this site, temperature trends are regulated by solar heating, combined with shallow water depth and relatively consistent air temperature. Our findings indicate that evaporation and air–water CO2 exchange over shallow, tropical, and subtropical seagrass ecosystems may be fundamentally different than in submerged vegetated environments elsewhere, in part due to the complex physical forcing of coastal air–sea gas transfer. %0 Artikel %@ 2690-0637 %A Adyasari, D. %A Waska, H. %A Daehnke, K. %A Oehler, T. %A Pracoyo, A. %A Putra, D. %A Moosdorf, N. %D 2021 %J ACS ES & T Water %N 3004 %P 1887 - 1900 %R doi:10.1021/acsestwater.1c00134 %T Terrestrial Nutrients and Dissolved Organic Matter Input to the Coral Reef Ecosystem via Submarine Springs %U https://dx.doi.org/10.1021/acsestwater.1c00134 8 %X Submarine groundwater discharge (SGD) transports terrestrial nutrients and dissolved organic matter (DOM) to the ocean. An elevated concentration of nutrients and DOM can act as stressors enhancing coral disease and mortality, but only a few studies address the impacts of groundwater-borne nutrients and DOM on coral reef ecosystems. This study quantifies and characterizes nutrients, nitrate (NO3–) stable isotopes, and DOM molecular composition of coastal groundwater discharging to the reef ecosystem via submarine springs in Lombok, Indonesia. NO3– isotopic values point to both natural (soil) and anthropogenic (wastewater and fertilizer) origins of nutrients in the coastal aquifer. Submarine springs are fed by different groundwater sources and deliver land-based NO3–, dissolved silica, phosphate, and labile DOM to the reef water column. Terrestrial nutrients and DOM undergo rapid turnover in the reef water column due to biogeochemical processes and biological uptake. Meanwhile, reef and offshore water likely act as sources of more stable, reworked DOM formulas and its mineralization product, ammonium. We observed that submarine springs consistently deliver similar nutrient loadings, creating a long-term environmental threat to coral reef sustainability. This study emphasizes the importance of understanding coastal biogeochemistry and hydrological processes in sensitive tropical ecosystems, particularly those adjacent to modified land-use watersheds. %0 Artikel %@ 0141-1136 %A Bolle, L. %A Hoek, R. %A Pennock, I. %A Poiesz, S. %A van Beusekom, J. %A van der Veer, H. %A Witte, J. %A Tulp, I. %D 2021 %J Marine Environmental Research %N 2398 %P 105364 %R doi:10.1016/j.marenvres.2021.105364 %T No evidence for reduced growth in resident fish species in the era of de-eutrophication in a coastal area in NW Europe %U https://dx.doi.org/10.1016/j.marenvres.2021.105364 %X Coastal areas in north-western Europe have been influenced by elevated nutrient levels starting in the 1960s. Due to efficient measures, both nitrate and phosphate levels decreased since the mid-1980s. The co-occurring declines in nutrient loadings and fish productivity are often presumed to be causally linked. We investigated whether four resident fish species (twaite shad, bull-rout, thick-lipped grey mullet and eelpout), that spend the majority of their life in the vicinity of the coast, differed in growth between the historic eutrophication period compared to the recent lower nutrient-level period. Based on Von Bertalanffy growth models of length at age, and the analysis of annual otolith increments, we investigated the difference in sex-specific growth patterns and related these to temperature, eutrophication level (Chlorophyll a), growth window and fish density. In all four species, annual otolith growth rates during the early life stages differed between the two periods, mostly resulting in larger lengths at age in the recent period. All species showed significant correlations between increment size and temperature, explaining the observed period differences. The lack of an effect of total fish biomass provided no evidence for density dependent growth. A correlation with chlorophyll was found in bull-rout, but the relationship was negative, thus not supporting the idea of growth enhanced by high nutrient levels. In conclusion, we found no evidence for reduced growth related to de-eutrophication. Our results indicate that temperature rise due to climate change had a greater impact on growth than reduced food availability due to de-eutrophication. We discuss potential consequences of growth changes for length-based indicators used in management. %0 Artikel %@ 2296-7745 %A Callies, U. %A Kreus, M. %A Petersen, W. %A Voynova, Y. %D 2021 %J Frontiers in Marine Science %N 2685 %P 666653 %R doi:10.3389/fmars.2021.666653 %T On Using Lagrangian Drift Simulations to Aid Interpretation of in situ Monitoring Data %U https://dx.doi.org/10.3389/fmars.2021.666653 %X One key challenge of marine monitoring programs is to reasonably combine information from different in situ observations spread in space and time. In that context, we suggest the use of Lagrangian transport simulations extending both forward and backward in time to identify the movements of water bodies from the time they were observed to the time of their synopsis. We present examples of how synoptic maps of salinity generated by this method support the identification and tracing of river plumes in coastal regions. We also demonstrate how we can use synoptic maps to delineate different water masses in coastal margins. These examples involve quasi-continuous observations of salinity taken along ferry routes. A third application is the synchronization of measurements between fixed stations and nearby moving platforms. Both observational platforms often see the same water body, but at different times. We demonstrate how the measurements from a fixed platform can be synchronized to measurements from a moving platform by taking into account simulation-based time shifts. %0 Artikel %@ 2296-7745 %A Pein, J. %A Eisele, A. %A Sanders, T. %A Daewel, U. %A Stanev, E. %A Beusekom, J. %A Staneva, J. %A Schrum, C. %D 2021 %J Frontiers in Marine Science %N 2685 %P 623714 %R doi:10.3389/fmars.2021.623714 %T Seasonal Stratification and Biogeochemical Turnover in the Freshwater Reach of a Partially Mixed Dredged Estuary %U https://dx.doi.org/10.3389/fmars.2021.623714 %X The Elbe estuary is a substantially engineered tidal water body that receives high loads of organic matter from the eutrophied Elbe river. The organic matter entering the estuary at the tidal weir is dominated by diatom populations that collapse in the deepened freshwater reach. Although the estuary’s freshwater reach is considered to manifest vertically homogenous density distribution (i.e., to be well-mixed), several indicators like trapping of particulate organic matter, near-bottom oxygen depletion and ammonium accumulation suggest that the vertical exchange of organic particles and dissolved oxygen is weakened at least temporarily. To better understand the causal links between the hydrodynamics and the oxygen and nutrient cycling in the deepened freshwater reach of the Elbe estuary, we establish a three-dimensional coupled hydrodynamical-biogeochemical model. The model demonstrates good skill in simulating the variability of the physical and biogeochemical parameters in the focal area. Coupled simulations reveal that this region is a hotspot of the degradation of diatoms and organic matter transported from the shallow productive upper estuary and the tidal weir. In summer, the water column weakly stratifies when at the bathymetric jump warmer water from the shallow upper estuary spreads over the colder water of the deepened mid reaches. Enhanced thermal stratification also occurs also in the narrow port basins and channels. Model results show intensification of the particle trapping due to the thermal gradients. The stratification also reduces the oxygenation of the near-bottom region and sedimentary layer inducing oxygen depletion and accumulation of ammonium. The study highlights that the vertical resolution is important for the understanding and simulation of estuarine ecological processes, because even weak stratification impacts the cycling of nutrients via modulation of the vertical mixing of oxygen, particularly in deepened navigation channels and port areas. %0 Artikel %@ 0967-0645 %A Pavlidou, A. %A Velaoras, D. %A Karageorgis, A. %A Rousselaki, E. %A Parinos, C. %A Dähnke, K. %A Möbius, J. %A Meador, T. %A Psarra, S. %A Frangoulis, C. %A Souvermezoglou, E. %A Androni, A. %A Assimakopoulou, G. %A Chaikalis, S. %A Kanellopoulos, T. %A Lagaria, A. %A Zachioti, P. %A Gogou, A. %D 2020 %J Deep-Sea Research Part II %N 2081 %P 104704 %R doi:10.1016/j.dsr2.2019.104704 %T Seasonal variations of biochemical and optical properties, physical dynamics and N stable isotopic composition in three northeastern Mediterranean basins (Aegean, Cretan and Ionian Seas) %U https://dx.doi.org/10.1016/j.dsr2.2019.104704 %X Multidisciplinary surveys were conducted in October 2014, May 2015 and December 2015 in three major deep basins of the Eastern Mediterranean Sea (EMED) - the north Aegean Sea, the south Aegean (Cretan Sea) and its straits, and the south Ionian Sea - providing the most recent information on physical, biochemical and particle dynamics, along with nitrogen stable isotope composition. A north-south gradient in oligotrophy was observed, presumably related to more pronounced nutrient supply through the inflow of Black Sea Water and riverine inputs in the surface waters of the north Aegean Sea, coinciding with the relatively higher productivity in this area. Consumption rates of Dissolved Oxygen (DO) in the deep waters of the north Aegean Sea reveal the physical dynamics of the subsurface layers. According to this, it seems that no deep water formation has occurred in the Athos basin after 2008. In the Cretan Sea, the Transitional Mediterranean Water mass was identified at the layer 700-1200 m showing a slight decrease in its core depth, when compared with previous studies in the area. Seasonal variations of DO and salinity in the deep waters of the Ionian Sea indicate the intrusion of more oxygenated and less saline waters of Adriatic origin in the bathypelagic layer of the south Ionian Sea. Detailed determination of stable isotope ratios for nitrate (δ15N-NO3) and suspended particulate nitrogen (δ15N-PN) in various water column depth of the three basins showed a further decrease of the overall low EMED δ15N signal, when compared with previous studies in the area. This trend can be attributed to the onward atmospheric deposition of anthropogenic N to the EMED. The δ15N-PN depth profiles exhibited clear Rayleigh-type isotope fractionation and associated with remineralisation throughout the water column, implying that the unique, isolated oceanic basins of the Eastern Mediterranean serve as important marine observatories of anthropogenic influences on marine nutrient budgets. %0 Artikel %@ 2363-6122 %A Bunzel, D. %A Milker, Y. %A Müller-Navarra, K. %A Arz, H. %A Friedrich, J. %A Lahajnar, N. %A Schmiedl, G. %D 2020 %J Newsletters on stratigraphy %N 2886 %P 415 - 442 %R doi:10.1127/nos/2020/0540 %T Integrated stratigraphy of foreland salt-marsh sediments of the south-eastern North Sea region %U https://dx.doi.org/10.1127/nos/2020/0540 4 %X Depositional processes in coastal wetlands respond to a changing climate as documented in the sediment sequences of salt marshes. In this context, robust chronologies are crucial for the reconstruction of salt-marsh depositional processes in the past. However, salt-marsh sediments from the highly dynamic North Sea coast often lack a reliable stratigraphy due to the combined influences of natural processes and human activities, causing a reworking and re-deposition of the sediments. Here, a combination of absolute and relative dating methods has been applied in order to establish an integrated stratigraphic framework for active foreland salt marshes along the south-eastern North Sea coast. This stratigraphic framework is based on radionuclides (210Pb, 137Cs, 241Am, 14C) and mercury (Hg) contaminations, together with ln(Zr/Rb) as a grain-size proxy for additional inter-correlation between the four studied sites. The studied salt marshes encompass different environmental settings concerning the inundation frequency and intensity, and anthropogenic influences. As a result, the reconstructed mean sediment-accretion rates range from 1.16 cm yr–1 in the anthropogenically modified and grazed coastal salt marsh at Friedrichskoog, to 1.31 cm yr–1 in the more sheltered and semi-enclosed salt marsh in the Bay of Tümlau, and up to 1.75 cm yr–1 in the dynamic open coastal salt-marsh at Kaiser-Wilhelm-Koog. Similar mean high accretion rates of 1.72 cm yr–1 are documented for the Eider estuary until AD 1965, before they dropped to 0.72 cm yr–1 after completion of the Eider tidal barrier in AD 1973. The results highlight the advantage of combining independent dating methods for the establishment of salt-marsh chronologies, which proves to be essential to compensate for absence or blurring of distinct stratigraphic signals in highly dynamic coastal depositional settings, such as the salt-marsh systems at the south-eastern North Sea coastal region. The reconstructed sediment-accretion rates suggest a high resilience of salt-marsh systems to ongoing sea-level rise as long as sediment availability and natural flooding dynamics are maintained. %0 Artikel %@ 0048-9697 %A Zimmermann, T. %A Mohammed, F. %A Reese, A. %A Wieser, M. %A Kleeberg, U. %A Pröfrock, D. %A Irrgeher, J. %D 2020 %J Science of the Total Environment %N 1562 %P 135219 %R doi:10.1016/j.scitotenv.2019.135219 %T Zinc isotopic variation of water and surface sediments from the German Elbe River %U https://dx.doi.org/10.1016/j.scitotenv.2019.135219 %X Recent studies suggested the use of the isotopic composition of Zn as a possible tracer for anthropogenic Zn emissions. Nevertheless, studies mainly focused on sampling areas of a few km2 with well-characterized anthropogenic Zn emissions. In contrast, this study focused on analyzing a large sample set of water and sediment samples taken throughout the course of the Elbe River, a large, anthropogenically impacted river system located in Central Europe. The primary objective was to evaluate the use of the isotopic composition of Zn to trace anthropogenic Zn emission on a large regional scale. In total 18 water and 26 surface sediment samples were investigated, covering the complete course of over 700 km of the German Elbe between the German/Czech border and the German North Sea, including six tributaries. Stable isotope abundance ratios of Zn were assessed by multi-collector inductively coupled plasma mass spectrometry (MC ICP-MS) in water filtrates (<0.45 µm) and total digests of the sieved surface sediment fraction (<63 µm) after analyte/matrix separation using Bio-Rad AG MP-1 resin via a micro-column approach and application of a 64Zn/67Zn double spike. Measured isotopic compositions of δ66Zn/64ZnIRMM-3702 ranged from −0.10 ‰ to 0.32 ‰ for sediment samples, and from −0.51 ‰ to 0.45 ‰ for water samples. In comparison to historical data some tributaries still feature high mass fractions of anthropogenic Zn (e.g. Mulde, Triebisch) combined with δ66Zn/64ZnIRMM-3702 values higher than the lithogenic background. The dissolved δ66Zn/64ZnIRMM-3702 values showed a potential correlation with pH. Our results indicate that biogeochemical processes like absorption may play a key role in natural Zn isotopic fractionation making it difficult to distinguish between natural and anthropogenic processes. %0 Artikel %@ 1726-4170 %A Delaigue, L. %A Thomas, H. %A Mucci, A. %D 2020 %J Biogeosciences %N 2118 %P 547 - 566 %R doi:10.5194/bg-17-547-2020 %T Spatial variations in CO2 fluxes in the Saguenay Fjord (Quebec, Canada) and results of a water mixing model %U https://dx.doi.org/10.5194/bg-17-547-2020 2 %X The Saguenay Fjord is a major tributary of the St. Lawrence Estuary and is strongly stratified. A 6–8 m wedge of brackish water typically overlies up to 270 m of seawater. Relative to the St. Lawrence River, the surface waters of the Saguenay Fjord are less alkaline and host higher dissolved organic carbon (DOC) concentrations. In view of the latter, surface waters of the fjord are expected to be a net source of CO2 to the atmosphere, as they partly originate from the flushing of organic-rich soil porewaters. Nonetheless, the CO2 dynamics in the fjord are modulated with the rising tide by the intrusion, at the surface, of brackish water from the Upper St. Lawrence Estuary, as well as an overflow of mixed seawater over the shallow sill from the Lower St. Lawrence Estuary. Using geochemical and isotopic tracers, in combination with an optimization multiparameter algorithm (OMP), we determined the relative contribution of known source waters to the water column in the Saguenay Fjord, including waters that originate from the Lower St. Lawrence Estuary and replenish the fjord's deep basins. These results, when included in a conservative mixing model and compared to field measurements, serve to identify the dominant factors, other than physical mixing, such as biological activity (photosynthesis, respiration) and gas exchange at the air–water interface, that impact the water properties (e.g., pH, pCO2) of the fjord. Results indicate that the fjord's surface waters are a net source of CO2 to the atmosphere during periods of high freshwater discharge (e.g., spring freshet), whereas they serve as a net sink of atmospheric CO2 when their practical salinity exceeds ∼5–10. %0 Artikel %@ 0043-1354 %A Liu, Z. %A Callies, U. %D 2020 %J Water Research %N 1591 %P 115196 %R doi:10.1016/j.watres.2019.115196 %T A probabilistic model of decision making regarding the use of chemical dispersants to combat oil spills in the German Bight %U https://dx.doi.org/10.1016/j.watres.2019.115196 %X Oil spills are one of the major threats to the marine environment in the German Bight (North Sea). In case of an accident, application of chemical dispersants would be one response option among others. Dispersion breaks oil slicks into small droplets which get then mixed into the water column. Removal of the oil from the water surface may reduce contamination of the coast. However, the window of opportunity for effective dispersant application is short and there are concerns about potential effects to the marine life. We propose a Bayesian network (BN) as an interactive and intuitive tool for responders to justify decisions on using chemical dispersants and possibly the provision of appropriate assets. The BN combines detailed sub-BNs for different criteria that govern the decision process. Expected drift trajectories are estimated based on comprehensive numerical ensemble simulations of hypothetical oil spills. Ecological impacts are represented prototypically, focusing on vulnerability of seabird concentrations to pollution in coastal areas. Dispersant effectiveness is estimated considering oil properties and weather conditions. Decision making is supposed to be based on expected satisfaction. The definition of what is considered satisfactory is of central importance for the whole analysis. %0 Artikel %@ 0892-0753 %A Maradino, C. %A van Doorn, E. %A McDonald, N. %A Johnson, M. %A Acma, B. %A Breviere, E. %A Campen, H. %A Carou, S. %A Cocco, E. %A Endres, S. %A Hilmi, N. %A Hopkins, F. %A Liss, P. %A Maes, F. %A Martensson, M. %A Oeffner, J. %A Oloyede, M. %A Peters, A. %A Quack, B. %A Singh, P. %A Thomas, H. %D 2020 %J Coastal Management %N 2304 %P 238 - 256 %R doi:10.1080/08920753.2020.1773208 %T From Monodisciplinary via Multidisciplinary to an Interdisciplinary Approach Investigating Air-Sea Interactions – a SOLAS Initiative %U https://dx.doi.org/10.1080/08920753.2020.1773208 4 %X Understanding the physical and biogeochemical interactions and feedbacks between the ocean and atmosphere is a vital component of environmental and Earth system research. The ability to predict and respond to future environmental change relies on a detailed understanding of these processes. The Surface Ocean-Lower Atmosphere Study (SOLAS) is an international research platform that focuses on the study of ocean-atmosphere interactions, for which Future Earth is a sponsor. SOLAS instigated a collaborative initiative process to connect efforts in the natural and social sciences related to these processes, as a contribution to the emerging Future Earth Ocean Knowledge-Action Network (Ocean KAN). This is imperative because many of the recent changes in the Earth system are anthropogenic. An understanding of adaptation and counteracting measures requires an alliance of scientists from both domains to bridge the gap between science and policy. To this end, three SOLAS research areas were targeted for a case study to determine a more effective method of interdisciplinary research: valuing carbon and the ocean’s role; air-sea interactions, policy and stewardship; and, air-sea interactions and the shipping industry. %0 Artikel %@ 1726-4170 %A Schwichtenberg, F. %A Pätsch, J. %A Böttcher, M. %A Thomas, H. %A Winde, V. %A Emeis, K. %D 2020 %J Biogeosciences %N 2118 %P 4223 - 4245 %R doi:10.5194/bg-17-4223-2020 %T The impact of intertidal areas on the carbonate system of the southern North Sea %U https://dx.doi.org/10.5194/bg-17-4223-2020 16 %X The coastal ocean is strongly affected by ocean acidification because of its shallow water depths, low volume, and the closeness to terrestrial dynamics. Earlier observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) in the southern part of the North Sea, a northwest European shelf sea, revealed lower acidification effects than expected. It has been assumed that anaerobic degradation and subsequent TA release in the adjacent back-barrier tidal areas (Wadden Sea) in summertime is responsible for this phenomenon. In this study the exchange rates of TA and DIC between the Wadden Sea tidal basins and the North Sea and the consequences for the carbonate system in the German Bight are estimated using a 3D ecosystem model. The aim of this study is to differentiate the various sources contributing to observed high summer TA in the southern North Sea. Measured TA and DIC in the Wadden Sea are considered as model boundary conditions. This procedure acknowledges the dynamic behaviour of the Wadden Sea as an area of effective production and decomposition of organic material. According to the modelling results, 39 Gmol TA yr−1 were exported from the Wadden Sea into the North Sea, which is less than a previous estimate but within a comparable range. The interannual variabilities in TA and DIC, mainly driven by hydrodynamic conditions, were examined for the years 2001–2009. Dynamics in the carbonate system are found to be related to specific weather conditions. The results suggest that the Wadden Sea is an important driver for the carbonate system in the southern North Sea. On average 41 % of TA inventory changes in the German Bight were caused by riverine input, 37 % by net transport from adjacent North Sea sectors, 16 % by Wadden Sea export, and 6 % were caused by internal net production of TA. The dominant role of river input for the TA inventory disappears when focusing on TA concentration changes due to the corresponding freshwater fluxes diluting the marine TA concentrations. The ratio of exported TA versus DIC reflects the dominant underlying biogeochemical processes in the Wadden Sea. Whereas aerobic degradation of organic matter played a key role in the North Frisian Wadden Sea during all seasons of the year, anaerobic degradation of organic matter dominated in the East Frisian Wadden Sea. Despite the scarcity of high-resolution field data, it is shown that anaerobic degradation in the Wadden Sea is one of the main contributors of elevated summer TA values in the southern North Sea. %0 Artikel %@ 1726-4170 %A Beaupré-Laperrière, A. %A Mucci, A. %A Thomas, H. %D 2020 %J Biogeosciences %N 2118 %P 3923 - 3942 %R doi:10.5194/bg-17-3923-2020 %T The recent state and variability of the carbonate system of the Canadian Arctic Archipelago and adjacent basins in the context of ocean acidification %U https://dx.doi.org/10.5194/bg-17-3923-2020 14 %X Ocean acidification driven by the uptake of anthropogenic CO2 by the surface oceans constitutes a potential threat to the health of marine ecosystems around the globe. The Arctic Ocean is particularly vulnerable to acidification and thus is an ideal region to study the progression and effects of acidification before they become globally widespread. The appearance of undersaturated surface waters with respect to the carbonate mineral aragonite (ΩA<1), an important threshold beyond which the calcification and growth of some marine organisms might be hindered, has recently been documented in the Canada Basin and adjacent Canadian Arctic Archipelago (CAA), a dynamic region with an inherently strong variability in biogeochemical processes. Nonetheless, few of these observations were made in the last 5 years and the spatial coverage in the latter region is poor. We use a dataset of carbonate system parameters measured in the CAA and its adjacent basins (Canada Basin and Baffin Bay) from 2003 to 2016 to describe the recent state of these parameters across the Canadian Arctic and investigate the amplitude and sources of the system's variability over more than a decade. Our findings reveal that, in the summers of 2014 to 2016, the ocean surface across our study area served as a net CO2 sink and was partly undersaturated with respect to aragonite in the Canada Basin and the Queen Maud Gulf, the latter region exhibiting undersaturation over its entire water column at some locations. We estimate, using measurements made across several years, that approximately a third of the interannual variability in surface dissolved inorganic carbon (DIC) concentrations in the CAA results from fluctuations in biological activity. In consideration of the system's variability resulting from these fluctuations, we derive times of emergence of the anthropogenic ocean acidification signal for carbonate system parameters in the study area. %0 Artikel %@ 1726-4170 %A Mears, C. %A Thomas, H. %A Henderson, P. %A Charette, M. %A MacIntyre, H. %A Dehairs, F. %A Monnin, C. %A Mucci, A. %D 2020 %J Biogeosciences %N 2118 %P 4937 - 4959 %R doi:10.5194/bg-17-4937-2020 %T Using 226Ra and 228Ra isotopes to distinguish water mass distribution in the Canadian Arctic Archipelago %U https://dx.doi.org/10.5194/bg-17-4937-2020 20 %X As a shelf dominated basin, the Arctic Ocean and its biogeochemistry are heavily influenced by continental and riverine sources. Radium isotopes (226Ra, 228Ra, 224Ra, 223Ra), are transferred from the sediments to seawater, making them ideal tracers of sediment-water exchange processes and ocean mixing. 226Ra and 228Ra are the two longer-lived isotopes of the Radium Quartet (226Ra, t1/2 = 1600 y and 228Ra, t1/2 = 5.8 y). Because of their long half-lives they can provide insight into the water mass compositions, distribution patterns, as well as mixing processes and the associated timescales throughout the Canadian Arctic Archipelago (CAA). The wide range of 226Ra, 228Ra, and of the 228Ra / 226Ra ratio, measured in water samples collected during the 2015 GEOTRACES cruise, complemented by additional chemical tracers (dissolved inorganic carbon (DIC), total alkalinity (AT), barium (Ba), and the stable oxygen isotope composition of water (δ18O)) highlight the dominant biogeochemical, hydrographic and bathymetric features of the CAA. Bathymetric features, such as the continental shelf and shallow coastal sills, are critical in modulating circulation patterns within the CAA, including the bulk flow of Pacific waters and the inhibited eastward flow of denser Atlantic waters through the CAA. Using a Principal Component Analysis, we unravel the dominant mechanisms and the apparent water mass end-members that shape the tracer distributions. We identify two distinct water masses located above and below the upper halocline layer throughout the CAA, as well as distinctly differentiate surface waters in the eastern and western CAA. Furthermore, we identify water exchange across 80° W, inferring a draw of Atlantic water, originating from Baffin Bay, into the CAA. In other words, this implies the presence of an Atlantic water U-turn located at Barrow Strait, where the same water mass is seen along the northernmost edge at 80° W as well as along south-easternmost confines of Lancaster Sound. Overall, this study provides a stepping stone for future research initiatives within the Canadian Arctic Archipelago, revealing how quantifying disparities in radioactive isotopes can provide valuable information on the potential effects of climate change within vulnerable areas such as the CAA. %0 Artikel %@ 1726-4170 %A Bratek, A. %A Beusekom, J. %A Neumann, A. %A Sanders, T. %A Friedrich, J. %A Emeis, K. %A Dähnke, K. %D 2020 %J Biogeosciences %N 2118 %P 2839 - 2851 %R doi:10.5194/bg-17-2839-2020 %T Spatial variations in sedimentary N-transformation rates in the North Sea (German Bight) %U https://dx.doi.org/10.5194/bg-17-2839-2020 10 %X In this study, we investigate the role of sedimentary N cycling in the southern North Sea. We present a budget of ammonification, nitrification and sedimentary NO−3 consumption and denitrification in contrasting sediment types of the German Bight (southern North Sea), including novel net ammonification rates. We incubated sediment cores from four representative locations in the German Bight (permeable, semi-permeable and impermeable sediments) with labeled nitrate and ammonium to calculate benthic fluxes of nitrate and ammonium and gross rates of ammonification and nitrification. Ammonium fluxes generally suggest oxic degradation of organic matter, but elevated fluxes at one sampling site point towards the importance of bioirrigation or short-term accumulation of organic matter. Sedimentary fluxes of dissolved inorganic nitrogen are an important source for primary producers in the water column, supporting ∼7 % to 59 % of the average annual primary production, depending on water depth. We find that ammonification and oxygen penetration depth are the main drivers of sedimentary nitrification, but this nitrification is closely linked to denitrification. One-third of freshly produced nitrate in impermeable sediment and two-thirds in permeable sediment were reduced to N2. The semi-permeable and permeable sediments are responsible for ∼68 % of the total benthic N2 production rates, which, based solely on our data, amounts to ∼1030 t N d−1 in the southern North Sea. Thus, we conclude that semi-permeable and permeable sediments are the main sinks of reactive N, counteracting eutrophication in the southern North Sea (German Bight). %0 Artikel %@ 1025-6016 %A Bratek, A. %A Emeis, K. %A Sanders, T. %A Wankel, S. %A Struck, U. %A Möbius, J. %A Dähnke, K. %D 2020 %J Isotopes in Environmental and Health Studies %N 2755 %P 14 - 35 %R doi:10.1080/10256016.2020.1723580 %T Nitrate sources and the effect of land cover on the isotopic composition of nitrate in the catchment of the Rhône River %U https://dx.doi.org/10.1080/10256016.2020.1723580 1 %X The Rhône River originates in the high Alps and drains an intensely cultivated and industrialised catchment before it discharges to the Gulf of Lion. We investigated the interaction of catchment geomorphology with nitrate sources (atmosphere, agriculture, and nitrification of soil organic matter) and removal processes in large and diverse watersheds on the basis of dual nitrate isotope signatures in river water. In March 2015, we took surface water samples along the Rhône River, including its main tributaries, and measured nutrient concentrations and the stable isotopic composition of nitrate (δ15N, δ18O and Δ17O), and water (δ18O-H2O). Results show that high altitude regions are dominated by nitrate from nitrification in pristine soils and atmospheric deposition, while nitrate in the downstream Rhône River originates mainly from nitrification of agricultural/urban sources. Parallel increases in δ15N and δ18O reflect the influence of primary production. Previous studies suggested robust correlations between land use and δ15N-NO–3 . Based on our observation that nitrate δ15N values at higher altitudes are lower than expected, we assume that lower nitrate δ15N values likely reflect limited nitrate consumption and lower soil nitrogen turnover rates. We propose that correlation between land use and nitrate δ15N is sensitive to slope and geomorphology. %0 Artikel %@ 2169-9275 %A Pätsch, J. %A Gouretski, V. %A Hinrichs, I. %A Koul, V. %D 2020 %J Journal of Geophysical Research : Oceans %N 2698 %P e2019JC015825 %R doi:10.1029/2019JC015825 %T Distinct Mechanisms Underlying Interannual to Decadal Variability of Observed Salinity and Nutrient Concentration in the Northern North Sea %U https://dx.doi.org/10.1029/2019JC015825 5 %X The influence of large‐scale oceanic circulation on salinity in the northern North Sea has lead to the hypothesis that nutrient concentrations in this region are also driven by remote oceanic anomalies. Here, using a newly established biogeochemical data set of the North Sea, we show that interannual to decadal variability in winter nutrient concentrations exhibits distinct phase deviations from salinity. The variability in salinity is explained by zonal shifts in the position of the subpolar front (SPF) in the eastern North Atlantic and the associated advective delay. However, the high correlation and absence of advective delay between the position of the SPF and winter nutrient concentrations in the Shetland region (59–61°N, 1°W to 3°E) point to the role of atmospheric variability in driving concurrent changes in winter nutrient concentrations and the SPF position. Our analysis suggests that the prevailing wind direction and local distribution of winter nutrient concentrations together determine the interannual to decadal variability in winter nutrient concentrations in this region. In the analyzed observations, we find a strong spatial gradient in mean winter nutrient concentrations northwest of the Shetland region, which is absent in salinity. The horizontal shift of this spatial gradient, forced by changes in wind direction, has a larger influence on winter nutrient concentration in the Shetland region than the nutrient signal in oceanic anomalies originating from the eastern subpolar North Atlantic. Overall, we conclude that interannual to decadal variability in the observed nutrient concentrations is mainly driven by atmospheric variability here expressed as wind direction. %0 Artikel %@ 1726-4170 %A Kerimoglu, O. %A Voynova, Y. %A Chegini, F. %A Brix, H. %A Callies, U. %A Hofmeister, R. %A Klingbeil, K. %A Schrum, C. %A van Beusekom, J. %D 2020 %J Biogeosciences %N 2118 %P 5097 - 5127 %R doi:10.5194/bg-17-5097-2020 %T Interactive impacts of meteorological and hydrological conditions on the physical and biogeochemical structure of a coastal system %U https://dx.doi.org/10.5194/bg-17-5097-2020 20 %X The German Bight was exposed to record high riverine discharges in June 2013, as a result of flooding of the Elbe and Weser rivers. Several anomalous observations suggested that the hydrodynamical and biogeochemical states of the system were impacted by this event. In this study, we developed a biogeochemical model and coupled it with a previously introduced high-resolution hydrodynamical model of the southern North Sea in order to better characterize these impacts and gain insight into the underlying processes. Performance of the model was assessed using an extensive set of in situ measurements for the period 2011–2014. We first improved the realism of the hydrodynamic model with regard to the representation of cross-shore gradients, mainly through inclusion of flow-dependent horizontal mixing. Among other characteristic features of the system, the coupled model system can reproduce the low salinities, high nutrient concentrations and low oxygen concentrations in the bottom layers observed within the German Bight following the flood event. Through a scenario analysis, we examined the sensitivity of the patterns observed during July 2013 to the hydrological and meteorological forcing in isolation. Within the region of freshwater influence (ROFI) of the Elbe–Weser rivers, the flood event clearly dominated the changes in salinity and nutrient concentrations, as expected. However, our findings point to the relevance of the peculiarities in the meteorological conditions in 2013 as well: a combination of low wind speeds, warm air temperatures and cold bottom-water temperatures resulted in a strong thermal stratification in the outer regions and limited vertical nutrient transport to the surface layers. Within the central region, the thermal and haline dynamics interactively resulted in an intense density stratification. This intense stratification, in turn, led to enhanced primary production within the central region enriched by nutrients due to the flood but led to reduction within the nutrient-limited outer region, and it caused a widespread oxygen depletion in bottom waters. Our results further point to the enhancement of the current velocities at the surface as a result of haline stratification and to intensification of the thermohaline estuarine-like circulation in the Wadden Sea, both driven by the flood event. %0 Artikel %@ 0944-1344 %A Zhu, L. %A Yu, J. %A Van Dam, B. %A Cao, H. %A Pu, Y. %A Shi, W. %A Qin, B. %D 2020 %J Environmental Science and Pollution Research %N 1113 %P 25870 - 25876 %R doi:10.1007/s11356-019-06436-9 %T Optimized methods for diffusive greenhouse gas flux analyses in inland waters %U https://dx.doi.org/10.1007/s11356-019-06436-9 21 %X Inland waters are considered hotspots of greenhouse gas (GHG) emissions and have been extensively researched. Static chamber (STAT) and thin boundary layer (BLE) are two commonly used methods for analyzing diffusive GHG emissions from inland waters. However, the STAT method is often disturbed by GHG bubbles; meanwhile, many kinds of headspace gas are used in the BLE method, but the differences between their diffusive GHG emission analysis results are not understood. In this study, the chamber in the STAT method was modified to combat the disturbances from GHG bubbles, and the typically used gases for the BLE method, namely, pure nitrogen, air, and filtered air, were comparatively studied. Results demonstrated that the modified chamber could effectively prevent the invasion of GHG bubbles; it increased the success rate from 67 to 90% in the field test, with no obvious impacts on the results of the GHG emission analyses. The use of air and filtered air in the BLE method yielded the lower values of GHG emissions relative to pure nitrogen, and this finding was potentially attributed to the inhibition effects of the residual GHGs and high humidity in air and filtered air on the extraction of diffusive GHGs from the surface water. This study improved the commonly used methods for diffusive GHG emission analysis, and the current findings are beneficial to the study of GHG emissions from inland waters. %0 Artikel %@ 2296-7745 %A Zeller, M. %A Van Dam, B. %A Lopes, C. %A Kominoski, J. %D 2020 %J Frontiers in Marine Science %N 2685 %P 580284 %R doi:10.3389/fmars.2020.580284 %T Carbonate-Associated Organic Matter Is a Detectable Dissolved Organic Matter Source in a Subtropical Seagrass Meadow %U https://dx.doi.org/10.3389/fmars.2020.580284 %X Seagrasses can enhance carbonate sediment dissolution on diel timescales through oxidation of the rhizosphere and production of acidic exudates of dissolved organic matter (DOM). Carbonates can also associate with DOM either from biogenesis or later adsorption. However, the impact of mineral dissolution on the release of carbonate-associated DOM and on surface water DOM quantity and quality is unclear. We analyzed sub-daily changes in EEMS-PARAFAC components (excitation-emission matrices with parallel factor analysis), fluorescence, and absorbance properties of surface waters over adjacent low- and high-density (LD and HD) Thalassia testudinum seagrass meadows in Florida Bay, United States. We compared fluorescent DOM characteristics of seagrass leaves, acidified (dissolved) sediment leachates, and surface water samples collected from the HD and LD sites with surface water from a nearby mangrove island. The HD site was higher in humic-like PARAFAC components, specific ultraviolet absorbance, and humification index. We did not observe changes in EEMs indices or PARAFAC components with cumulative photosynthetically active radiation, indicating that photodegradation was unlikely to contribute to temporal variability in DOM. Similarities among DOM optical properties from acidified sediment leachates and surface waters at both sites suggest the importance of carbonate dissolution/reprecipitation for DOM cycling, while seagrass leaf leachates were markedly dissimilar to surface waters. We observed similarities among the acidified sediment leachate, surface water, and porewater elsewhere in Florida Bay, indicating dynamic coupling between these DOM pools. From this short study, Florida Bay DOM cycling appears to be more sensitive to carbonate dissolution than to additional photodegradation or authigenic seagrass leaching. %0 Artikel %@ 0013-936X %A Zhu, L. %A Shi, W. %A Van Dam, B. %A Kong, L. %A Yu, J. %A Qin, B. %D 2020 %J Environmental Science and Technology %N 1114 %P 6194 - 6201 %R doi:10.1021/acs.est.9b05549 %T Algal Accumulation Decreases Sediment Nitrogen Removal by Uncoupling Nitrification-Denitrification in Shallow Eutrophic Lakes %U https://dx.doi.org/10.1021/acs.est.9b05549 10 %X In eutrophic lakes, the decay of settled algal biomass generates organic carbon and consumes oxygen, favoring sediment nitrogen loss via denitrification. However, persistent winds can cause algae to accumulate into dense mats, with uncertain impacts on sediment nitrogen removal. In this study, we investigated the effects of algal accumulation on sediment nitrogen removal in a shallow and eutrophic Chinese lake, Taihu. We found that experimental treatments of increased algal accumulation were associated with decreased sediment nitrogen losses, indicating the potential for a break in coupled nitrification-denitrification. Likewise, field measurements indicated similar decreases in sediment nitrogen losses when algal accumulation occurred. It is possibly caused by the decay of excess algal biomass, which likely depleted dissolved oxygen, and could have inhibited nitrification and thereby denitrification in sediments. We estimate that if such algal accumulations occurred over 20% or 10% of lake area in Taihu, sediment nitrogen removal rates decreased from 835.6 to 167.2 and 77.2 μmol N m–2h–1, respectively, during algal accumulation period. While nitrogen removal may recover later, the apparent nitrogen removal decrease may create a window for algal proliferation and intensification. This study advances our knowledge on the impacts of algal blooms on nitrogen removal in shallow eutrophic lakes. %0 Artikel %@ 2296-7745 %A Beusekom, J.E.E.van %A Carstensen, J. %A Dolch, T. %A Grage, A. %A Hofmeister, R. %A Lenhart, H. %A Kerimoglu, O. %A Kolbe, K. %A Paetsch, J. %A Rick, J. %A Roenn, L. %A Ruiter, H. %D 2019 %J Frontiers in Marine Science %N 2685 %P 370 %R doi:10.3389/fmars.2019.00370 %T Wadden Sea Eutrophication: Long-Term Trends and Regional Differences %U https://dx.doi.org/10.3389/fmars.2019.00370 %X The Wadden Sea is a shallow intertidal coastal sea, largely protected by barrier islands and fringing the North Sea coasts of Netherlands, Germany, and Denmark. It is subject to influences from both the North Sea and major European rivers. Nutrient enrichment from these rivers since the 1950s has impacted the Wadden Sea ecology including loss of seagrass, increased phytoplankton blooms, and increased green macroalgae blooms. Rivers are the major source of nutrients causing Wadden Sea eutrophication. The nutrient input of the major rivers impacting the Wadden Sea reached a maximum during the 1980s and decreased at an average pace of about 2.5% per year for total Nitrogen (TN) and about 5% per year for total Phosphorus (TP), leading to decreasing nutrient levels but also increasing N/P ratios. During the past decade, the lowest nutrient inputs since 1977 were observed but these declining trends are leveling out for TP. Phytoplankton biomass (measured as chlorophyll a) in the Wadden Sea has decreased since the 1980s and presently reached a comparatively low level. In tidal inlet stations with a long-term monitoring, summer phytoplankton levels correlate with riverine TN and TP loads but stations located closer to the coast behave in a more complex manner. Regional differences are observed, with highest chlorophyll a levels in the southern Wadden Sea and lowest levels in the northern Wadden Sea. Model data support the hypothesis that the higher eutrophication levels in the southern Wadden Sea are linked to a more intense coastward accumulation of organic matter produced in the North Sea. %0 Artikel %@ 0016-7460 %A Callies, U. %A Kleeberg, U. %D 2019 %J Geographische Rundschau %N 1138 %P 34 - 39 %T Stroemungen in der Deutschen Bucht - Zur Bedeutung mariner Transporte %U 4 %X Eine detaillierte Kenntnis mariner Transporte ist für viele Analysen und praktische Problemlösungen von großer Bedeutung. Abhängig von der jeweiligen Fragestellung können sich dabei die relevanten Zeitskalen stark unterscheiden: Müssen etwa Schiffsbrüchige oder von Bord gefallene Gegenstände lokalisiert werden, so sind Entwicklungen über Stunden bis Tage von Interesse. Andererseits würden Ökosystemforscher, die etwa an Mustern der Larvenverdriftung oder Nährstoffkonzentration interessiert sind, eher lange Zeiträume von Monaten oder gar Jahren betrachten. Strömungen beeinflussen die räumlichen Verteilungen aller Wasserinhaltsstoffe, weswegen ihre Kenntnis auch für eine sachgerechte Interpretation lokaler Beobachtungen relevant ist. %0 Artikel %@ 1726-4170 %A Rixen, T. %A Gaye, B. %A Emeis, K. %A Ramaswamy, V. %D 2019 %J Biogeosciences %N 2118 %P 485 - 503 %R doi:10.5194/bg-16-485-2019 %T The ballast effect of lithogenic matter and its influences on the carbon fluxes in the Indian Ocean %U https://dx.doi.org/10.5194/bg-16-485-2019 2 %X Data obtained from long-term sediment trap experiments in the Indian Ocean in conjunction with satellite observations illustrate the influence of primary production and the ballast effect on organic carbon flux into the deep sea. They suggest that primary production is the main control on the spatial variability of organic carbon fluxes at most of our study sites in the Indian Ocean, except at sites influenced by river discharges. At these sites the spatial variability of organic carbon flux is influenced by lithogenic matter content. To quantify the impact of lithogenic matter on the organic carbon flux, the densities of the main ballast minerals, their flux rates and seawater properties were used to calculate sinking speeds of material intercepted by sediment traps. Sinking speeds in combination with satellite-derived export production rates allowed us to compute organic carbon fluxes. Flux calculations imply that lithogenic matter ballast increases organic carbon fluxes at all sampling sites in the Indian Ocean by enhancing sinking speeds and reducing the time of organic matter respiration in the water column. We calculated that lithogenic matter content in aggregates and pellets enhances organic carbon flux rates on average by 45 % and by up to 62 % at trap locations in the river-influenced regions of the Indian Ocean. Such a strong lithogenic matter ballast effect explains the fact that organic carbon fluxes are higher in the low-productive southern Java Sea compared to the high-productive western Arabian Sea. It also implies that land use changes and the associated enhanced transport of lithogenic matter from land into the ocean may significantly affect the CO2 uptake of the organic carbon pump in the receiving ocean areas. %0 Artikel %@ 0079-6611 %A Rixen, T. %A Gaye, B. %A Emeis, K. %D 2019 %J Progress in Oceanography %N 1956 %P 24 - 39 %R doi:10.1016/j.pocean.2019.03.001 %T The monsoon, carbon fluxes, and the organic carbon pump in the northern Indian Ocean %U https://dx.doi.org/10.1016/j.pocean.2019.03.001 %X Time series sediment trap experiments were carried out at fifteen sites in the northern Indian Ocean between 1986 and 2007. The data on particle flux rates and composition are analyzed in combination with satellite-derived estimates of primary production and results of surface ocean studies during the Joint Global Ocean Flux Study in the Arabian Sea (JGOFS-Indik). The data highlight the influence of the monsoon on the transport of organic carbon into the deep sea and the associated functioning of the organic carbon pump. The results illustrate the well-known concept of export production, which is driven by inputs of nutrients from the aphotic zone and external reservoirs (the atmosphere and the land) into the euphotic zone. The monsoon drives the organic carbon export through its impact on the physical nutrient supply mechanisms, such as upwelling, vertical mixing, and river discharges. Eolian dust and especially riverine supply of lithogenic matter increase organic carbon fluxes by accelerating the transport of organic matter into the deep sea. Nevertheless, it is preferentially respired in the sub-thermocline and the resulting trapping of remineralized nutrients at this water-depth enforces the influence of upwelling and vertical mixing on the organic carbon fluxes which in the northern Indian Ocean are among the highest worldwide. Model experiments and measured organic carbon burial rates indicate that a weakening of the summer monsoon strength hardly affected the long-term annual average organic carbon export flux into the deep sea during the last approximately 7000 years. In addition to the summer and winter monsoon strength, which are assumed to be inversely related to each other, monsoon-driven physical impacts on the nutrient trapping efficiency seem to have kept organic carbon fluxes at a high level. A feedback mechanism caused by negative impacts of oxygen concentrations on the respiration and thus nutrient trapping efficiency apparently prevents the development of anoxia to the point where sulfate reduction occurs and sets an upper limit to organic carbon fluxes. Whether changes in the phytoplankton community structure observed in recent decades indicate that this self-regulating system is becoming unstable is open to question. %0 Artikel %@ 1812-0784 %A Callies, U. %A Carrasco, R. %A Floeter, J. %A Horstmann, J. %A Quante, M. %D 2019 %J Ocean Science %N 2310 %P 865 - 889 %R doi:10.5194/os-15-865-2019 %T Submesoscale dispersion of surface drifters in a coastal sea near offshore wind farms %U https://dx.doi.org/10.5194/os-15-865-2019 4 %X We analyse relative dispersion of surface drifters released as pairs (6 instances) or triplets (2 instances) during three field experiments in the German Bight in close proximity to wind farms. Drifter pairs can be classified in a remarkably clear way into those with spatial separation growing either exponentially or non-monotonously. There is some tentative evidence that exponential relative dispersion growth rates preferably occur for drifter pairs that are most exposed to the possible influence of a wind farm. Kinetic energy spectra and velocity structure functions suggest that turbulent energy could be injected by tides, possibly also via an interaction between tidal currents and wind turbine towers. Applicability of inertial range turbulence theory, however, can be doubted given distinct peaks of overtides observed in velocity power spectra. More comprehensive studies would be needed to better separate submesoscale effects of wind farms, tides and possibly baroclinic instabilities on observed drifter behaviour in a complex coastal environment. %0 Artikel %@ 2169-8961 %A Van Dam, B.R. %A Edson, J.B. %A Tobias, C. %D 2019 %J Journal of Geophysical Research : Biogeosciences %N 2766 %P 2351 - 2363 %R doi:10.1029/2018JG004908 %T Parameterizing Air‐Water Gas Exchange in the Shallow, Microtidal New River Estuary %U https://dx.doi.org/10.1029/2018JG004908 7 %X Estuarine CO2 emissions are important components of regional and global carbon budgets, but assessments of this flux are plagued by uncertainties associated with gas transfer velocity (k) parameterization. We combined direct eddy covariance measurements of CO2 flux with water‐side pCO2 determinations to generate more reliable k parameterizations for use in small estuaries. When all data were aggregated, k was described well by a linear relationship with wind speed (U10), in a manner consistent with prior open‐ocean and estuarine k parameterizations. However, k was significantly greater at night and under low wind speed, and nighttime k was best predicted by a parabolic, rather than linear, relationship with U10. We explored the effect of water‐side thermal convection, but found only a weak correlation between convective scale and k. Hence, while convective forcing may be important at times, it appears that factors besides water‐side thermal convection were likely responsible for the bulk of the observed nighttime enhancement in k. Regardless of source, we show that these day‐night differences in k should be accounted for when CO2 emissions are assessed over short time scales, or when pCO2 is constant and U10 varies. On the other hand, when temporal variability in pCO2 is large, it exerts greater control over CO2 fluxes than does k parameterization. In these cases, the use of a single k value, or a simple linear relationship with U10 is often sufficient. This study provides important guidance for k parameterization in shallow, or microtidal estuaries, especially when diel processes are considered. %0 Artikel %@ 2076-3263 %A Neumann, A. %A Hass, H.C. %A Moebius, J. %A Naderipour, C. %D 2019 %J Geosciences %N 2865 %P 344 %R doi:10.3390/geosciences9080344 %T Ballasted Flocs Capture Pelagic Primary Production and Alter the Local Sediment Characteristics in the Coastal German Bight (North Sea) %U https://dx.doi.org/10.3390/geosciences9080344 8 %X Suspended, organic matter, especially in the form of adhesive extracellular polymers (EPS), tends to form flocs, which may also incorporate suspended lithogenic particles in coastal environments. With an increased settling velocity, these ballasted flocs form in a narrow zone along the coast and potentially represent a major source of pelagic primary production for the benthic community. We sought support for this hypothesis by examining our measurements of the mud content, porosity, permeability, pigment content, and specific respiration rate of sediment from the German Bight (North Sea) for signs that the pelagic zone of ballasted floc formation is affecting the local sediment characteristics. Based on a simple bottom-shear stress model and by employing empirical correlations of sediment characteristics we were able to find strong indications that this is actually the case. Our results demonstrate how ballasted flocs contribute to the benthic pelagic coupling in a high turbulence environment. %0 Artikel %@ 2296-7745 %A Stevens, T. %A Mee, L. %A Friedrich, J. %A Aleynik, D. %A Minicheva, G. %D 2019 %J Frontiers in Marine Science %N 2685 %P 474 %R doi:10.3389/fmars.2019.00474 %T Partial Recovery of Macro-Epibenthic Assemblages on the North-West Shelf of the Black Sea %U https://dx.doi.org/10.3389/fmars.2019.00474 %X The north-west shelf of the Black Sea has suffered well-documented declines in biodiversity since the 1960s, and by the 1990s was considered a dead zone with virtually no sign of macroscopic epibenthic life. It was characterised by high levels of anthropogenic input, massive phytoplankton blooms, and periodically hypoxic to anoxic bottom waters. An important contributor to primary production on the northwest shelf is the red alga Phyllophora spp. growing in waters to 70 m depth. Phyllophora is a habitat forming taxon supporting complex assemblages of bivalves, sponges, and ascidians, with an associated rich fish fauna. From 1990 on, nutrient loads entering the system plummeted and the severity of algal blooms decreased. Changes to benthic communities, however, were far less rapid, and the trajectory and rate of any recovery of the dead zone, in particular Zernov’s Phyllophora Field, is far from certain. This study used towed underwater video imagery from research cruises in summer 2006 and spring 2008 to classify and map macro-epibenthic assemblage structure, and related this to putative physical, chemical and spatial drivers. Distinct and relatively stable benthic communities were in evidence across the northwest shelf at that time. These communities were largely structured by substrate type and depth, but there is some evidence that nutrients continued to play a role. Phyllophora spp. was present across much, but not all, of its former range, but at far lower percent cover than previously. The pattern of abundance of Phyllophora in 2006-08 did not correlate with the documented pre-eutrophication pattern from 1966. There is some evidence that faster-growing opportunistic species have hindered to recovery. We conclude that while there was evidence of sustained recovery, by 2008 the macro-epibenthic communities of the northwest shelf of the Black Sea were far from their pre-eutrophication state. %0 Artikel %@ 0016-7037 %A Kowalski, N. %A Dellwig, O. %A Beck, M. %A Gräwe, U. %A Neubert, N. %A Nägler, T.F. %A Badewien, T.H. %A Brumsack, H.-J. %A van Beusekom, J.E.E. %A Böttcher, M.E. %D 2019 %J Geochimica et Cosmochimica Acta %N 1137 %P 243 - 244 %R doi:10.1016/j.gca.2019.07.023 %T Corrigendum to ‘‘Pelagic molybdenum concentration anomalies and the impact of sediment resuspension on the molybdenum budget in two tidal systems of the North Sea” [Geochim. Cosmochim. Acta 119 (2013) 198–211] %U https://dx.doi.org/10.1016/j.gca.2019.07.023 %X %0 Artikel %@ 1726-4170 %A Horwitz, R. %A Hay, A. %A Burt, W. %A Cheel, R. %A Salisbury, J. %A Thomas, H. %D 2019 %J Biogeosciences %N 2118 %P 605 - 616 %R doi:10.5194/bg-16-605-2019 %T High-frequency variability of CO2 in Grand Passage, Bay of Fundy, Nova Scotia %U https://dx.doi.org/10.5194/bg-16-605-2019 2 %X Assessing changes in the marine carbon cycle arising from anthropogenic CO2 emissions requires a detailed understanding of the carbonate system's natural variability. Coastal ecosystems vary over short spatial and temporal scales, so their dynamics are not well described by long-term and broad regional averages. A year-long time series of pCO2, temperature, salinity, and currents is used to quantify the high-frequency variability of the carbonate system at the mouth of the Bay of Fundy, Nova Scotia. The seasonal cycle of pCO2 is modulated by a diel cycle that is larger in summer than in winter and a tidal contribution that is primarily M2, with amplitude roughly half that of the diel cycle throughout the year. The interaction between tidal currents and carbonate system variables leads to lateral transport by tidal pumping, which moves alkalinity and dissolved inorganic carbon (DIC) out of the bay, opposite to the mean flow in the region, and constitutes a new feature of how this strongly tidal region connects to the larger Gulf of Maine and northwest Atlantic carbon system. These results suggest that tidal pumping could substantially modulate the coastal ocean's response to global ocean acidification in any region with large tides and spatial variation in biological activity, requiring that high-frequency variability be accounted for in assessments of carbon budgets of coastal regions. %0 Artikel %@ 2076-2607 %A Sanders, T. %A Fiencke, C. %A Hüpeden, J. %A Pfeiffer, E.M. %A Spieck, E. %D 2019 %J Microorganisms %N 2876 %P 699 %R doi:10.3390/microorganisms7120699 %T Cold Adapted Nitrosospira sp.: A Potential Crucial Contributor of Ammonia Oxidation in Cryosols of Permafrost-Affected Landscapes in Northeast Siberia %U https://dx.doi.org/10.3390/microorganisms7120699 12 %X Permafrost-affected landscape soils are rich in organic matter and contain a high fraction of organic nitrogen, but much of this organic matter remains inaccessible due to nitrogen limitation. Microbial nitrification is a key process in the nitrogen cycle, controlling the availability of dissolved inorganic nitrogen (DIN) such as ammonium and nitrate. In this study, we investigate the microbial diversity of canonical nitrifiers and their potential nitrifying activity in the active layer of different Arctic cryosols in the Lena River Delta in North-East Siberia. These cryosols are located on Samoylov Island, which has two geomorphological landscapes with mineral soils in the modern floodplain and organic-rich soils in the low-centered polygonal tundra of the Holocene river terrace. Microcosm incubations show that the highest potential ammonia oxidation rates are found in low organic soils, and the rates depend on organic matter content and quality, vegetation cover, and water content. As shown by 16S rRNA amplicon sequencing, nitrifiers represented 0.6% to 6.2% of the total microbial community. More than 50% of the nitrifiers belonged to the genus Nitrosospira. Based on PCR amoA analysis, ammonia-oxidizing bacteria (AOB) were found in nearly all soil types, whereas ammonia-oxidizing archaea (AOA) were only detected in low-organic soils. In cultivation-based approaches, mainly Nitrosospira-like AOB were enriched and characterized as psychrotolerant, with temperature optima slightly above 20 °C. This study suggests a ubiquitous distribution of ammonia-oxidizing microorganisms (bacteria and archaea) in permafrost-affected landscapes of Siberia with cold-adapted AOB, especially of the genus Nitrosospira, as potentially crucial ammonia oxidizers in the cryosols. %0 Artikel %@ 1726-4170 %A Van Dam, B. %A Lopes, C. %A Osburn, C. %A Fourqurean, J. %D 2019 %J Biogeosciences %N 2118 %P 4411 - 4428 %R doi:10.5194/bg-16-4411-2019 %T Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows %U https://dx.doi.org/10.5194/bg-16-4411-2019 22 %X The net ecosystem productivity (NEP) of two seagrass meadows within one of the largest seagrass ecosystems in the world, Florida Bay, was assessed using direct measurements over consecutive diel cycles during a short study in the fall of 2018. We report significant differences between NEP determined by dissolved inorganic carbon (NEPDIC) and by dissolved oxygen (NEPDO), likely driven by differences in air–water gas exchange and contrasting responses to variations in light intensity. We also acknowledge the impact of advective exchange on metabolic calculations of NEP and net ecosystem calcification (NEC) using the “open-water” approach and attempt to quantify this effect. In this first direct determination of NEPDIC in seagrass, we found that both seagrass ecosystems were net heterotrophic, on average, despite large differences in seagrass net above-ground primary productivity. NEC was also negative, indicating that both sites were net dissolving carbonate minerals. We suggest that a combination of carbonate dissolution and respiration in sediments exceeded seagrass primary production and calcification, supporting our negative NEP and NEC measurements. However, given the limited spatial (two sites) and temporal (8 d) extent of this study, our results may not be representative of Florida Bay as a whole and may be season-specific. The results of this study highlight the need for better temporal resolution, accurate carbonate chemistry accounting, and an improved understanding of physical mixing processes in future seagrass metabolism studies. %0 Artikel %@ 1726-4170 %A Harms, N. %A Lahajnar, N. %A Gaye, B. %A Rixen, T. %A Dähnke, K. %A Ankele, M. %A Schwarz-Schampera, U. %A Emeis, K. %D 2019 %J Biogeosciences %N 2118 %P 2715 - 2732 %R doi:10.5194/bg-16-2715-2019 %T Nutrient distribution and nitrogen and oxygen isotopic compositionof nitrate in water masses of the subtropical southern Indian Ocean %U https://dx.doi.org/10.5194/bg-16-2715-2019 13 %X The Indian Ocean subtropical gyre (IOSG) is one of five extensive subtropical gyres in the world's ocean. In contrast to those of the Atlantic and Pacific oceans, the IOSG has been sparsely studied. We investigate the water mass distributions based on temperature, salinity and oxygen data, and the concentrations of water column nutrients and the stable isotope composition of nitrate, using water samples collected between ∼30∘ S and the Equator during two expeditions: MSM 59/2 in 2016 and SO 259 in 2017. Our results are the first from this oceanic region and provide new information on nitrogen sources and transformation processes. We identify the thick layer of nutrient-depleted surface waters of the oligotrophic IOSG with nitrate (NO−3) and phosphate (PO3−4) concentrations of < 3 and < 0.3 µmol kg−1, respectively (< 300 m; σ < 26.4 kg−1 m−3). Increased nutrient concentrations towards the Equator represent the northern limb of the gyre, which is characterized by typical strong horizontal gradients of the outcropping nutriclines. The influx of the Subantarctic Mode Water (SAMW) from the Southern Ocean injects oxygen-saturated waters with preformed nutrients, indicated by the increased N and O isotope composition of nitrate (δ15N > 7 ‰; δ18O > 4 ‰) at 400–500 m (26.6–26.7 kg−1 m−3), into the subtropical thermocline. These values reflect partial N assimilation in the Southern Ocean. Moreover, in the northern study area, a residue of nitrate affected by denitrification in the Arabian Sea is imported into intermediate and deep water masses (> 27.0 kg−1 m−3) of the gyre, indicated by an N deficit (N* ∼−1 to −4 µmol kg−1) and by elevated isotopic ratios of nitrate (δ15N > 7 ‰; δ18O > 3 ‰). Remineralization of partially assimilated organic matter, produced in the subantarctic, leads to a decoupling of N and O isotopes in nitrate and results in a relatively low Δ(15–18) value of < 3 ‰ within the SAMW. In contrast, remineralization of 15N-enriched organic matter from the Arabian Sea indicates higher Δ(15–18) values of > 4 ‰ within the Red Sea–Persian Gulf Intermediate Water (RSPGIW). Thus, the subtropical southern Indian Ocean is supplied by preformed nitrate from the lateral influx of water masses from regions exhibiting distinctly different N-cycle processes documented in the dual isotope composition of nitrate. Additionally, a significant contribution of N2 fixation between 20.36 and 23.91∘ S is inferred from reduced δ15N–NO−3 values towards surface waters (upward decrease of δ15N ∼2.4 ‰), N* values of > 2 µmol kg−1 and a relatively low Δ(15–18) value of < 3 ‰. A mass and isotope budget implies that at least 32 %–34 % of the nitrate in the upper ocean between 20.36 and 23.91∘ S is provided from newly fixed nitrogen, whereas N2 fixation appears to be limited by iron or temperature south of 26∘ S. %0 Artikel %@ 0269-7491 %A Liu, Z. %A Callies, U. %D 2019 %J Environmental Pollution %N 2052 %P 609 - 620 %R doi:10.1016/j.envpol.2019.02.063 %T Implications of using chemical dispersants to combat oil spills in the German Bight – Depiction by means of a Bayesian network %U https://dx.doi.org/10.1016/j.envpol.2019.02.063 %X Application of chemical dispersants is one option for combatting oil spills, dispersing oil into the water column and thereby reducing potential pollution to coastal areas. Efficiency of dispersant application depends on oil characteristics, sea and weather conditions. Potential environmental impacts must also be taken into account. Referring to the German Bight region (North Sea), we show how probabilistic Bayesian network (BN) technology can integrate all these aspects to support contingency planning. Expected effects of chemical dispersion on oil spill drift paths are quantified based on comprehensive numerical ensemble simulations. Ecological impacts are represented just in simplified terms focusing on nearshore seabird distributions. The intuitive and interactive BN summarizes expected benefits from chemical dispersion depending on where and under which weather conditions a hypothetical pollution occurs. %0 Artikel %@ 0967-0645 %A Burdanowitz, N. %A Gaye, B. %A Hilbig, L. %A Lahajnar, N. %A Lückge, A. %A Rixen, T. %A Emeis, K.-C. %D 2019 %J Deep Sea Research Part II: Topical Studies in Oceanography %N 2081 %P 6 - 18 %R doi:10.1016/j.dsr2.2019.03.003 %T Holocene monsoon and sea level-related changes of sedimentation in the northeastern Arabian Sea %U https://dx.doi.org/10.1016/j.dsr2.2019.03.003 %X The Indian Monsoon and the westerlies strongly influence the sedimentation in the northeastern Arabian Sea by impacting rainfall and erosion on land and on biogeochemical processes in the ocean. To disentangle the terrestrial and oceanic processes, we analysed mineralogical and bulk geochemical components of a Holocene sediment core offshore Pakistan. Endmember modelling of grain sizes and principal component analyses (PCA) of major and trace elements identify the origin of sediments and their dominant mode of transport. Sedimentation processes during the early Holocene (10.8–8.2 ka BP) were influenced by the post-glacial sea level rise and orbitally forced strengthening of the Indian summer monsoon (ISM) and westerlies. This led to a shift from rather terrestrial-dominated towards a marine-dominated sedimentation, whereas the fluvial source shifted from the Makran rivers to the Hab River near Karachi. During the mid-Holocene (8.2–4.2 ka BP) a combination of weakening ISM and southward displacement of the ITCZ enhanced the influence of the westerlies, together decreasing river discharges and enhancing aeolian input (probably from the Sistan Basin region). This trend continued during the last ca. 4 ka when the increasing aridification of the Hab River catchment further increased the aeolian inputs. Solar and lunar driven short-term variations as well as Bond events known from the North Atlantic Ocean superpose these trends. They lead to a pronounced increase of fluvial inputs between 8.6–8.4 ka BP and at ca. 3 ka BP as well as to dry events around 4.2 ka and 1.2–1 ka BP. Our study highlights the increasing influence of the westerlies on the sedimentation processes in the northeastern Arabian Sea towards the late Holocene. %0 Artikel %@ 0272-7714 %A Müller-Navarra, K. %A Milker, Y. %A Bunzel, D. %A Lindhorst, S. %A Friedrich, J. %A Arz, H. %A Schmiedl, G. %D 2019 %J Estuarine, Coastal and Shelf Science %N 1123 %P 268 - 277 %R doi:10.1016/j.ecss.2018.12.022 %T Evolution of a salt marsh in the southeastern North Sea region – Anthropogenic and natural forcing %U https://dx.doi.org/10.1016/j.ecss.2018.12.022 %X Salt-marsh sediments of the southeastern North Sea provide an archive to unravel the influences of coastal management and natural processes such as storm-tide deposition on salt-marsh development. We present a record of salt-marsh evolution during the past century from the Bay of Tümlau (northwestern Germany) based on fossil foraminiferal assemblages and sedimentological data. After diking the hinterland of the Bay of Tümlau in 1935 CE and commencing marsh management, the environment at the study site changed from a tidal flat to a salt marsh. Salt-marsh sediment accretion is influenced by recurrent dredging events, as indicated by layers rich in calcareous tidal-flat foraminifera, and redeposition of siliciclastic particles from the surrounding tidal flats during storm tides. The latter fostered the establishment of a typical salt-marsh foraminiferal fauna dominated by the agglutinating species Entzia macrescens. Storm-tide layers have a lighter sediment color and commonly a more negatively skewed grain-size distribution with variable sorting. The observed long-term coarsening of the salt-marsh sediment likely reflects the landward progression of the vertical erosional cliff and the depletion of fine-grained sediment particles in the tidal flats under the influence of sea-level rise. Supra-tidal conditions, resulting from natural protection measures and abandonment of dredging, are indicated by the occurrence of Balticammina pseudomacrescens around 2001 CE. This species is adapted to only occasional submergence during storm tides. The recent increase in elevation is accompanied by establishment of high-marsh vegetation and characterized by a present height of the marsh surface 50 cm above mean high water springs. During the past sixty years, average sediment accretion rates decreased from 18 to 11 mm yr−1 reflecting the maturing of the salt marsh. These rates clearly outpace the recent mean sea-level rise in the southern North Sea demonstrating that the regional salt marshes are still resilient to sea-level rise. %0 Artikel %@ 2190-4979 %A Tim, N. %A Zorita, E. %A Emeis, K. %A Schwarzkopf, F. %A Biastoch, A. %A Hünicke, B. %D 2019 %J Earth System Dynamics %N 2386 %P 847 - 858 %R doi:10.5194/esd-10-847-2019 %T Analysis of the position and strength of westerlies and trades with implications for Agulhas leakage and South Benguela upwelling %U https://dx.doi.org/10.5194/esd-10-847-2019 4 %X The westerlies and trade winds over the South Atlantic and Indian Ocean are important drivers of the regional oceanography around southern Africa, including features such as the Agulhas Current, the Agulhas leakage, and the Benguela upwelling. Agulhas leakage constitutes a fraction of warm and saline water transport from the Indian Ocean into the South Atlantic. The leakage is stronger during intensified westerlies. Here, we analyze the wind stress of different observational and modeled atmospheric data sets (covering the last 2 millennia, the recent decades, and the 21st century) with regard to the intensity and position of the southeasterly trades and the westerlies. The analysis reveals that variations of both wind systems go hand in hand and that a poleward shift of the westerlies and trades and an intensification of westerlies took place during the recent decades. Furthermore, upwelling in South Benguela is slightly intensified when trades are shifted poleward. Projections for strength and position of the westerlies in the 21st century depend on assumed CO2 emissions and on their effect relative to the ozone forcing. In the strongest emission scenario (RCP8.5) the simulations show a further southward displacement, whereas in the weakest emission scenario (RCP2.6) a northward shift is modeled, possibly due to the effect of ozone recovery dominating the effect of anthropogenic greenhouse forcing. We conclude that the Agulhas leakage has intensified during the last decades and is projected to increase if greenhouse gas emissions are not reduced. This will have a small impact on Benguela upwelling strength and may also have consequences for water mass characteristics in the upwelling region. An increased contribution of Agulhas water to the upwelling water masses will import more preformed nutrients and oxygen into the upwelling region. %0 Artikel %@ 0079-6611 %A Schartau, M. %A Riethmueller, R. %A Floeser, G. %A Beusekom, J.E.E.van %A Krasemann, H. %A Hofmeister, R. %A Wirtz, K. %D 2019 %J Progress in Oceanography %N 1956 %P 231 - 250 %R doi:10.1016/j.pocean.2018.12.011 %T On the separation between inorganic and organic fractions of suspended matter in a marine coastal environment %U https://dx.doi.org/10.1016/j.pocean.2018.12.011 %X A central aspect of coastal biogeochemistry is to determine how nutrients, lithogenic and organic matter are distributed and transformed within coastal and estuarine environments. Analyses of the spatio-temporal changes of total suspended matter (TSM) concentration indicate strong and variable linkages between intertidal fringes and pelagic regions. In particular, knowledge about the organic fraction of TSM provides insight to how biogenic and lithogenic particulate matter are distributed in suspension. In our study we take advantage of a set of over 3000 in situ Loss on Ignition (LoI) data from the Southern North Sea that represent fractions of particulate organic matter (POM) relative to TSM (LoI POM:TSM). We introduce a parameterization (POM-TSM model) that distinguishes between two POM fractions incorporated in TSM. One fraction is described in association with mineral particles. The other represents a seasonally varying fresh pool of POM. The performance of the POM-TSM model is tested against data derived from MERIS/ENVISAT-TSM products of the German Bight. Our analysis of remote sensing data exhibits specific qualitative features of TSM that can be attributed to distinct coastal zones. Most interestingly, a transition zone between the Wadden Sea and seasonally stratified regions of the Southern North Sea is identified where mineral associated POM appears in concentrations comparable to those of freshly produced POM. We will discuss how this transition is indicative for a zone of effective particle interaction and sedimentation.The dimension of this transition zone varies between seasons and with location. Our proposed POM-TSM model is generic and can be calibrated against in situ data of other coastal regions. %0 Artikel %@ 0094-8276 %A Mellon, S. %A Kienast, M. %A Algar, C. %A Menocal, P. %A Kienast, S. %A Marchitto, T. %A Moros, M. %A Thomas, H. %D 2019 %J Geophysical Research Letters %N 1141 %P 14683 - 14691 %R doi:10.1029/2019GL084965 %T Foraminifera Trace Anthropogenic CO2 in the NW Atlantic by 1950 %U https://dx.doi.org/10.1029/2019GL084965 24 %X The Northwest Atlantic is a region of major climate change over the twentieth century, affected by the weakening of the Atlantic meridional overturning circulation. To assess whether the ability of this region to absorb anthropogenic CO2 has been impacted by this change, we present the region's first long‐term carbon isotope (δ13C) time series of fossil foraminifera spanning the past 4,000 years. These records reveal an unprecedented negative δ13C excursion driven by anthropogenic CO2 penetration into the surface ocean, the “Suess effect” signal. This signal (amplitude −0.45‰) emerges in 1950 CE ± 15 with a decrease rate of 0.009 ± 0.001‰/yr. This marine signal is ~30% of the atmospheric Suess effect and emerges over a century later. Based on current estimates of the ratio of δ13CDIC change to dissolved inorganic carbon change and limited constraints on surface ocean residence times, we calculate a mean anthropogenic CO2 uptake rate of 0.6 ± 0.2 μmol/(kg yr) from 1950 to 2005. %0 Artikel %@ 2169-8961 %A Omar, A. %A Thomas, H. %A Olsen, A. %A Becker, M. %A Skjelvan, I. %A Reverdin, G. %D 2019 %J Journal of Geophysical Research : Biogeosciences %N 2766 %P 3088 - 3103 %R doi:10.1029/2018JG004992 %T Trends of Ocean Acidification and pCO2 in the Northern North Sea, 2003–2015 %U https://dx.doi.org/10.1029/2018JG004992 10 %X For continental shelf regions, the long‐term trend in sea surface carbon dioxide (CO2) partial pressure (pCO2) and rates of ocean acidification are not accurately known. Here, we investigate the decadal trend of observed wintertime pCO2 as well as computed wintertime pH and aragonite saturation state (Ωar) in the northern North Sea, using the first decade long monthly underway data from a voluntary observing ship covering the period 2004–2015. We also evaluate how seawater CO2 chemistry, in response to physical and biological processes, drives variations in the above parameters on seasonal and interannual timescales. In the northern North Sea, pCO2, pH, and Ωar are subject to strong seasonal variations with mean wintertime values of 375 ± 11 μatm, 8.17 ± 0.01, and 1.96 ± 0.05. Dissolved inorganic carbon is found to be the primary driver of both seasonal and interannual changes while total alkalinity and sea surface temperature have secondary effects that reduce the changes produced by dissolved inorganic carbon. Average interannual variations during winter are around 3%, 0.1%, and 2% for pCO2, pH, and Ωar, respectively and slightly larger in the eastern part of the study area (Skagerrak region) than in the western part (North Atlantic Water region). Statistically significant long‐term trends were found only in the North Atlantic Water region with mean annual rates of 2.39 ± 0.58 μatm/year, −0.0024 ± 0.001 year‐1, and −0.010 ± 0.003 year‐1 for pCO2, pH, and Ωar, respectively. The drivers of the observed trends as well as reasons for the lack of statistically significant trends in the Skagerrak region are discussed. %0 Artikel %@ 0171-8630 %A Wrede, A. %A Andresen, H. %A Asmus, R. %A Wiltshire, K. %A Brey, T. %D 2019 %J Marine Ecology Progress Series %N 1291 %P 27 - 42 %R doi:10.3354/meps13165 %T Macrofaunal irrigation traits enhance predictability of nutrient fluxes across the sediment-water interface %U https://dx.doi.org/10.3354/meps13165 %X This study shows that macrofaunal irrigation traits constitute a valuable complement to sediment reworking traits in estimating macrofaunal impact on nutrient fluxes across the sediment-water interface. We correlated density, biomass, community bioturbation potential (BPc, an index based on reworking traits, body mass and density) and community irrigation potential (IPc, an index based on irrigation traits, body mass and density) with nitrite, nitrate, ammonium, silicate and phosphate flux data under different environmental conditions. Generalized linear models performed best with a combination of environmental conditions and irrigation trait-based indices. This was not only a direct effect of the irrigation traits, but also of the scaling factor 0.75 employed in IPc to infer metabolic activity from body mass. Accordingly, predictive models of nutrient flux across the sediment-water interface will profit greatly from incorporating macrofaunal irrigation behaviour by means of trait-based indices. %0 Artikel %@ 2169-9275 %A Tim, N. %A Zorita, E. %A Schwarzkopf, F.U. %A Ruehs, S. %A Emeis, K.-C. %A Biastoch, A. %D 2018 %J Journal of Geophysical Research : Oceans %N 2698 %P 9416 - 9428 %R doi:10.1029/2018JC014218 %T The impact of Agulhas leakage on the central water masses in the Benguela upwelling system from a high-resolution ocean simulation %U https://dx.doi.org/10.1029/2018JC014218 12 %X We analyze the contribution of the Agulhas Current on the central water masses of the Benguela upwelling system (BUS) over the last decades in a high‐resolution ocean simulation driven by atmospheric reanalysis. The BUS is an eastern boundary upwelling system where upwelling of cold nutrient‐rich water favors biomass growth. The two distinct subregions, North and South Benguela, differ in nutrient and oxygen properties of the upwelling water mass. Our analysis indicates that the contribution of Agulhas water to the upwelling is very strong in both subregions. Although the water masses feeding the upwelling have a common origin, their pathways are distinct in both regions. Whereas for the central waters of South Benguela the path is rather direct from where it is formed, the central waters of North Benguela takes a longer route through the equatorial current system. Not only the travel time from the Agulhas Current to the BUS is longer but the central water mass is twice as old for the northern part when compared to the southern. Our analysis traces the pathways, history and origin of the central water masses feeding upwelling in the BUS and emphasizes the direct impact of the Agulhas Current on the upwelling region. The variability of that link between the Indian Ocean and the South Atlantic is likely to change the nutrient and oxygen content, as well as temperature and salinity of the water masses in the upwelling region. %0 Artikel %@ 0301-4797 %A Cormier, R. %A Stelzenmueller, V. %A Creed, I.F. %A Igras, J. %A Rambo, H. %A Callies, U. %A Johnson, L.B. %D 2018 %J Journal of Environmental Management %N 2070 %P 340 - 346 %R doi:10.1016/j.jenvman.2018.08.053 %T The science-policy interface of risk-based freshwater and marine management systems: From concepts to practical tools %U https://dx.doi.org/10.1016/j.jenvman.2018.08.053 %X Maintaining the current state of ecosystem services from freshwater and marine ecosystems around the world is at risk. Cumulative effects of multiple human pressures on ecosystem components and functions are indicative of residual pressures that “fall through” the cracks of current industry sector management practices. Without an understanding of the level of residual pressures generated by these measures, we are unlikely to reconcile the root causes of ecosystem effects to improve these management practices to reduce their residual pressures. In this paper, we present a new modelling framework that combines a qualitative and quantitative assessments of the effectiveness of the measures used in the daily operations of industry sectors to predict their residual pressure that is delivered to the ecosystem. The predicted residual pressure can subsequently be used as an input variable for ecosystem models. We combine the Bow-tie analysis of the measures with a Bayesian belief network to quantify the effectiveness of the measures and predict the residual pressures. %0 Artikel %@ 1015-1621 %A Sanders, T. %A Laanbroek, H.J. %D 2018 %J Aquatic Sciences / Research Across Boundaries %N 1046 %P 33 %R doi:10.1007/s00027-018-0584-1 %T The distribution of sediment and water column nitrification potential in the hyper-turbid Ems estuary %U https://dx.doi.org/10.1007/s00027-018-0584-1 %X Estuaries, being transition zones between land and ocean, act as sink or source of nitrate and thus influence the conditions in adjacent coastal waters. Hence, nitrification, which is the process oxidizing ammonium via nitrite to nitrate and simultaneously consuming oxygen, is important in estuaries. The process has been studied in sediment and water column of many estuaries, but seldom in both estuarine compartments at the same time. In August 2014, we collected water and sediment samples during a sampling trip along the salinity gradient of the hyper-turbid Ems estuary, which ends up in the North Sea. We conducted nitrification incubations in microcosms to determine nitrification potentials and we measured a suite of abiotic factors like oxygen saturation, salinity, and dissolved inorganic nitrogen (DIN). Two approaches were used, one isotope dilution method for net (NNP) and gross (GNP) nitrification potentials and one method with substrate addition for substrate induced nitrification potentials (SNP). The long-term incubation set-ups of several days include inseparably nitrification-coupled processes like remineralization and nitrate consumption, as well as cell growth, and hence they do not represent in-situ rates of nitrification. DNA was also isolated and used for quantitative PCR of the archaeal and bacterial amoA genes, which encode for the ammonia-oxidizing enzyme ammonia monooxygenase (AMO). Nitrification varied over the salinity gradient of the estuary. GNP in water and sediments decreased with increasing salinity. No NNP could be measured in the sediments of the oligohaline part of the estuary, while SNP was four-fold higher than GNP in this part of the estuary. Generally, the gene abundance of the amoA gene was higher in the oligohaline/mesohaline area than in the polyhaline area, and archaea dominated the ammonia-oxidizing communities in all samples. The local similarity in partitioning of archaeal and bacterial amoA genes over the water column and sediment at each sampling station along the estuarine gradient implied a link between the archaeal and bacterial ammonia oxidizers in both compartments, which is likely due to resuspension of sediment particles in the water column of this hyper-turbid estuary. %0 Artikel %@ 1814-232X %A Neumann, A. %A Flohr, A. %D 2018 %J African Journal of Marine Science %N 2754 %P 91 - 96 %R doi:10.2989/1814232X.2018.1437774 %T The bivalve Lembulus bicuspidatus may enhance denitrification in shelf sediment at the Angola–Benguela Frontal Zone %U https://dx.doi.org/10.2989/1814232X.2018.1437774 1 %X We collected living individuals of the bivalve Lembulus bicuspidatus, which shows an unusual preference for the oxygen-deficient habitat found at the Angola–Benguela Frontal Zone of the southeastern Atlantic. With a series of incubation experiments with 15N-labelled nitrate as a tracer in combination with membrane-inlet mass spectrometry, we studied the potential contribution of L. bicuspidatus to nitrate reduction in the upper sediment layer. Our preliminary results suggest that L. bicuspidatus enhances nitrate reduction if the oxygen concentration is sufficiently low. The Lembulus-mediated nitrate reduction rate is then similar to the rate of microbial nitrate reduction in the surrounding sediment. %0 Artikel %@ 1025-6016 %A Brase, L. %A Sanders, T. %A Daehnke, K. %D 2018 %J Isotopes in Environmental and Health Studies %N 2755 %P 168 - 184 %R doi:10.1080/10256016.2018.1428580 %T Anthropogenic changes of nitrogen loads in a small river: external nutrient sources vs. internal turnover processes %U https://dx.doi.org/10.1080/10256016.2018.1428580 2 %X Anthropogenic nutrient inputs increase the N-load in many aquatic systems, leading to eutrophication and potential changes of biological N-retention capacity. In this study, nitrate inputs in a small river were investigated along a gradient of anthropogenic influence. We aimed to determine changes in nitrate load and isotope signatures in the water column and to identify the anthropogenic influence on biological nitrogen assimilation and nitrification or denitrification in sediments. In seasonal sampling campaigns, we analysed dissolved inorganic nitrogen concentrations, and stable isotopes of nitrate. To differentiate rates of nitrate production and consumption in the pristine vs. agricultural river section, intact sediment cores were incubated with 15N-labelled nitrate. δ15N values of nitrate in the pristine river section were low, reflecting natural sources, but, as expected, increased with nitrate concentration in all seasons along the gradient. In general, nitrate retention and consumption were higher in the anthropogenically impacted than in the pristine river section, and nitrate consumption exceeded production. In addition to our measurements, modelled results also show that even in a small river, the anthropogenically enhanced consumption capacity is overwhelmed by surplus N-inputs, and nitrate consumption cannot increase in turn with external loads. %0 Artikel %@ 0025-3227 %A Bockelmann, F.-D. %A Puls, W. %A Kleeberg, U. %A Mueller, D. %A Emeis, K.-C. %D 2018 %J Marine Geology %N 2273 %P 60 - 71 %R doi:10.1016/j.margeo.2017.11.003 %T Mapping mud content and median grain-size of North Sea sediments – A geostatistical approach %U https://dx.doi.org/10.1016/j.margeo.2017.11.003 %X Sediment grain size is well known for its influence on biogeophysical processes and hence, grain size parameter maps, important elements in an integrated ecological modelling strategy. In this study, a large database was compiled from legacy data on grain size parameters and distributions in North Sea surface sediments. The database was analysed by means of non-linear regression to enable a consistent quantification of various grain size parameters. In a second step, multivariate geostatistics (kriging) were employed to predict the spatial distribution of percentage mud content and median grain size in the North Sea with a resolution of 1 × 1 nautical miles. The results show that incorporation of secondary information in the interpolation led to a physically more realistic representation of large-scale patterns compared to deterministic approaches. An evaluation of map confidence, however, suggests only minor differences in the quality obtained by different kriging techniques. It appears that the data density and distribution are not an issue when it comes to performance. Instead, insufficient metadata constrain the assessment and harmonisation of data sets and introduce uncertainty into the predictions. %0 Artikel %@ 0025-326X %A Grote, M. %A Bernem, C.van %A Boehme, B. %A Callies, U. %A Calvez, I. %A Christie, B. %A Colcomb, K. %A Damian, H.-P. %A Farke, H. %A Graebsch, C. %A Hunt, A. %A Hoefer, T. %A Knaack, J. %A Kraus, U. %A Le Floch, S. %A Le Lann, G. %A Leuchs, H. %A Nagel, A. %A Nies, H. %A Nordhausen, W. %A Rauterberg, J. %A Reichenbach, D. %A Scheiffarth, G. %A Schwichtenberg, F. %A Theobald, N. %A Voß, J. %A Wahrendorf, D.-S. %D 2018 %J Marine Pollution Bulletin %N 1292 %P 623 - 632 %R doi:10.1016/j.marpolbul.2017.10.050 %T The potential for dispersant use as a maritime oil spill response measure in German waters %U https://dx.doi.org/10.1016/j.marpolbul.2017.10.050 2 %X In case of an oil spill, dispersant application represents a response option, which enhances the natural dispersion of oil and thus reduces coating of seabirds and coastal areas. However, as oil is transferred to the water phase, a trade-off of potential harmful effects shifted to other compartments must be performed. This paper summarizes the results of a workshop on the current knowledge on risks and benefits of the use of dispersants with respect to specific conditions encountered at the German sea areas. The German North Sea coast is a sensitive ecosystem characterised by tidal flats, barrier islands and salt marshes. Many prerequisites for a potential integration of dispersants as spill response option are available in Germany, including sensitivity maps and tools for drift modelling of dispersed and undispersed oil. However, open scientific questions remain concerning the persistence of dispersed oil trapped in the sediments and potential health effects. %0 Artikel %@ 1559-2723 %A Sanders, T. %A Schoel, A. %A Daehnke, K. %D 2018 %J Estuaries and Coasts %N 2282 %P 128 - 138 %R doi:10.1007/s12237-017-0264-8 %T Hot spots of nitrification in the Elbe Estuary and their impact on nitrate regeneration %U http://dx.doi.org/10.1007/s12237-017-0264-8 1 %X Estuaries act as an organic matter and nutrient filter in the transition between the land, rivers and the ocean. In the past, high nutrient and organic carbon load and low oxygen concentration made the Elbe River estuary (NW Europe) a sink for dissolved inorganic nitrogen. A recent reduction in loads and subsequent recovery of the estuary changed its biogeochemical function, so that nitrate is no longer removed on its transition towards the coastal North Sea. Nowadays in the estuary, nitrification appears to be a significant nitrate source. To quantify nitrification and determine actively nitrifying regions in the estuary, we measured the concentrations of ammonium, nitrite and nitrate, the dual stable isotopes of nitrate and net nitrification rates in the estuary on five cruises from August 2012 to August 2013. The nitrate concentration increased markedly downstream of the port of Hamburg in summer and spring, accompanied by a decrease of nitrate isotope values that was clearest in summer exactly at the location where nitrate concentration started to increase. Ammonium and nitrite peaked in the Hamburg port region (up to 18 and 8 μmol L−1, respectively), and nitrification rates in this region were up to 7 μmol L−1 day−1. Our data show that coupled re-mineralization and nitrification are significant internal nitrate sources that almost double the estuary’s summer nitrate concentration. Furthermore, we find that the port of Hamburg is a hot spot of nitrification, whereas the maximum turbidity zone (MTZ) only plays a subordinate role in turnover of nitrate. %0 Artikel %@ 1726-4170 %A Gaye, B. %A Boell, A. %A Segschneider, J. %A Burdanowitz, N. %A Emeis, K.-C. %A Ramaswamy, V. %A Lahajnar, N. %A Lueckge, A. %A Rixen, T. %D 2018 %J Biogeosciences %N 2118 %P 507 - 527 %R doi:10.5194/bg-15-507-2018 %T Glacial–interglacial changes and Holocene variations in Arabian Sea denitrification %U https://dx.doi.org/10.5194/bg-15-507-2018 %X At present, the Arabian Sea has a permanent oxygen minimum zone (OMZ) at water depths between about 100 and 1200 m. Active denitrification in the upper part of the OMZ is recorded by enhanced δ15N values in the sediments. Sediment cores show a δ15N increase during the middle and late Holocene, which is contrary to the trend in the other two regions of water column denitrification in the eastern tropical North and South Pacific. We calculated composite sea surface temperature (SST) and δ15N ratios in time slices of 1000 years of the last 25 kyr to better understand the reasons for the establishment of the Arabian Sea OMZ and its response to changes in the Asian monsoon system. Low δ15N values of 4–7 ‰ during the last glacial maximum (LGM) and stadials (Younger Dryas and Heinrich events) suggest that denitrification was inactive or weak during Pleistocene cold phases, while warm interstadials (ISs) had elevated δ15N. Fast changes in upwelling intensities and OMZ ventilation from the Antarctic were responsible for these strong millennial-scale variations during the glacial. During the entire Holocene δ15N values > 6 ‰ indicate a relatively stable OMZ with enhanced denitrification. The OMZ develops parallel to the strengthening of the SW monsoon and monsoonal upwelling after the LGM. Despite the relatively stable climatic conditions of the Holocene, the δ15N records show regionally different trends in the Arabian Sea. In the upwelling areas in the western part of the basin, δ15N values are lower during the mid-Holocene (4.2–8.2 ka BP) compared to the late Holocene (< 4.2 ka BP) due to stronger ventilation of the OMZ during the period of the most intense southwest monsoonal upwelling. In contrast, δ15N values in the northern and eastern Arabian Sea rose during the last 8 kyr. The displacement of the core of the OMZ from the region of maximum productivity in the western Arabian Sea to its present position in the northeast was established during the middle and late Holocene. This was probably caused by (i) reduced ventilation due to a longer residence time of OMZ waters and (ii) augmented by rising oxygen consumption due to enhanced northeast-monsoon-driven biological productivity. This concurs with the results of the Kiel Climate Model, which show an increase in OMZ volume during the last 9 kyr related to the increasing age of the OMZ water mass. %0 Artikel %@ 0790-0627 %A Bradley, C. %A Bowes, M.J. %A Brils, J. %A Friedrich, J. %A Gault, J. %A Groom, S. %A Hein, T. %A Heininger, P. %A Michalopoulos, P. %A Panin, N. %A Schultz, M. %A Stanica, A. %A Andrei, I. %A Tyler, A. %A Umgiesser, G. %D 2018 %J International Journal of Water Resources Development %N 2818 %P 888 - 899 %R doi:10.1080/07900627.2017.1399107 %T Advancing integrated research on European river–sea systems: the DANUBIUS-RI project %U https://dx.doi.org/10.1080/07900627.2017.1399107 6 %X Research at the interface between terrestrial, riverine, estuarine and marine environments is frequently constrained by significant disciplinary and geographical boundaries. This article outlines an international initiative, DANUBIUS-RI, which aims to address these problems by facilitating biogeochemical monitoring and interdisciplinary research on river–sea systems. The scope of the project spans the environmental, social and economic sciences and was accepted into the European Strategy Forum on Research Infrastructures roadmap in 2016. When operational, DANUBIUS-RI will offer researchers access to interdisciplinary expertise, facilities and European river–sea systems, providing a comprehensive platform for multidisciplinary research and training. %0 Artikel %@ 0967-0637 %A Roca-Marti, M. %A Puigcorbe, V. %A Friedrich, J. %A Loeff, M.R.van der %A Rabe, B. %A Korhonen, M. %A Camara-Mor, P. %A Garcia-Orellana, J. %A Masque, P. %D 2018 %J Deep-Sea Research Part I %N 2095 %P 94 - 106 %R doi:10.1016/j.dsr.2018.09.011 %T Distribution of 210Pb and 210Po in the Arctic water column during the 2007 sea-ice minimum: Particle export in the ice-covered basins %U https://dx.doi.org/10.1016/j.dsr.2018.09.011 %X 210Pb and 210Po are naturally occurring radionuclides that are commonly used as a proxy for particle and carbon export. In this study, the distribution of the 210Po/210Pb pair was investigated in the water column of the Barents, Kara and Laptev Seas and the Nansen, Amundsen and Makarov Basins in order to understand the particle dynamics in the Arctic Ocean during the 2007 sea-ice minimum (August–September). Minimum activities of total 210Pb and 210Po were found in the upper and lower haloclines (approx. 60–130 m), which are partly attributed to particle scavenging over the shelves, boundary current transport and subsequent advection of the water with low 210Pb and 210Po activities into the central Arctic. Widespread and substantial (> 50%) deficits of 210Po with respect to 210Pb were detected from surface waters to 200 m on the shelves, but also in the basins. This was particularly important in the Makarov Basin where, despite very low chlorophyll-a levels, estimates of annual new primary production were three times higher than in the Eurasian Basin. In the Nansen, Amundsen and Makarov Basins, estimates of annual new primary production correlated with the deficits of 210Po in the upper 200 m of the water column, suggesting that in situ production and subsequent export of biogenic material were the mechanisms that controlled the removal of 210Po in the central Arctic. Unlike 210Po, 234Th deficits measured during the same expedition were found to be very small and not significant below 25 m in the basins (Cai et al., 2010), which indicates, given the shorter half-life of 234Th, that particle export fluxes in the central Arctic would have been higher before July–August in 2007 than later in the season. %0 Artikel %@ 0013-936X %A Tang, J. %A Mi, W. %A Tian, C. %A Emeis, K. %A Ebinghaus, R. %A Xie, Z. %D 2018 %J Environmental Science and Technology %N 1114 %P 89 - 97 %R doi:10.1021/acs.est.7b03807 %T Spatial Distribution and Seasonal Variation of Organophosphate Esters in Air above the Bohai and Yellow Seas; China %U https://dx.doi.org/10.1021/acs.est.7b03807 1 %X Nine organophosphate esters (OPEs) were investigated in air samples collected over the Bohai and Yellow Seas (East Asia) during a research cruise between June 28 and July 13, 2016. These same OPEs were quantified at a research site (North Huangcheng Island, NHI) in the middle of the Bohai Strait from May 16, 2015, to March 21, 2016. The median total OPE (ΣOPE) concentration over the Bohai and Yellow Seas was 280 pg/m3. Tris(1-chloro-2-propyl) (TCPP) was the most abundant OPE, followed by tris(2-chloroethyl) phosphate (TCEP), tri-iso-butyl phosphate (TiBP), and tri-n-butyl phosphate (TnBP). Particle-bound OPEs accounted for 51 ± 21% of the total OPEs. On NHI, the median ΣOPE concentration was 210 pg/m3, and the average particle-bound fraction was 82 ± 17%. For samples collected on NHI, significant negative linear correlations were found between the gaseous OPEs and 1/T (T: temperature (K)) (except TDCP, TPeP, and TCP). Among the 79 investigated samples, significant correlations between the measured OPE gas/particle partitioning coefficients (Kp,m) and subcooled liquid pressure (PL◦) (p < 0.05) were found for only 14 samples, suggesting that OPEs have low potential to achieve equilibrium or ascribe to the artificial sampling. The annual dry deposition input of OPEs into the Bohai and Yellow Seas is estimated to be 12 tons/year. %0 Artikel %@ 0048-9697 %A Kerimoglu, O. %A Große, F. %A Kreus, M. %A van Beusekom, J. %D 2018 %J Science of the Total Environment %N 1562 %P 1311 - 1323 %R doi:10.1016/j.scitotenv.2018.05.215 %T A model-based projection of historical state of a coastal ecosystem: Relevance of phytoplankton stoichiometry %U https://dx.doi.org/10.1016/j.scitotenv.2018.05.215 %X We employed a coupled physical-biogeochemical modelling framework for the reconstruction of the historic (H), pre-industrial state of a coastal system, the German Bight (southeastern North Sea), and we investigated its differences with the recent, control (C) state of the system. According to our findings: i) average winter concentrations of dissolved inorganic nitrogen and phosphorus (DIN and DIP) concentrations at the surface are ∼70–90% and ∼50–70% lower in the H state than in the C state within the nearshore waters, and differences gradually diminish towards off-shore waters; ii) differences in average growing season chlorophyll a (Chl) concentrations at the surface between the two states are mostly less than 50%; iii) in the off-shore areas, Chl concentrations in the deeper layers are affected less than in the surface layers; iv) reductions in phytoplankton carbon (C) biomass under the H state are weaker than those in Chl, due to the generally lower Chl:C ratios; v) in some areas the differences in growth rates between the two states are negligible, due to the compensation by lower light limitation under the H state, which in turn explains the lower Chl:C ratios; vi) zooplankton biomass, and hence the grazing pressure on phytoplankton is lower under the H state. This trophic decoupling is caused by the low nutritional quality (i.e., low N:C and P:C) of phytoplankton. These results call for increased attention to the relevance of the acclimation capacity and stoichiometric flexibility of phytoplankton for the prediction of their response to environmental change. %0 Artikel %@ 0924-7963 %A Vorrath, M. %A Lahajnar, N. %A Fischer, G. %A Libuku, V. %A Schmidt, M. %A Emeis, K. %D 2018 %J Journal of Marine Systems %N 1217 %P 59 - 75 %R doi:10.1016/j.jmarsys.2017.12.002 %T Spatiotemporal variation of vertical particle fluxes and modelled chlorophyll a standing stocks in the Benguela Upwelling System %U https://dx.doi.org/10.1016/j.jmarsys.2017.12.002 %X Marine particle fluxes from high productive coastal upwelling systems return upwelled CO2 and nutrients to the deep ocean and sediments and have a substantial impact on the global carbon cycle. This study examines relations between production regimes on the shelf and over the continental margin of the Benguela Upwelling System (BUS) in the SE Atlantic Ocean. Data of composition and timing of vertical particle flux come from sediment trap time series (deployed intermittently between 1988 and 2014) in the regions Walvis Ridge, Walvis Bay, Luederitz and Orange River. We compare their seasonal variability to modelled patterns of chlorophyll concentrations in a 3-D ecosystem model. Both modelled seasonal chlorophyll a standing stocks and sampled particle flux patterns are highly correspondent with a bimodal seasonal cycle offshore the BUS. The material in the particle flux in offshore traps is dominantly carbonate (40–70%), and flux peaks in offshore particle flux originate from two independent events: in austral autumn thermocline shoaling and vertical mixing are decoupled from coastal upwelling, while fluxes in spring coincide with the upwelling season, indicated by slightly elevated biogenic opal values at some locations. Coastal particle fluxes are characterized by a trimodal pattern and are dominated by biogenic opal (22–35%) and organic matter (30–60%). The distinct seasonality in observed fluxes on the shelf is caused by high variability in production, sinking behaviour, wind stress, and hydrodynamic processes. We speculate that global warming will increase ocean stratification and alter coastal upwelling, so that consequences for primary production and particle flux in the BUS are inevitable. %0 Artikel %@ 0924-7963 %A Emeis, K. %A Eggert, A. %A Flohr, A. %A Lahajnar, N. %A Nausch, G. %A Neumann, A. %A Rixen, T. %A Schmidt, A. %A Van der Plas, A. %A Wasmund, N. %D 2018 %J Journal of Marine Systems %N 1217 %P 63 - 80 %R doi:10.1016/j.jmarsys.2017.10.001 %T Biogeochemical processes and turnover rates in the Northern Benguela Upwelling System %U https://dx.doi.org/10.1016/j.jmarsys.2017.10.001 %X Biogeochemical cycles of carbon, nutrients, and oxygen transmit mean states, trends and variations of the physical realm in coastal upwelling systems to their food webs and determine their role in regional budgets of greenhouse gases. This contribution focuses on biogeochemical processes in the northern Benguela Upwelling System (NBUS), where low oxygen levels in upwelling source water are a major influence on carbon and nutrient cycles. Based on measurements during numerous expeditions and results of 3-D regional ecosystem modeling (project GENUS; Geochemistry and Ecology of the Namibian Upwelling System) we here examine source water character, effects of low oxygen conditions on nutrient masses and ratios, and of diazotrophic N2-fixation on productivity of the system and its transition to the adjacent eastern South Atlantic. In available observations, the effects of denitrification in water and sediment and phosphate release from sediments are minor influences on nitrate:phosphate ratios of the system, and excess phosphate in aged upwelling water is inherited from upwelling source water. Contrary to expectation and model results, the low N:P ratios do not trigger diazotrophic N2-fixation in the fringes of the upwelling system, possibly due to a lack of seeding populations of Trichodesmium. We also examine the flux of carbon from the sea surface to either sediment, the adjacent sub-thermocline ocean, or to regenerated nutrients and CO2. Observed fluxes out of the surface mixed layer are significantly below modeled fluxes, and suggest that regeneration of nutrients and CO2 is unusually intense in the mixed layer. This contributes to very high fluxes of CO2 from the ocean to the regional atmosphere, which is not compensated for by N2-fixation. Based on observations, the NBUS thus is a significant net CO2 source (estimated at 14.8 Tg C a− 1), whereas the CO2 balance is closed by N2-fixation in the model. Methane concentrations were low in surface waters in on-line measurements during 1 expedition, and based on these our estimate for the emission of methane for the entire Benguela system is below 0.2 Tg CH4 a− 1. %0 Artikel %@ 0009-2541 %A Schlitzer, R. %A Anderson, R.F. %A Dodas, E.M. %A Lohan, M. %A Geibert, W. %A Tagliabue, A. %A Bowie, A. %A Jeandel, C. %A Maldonado, M.T. %A Landing, W.M. %A Cockwell, D. %A Abadie, C. %A Abouchami, W. %A Achterberg, E.P. %A Agather, A. %A Aguliar-Islas, A. %A van Aken, H.M. %A Andersen, M. %A Archer, C. %A Auro, M. %A de Baar, H.J. %A Baars, O. %A Baker, A.R. %A Bakker, K. %A Basak, C. %A Baskaran, M. %A Bates, N.R. %A Bauch, D. %A van Beek, P. %A Behrens, M.K. %A Black, E. %A Bluhm, K. %A Bopp, L. %A Bouman, H. %A Bowman, K. %A Bown, J. %A Boyd, P. %A Boye, M. %A Boyle, E.A. %A Branellec, P. %A Bridgestock, L. %A Brissebrat, G. %A Browning, T. %A Bruland, K.W. %A Brumsack, H.-J. %A Brzezinski, M. %A Buck, C.S. %A Buck, K.N. %A Buesseler, K. %A Bull, A. %A Butler, E. %A Cai, P. %A Mor, P.C. %A Cardinal, D. %A Carlson, C. %A Carrasco, G. %A Casacuberta, N. %A Casciotti, K.L. %A Castrillejo, M. %A Chamizo, E. %A Chance, R. %A Charette, M.A. %A Chaves, J.E. %A Cheng, H. %A Chever, F. %A Christl, M. %A Church, T.M. %A Closset, I. %A Colman, A. %A Conway, T.M. %A Cossa, D. %A Croot, P. %A Cullen, J.T. %A Cutter, G.A. %A Daniels, C. %A Dehairs, F. %A Deng, F. %A Dieu, H.T. %A Duggan, B. %A Dulaquais, G. %A Dumousseaud, C. %A Echegoyen-Sanz, Y. %A Edwards, R.L. %A Ellwood, M. %A Fahrbach, E. %A Fitzsimmons, J.N. %A Russell Flegal, A. %A Fleisher, M.Q. %A van de Flierdt, T. %A Frank, M. %A Friedrich, J. %A Fripiat, F. %A Fröllje, H. %A Galer, S.J.G. %A Gamo, T. %A Ganeshram, R.S. %A Garcia-Orellana, J. %A Garcia-Solsona, E. %A Gault-Ringold, M. %A George, E. %A Gerringa, L.J.A. %A Gilbert, M. %A Godoy, J.M. %A Goldstein, S.L. %A Gonzalez, S.R. %A Grissom, K. %A Hammerschmidt, C. %A Hartman, A. %A Hassler, C.S. %A Hathorne, E.C. %A Hatta, M. %A Hawco, N. %A Hayes, C.T. %A Heimbürger, L.-E. %A Helgoe, J. %A Heller, M. %A Henderson, G.M. %A Henderson, P.B. %A van Heuven, S. %A Ho, P. %A Horner, T.J. %A Hsieh, Y.-T. %A Huang, K.-F. %A Humphreys, M.P. %A Isshiki, K. %A Jacquot, J.E. %A Janssen, D.J. %A Jenkins, W.J. %A John, S. %A Jones, E.M. %A Jones, J.L. %A Kadko, D.C. %A Kayser, R. %A Kenna, T.C. %A Khondoker, R. %A Kim, T. %A Kipp, L. %A Klar, J.K. %A Klunder, M. %A Kretschmer, S. %A Kumamoto, Y. %A Laan, P. %A Labatut, M. %A Lacan, F. %A Lam, P.J. %A Lambelet, M. %A Lamborg, C.H. %A Le Moigne, F.A.C. %A Le Roy, E. %A Lechtenfeld, O.J. %A Lee, J.-M. %A Lherminier, P. %A Little, S. %A López-Lora, M. %A Lu, Y. %A Masque, P. %A Mawji, E. %A Mcclain, C.R. %A Measures, C. %A Mehic, S. %A Barraqueta, J.-L.M. %A van der Merwe, P. %A Middag, R. %A Mieruch, S. %A Milne, A. %A Minami, T. %A Moffett, J.W. %A Moncoiffe, G. %A Moore, W.S. %A Morris, P.J. %A Morton, P.L. %A Nakaguchi, Y. %A Nakayama, N. %A Niedermiller, J. %A Nishioka, J. %A Nishiuchi, A. %A Noble, A. %A Obata, H. %A Ober, S. %A Ohnemus, D.C. %A van Ooijen, J. %A O'Sullivan, J. %A Owens, S. %A Pahnke, K. %A Paul, M. %A Pavia, F. %A Pena, L.D. %A Peters, B. %A Planchon, F. %A Planquette, H. %A Pradoux, C. %A Puigcorbé, V. %A Quay, P. %A Queroue, F. %A Radic, A. %A Rauschenberg, S. %A Rehkämper, M. %A Rember, R. %A Remenyi, T. %A Resing, J.A. %A Rickli, J. %A Rigaud, S. %A Rijkenberg, M.J.A. %A Rintoul, S. %A Robinson, L.F. %A Roca-Martí, M. %A Rodellas, V. %A Roeske, T. %A Rolison, J.M. %A Rosenberg, M. %A Roshan, S. %A Rutgers van der Loeff, M.M. %A Ryabenko, E. %A Saito, M.A. %A Salt, L.A. %A Sanial, V. %A Sarthou, G. %A Schallenberg, C. %A Schauer, U. %A Scher, H. %A Schlosser, C. %A Schnetger, B. %A Scott, P. %A Sedwick, P.N. %A Semiletov, I. %A Shelley, R. %A Sherrell, R.M. %A Shiller, A.M. %A Sigman, D.M. %A Singh, S.K. %A Slagter, H.A. %A Slater, E. %A Smethie, W.M. %A Snaith, H. %A Sohrin, Y. %A Sohst, B. %A Sonke, J.E. %A Speich, S. %A Steinfeldt, R. %A Stewart, G. %A Stichel, T. %A Stirling, C.H. %A Stutsman, J. %A Swarr, G.J. %A Swift, J.H. %A Thomas, A. %A Thorne, K. %A Till, C.P. %A Till, R. %A Townsend, A.T. %A Townsend, E. %A Tuerena, R. %A Twining, B.S. %A Vance, D. %A Velazquez, S. %A Venchiarutti, C. %A Villa-Alfageme, M. %A Vivancos, S.M. %A Voelker, A.H.L. %A Wake, B. %A Warner, M.J. %A Watson, R. %A van Weerlee, E. %A Alexandra Weigand, M. %A Weinstein, Y. %A Weiss, D. %A Wisotzki, A. %A Woodward, E.M.S. %A Wu, J. %A Wu, Y. %A Wuttig, K. %A Wyatt, N. %A Xiang, Y. %A Xie, R.C. %A Xue, Z. %A Yoshikawa, H. %A Zhang, J. %A Zhang, P. %A Zhao, Y. %A Zheng, L. %A Zheng, X.-Y. %A Zieringer, M. %A Zimmer, L.A. %A Ziveri, P. %A Zunino, P. %A Zurbrick, C. %D 2018 %J Chemical Geology %N 2949 %P 210 - 223 %R doi:10.1016/j.chemgeo.2018.05.040 %T The GEOTRACES Intermediate Data Product 2017 %U https://dx.doi.org/10.1016/j.chemgeo.2018.05.040 %X The GEOTRACES Intermediate Data Product 2017 (IDP2017) is the second publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2016. The IDP2017 includes data from the Atlantic, Pacific, Arctic, Southern and Indian oceans, with about twice the data volume of the previous IDP2014. For the first time, the IDP2017 contains data for a large suite of biogeochemical parameters as well as aerosol and rain data characterising atmospheric trace element and isotope (TEI) sources. The TEI data in the IDP2017 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at crossover stations. The IDP2017 consists of two parts: (1) a compilation of digital data for more than 450 TEIs as well as standard hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing an on-line atlas that includes more than 590 section plots and 130 animated 3D scenes. The digital data are provided in several formats, including ASCII, Excel spreadsheet, netCDF, and Ocean Data View collection. Users can download the full data packages or make their own custom selections with a new on-line data extraction service. In addition to the actual data values, the IDP2017 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering and for statistical analysis. Metadata about data originators, analytical methods and original publications related to the data are linked in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2017 as section plots and rotating 3D scenes. The basin-wide 3D scenes combine data from many cruises and provide quick overviews of large-scale tracer distributions. These 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of tracer plumes near ocean margins or along ridges. The IDP2017 is the result of a truly international effort involving 326 researchers from 25 countries. This publication provides the critical reference for unpublished data, as well as for studies that make use of a large cross-section of data from the IDP2017. %0 Artikel %@ 2045-2322 %A Kraemer, K. %A Holler, P. %A Herbst, G. %A Bratek, A. %A Ahmerkamp, S. %A Neumann, A. %A Bartholomae, A. %A Beusekom, J.E.E.van %A Holtappels, M. %A Winter, C. %D 2017 %J Scientific Reports %N 2562 %P 5150 %R doi:10.1038/s41598-017-05536-1 %T Abrupt emergence of a large pockmark field in the German Bight, southeastern North Sea %U http://dx.doi.org/10.1038/s41598-017-05536-1 %X A series of multibeam bathymetry surveys revealed the emergence of a large pockmark field in the southeastern North Sea. Covering an area of around 915 km2, up to 1,200 pockmarks per square kilometer have been identified. The time of emergence can be confined to 3 months in autumn 2015, suggesting a very dynamic genesis. The gas source and the trigger for the simultaneous outbreak remain speculative. Subseafloor structures and high methane concentrations of up to 30 μmol/l in sediment pore water samples suggest a source of shallow biogenic methane from the decomposition of postglacial deposits in a paleo river valley. Storm waves are suggested as the final trigger for the eruption of the gas. Due to the shallow water depths and energetic conditions at the presumed time of eruption, a large fraction of the released gas must have been emitted to the atmosphere. Conservative estimates amount to 5 kt of methane, equivalent to 67% of the annual release from the entire North Sea. These observations most probably describe a reoccurring phenomenon in shallow shelf seas, which may have been overlooked before because of the transient nature of shallow water bedforms and technology limitations of high resolution bathymetric mapping. %0 Artikel %@ 1385-1101 %A Hufnagl, M. %A Payne, M. %A Lacroix, G. %A Bolle, L.J. %A Daewel, U. %A Dickey-Collas, M. %A Gerkema, T. %A Huret, M. %A Janssen, F. %A Kreus, M. %A Paetsch, J. %A Pohlmann, T. %A Ruardij, P. %A Schrum, C. %A Skogen, M.D. %A Tiessen, M.C.H. %A Petitgas, P. %A Beek, J.K.L.van %A Veer, H.W.van der %A Callies, U. %D 2017 %J Journal of Sea Research %N 1337 %P 133 - 149 %R doi:10.1016/j.seares.2017.04.009 %T Variation that can be expected when using particle tracking models in connectivity studies %U https://dx.doi.org/10.1016/j.seares.2017.04.009 %X Hydrodynamic Ocean Circulation Models and Lagrangian particle tracking models are valuable tools e.g. in coastal ecology to identify the connectivity between offshore spawning and coastal nursery areas of commercially important fish, for risk assessment and more for defining or evaluating marine protected areas. Most studies are based on only one model and do not provide levels of uncertainty. Here this uncertainty was addressed by applying a suite of 11 North Sea models to test what variability can be expected concerning connectivity. Different notional test cases were calculated related to three important and well-studied North Sea fish species: herring (Clupea harengus), and the flatfishes sole (Solea solea) and plaice (Pleuronectes platessa). For sole and plaice we determined which fraction of particles released in the respective spawning areas would reach a coastal marine protected area. For herring we determined the fraction located in a wind park after a predefined time span. As temperature is more and more a focus especially in biological and global change studies, furthermore inter-model variability in temperatures experienced by the virtual particles was determined. The main focus was on the transport variability originating from the physical models and thus biological behavior was not included. Depending on the scenario, median experienced temperatures differed by 3 °C between years. The range between the different models in one year was comparable to this temperature range observed between modelled years. Connectivity between flatfish spawning areas and the coastal protected area was highly dependent on the release location and spawning time. No particles released in the English Channel in the sole scenario reached the protected area while up to 20% of the particles released in the plaice scenario did. Interannual trends in transport directions and connectivity rates were comparable between models but absolute values displayed high variations. Most models showed systematic biases during all years in comparison to the ensemble median, indicating that in general interannual variation was represented but absolute values varied. In conclusion: variability between models is generally high and management decisions or scientific analysis using absolute values from only one single model might be biased and results or conclusions drawn from such studies need to be treated with caution. We further concluded that more true validation data for particle modelling are required. %0 Artikel %@ 1812-0784 %A Callies, U. %A Groll, N. %A Horstmann, J. %A Kapitza, H. %A Klein, H. %A Massmann, S. %A Schwichtenberg, F. %D 2017 %J Ocean Science %N 2310 %P 799 - 827 %R doi:10.5194/os-13-799-2017 %T Surface drifters in the German Bight: model validation considering windage and Stokes drift %U https://dx.doi.org/10.5194/os-13-799-2017 5 %X Six surface drifters (drogued at about 1 m depth) deployed in the inner German Bight (North Sea) were tracked for between 9 and 54 days. Corresponding simulations were conducted offline based on surface currents from two independent models (BSHcmod and TRIM). Inclusion of a direct wind drag (0.6 % of 10 m wind) was needed for successful simulations based on BSHcmod currents archived for a 5 m depth surface layer. Adding 50 % of surface Stokes drift simulated with a third-generation wave model (WAM) was tested as an alternative approach. Results resembled each other during most of the time. Successful simulations based on TRIM surface currents (1 m depth) suggest that both approaches were mainly needed to compensate insufficient vertical resolution of hydrodynamic currents. The study suggests that the main sources of simulation errors were inaccurate Eulerian currents and lacking representation of sub-grid-scale processes. Substantial model errors often occurred under low wind conditions. A lower limit of predictability (about 3–5 km day−1) was estimated from two drifters that were initially spaced 20 km apart but converged quickly and diverged again after having stayed at a distance of 2 km or less for about 10 days. In most cases, errors in simulated 25 h drifter displacements were of similar order of magnitude. %0 Artikel %@ 0024-3590 %A Ahmerkamp, S. %A Winter, C. %A Kraemer, K. %A de Beer, D. %A Janssen, F. %A Friedrich, J. %A Kuypers, M.M.M. %A Holtappels, M. %D 2017 %J Limnology and Oceanography %N 1281 %P 1935 - 1954 %R doi:10.1002/lno.10544 %T Regulation of benthic oxygen fluxes in permeable sediments of the coastal ocean %U http://dx.doi.org/10.1002/lno.10544 5 %X Large areas of the oceanic shelf are composed of sandy sediments through which reactive solutes are transported via porewater advection fueling active microbial communities. The advective oxygen transport in permeable sands of the North Sea was investigated under in situ conditions using a new benthic observatory to assess the dynamic interaction of hydrodynamics, sediment morphodynamics, and oxygen penetration depth. During 16 deployments, concurrent measurement of current velocity, sediment topography, and porewater oxygen concentration were carried out. In all cases the oxyclines were found at depths of 1–6 cm, correlating with the topography of stationary and migrating bedforms (ripples). Different conditions in terms of bottom water currents and bedform migration led to fluctuating oxygen penetration depths and, hence, highly variable redox conditions in up to 2.5 cm thick layers beneath the surface. Volumetric oxygen consumption rates of surface sediments were measured on board in flow-through reactors. Bedform migration was found to reduce consumption rates by up to , presumably caused by the washout of organic carbon that is otherwise trapped in the pore space of the sediment. Based on the observations we found oxygen penetration depths to be largely controlled by oxygen consumption rates, grain size, and current velocity. These controlling variables are summarized by an adapted Damköhler number which allows for prediction of oxygen penetretion depths based on a simple scaling law. By integrating the oxygen consumption rates over the oxygen penetration depth, oxygen fluxes of 8–34 mmol m−2 d−1 were estimated. %0 Artikel %@ 1385-1101 %A Neumann, A. %A Beusekom, J.E.E.van %A Holtappels, M. %A Emeis, K.-C. %D 2017 %J Journal of Sea Research %N 1337 %P 26 - 35 %R doi:10.1016/j.seares.2017.06.012 %T Nitrate consumption in sediments of the German Bight (North Sea) %U http://dx.doi.org/10.1016/j.seares.2017.06.012 %X Denitrification on continental margins and in coastal sediments is a major sink of reactive N in the present nitrogen cycle and a major ecosystem service of eutrophied coastal waters. We analyzed the nitrate removal in surface sediments of the Elbe estuary, Wadden Sea, and adjacent German Bight (SE North Sea) during two seasons (spring and summer) along a eutrophication gradient ranging from a high riverine nitrate concentrations at the Elbe Estuary to offshore areas with low nitrate concentrations. The gradient encompassed the full range of sediment types and organic carbon concentrations of the southern North Sea. Based on nitrate penetration depth and concentration gradient in the porewater we estimated benthic nitrate consumption rates assuming either diffusive transport in cohesive sediments or advective transport in permeable sediments. For the latter we derived a mechanistic model of porewater flow. During the peak nitrate discharge of the river Elbe in March, the highest rates of diffusive nitrate uptake were observed in muddy sediments (up to 2.8 mmol m− 2 d− 1). The highest advective uptake rate in that period was observed in permeable sediment and was tenfold higher (up to 32 mmol m− 2 d− 1). The intensity of both diffusive and advective nitrate consumption dropped with the nitrate availability and thus decreased from the Elbe estuary towards offshore stations, and were further decreased during late summer (minimum nitrate discharge) compared to late winter (maximum nitrate discharge). In summary, our rate measurements indicate that the permeable sediment accounts for up to 90% of the total benthic reactive nitrogen consumption in the study area due to the high efficiency of advective nitrate transport into permeable sediment. Extrapolating the averaged nitrate consumption of different sediment classes to the areas of Elbe Estuary, Wadden Sea and eastern German Bight amounts to an N-loss of 3.1 ∗ 106 mol N d− 1 from impermeable, diffusion-controlled sediment, and 5.2 ∗ 107 mol N d− 1 from permeable sediment with porewater advection. %0 Artikel %@ 0079-6611 %A Floeter, J. %A Beusekom, J.E.E.van %A Auch, D. %A Callies, U. %A Carpenter, J. %A Dudeck, T. %A Eberle, S. %A Eckhardt, A. %A Gloe, D. %A Haenselmann, K. %A Hufnagl, M. %A Janssen, S. %A Lenhart, H. %A Moeller, K.O. %A North, R.P. %A Pohlmann, T. %A Riethmueller, R. %A Schulz, S. %A Spreizenbarth, S. %A Temming, A. %A Walter, B. %A Zielinski, O. %A Moellmann, C. %D 2017 %J Progress in Oceanography %N 1956 %P 154 - 173 %R doi:10.1016/j.pocean.2017.07.003 %T Pelagic effects of offshore wind farm foundations in the stratified North Sea %U http://dx.doi.org/10.1016/j.pocean.2017.07.003 %X A recent increase in the construction of Offshore Wind Farms (OWFs) has initiated numerous environmental impact assessments and monitoring programs. These focus on sea mammals, seabirds, benthos or demersal fish, but generally ignore any potential effects OWFs may have on the pelagic ecosystem. The only work on the latter has been through modelling analyses, which predict localised impacts like enhanced vertical mixing leading to a decrease in seasonal stratification, as well as shelf-wide changes of tidal amplitudes. Here we provide for the first-time empirical bio-physical data from an OWF. The data were obtained by towing a remotely operated vehicle (TRIAXUS ROTV) through two non-operating OWFs in the summer stratified North Sea. The undulating TRIAXUS transects provided high-resolution CTD data accompanied by oxygen and chlorophyll-a measurements. We provide empirical indication that vertical mixing is increased within the OWFs, leading to a doming of the thermocline and a subsequent transport of nutrients into the surface mixed layer (SML). Nutrients were taken up rapidly because underwater photosynthetically active radiation (PAR) enabled net primary production in the entire water column, especially within submesoscale chlorophyll-a pillars that were observed at regular intervals within the OWF regions. Video Plankton Recorder (VPR) images revealed distinct meroplankton distribution patterns in a copepod-dominated plankton community. Hydroacoustic records did not show any OWF effects on the distribution of pelagic fish. The results of a pre-OWF survey show however, that it is difficult to fully separate the anthropogenic impacts from the natural variability. %0 Artikel %@ 0013-936X %A Xie, Z. %A Mi, W. %A Lai, S. %A Tian, C. %A Emeis, K. %A Ebinghaus, R. %D 2017 %J Environmental Science and Technology %N 1114 %P 6887 - 6896 %R doi:10.1021/acs.est.7b01289 %T Organophosphate Esters in Air, Snow, and Seawater in the North Atlantic and the Arctic %U https://dx.doi.org/10.1021/acs.est.7b01289 12 %X The concentrations of eight organophosphate esters (OPEs) have been investigated in air, snow and seawater samples collected during the cruise of ARK-XXVIII/2 from sixth June to third July 2014 across the North Atlantic and the Arctic. The sum of gaseous and particle concentrations (ΣOPE) ranged from 35 to 343 pg/m3. The three chlorinated OPEs accounted for 88 ± 5% of the ΣOPE. The most abundant OPE was tris(2-chloroethyl) phosphate (TCEP), with concentrations ranging from 30 to 227 pg/m3, followed by three major OPEs, such as tris(1-chloro-2-propyl) phosphate (TCPP, 0.8 to 82 pg/m3), tri-n-butyl phosphate (TnBP, 2 to 19 pg/m3), and tri-iso-butyl phosphate (TiBP, 0.3 to 14 pg/m3). The ΣOPE concentrations in snow and seawater ranged from 4356 to 10561 pg/L and from 348 to 8396 pg/L, respectively. The atmospheric particle-bound dry depositions of TCEP ranged from 2 to 12 ng/m2/day. The air–seawater gas exchange fluxes were dominated by net volatilization from seawater to air for TCEP (mean, 146 ± 239 ng/m2/day), TCPP (mean, 1670 ± 3031 ng/m2/day), TiBP (mean, 537 ± 581 ng/m2/day) and TnBP (mean, 230 ± 254 ng/m2/day). This study highlighted that OPEs are subject to long-range transport via both air and seawater from the European continent and seas to the North Atlantic and the Arctic. %0 Artikel %@ 2296-7745 %A Brase, L. %A Bange, H.W. %A Lendt, R. %A Sanders, T. %A Daehnke, K. %D 2017 %J Frontiers in Marine Science %N 2685 %P 162 %R doi:10.3389/fmars.2017.00162 %T High Resolution Measurements of Nitrous Oxide (N2O) in the Elbe Estuary %U https://dx.doi.org/10.3389/fmars.2017.00162 %X Nitrous oxide (N2O) is one of the most important greenhouse gases and a major sink for stratospheric ozone. Estuaries are sites of intense biological production and N2O emissions. We aimed to identify hot spots of N2O production and potential pathways contributing to N2O concentrations in the surface water of the tidal Elbe estuary. During two research cruises in April and June 2015, surface water N2O concentrations were measured along the salinity gradient of the Elbe estuary by using a laser-based on-line analyzer coupled to an equilibrator. Based on these high-resolution N2O profiles, N2O saturations, and fluxes across the surface water/atmosphere interface were calculated. Additional measurements of DIN concentrations, oxygen concentration, and salinity were performed. Highest N2O concentrations were determined in the Hamburg port region reaching maximum values of 32.3 nM in April 2015 and 52.2 nM in June 2015. These results identify the Hamburg port region as a significant hot spot of N2O production, where linear correlations of AOU-N2Oxs indicate nitrification as an important contributor to N2O production in the freshwater part. However, in the region with lowest oxygen saturation, sediment denitrification obviously affected water column N2O saturation. The average N2O saturation over the entire estuary was 201% (SD: ±94%), with an average estuarine N2O flux density of 48 μmol m−2 d−1 and an overall emission of 0.18 Gg N2O y−1. In comparison to previous studies, our data indicate that N2O production pathways over the whole estuarine freshwater part have changed from predominant denitrification in the 1980s toward significant production from nitrification in the present estuary. Despite a significant reduction in N2O saturation compared to the 1980s, N2O concentrations nowadays remain on a high level, comparable to the mid-90s, although a steady decrease of DIN inputs occurred over the last decades. Hence, the Elbe estuary still remains an important source of N2O to the atmosphere. %0 Artikel %@ 0276-0460 %A Schwichtenberg, F. %A Callies, U. %A Beusekom, J.E.E.van %D 2017 %J Geo-Marine Letters %N 2056 %P 171 - 177 %R doi:10.1007/s00367-016-0482-2 %T Residence times in shallow waters help explain regional differences in Wadden Sea eutrophication %U http://dx.doi.org/10.1007/s00367-016-0482-2 2 %X Regional variations in eutrophication levels of tidal basins in the Wadden Sea can be caused by external factors, like organic matter import, and internal factors like the morphology and hydrodynamics of the receiving tidal basin. For instance, benthic nutrients from remineralized organic matter may be more concentrated in shallow basins or diluted in basins with high exchange rates. In addition, the location of a monitoring station may determine which basin-specific water masses are actually observed. In the present paper a hydrodynamic intertidal imprint (IMP) is estimated for ten stations in various tidal basins of the Wadden Sea. The fraction of time water masses spent in intertidal areas prior to observation is calculated by linking the Lagrangian transport module PELETS to already existing hourly reconstructions of currents between 1959 and 2003. Irrespective of water depth, additional calculations of mean residence times (MRT) in the Wadden Sea indicate whether, in the case of low IMP values, water masses originate from coastal areas or tidal channels. Results show distinct regional differences, with highest values in the eastern part of the Dutch sector of the southern Wadden Sea (IMP=77%, MRT=99%) and lowest values in the German/Danish sector of the northern Wadden Sea (IMP=1.1%, MRT=21%). The IMP correlates positively with observed nutrient levels (R2=0.83). Evidently, this residence time-based intertidal signal is pivotal in explaining regional variations in eutrophication levels revealed by long-term comparative data from different monitoring stations. %0 Artikel %@ 0276-0460 %A Callies, U. %A Gaslikova, L. %A Kapitza, H. %A Scharfe, M. %D 2017 %J Geo-Marine Letters %N 2056 %P 151 - 162 %R doi:10.1007/s00367-016-0466-2 %T German Bight residual current variability on a daily basis: principal components of multi-decadal barotropic simulations %U http://dx.doi.org/10.1007/s00367-016-0466-2 2 %X Time variability of Eulerian residual currents in the German Bight (North Sea) is studied drawing on existing multi-decadal 2D barotropic simulations (1.6 km resolution) for the period Jan. 1958–Aug. 2015. Residual currents are calculated as 25 h means of velocity fields stored every hour. Principal component analysis (PCA) reveals that daily variations of these residual currents can be reasonably well represented in terms of only 2–3 degrees of freedom, partly linked to wind directions. The daily data refine monthly data already used in the past. Unlike existing classifications based on subjective assessment, numerical principal components (PCs) provide measures of strength and can directly be incorporated into more comprehensive statistical data analyses. Daily resolution in particular fits the time schedule of data sampled at the German Bight long-term monitoring station at Helgoland Roads. An example demonstrates the use of PCs and corresponding empirical orthogonal functions (EOFs) for the interpretation of short-term variations of these local observations. On the other hand, monthly averaging of the daily PCs enables to link up with previous studies on longer timescales. %0 Artikel %@ 0276-0460 %A Schwichtenberg, F. %A Callies, U. %A Groll, N. %A Massmann, S. %D 2017 %J Geo-Marine Letters %N 2056 %P 163 - 170 %R doi:10.1007/s00367-016-0454-6 %T Effects of chemical dispersants on oil spill drift paths in the German Bight—probabilistic assessment based on numerical ensemble simulations %U http://dx.doi.org/10.1007/s00367-016-0454-6 2 %X Oil dispersed in the water column remains sheltered from wind forcing, so that an altered drift path is a key consequence of using chemical dispersants. In this study, ensemble simulations were conducted based on 7 years of simulated atmospheric and marine conditions, evaluating 2,190 hypothetical spills from each of 636 cells of a regular grid covering the inner German Bight (SE North Sea). Each simulation compares two idealized setups assuming either undispersed or fully dispersed oil. Differences are summarized in a spatial map of probabilities that chemical dispersant applications would help prevent oil pollution from entering intertidal coastal areas of the Wadden Sea. High probabilities of success overlap strongly with coastal regions between 10 m and 20 m water depth, where the use of chemical dispersants for oil spill response is a particularly contentious topic. The present study prepares the ground for a more detailed net environmental benefit analysis (NEBA) accounting also for toxic effects. %0 Artikel %@ 0948-3055 %A Jacob, J. %A Nowka, B. %A Merten, V. %A Sanders, T. %A Spieck, E. %A Daehnke, K. %D 2017 %J Aquatic Microbial Ecology %N 2399 %P 289 - 300 %R doi:10.3354/ame01859 %T Oxidation kinetics and inverse isotope effect of marine nitrite-oxidizing isolates %U https://dx.doi.org/10.3354/ame01859 3 %X Nitrification, the step-wise oxidation of ammonium to nitrite and nitrate, is important in the marine environment, because it produces nitrate, the most abundant marine dissolved inorganic nitrogen (DIN) component and N-source for phytoplankton and microbes. This study focuses on the second step of nitrification, which is carried out by a distinct group of organisms, nitrite-oxidizing bacteria (NOB). The growth of NOB is characterized by nitrite oxidation kinetics, which we investigate for four pure cultures of marine NOB (Nitrospina watsonii 347, Nitrospira Ecomares 2.1, Nitrococcus mobilis 231, and Nitrobacter sp. 311). We further compare the kinetics to those of non-marine species, because substrate concentrations in marine environments are comparatively low, which likely influences kinetics and highlights the importance of this study. We also determine the isotope effect during nitrite oxidation of a pure culture of Nitrospina (Nitrospina watsonii 347), belonging to one of the most abundant marine NOB genera, and for a Nitrospira strain (Nitrospira Ecomares 2.1). The enzyme kinetic of nitrite oxidation, described by Michaelis-Menten kinetics, of four marine genera are rather narrow and fall in the low end of Km values reported so far, which span over three orders of magnitude between 9 to >1000 µM NO2-. Nitrospina has the lowest half-saturation constant Km (19 µM NO2-), followed by Nitrobacter (28 µM NO2-), Nitrospira (Km of 54 µM NO2-), and Nitrococcus (120 µM NO2-). The isotope effect during nitrite oxidation by Nitrospira watsonii 347 and Nitrospina Ecomares 2.1 is 10.2±0.9‰ and 9.7±0.8‰, respectively. This confirms the inverse isotope effect of NOB described previously; however, it is at the lower end of reported isotope effects. We speculate that differences in isotope effects reflect distinct NXR orientation. %0 Artikel %@ 1385-1101 %A Neumann, A. %A Moebius, J. %A Hass, H.C. %A Puls, W. %A Friedrich, J. %D 2017 %J Journal of Sea Research %N 1337 %P 36 - 45 %R doi:10.1016/j.seares.2016.12.002 %T Empirical model to estimate permeability of surface sediments in the German Bight (North Sea) %U http://dx.doi.org/10.1016/j.seares.2016.12.002 %X As the determinant of solute and particle fluxes through sediments, quantifying sediment permeability is vital step in understanding of the exchange phenomena between the water column and sediment as permeability determines the mode and intensity of solute and particle fluxes. Reliable estimates of sediment permeability are therefore a constraint on the accurate implementation of benthic biogeochemical models. This is particularly true for the North Sea, as field data are scarce and available grain-size-based models fail to represent the full range of sediment types. In this study, we combine measurements of sediment permeability and grain size analysis with a generic permeability model to establish a high-resolution permeability map of the sediment in the German Bight (North Sea). Our results show a good agreement between model-based prediction and measurements of permeability, even for a wide range of permeability values. %0 Artikel %@ 1726-4170 %A Cox, T. %A van Beusekom, J. %A Soetaert, K. %D 2017 %J Biogeosciences %N 2118 %P 5271 - 5280 %R doi:10.5194/bg-14-5271-2017 %T Tune in on 11.57 µHz and listen to primary production %U https://dx.doi.org/10.5194/bg-14-5271-2017 22 %X In this paper we present an elegant approach to reconstruct slowly varying gross primary production (GPP) as a function of time, based on O2 time series. The approach, called complex demodulation, is based on a direct analogy with amplitude-modulated (AM) radio signals. The O2 concentrations oscillating at the diel frequency (or 11.57 µHz) can be seen as a "carrier wave", while the time variation in the amplitude of this carrier wave is related to the time-varying GPP. The relation follows from an analysis in the frequency domain of the governing equations of O2 dynamics. After the theoretical derivation, we assess the performance of the approach by applying it to three artificial O2 time series, generated with models representative of a well-mixed vertical water column, a river and an estuary. These models are forced with hourly observed incident irradiance, resulting in a variability of GPP on scales from hours to months. The dynamic build-up of algal biomass further increases the seasonality. Complex demodulation allows for reconstruction, with great precision, of time-varying GPP of the vertical water column and the river model. Surprisingly, it is possible to derive daily averaged GPP – complex demodulation thus reconstructs the amplitude of every single diel cycle. Also, in estuaries time-varying GPP can be reconstructed to a great extent. But there, the influence of the tides prevent achieving the same temporal resolution. In particular, the combination of horizontal O2 gradients with quasi-diurnal harmonics in the tides interferes with the complex demodulation procedure and introduces spurious amplitude variation that can not be attributed to GPP. We demonstrate that these spurious effects also occur in real-world time series (Hörnum Tief, Germany). The spurious effects due to K1 and P1 quasi-diurnals can not be distinguished from GPP. However, the spurious fluctuations introduced by O1 and Q1 can be removed to a large extent by increasing the averaging time to 15 days. As such, we demonstrate that a good estimate of the running 15-day average of GPP can be obtained in tidal systems. Apart from the direct merits of estimating GPP from O2 time series, the analysis in the frequency domain enhances our insights into O2 dynamics in tidal systems in general, and into the performance of O2 methods to estimate GPP in particular. %0 Artikel %@ 0013-936X %A Tang, J. %A Mi, W. %A Tian, C. %A Emeis, K. %A Ebinghaus, R. %A Xie, Z. %D 2017 %J Environmental Science and Technology %N 1114 %P 89 - 97 %R doi:10.1021/acs.est.7b03807 %T Spatial Distribution and Seasonal Variation of Organophosphate Esters in Air above the Bohai and Yellow Seas, China %U https://dx.doi.org/10.1021/acs.est.7b03807 1 %X Nine organophosphate esters (OPEs) were investigated in air samples collected over the Bohai and Yellow Seas (East Asia) during a research cruise between June 28 and July 13, 2016. These same OPEs were quantified at a research site (North Huangcheng Island, NHI) in the middle of the Bohai Strait from May 16, 2015, to March 21, 2016. The median total OPE (ΣOPE) concentration over the Bohai and Yellow Seas was 280 pg/m3. Tris(1-chloro-2-propyl) (TCPP) was the most abundant OPE, followed by tris(2-chloroethyl) phosphate (TCEP), tri-iso-butyl phosphate (TiBP), and tri-n-butyl phosphate (TnBP). Particle-bound OPEs accounted for 51 ± 21% of the total OPEs. On NHI, the median ΣOPE concentration was 210 pg/m3, and the average particle-bound fraction was 82 ± 17%. For samples collected on NHI, significant negative linear correlations were found between the gaseous OPEs and 1/T (T: temperature (K)) (except TDCP, TPeP, and TCP). Among the 79 investigated samples, significant correlations between the measured OPE gas/particle partitioning coefficients (Kp,m) and subcooled liquid pressure (PL◦) (p < 0.05) were found for only 14 samples, suggesting that OPEs have low potential to achieve equilibrium or ascribe to the artificial sampling. The annual dry deposition input of OPEs into the Bohai and Yellow Seas is estimated to be 12 tons/year. %0 Artikel %@ 0141-1136 %A Neumann, H. %A Diekmann, R. %A Emeis, K.-C. %A Kleeberg, U. %A Moll, A. %A Kröncke, I. %D 2017 %J Marine Environmental Research %N 2398 %P 1 - 11 %R doi:10.1016/j.marenvres.2017.07.010 %T Full-coverage spatial distribution of epibenthic communities in the south-eastern North Sea in relation to habitat characteristics and fishing effort %U https://dx.doi.org/10.1016/j.marenvres.2017.07.010 %X Full-coverage spatial data of occurrence and a detailed description of habitat requirements of epibenthic communities are needed in many conservation and management contexts. In the North Sea the focus has so far been on small benthic infauna, whereas structure and ecosystem functions of larger epifaunal communities have been largely ignored. This study provides a comprehensive analysis of epibenthic community structure in the south-eastern North Sea, including a detailed inventory of species, diversity and spatially contiguous distribution of communities. Data from nearly 400 stations were compiled for the study, enabling us to describe epibenthic community structure at unprecedented spatial resolution. Eight distinct epibenthic communities were found in the south-eastern North Sea by using multivariate analysis. Distribution modelling with eight environmental variables (bottom temperature and salinity, temperature differences between summer and winter, mud content of sediments, maximum bottom shear stress, stratification, water depth and annual primary production) and one human pressure (fishing effort) was used to extrapolate probable spatial distributions and to identify associated habitat characteristics of the communities in the south-eastern North Sea. Three large epibenthic communities “Coast”, “Oysterground” and “Tail End” reflect a gradual habitat change from the coast towards offshore regions, expressed in gradients of bottom salinity, seasonal temperature differences and stratification as the dominant environmental factors. Five smaller communities (“Amrum Bank”, “Frisian Front”, “Deeps”, “Dogger Bank” and “Dogger Slope”) outline specific habitats in the south-eastern North Sea. The “Dogger Slope” community has not been recognized before, but has a predicted spatial extent of 7118 km2. Due to the high occurrence of long-lived, sessile species such as sponges this community is very sensitive to demersal fishing. %0 Artikel %@ 0043-1397 %A Kunz, V. %A Hensley, R. %A Brase, L. %A Borchardt, D. %A Rode, M. %D 2017 %J Water Resources Research %N 1852 %P 328 - 343 %R doi:10.1002/2016WR019355 %T High frequency measurements of reach scale nitrogen uptake in a fourth order river with contrasting hydromorphology and variable water chemistry (Weiße Elster, Germany) %U https://dx.doi.org/10.1002/2016WR019355 1 %X River networks exhibit a globally important capacity to retain and process nitrogen. However direct measurement of in‐stream removal in higher order streams and rivers has been extremely limited. The recent advent of automated sensors has allowed high frequency measurements, and the development of new passive methods of quantifying nitrogen uptake which are scalable across river size. Here we extend these methods to higher order streams with anthropogenically elevated nitrogen levels, substantial tributaries, complex input signals, and multiple N species. We use a combination of two station time‐series and longitudinal profiling of nitrate to assess differences in nitrogen processing dynamics in a natural versus a channelized impounded reach with WWTP effluent impacted water chemistry. Our results suggest that net mass removal rates of nitrate were markedly higher in the unmodified reach. Additionally, seasonal variations in temperature and insolation affected the relative contribution of assimilatory versus dissimilatory uptake processes, with the latter exhibiting a stronger positive dependence on temperature. From a methodological perspective, we demonstrate that a mass balance approach based on high frequency data can be useful in deriving quantitative uptake estimates, even under dynamic inputs and lateral tributary inflow. However, uncertainty in diffuse groundwater inputs and more importantly the effects of alternative nitrogen species, in this case ammonium, pose considerable challenges to this method. %0 Artikel %@ 0278-4343 %A Neumann, A. %A Lahajnar, N. %A Emeis, K.-C. %D 2016 %J Continental Shelf Research %N 1087 %P 47 - 61 %R doi:10.1016/j.csr.2015.12.009 %T Benthic remineralisation rates in shelf and slope sediments of the northern Benguela upwelling margin %U https://dx.doi.org/10.1016/j.csr.2015.12.009 %X The Benguela Upwelling System off Namibia is a region of intensive plankton production. Remineralisation of this biomass frequently causes the formation of an oxygen minimum zone. A part of the organic matter is further deposited on the broad shelf in form of an extensive mudbelt with high TOC concentrations. During February 2011 we retrieved sediment samples from shelf and slope sediment along the Namibian coast to establish fluxes of nutrients, oxygen, and N2 on the basis of pore water concentrations. In mudbelt sediment, fluxes were estimated as high as 8 mmol NH4+ m−2 d−1 and 0.9 mmol PO43− m−2 d−1, which is probably attributable to the activity of large sulphur bacteria. Especially phosphate is mobilised from sediment overlain by oxygen deficient bottom water when and where bottom water oxygen concentrations fall below 50 µmol l−1. In comparison to nutrient transport by Southern Atlantic Central Water flowing onto the Namibian shelf, benthic nutrient fluxes of the mudbelt contribute less than 5% to the nutrient budget of the shelf. %0 Artikel %@ 1664-302X %A Lucas, J. %A Koester, I. %A Wichels, A. %A Niggemann, J. %A Dittmer, T. %A Callies, U. %A Wiltshire, K.H. %A Gerdts, G. %D 2016 %J Frontiers in Microbiology %N 2630 %P 321 %R doi:10.3389/fmicb.2016.00321 %T Short-Term Dynamics of North Sea Bacterioplankton-Dissolved Organic Matter Coherence on Molecular Level %U http://dx.doi.org/10.3389/fmicb.2016.00321 %X Remineralization and transformation of dissolved organic matter (DOM) by marine microbes shape the DOM composition and thus, have large impact on global carbon and nutrient cycling. However, information on bacterioplankton-DOM interactions on a molecular level is limited. We examined the variation of bacterial community composition (BCC) at Helgoland Roads (North Sea) in relation to variation of molecular DOM composition and various environmental parameters on short-time scales. Surface water samples were taken daily over a period of 20 days. Bacterial community and molecular DOM composition were assessed via 16S rRNA gene tag sequencing and ultrahigh resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), respectively. Environmental conditions were driven by a coastal water influx during the first half of the sampling period and the onset of a summer phytoplankton bloom toward the end of the sampling period. These phenomena led to a distinct grouping of bacterial communities and DOM composition which was particularly influenced by total dissolved nitrogen (TDN) concentration, temperature, and salinity, as revealed by distance-based linear regression analyses. Bacterioplankton-DOM interaction was demonstrated in strong correlations between specific bacterial taxa and particular DOM molecules, thus, suggesting potential specialization on particular substrates. We propose that a combination of high resolution techniques, as used in this study, may provide substantial information on substrate generalists and specialists and thus, contribute to prediction of BCC variation. %0 Artikel %@ 1812-0784 %A Tim, N. %A Zorita, E. %A Huenicke, B. %A Yi, X. %A Emeis, K.-C. %D 2016 %J Ocean Science %N 2310 %P 807 - 823 %R doi:10.5194/os-12-807-2016 %T The importance of external climate forcing for the variability and trends of coastal upwelling in past and future climate %U http://dx.doi.org/10.5194/os-12-807-2016 3 %X The eastern boundary upwelling systems, located in the subtropics at the eastern boundary of the Atlantic and Pacific oceans and mainly driven by the trade winds, are the major coastal upwelling regions. Previous studies have suggested that the intensity of upwelling in these areas in the past centuries may have been influenced by the external radiative forcing, for instance by changes in solar irradiance, and it will also be influenced in the future by the increasing atmospheric greenhouse gases. Here, we analyse the impact of the external climate forcing on these upwelling systems in ensembles of simulations of two Earth system models. The ensembles contain three simulations for each period covering the past millennium (900–1849) and the 20th century (1850–2005). One of these Earth system models additionally includes the near future (2006–2100). Using a set of simulations, differing only in their initial conditions, enables us to test whether the observed variability and trends are driven by the external radiative forcing. Our analysis shows that the variability of the simulated upwelling is largely not affected by the external forcing and that, generally, there are no significant trends in the periods covering the past and future. Only in future simulations with the strongest increase of greenhouse gas concentrations the upwelling trends are significant and appear in all members of the ensemble. %0 Artikel %@ 0075-9511 %A Mbaye, M. %A Gaye, A. %A Spitzy, A. %A Dähnke, K. %A Afouda, A. %A Gaye, B. %D 2016 %J Limnologica %N 1279 %P 1 - 13 %R doi:10.1016/j.limno.2015.12.003 %T Seasonal and spatial variation in suspended matter, organic carbon, nitrogen, and nutrient concentrations of the Senegal River in West Africa %U https://dx.doi.org/10.1016/j.limno.2015.12.003 %X The Senegal River is of intermediate size accommodating at present about 3.5 million inhabitants in its catchment. Its upstream tributaries flow through different climatic zones from the wet tropics in the source area in Guinea to the dry Sahel region at the border between Senegal and Mauritania. Total suspended matter, particulate and dissolved organic carbon and nitrogen as well as nutrient concentrations were determined during the dry and wet seasons at 19 locations from the up- to downstream river basin. The aims of the study were to evaluate the degree of human interference, to determine the dissolved and particulate river discharges into the coastal sea and to supply data to validate model results. Statistical analyses showed that samples from the wet and dry season are significantly different in composition and that the upstream tributaries differ mainly in their silicate and suspended matter contents. Nutrient concentrations are relatively low in the river basin, indicating low human impact. Increasing nitrate concentrations, however, show the growing agriculture in the irrigated downstream areas. Particulate organic matter is dominated by C4 plants during the wet season and by aquatic plankton during the dry season. The total suspended matter (TSM) discharge at the main gauging station Bakel was about 1.93 Tg yr−1 which is in the range of the only available literature data from the 1980s. The calculated annual discharges of particulate organic carbon (POC), dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) are 55.8 Gg yr−1, 54.1 Gg yr−1, and 5.3 Gg yr−1, respectively. These first estimates from the Senegal River need to be verified by further studies. %0 Artikel %@ 1614-3795 %A Callies, U. %A Schwichtenberg, F. %D 2016 %J BfR-Wissenschaft %N 2643 %P 31 - 35 %T Regions where the application of dispersants can be expected to be beneficial - an assessment based on drift modelling %U 2 %X The use of hydrodynamic models for predicting oil slick movements and effects of weathering processes is nowadays an essential component of any contingency planning. When the use of dispersants is an option, hydrodynamic modelling can also support corresponding decision making. %0 Artikel %@ 0304-4203 %A Nagel, B. %A Gaye, B. %A Lahajnar, N. %A Struck, U. %A Emeis, K.-C. %D 2016 %J Marine Chemistry %N 1290 %P 121 - 132 %R doi:10.1016/j.marchem.2016.09.001 %T Effects of current regimes and oxygenation on particulate matter preservation on the Namibian shelf: Insights from amino acid biogeochemistry %U https://dx.doi.org/10.1016/j.marchem.2016.09.001 %X Many reconstructions of past biogeochemical states rely on proxies such as δ15N that in turn are affected by the preservation state of organic matter. N-turnover processes in the upwelling system on the Namibian shelf are difficult to reconstruct because lateral particle advection and differential degradation under oxic to anoxic conditions complicate particle tracing in suspended matter and surface sediments as well as the interpretation of sedimentary δ15N records. We analysed the amino acid composition of suspended matter, sinking particles, phytoplankton biomass and surface sediments in order to investigate the degradation pathway of organic matter from the sea surface to the surface sediment. A principal component analysis carried out with the amino acid data set results in a triangular-shaped model. Two branches evolve from phytoplankton biomass on the apex: The suspended matter branch is characterized by relatively enhanced contents of Glu, Ser and Leu, whereas the non-protein amino acids and Lys mark the sinking particle and sediment branch. The results suggest that both pools have taken different diagenetic pathways and that there is only limited exchange between them. The preservation state of organic matter in surface sediments within the oxygen minimum zone is generally better than on the oxic outer shelf, where organic matter preservation depends on water depth. A vertical increase in δ15N ratios from phytoplankton biomass to the surface sediment by ~ 2.5‰ is attributed to early diagenetic degradation in the water column and at the water/sediment interface. The δ15N ratios of sediments are mainly controlled by the N-isotope signature of nitrate on the outer shelf and upper continental slope. Nutrient-enriched deep water ascends at the shelf breaks due to the influence of internal waves and tides or curl-driven shelf break upwelling. The δ15N of upwelling nitrate at the shelf breaks is ~ 3‰ lower than that of nitrate from the inner shelf. This difference in nitrate sources is expressed in a band of decreasing δ15N ratios of surface sediments at the shelf breaks. The hydrodynamic upwelling regime at the shelf breaks flushes significant amounts of suspended matter from the mesopelagic ocean across the shelf break as indicated by amino acid monomer patterns of suspended matter. %0 Artikel %@ 1726-4170 %A Jacob, J. %A Sanders, T. %A Daehnke, K. %D 2016 %J Biogeosciences %N 2118 %P 5649 - 5659 %R doi:10.5194/bg-13-5649-2016 %T Nitrite consumption and associated isotope changes during a river flood event %U http://dx.doi.org/10.5194/bg-13-5649-2016 19 %X In oceans, estuaries, and rivers, nitrification is an important nitrate source, and stable isotopes of nitrate are often used to investigate recycling processes (e.g. remineralisation, nitrification) in the water column. Nitrification is a two-step process, where ammonia is oxidised via nitrite to nitrate. Nitrite usually does not accumulate in natural environments, which makes it difficult to study the single isotope effect of ammonia oxidation or nitrite oxidation in natural systems. However, during an exceptional flood in the Elbe River in June 2013, we found a unique co-occurrence of ammonium, nitrite, and nitrate in the water column, returning towards normal summer conditions within 1 week. Over the course of the flood, we analysed the evolution of δ15N–NH4+ and δ15N–NO2− in the Elbe River. In concert with changes in suspended particulate matter (SPM) and δ15N SPM, as well as nitrate concentration, δ15N–NO3− and δ18O–NO3−, we calculated apparent isotope effects during net nitrite and nitrate consumption. During the flood event, > 97 % of total reactive nitrogen was nitrate, which was leached from the catchment area and appeared to be subject to assimilation. Ammonium and nitrite concentrations increased to 3.4 and 4.4 µmol L−1, respectively, likely due to remineralisation, nitrification, and denitrification in the water column. δ15N–NH4+ values increased up to 12 ‰, and δ15N–NO2− ranged from −8.0 to −14.2 ‰. Based on this, we calculated an apparent isotope effect 15ε of −10.0 ± 0.1 ‰ during net nitrite consumption, as well as an isotope effect 15ε of −4.0 ± 0.1 ‰ and 18ε of −5.3 ± 0.1 ‰ during net nitrate consumption. On the basis of the observed nitrite isotope changes, we evaluated different nitrite uptake processes in a simple box model. We found that a regime of combined riparian denitrification and 22 to 36 % nitrification fits best with measured data for the nitrite concentration decrease and isotope increase. %0 Artikel %@ 0021-8901 %A Folmer, E.O. %A Beusekom, J.E.E.van %A Dolch, T. %A Graewe, U. %A Katwijk, M.M.van %A Kolbe, K. %A Philippart, C.J.M. %D 2016 %J The Journal of Applied Ecology %N 2778 %P 1800 - 1813 %R doi:10.1111/1365-2664.12681 %T Consensus forecasting of intertidal seagrass habitat in the Wadden Sea %U https://dx.doi.org/10.1111/1365-2664.12681 6 %X • After the dramatic eutrophication-induced decline of intertidal seagrasses in the 1970s, the Wadden Sea has shown diverging developments. In the northern Wadden Sea, seagrass beds have expanded and become denser, while in the southern Wadden Sea, only small beds with low shoot densities are found. A lack of documentation of historical distributions hampers conservation management. Yet, the recovery in the northern Wadden Sea provides opportunity to construct robust habitat suitability models to support management. • We tuned habitat distribution models based on 17 years of seagrass surveys in the northern Wadden Sea and high-resolution hydrodynamics and geomorphology for the entire Wadden Sea using five machine learning approaches. To obtain geographically transferable models, hyperparameters were tuned on the basis of prediction accuracy assessed by non-random, spatial cross-validation. The spatial cross-validation methodology was combined with a consensus modelling approach. • The predicted suitability scores correlated amongst each other and with the hold-out observations in the training area indicating that the models converged and were transferable across space. Prediction accuracy was improved by averaging the predictions of the best models. • We graphically examined the relationship between the consensus suitability score and independent presence-only data from outside the training area using the area-adjusted seagrass frequency per suitability class (continuous Boyce index). The Boyce index was positively correlated with the suitability score indicating the adequacy of the prediction methodology. • We used the plot of the continuous Boyce index against habitat suitability score to demarcate three habitat classes – unsuitable, marginal and suitable – for the entire international Wadden Sea. This information is valuable for habitat conservation and restoration management. • Divergence between predicted suitability and actual distributions from the recent past indicates that unaccounted factors limit seagrass development in the southern Wadden Sea. • Synthesis and applications. Our methodology and data enabled us to produce a robust and validated consensus habitat suitability model. We identified highly suitable areas where intertidal seagrass meadows may establish and persist. Our work provides scientific underpinning for effective conservation planning in a dynamic landscape and sets monitoring priorities. %0 Artikel %@ 1531-8508 %A Baturin, G. %A Zavjalov, P. %A Friedrich, J. %D 2015 %J Oceanology %N 2943 %P 253 - 262 %R doi:10.1134/S0001437015020022 %T Geochemistry of sediments in the modern Aral Basin %U https://dx.doi.org/10.1134/S0001437015020022 %X The study presents the first geochemical data on the bottom sediments from the modern desiccating Aral Sea, which allowed a direct comparison between the compositions of the sediments collected during the pre- and postdesiccation periods. This study revealed the differences and similarities in the major and trace element composition of the sediments collected from the former bottom of the Large Aral Sea, the present-day sea bottom, the desiccated sea bottom, and the Amu Darya suspended sediments with respect to the average shale composition. The euxinic sediments from the western deep-water depression are characterized by high concentrations of U, Mo, and organic matter. The precipitation of evaporite salts occurs at the shallowest depths and in the western depression. The salt deposits exposed by the shrinking sea tend to be desalinated due to intense weathering. The mercury detected at high levels in the river suspended sediments of the former Amu Darya discharge was found to be absent in the modern marine sediments due to reductions in the river flow and the possible migration to the atmosphere. Many other trace elements, besides uranium, may also accumulate in seawater. %0 Artikel %@ 1054-3139 %A Walter, B. %A Peters, J. %A van Beusekom, J. %A St.John, M. %D 2015 %J ICES Journal of Marine Science %N 2244 %P 2061 - 2071 %R doi:10.1093/icesjms/fsu218 %T Interactive effects of temperature and light during deep convection: a case study on growth and condition of the diatom Thalassiosira weissflogii %U https://dx.doi.org/10.1093/icesjms/fsu218 6 %X Aim of this study was to expose phytoplankton to growth conditions simulating deep winter convection in the North Atlantic and thereby to assess changes in physiology enabling their survival. Growth rate, biochemical composition, and photosynthetic activity of the diatom Thalassiosira weissflogii were determined under two different light scenarios over a temperature range of 5–15°C to simulate conditions experienced by cells during winter deep convection. These metrics were examined under a low light scenario (20 µmol m−2 s−1, 12/12 h light/dark), and compared with a scenario of short light pulses of a higher light intensity (120 µmol m−2 s−1, 2/22 h light/dark). Both experimental light conditions offered the same daily light dose. No growth was observed at temperatures below 8°C. Above 8°C, growth rates were significantly higher under low light conditions compared with those of short pulsed light exposures, indicating a higher efficiency of light utilization. This could be related to (i) a higher content of Chl a per cell in the low light trial and/or (ii) a more efficient transfer of light energy into growth as indicated by constantly low carbohydrate levels. In contrast, pulsed intense light led to an accumulation of carbohydrates, which were catabolized during the longer dark period for maintaining metabolism. Light curves measured via Chl a fluorescence indicated low light assimilation for the algae exposed to short pulsed light. We postulate that our trial with short light pluses did not provide sufficient light to reach full light saturation. In general, photosynthesis was more strongly affected by temperature under pulsed light than under low light conditions. Our results indicate that model estimates of primary production in relation to deep convection, which are based on average low light conditions, not considering vertical transportation of algae will lead to an overestimation of in situ primary production. %0 Artikel %@ 1708-3087 %A Potts, T. %A O'Higgins, T. %A Brennan, R. %A Cinnirella, S. %A Steiner Brandt, U. %A De Vivero, J. %A van Beusekom, J. %A Troost, T. %A Paltriguera, L. %A Hosgor, A. %D 2015 %J Ecology and Society %N 2433 %P 29 %R doi:10.5751/ES-07280-200129 %T Detecting critical choke points for achieving Good Environmental Status in European seas %U http://dx.doi.org/10.5751/ES-07280-200129 1 %X Choke points are social, cultural, political, institutional, or psychological obstructions of social-ecological systems that constrain progress toward an environmental objective. Using a soft systems methodology, different types of chokes points were identified in the Outer Hebrides of Scotland, the Baltic, and the North and Mediterranean seas. The choke points were of differing types: cultural and political choke points were identified in Barra and the Mediterranean, respectively, whereas the choke points in the North Sea and Baltic Sea were dependent on differing values toward the mitigation of eutrophication. We conclude with suggestions to identify and address choke points. %0 Artikel %@ 2041-1723 %A Grimm, R. %A Maier-Reimer, E. %A Mikolajewicz, U. %A Schmiedel, G. %A Müller-Navarra, K. %A Adloff, F. %A Grant, K. %A Ziegler, M. %A Lourens, L. %A Emeis, K. %D 2015 %J Nature Communications %N 2484 %P 7099 %R doi:10.1038/ncomms8099 %T Late glacial initiation of Holocene eastern Mediterranean sapropel formation %U https://dx.doi.org/10.1038/ncomms8099 %X Recurrent deposition of organic-rich sediment layers (sapropels) in the eastern Mediterranean Sea is caused by complex interactions between climatic and biogeochemical processes. Disentangling these influences is therefore important for Mediterranean palaeo-studies in particular, and for understanding ocean feedback processes in general. Crucially, sapropels are diagnostic of anoxic deep-water phases, which have been attributed to deep-water stagnation, enhanced biological production or both. Here we use an ocean-biogeochemical model to test the effects of commonly proposed climatic and biogeochemical causes for sapropel S1. Our results indicate that deep-water anoxia requires a long prelude of deep-water stagnation, with no particularly strong eutrophication. The model-derived time frame agrees with foraminiferal δ13C records that imply cessation of deep-water renewal from at least Heinrich event 1 to the early Holocene. The simulated low particulate organic carbon burial flux agrees with pre-sapropel reconstructions. Our results offer a mechanistic explanation of glacial–interglacial influence on sapropel formation. %0 Artikel %@ 1385-1101 %A Callies, U. %A Scharfe, M. %D 2015 %J Journal of Sea Research %N 1337 %P 1 - 11 %R doi:10.1016/j.seares.2014.06.008 %T Mean spring conditions at Helgoland Roads, North Sea: Graphical modeling of the influence of hydro-climatic forcing and Elbe River discharge %U http://dx.doi.org/10.1016/j.seares.2014.06.008 %X We analyze inter-annual changes of marine observations at Helgoland Roads (nitrate, phosphate, salinity, Secchi depth) in relation to hydro-climatic conditions and Elbe River discharge as potential drivers. Focusing on mean spring conditions we explore graphical covariance selection modeling as a means to both identify and represent the structure of parameter interactions. While river discharge is able to modify spatial distributions and related gradients in the station's vicinity, atmospherically forced regional transport patterns govern the time dependent local conditions the station is actually exposed to. A model consistent with the data confirms the interplay of the two forcing factors for observations at station Helgoland Roads. Introducing water temperature as a third predictor of inter-annual variability does not much improve the model. Comparing a Helgoland Roads dependence graph with corresponding graphs for other stations or related model simulations, for instance, could help identify differences in underlying mechanisms without referring to specific realizations of external forcing. With regard to prediction, supplementary numerical experiments reveal that imposing constraints on parameter interactions can reduce the chance of fitting regression models to noise. %0 Artikel %@ 0304-4203 %A Mawji, E. %A Schlitzer, R. %A Masferrer Dodas, E. %A Abadie, C. %A Abouchami, W. %A Anderson, R.F. %A Baars, O. %A Bakker, K. %A Baskaran, M. %A Bates, N.R. %A Bluhm, K. %A Bowie, A. %A Bown, J. %A Boye, M. %A Boyle, E.A. %A Branellec, P. %A Bruland, K.W. %A Brzezinski, M.A. %A Bucciarelli, E. %A Buesseler, K. %A Butler, E. %A Cai, P. %A Cardinal, D. %A Casciotti, K. %A Chaves, J. %A Cheng, H. %A Chever, F. %A Church, T.M. %A Colman, A.S. %A Conway, T.M. %A Croot, P.L. %A Cutter, G.A. %A de Baar, H.J.W. %A de Souza, G.F. %A Dehairs, F. %A Deng, F. %A Thi Dieu, H. %A Dulaquais, G. %A Echegoyen-Sanz, Y. %A Edwards, R.L. %A Fahrbach, E. %A Fitzsimmons, J. %A Fleisher, M. %A Frank, M. %A Friedrich, J. %A Fripiat, F. %A Galer, S.J.G. %A Gamo, T. %A Garcia Solsona, E. %A Loes J.A. Gerringa, L.J.A. %A Godoy, J.M. %A Gonzalez, S. %A Grossteffan, E. %A Hatta, M. %A Hayes, C.T. %A Heller, M.I. %A Henderson, G. %A Huang, K.-F. %A Jeandel, C. %A Jenkins, W.J. %A John, S. %A Kenna, T.C. %A Klunder, M. %A Kretschmer, S. %A Kumamoto, Y. %A Laan, P. %A Labatut, M. %A Lacan, F. %A Lam, P.J. %A Lannuzel, D. %A le Moigne, F. %A Lechtenfeld, O.J. %A Lohan, M.C. %A Lu, Y. %A Masque, P. %A McClain, C.R. %A Measures, C. %A Middag, R. %A Moffett, J. %A Navidad, A. %A Nishioka, J. %A Noble, A. %A Obata, H. %A Ohnemus, D.C. %A Owens, S. %A Planchon, F. %A Pradoux, C. %A Puigcorbe, V. %A Quay, P. %A Radic, A. %A Rehkaemper, M. %A Remenyi, T. %A Rijkenberg, M.J.A. %A Rintoul, S. %A Robinson, L.F. %A Roeske, T. %A Rosenberg, M. %A van der Loeff, M.R. %A Ryabenko, E. %A Saito, M.A. %A Roshan, S. %A Salt, L. %A Sarthou, G. %A Schauer, U. %A Scott, P. %A Sedwick, P.N. %A Sha, L. %A Shiller, A.M. %A Sigman, D.M. %A Smethie, W. %A Smith, G.J. %A Sohrin, Y. %A Speich, S. %A Stichel, T. %A Stutsman, J. %A Swift, J.H. %A Tagliabue, A. %A Thomas, A. %A Tsunogai, U. %A Twining, B.S. %A Aken, H.M.van %A Heuven, S.van %A Ooijen, J.van %A Weerlee, E.van %A Venchiarutti, C. %A Voelker, A.H.L. %A Wake, B. %A Warner, M.J. %A Woodward, E.M.S. %A Wu, J. %A Wyatt, N. %A Yoshikawa, H. %A Zheng, X.-Y. %A Xue, Z. %A Zieringer, M. %A Zimmer, L.A. %D 2015 %J Marine Chemistry %N 1290 %P 1 - 8 %R doi:10.1016/j.marchem.2015.04.005 %T The GEOTRACES Intermediate Data Product 2014 %U http://dx.doi.org/10.1016/j.marchem.2015.04.005 %X The GEOTRACES Intermediate Data Product 2014 (IDP2014) is the first publicly available data product of the international GEOTRACES programme, and contains data measured and quality controlled before the end of 2013. It consists of two parts: (1) a compilation of digital data for more than 200 trace elements and isotopes (TEIs) as well as classical hydrographic parameters, and (2) the eGEOTRACES Electronic Atlas providing a strongly inter-linked on-line atlas including more than 300 section plots and 90 animated 3D scenes. The IDP2014 covers the Atlantic, Arctic, and Indian oceans, exhibiting highest data density in the Atlantic. The TEI data in the IDP2014 are quality controlled by careful assessment of intercalibration results and multi-laboratory data comparisons at cross-over stations. The digital data are provided in several formats, including ASCII spreadsheet, Excel spreadsheet, netCDF, and Ocean Data View collection. In addition to the actual data values the IDP2014 also contains data quality flags and 1-σ data error values where available. Quality flags and error values are useful for data filtering. Metadata about data originators, analytical methods and original publications related to the data are linked to the data in an easily accessible way. The eGEOTRACES Electronic Atlas is the visual representation of the IDP2014 data providing section plots and a new kind of animated 3D scenes. The basin-wide 3D scenes allow for viewing of data from many cruises at the same time, thereby providing quick overviews of large-scale tracer distributions. In addition, the 3D scenes provide geographical and bathymetric context that is crucial for the interpretation and assessment of observed tracer plumes, as well as for making inferences about controlling processes. %0 Artikel %@ 1054-3139 %A Stelzenmueller, V. %A Fock, H.O. %A Gimpel, A. %A Rambo, H. %A Diekmann, R. %A Probst, W.N. %A Callies, U. %A Bockelmann, F. %A Neumann, H. %A Kroencke, I. %D 2015 %J ICES Journal of Marine Science : Journal du Conseil %N 2244 %P 1022 - 1042 %R doi:10.1093/icesjms/fsu206 %T Quantitative environmental risk assessments in the context of marine spatial management: current approaches and some perspectives %U http://dx.doi.org/10.1093/icesjms/fsu206 3 %X Marine spatial planning (MSP) requires spatially explicit environmental risk assessment (ERA) frameworks with quantitative or probabilistic measures of risk, enabling an evaluation of spatial management scenarios. ERAs comprise the steps of risk identification, risk analysis, and risk evaluation. A review of ERAs in in the context of spatial management revealed a synonymous use of the concepts of risk, vulnerability and impact, a need to account for uncertainty and a lack of a clear link between risk analysis and risk evaluation. In a case study, we addressed some of the identified gaps and predicted the risk of changing the current state of benthic disturbance by bottom trawling due to future MSP measures in the German EEZ of the North Sea. We used a quantitative, dynamic, and spatially explicit approach where we combined a Bayesian belief network with GIS to showcase the steps of risk characterization, risk analysis, and risk evaluation. We distinguished 10 benthic communities and 6 international fishing fleets. The risk analysis produced spatially explicit estimates of benthic disturbance, which was computed as a ratio between relative local mortality by benthic trawling and the recovery potential after a trawl event. Results showed great differences in spatial patterns of benthic disturbance when accounting for different environmental impacts of the respective fleets. To illustrate a risk evaluation process, we simulated a spatial shift of the international effort of two beam trawl fleets, which are affected the most by future offshore wind development. The Bayesian belief network (BN) model was able to predict the proportion of the area where benthic disturbance likely increases. In conclusion, MSP processes should embed ERA frameworks which allow for the integration of multiple risk assessments and the quantification of related risks as well as uncertainties at a common spatial scale. %0 Artikel %@ 0924-7963 %A Liu, K. %A Emeis, K. %A Levin, L. %A Naqvi, W. %A Roman, M. %D 2015 %J Journal of Marine Systems %N 1217 %P 1 - 2 %R doi:10.1016/j.jmarsys.2014.07.020 %T Preface - “Biogeochemistry–ecosystem interaction on changing continental margins in the Anthropocene” %U https://dx.doi.org/10.1016/j.jmarsys.2014.07.020 %X %0 Artikel %@ 0924-7963 %A Emeis, K. %A van Beusekom, J. %A Callies, U. %A Ebinghaus, R. %A Kannen, A. %A Kraus, G. %A Kröncke, I. %A Lenhatz, H. %A Lorkoswski, I. %A Matthias, V. %A Möllmann, H. %A Pätsch, J. %A Scharfe, M. %A Thomas, H. %A Weisse, R. %A Zorita, E. %D 2015 %J Journal of Marine Systems %N 1217 %P 18 - 33 %R doi:10.1016/j.jmarsys.2014.03.012 %T The North Sea - A shelf sea in the Anthropocene %U https://dx.doi.org/10.1016/j.jmarsys.2014.03.012 %X Global and regional change clearly affects the structure and functioning of ecosystems in shelf seas. However, complex interactions within the shelf seas hinder the identification and unambiguous attribution of observed changes to drivers. These include variability in the climate system, in ocean dynamics, in biogeochemistry, and in shelf sea resource exploitation in the widest sense by societies. Observational time series are commonly too short, and resolution, integration time, and complexity of models are often insufficient to unravel natural variability from anthropogenic perturbation. The North Sea is a shelf sea of the North Atlantic and is impacted by virtually all global and regional developments. Natural variability (from interannual to multidecadal time scales) as response to forcing in the North Atlantic is overlain by global trends (sea level, temperature, acidification) and alternating phases of direct human impacts and attempts to remedy those. Human intervention started some 1000 years ago (diking and associated loss of wetlands), expanded to near-coastal parts in the industrial revolution of the mid-19th century (river management, waste disposal in rivers), and greatly accelerated in the mid-1950s (eutrophication, pollution, fisheries). The North Sea is now a heavily regulated shelf sea, yet societal goals (good environmental status versus increased uses), demands for benefits and policies diverge increasingly. Likely, the southern North Sea will be re-zoned as riparian countries dedicate increasing sea space for offshore wind energy generation — with uncertain consequences for the system's environmental status. We review available observational and model data (predominantly from the southeastern North Sea region) to identify and describe effects of natural variability, of secular changes, and of human impacts on the North Sea ecosystem, and outline developments in the next decades in response to environmental legislation, and in response to increased use of shelf sea space. %0 Artikel %@ 1877-3435 %A Glavovic, B. %A Limburg, K. %A Liu, K. %A Emeis, K. %A Thomas, H. %A Kremer, H. %A Avril, B. %A Zhang, J. %A Mulholland, M. %A Glaser, M. %A Swaney, D. %D 2015 %J Current Opinion in Environmental Sustainability %N 2688 %P 232 - 238 %R doi:10.1016/j.cosust.2015.06.003 %T Living on the Margin in the Anthropocene: engagement arenas for sustainability research and action at the ocean–land interface %U https://dx.doi.org/10.1016/j.cosust.2015.06.003 %X The advent of the Anthropocene underscores the need to develop and implement transformative governance strategies that safeguard the Earth's life-support systems, most critically at the ocean–land interface — the Margin. The seaward realm of the Margin is the new frontier for resource exploitation and colonization to meet the needs of coastal nations and humanity overall. Here, we spotlight the pivotal role of the Margin for planetary resilience and sustainability, highlight priority issues, and outline a research strategy which aims to: (a) better understand Margin social-ecological systems; (b) guide sustainable development of Margin resources; (c) design governance regimes to reverse unsustainable practices; (d) facilitate equitable sharing of Margin resources; and (e) evaluate alternative research approaches and partnerships that address major Margin challenges. %0 Artikel %@ 0924-7963 %A Levin, L. %A Liu, K. %A Emeis, K. %A Breitburg, D. %A Cloern, J. %A Deutsch, C. %A Giani, M. %A Goffart, A. %A Hofmann, E. %A Lachkar, Z. %A Limburg, K. %A Liu, S. %A Montes, E. %A Naqvi, W. %A Ragueneau, O. %A Rabouille, C. %A Sarkar, S. %A Swaney, D. %A Wassman, P. %A Wishner, K. %D 2015 %J Journal of Marine Systems %N 1217 %P 3 - 17 %R doi:10.1016/j.jmarsys.2014.04.016 %T Comparative biogeochemistry–ecosystem–human interactions on dynamic continental margins %U https://dx.doi.org/10.1016/j.jmarsys.2014.04.016 %X The oceans' continental margins face strong and rapid change, forced by a combination of direct human activity, anthropogenic CO2-induced climate change, and natural variability. Stimulated by discussions in Goa, India at the IMBER IMBIZO III, we (1) provide an overview of the drivers of biogeochemical variation and change on margins, (2) compare temporal trends in hydrographic and biogeochemical data across different margins, (3) review ecosystem responses to these changes, (4) highlight the importance of margin time series for detecting and attributing change and (5) examine societal responses to changing margin biogeochemistry and ecosystems. We synthesize information over a wide range of margin settings in order to identify the commonalities and distinctions among continental margin ecosystems. Key drivers of biogeochemical variation include long-term climate cycles, CO2-induced warming, acidification, and deoxygenation, as well as sea level rise, eutrophication, hydrologic and water cycle alteration, changing land use, fishing, and species invasion. Ecosystem responses are complex and impact major margin services. These include primary production, fisheries production, nutrient cycling, shoreline protection, chemical buffering, and biodiversity. Despite regional differences, the societal consequences of these changes are unarguably large and mandate coherent actions to reduce, mitigate and adapt to multiple stressors on continental margins. %0 Artikel %@ 0272-7714 %A de Jonge, V. %A Schuttelaars, H. %A van Beusekom, J. %A Talke, S. %A de Swart, H. %D 2014 %J Estuarine, Coastal and Shelf Science %N 1123 %P 46 - 59 %R doi:10.1016/j.ecss.2013.12.030 %T The influence of channel deepening on estuarine turbidity levels and dynamics, as exemplified by the Ems estuary %U https://dx.doi.org/10.1016/j.ecss.2013.12.030 %X Active deepening of tidal channels usually results in the alteration of the vertical and the horizontal tide. This may lead to concurrent significant increases in mean suspended matter concentrations (SPM) in coastal plain estuaries, the turbidity maximum (ETM) included. This is exemplified by an extensive analysis of the Ems estuary, a prototypical heavily stressed estuary in the Dutch-German border area. Measurements show that the SPM concentrations in the lower reaches of the estuary have increased an average of 2- to 3-fold between 1954 and 2005, with a 10-fold increase observed in the upper estuary (tidal river). Longitudinal profiles of surface SPM demonstrate that the ETM has moved upstream by up to 25 km and has broadened into a zone 30 km in length which extends into the freshwater tidal river. On an annual scale, variations in freshwater discharge significantly influence the formation and breakdown of the ETM: during low river discharge the ETM approaches equilibrium over 2–3 months, whilst elevated river discharges relocate the ETM downstream over several weeks. An exploratory, semi-analytical model is calibrated to simulate the equilibrium SPM distribution in the upper estuary during five time periods from 1965 to 2005, using archival bathymetric and tidal data. Results suggest that the deepening of tidal channels and a reduction in hydraulic drag have most likely resulted in a landward shift of the SPM trapping location. The measured increase in SPM concentrations and the development of fluid mud around the 1990s likely contributed to reduced mixing and bottom drag, creating a feedback loop that further altered tidal and SPM dynamics. It is argued that the removal of some non-erodible (consolidated) layers in the lower reaches of the estuary has created new internal sediment sources that may be responsible for feeding the observed high SPM concentrations, rather than increased sediment input from the boundaries. All findings are based on and supported by measured short-term seasonal fluctuations, as well as long-term developments of yearly averaged concentrations in the longitudinal SPM distribution. %0 Artikel %@ 0025-326X %A Neumann, D. %A Callies, U. %A Matthies, M. %D 2014 %J Marine Pollution Bulletin %N 1292 %P 219 - 228 %R doi:10.1016/j.marpolbul.2014.07.016 %T Marine litter ensemble transport simulations in the southern North Sea %U http://dx.doi.org/10.1016/j.marpolbul.2014.07.016 1-2 %X The drift of marine litter in the southern North Sea was simulated with the offline Lagrangian transport model PELETS-2D. Assuming different source regions, passive tracer particles were released every 28 h within a nine-year period. Based on pre-calculated hourly wind and ocean current data, drift simulations were carried out forward and backward in time with and without the assumption of extra wind forces influencing particle movement. Due to strong variability of currents, backward simulations did not allow for the identification of particular source regions influencing given monitoring sites. Neither accumulation regions at open sea could be identified by forward simulations. A seasonal signal, however, could be identified in the number of tracer particles that reached the coastal areas. Both particle drift velocity and variability of drift paths further increased when an extra wind drift was assumed. %0 Artikel %@ 1436-9095 %A Winter, C. %A Herrling, G. %A Bartholomae, A. %A Capperucci, R. %A Callies, U. %A Heipke, C. %A Schmidt, A. %A Hillebrand, H. %A Reimers, C. %A Bremer, P. %A Weiler, R. %D 2014 %J Wasser und Abfall %N 2539 %P 21 - 26 %T Wissenachftliche Konzepte fuer ein Monitoring des oekologischen Zustands des deutschen Kuestenmeeres %U 7-8 %X Aussagen zum Zustand und der Entwicklung von Kuestenmeeren koennen nur durch langfristige Beobachtungen und Modellansaetze erfolgen. Im Verbundprojekt .... %0 Artikel %@ 1726-4170 %A Flohr, A. %A van der Plas, A. %A Emeis, K. %A Mohrholz, V. %A Rixen, T. %D 2014 %J Biogeosciences %N 2118 %P 885 - 897 %R doi:10.5194/bg-11-885-2014 %T Spatio-temporal patterns of C : N : P ratios in the northern Benguela upwelling system %U https://dx.doi.org/10.5194/bg-11-885-2014 3 %X On a global scale the ratio of fixed nitrogen (N) and phosphate (P) is characterized by a deficit of N with regard to the classical Redfield ratio of N : P = 16 : 1 reflecting the impact of N loss occurring in the oceanic oxygen minimum zones. The northern Benguela upwelling system (NBUS) is known for losses of N and the accumulation of P in sub- and anoxic bottom waters and sediments of the Namibian shelf resulting in low N : P ratios in the water column. To study the impact of the N : P anomalies on the regional carbon cycle and their consequences for the export of nutrients from the NBUS into the oligotrophic subtropical gyre of the South Atlantic, we measured dissolved inorganic carbon (CT), total alkalinity (AT), oxygen (O2) and nutrient concentrations in February 2011. The results indicate increased P concentrations over the Namibian shelf due to P efflux from sediments resulting in a C : N : P : -O2 ratio of 106 : 16 : 1.6 : 138. N reduction further increase C : N and reduce N : P ratios in those regions where O2 concentrations in bottom waters are < 20 μmol kg−1. However, off the shelf along the continental margin, the mean C : N : P : -O2 ratio is again close to the Redfield stoichiometry. Additional nutrient data measured during two cruises in 2008 and 2009 imply that the amount of excess P, which is created in the bottom waters on the shelf, and its export into the subtropical gyre after upwelling varies through time. The results further reveal an inter-annual variability of excess N within the South Atlantic Central Water (SACW) that flows from the north into the NBUS, with highest N values observed in 2008. It is postulated that the N excess in SACW occurred due to the impact of remineralized organic matter produced by N2 fixation and that the magnitude of excess P formation and its export is governed by inputs of excess N along with SACW flowing into the NBUS. Factors controlling N2 fixation north of the BUS need to be addressed in future studies to better understand the role of the NBUS as a P source and N sink in the coupled C : N : P cycles. %0 Artikel %@ 1726-4170 %A Friedrich, J. %A Janssen, F. %A Aleynik, D. %A Bange, H. W. %A Boltacheva, N. %A agatay, M. N. %A Dale, A. W. %A Etiope, G. %A Erdem, Z. %A Geraga, M. %A Gilli, A. %A Gomoiu, M. T. %A Hall, P. O. J. %A Hansson, D. %A He, Y. %A Holtappels, M. %A Kirf, M. K. %A Kononets, M. %A Konovalov, S. %A Lichtschlag, A. %A Livingstone, D. M. %A Marinaro, G. %A Mazlumyan, S. %A Naeher, S. %A North, R. P. %A Papatheodorou, G. %A Pfannkuche, O. %A Prien, R. %A Rehder, G. %A Schubert, C. J. %A Soltwedel, T. %A Sommer, S. %A Stahl, H. %A Stanev, E. V. %A Teaca, A. %A Tengberg, A. %A Waldmann, C. %A Wehrli, B. %A Wenzhoefer, F. %D 2014 %J Biogeosciences %N 2118 %P 1215 - 1259 %R doi:10.5194/bg-11-1215-2014 %T Investigating hypoxia in aquatic environments: diverse approaches to addressing a complex phenomenon %U http://dx.doi.org/10.5194/bg-11-1215-2014 %X In this paper we provide an overview of new knowledge on oxygen depletion (hypoxia) and related phenomena in aquatic systems resulting from the EU-FP7 project HYPOX ("In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and landlocked water bodies", http://www.hypox.net). In view of the anticipated oxygen loss in aquatic systems due to eutrophication and climate change, HYPOX was set up to improve capacities to monitor hypoxia as well as to understand its causes and consequences. Temporal dynamics and spatial patterns of hypoxia were analyzed in field studies in various aquatic environments, including the Baltic Sea, the Black Sea, Scottish and Scandinavian fjords, Ionian Sea lagoons and embayments, and Swiss lakes. Examples of episodic and rapid (hours) occurrences of hypoxia, as well as seasonal changes in bottom-water oxygenation in stratified systems, are discussed. Geologically driven hypoxia caused by gas seepage is demonstrated. Using novel technologies, temporal and spatial patterns of water-column oxygenation, from basin-scale seasonal patterns to meter-scale sub-micromolar oxygen distributions, were resolved. Existing multidecadal monitoring data were used to demonstrate the imprint of climate change and eutrophication on long-term oxygen distributions. Organic and inorganic proxies were used to extend investigations on past oxygen conditions to centennial and even longer timescales that cannot be resolved by monitoring. The effects of hypoxia on faunal communities and biogeochemical processes were also addressed in the project. An investigation of benthic fauna is presented as an example of hypoxia-devastated benthic communities that slowly recover upon a reduction in eutrophication in a system where naturally occurring hypoxia overlaps with anthropogenic hypoxia. Biogeochemical investigations reveal that oxygen intrusions have a strong effect on the microbially mediated redox cycling of elements. Observations and modeling studies of the sediments demonstrate the effect of seasonally changing oxygen conditions on benthic mineralization pathways and fluxes. Data quality and access are crucial in hypoxia research. Technical issues are therefore also addressed, including the availability of suitable sensor technology to resolve the gradual changes in bottom-water oxygen in marine systems that can be expected as a result of climate change. Using cabled observatories as examples, we show how the benefit of continuous oxygen monitoring can be maximized by adopting proper quality control. Finally, we discuss strategies for state-of-the-art data archiving and dissemination in compliance with global standards, and how ocean observations can contribute to global earth observation attempts. %0 Artikel %@ 2070-2000 %A Renaud, F.G. %A Friedrich, J. %A Sebesvari, Z. %A Giosan, L. %D 2014 %J INPRINT / Land-Ocean Interactions in the Coastal Zone %N 2476 %P 5 - 13 %T Tipping points for delta social-ecological systems %U %X Many deltas globally are centers for social and economic development, so much so that their natural environment has been rapidly transformed over relatively short periods of times. These changes are manifested within the deltas themselves through, for example, land use changes towards intensive agriculture, but also at the river basin scale through, for example, the development of dams and reservoirs along river systems. In many cases, delta social-ecological systems have tipped from Holocene characteristics to Anthropocene characteristics and some deltas could tip to other system states (we refer to them as “collapsed”) which would be unfavorable from an anthropocentric perspective. We discuss this notion of tipping points in deltas social-ecological systems as well as opportunities to “tip back” to a previous state. We present two examples, the Danube delta which is considered an Anthropocene delta providing many opportunities for sustainable social-ecological system development and the Mekong delta, another Anthropocene delta where current development decisions locally and at the basin scale could either increase the resilience of social-ecological systems or tip these systems towards an undesirable state. %0 Artikel %@ 1385-1101 %A Loebl, M. %A van Beusekom, J. %A Philipppart, C. %D 2013 %J Journal of Sea Research %N 1337 %P 80 - 85 %R doi:10.1016/j.seares.2012.09.010 %T No microzooplankton grazing during a Mediopyxis helysia dominated diatom bloom %U https://dx.doi.org/10.1016/j.seares.2012.09.010 %X The new diatom species Mediopyxis helysia was described to science from clones found in 2003 in the North Sea, northern Wadden Sea, and the Gulf of Maine. Seven years after its first occurrence, we observed Mediopyxis to contribute up to almost 50% of the biovolume of the diatoms during a diatom spring bloom in the western Wadden Sea. Grazing experiments based on the dilution technique could not detect any microzooplankton grazing impact on the bloom community. Mediopyxis is now also well established in the western Wadden Sea and does have the potential to become a dominant species. The reasons for its success remain largely unresolved but avoidance of being grazed might be one factor. Future research on this new species is needed to understand the success and forecast the ecological footprint of this large diatom species arriving in the western European Seas. %0 Artikel %@ 1877-3435 %A Renaud, F.G. %A Syvitski, J.P.M. %A Sebesvari, Z. %A Werners, S.E. %A Kremer, H. %A Kuenzer, C. %A Ramesh, R. %A Jeuken, A. %A Friedrich, J. %D 2013 %J Current Opinion in Environmental Sustainability %N 2688 %P 644 - 654 %R doi:10.1016/j.cosust.2013.11.007 %T Tipping from the Holocene to the Anthropocene: How threatened are major world deltas? %U http://dx.doi.org/10.1016/j.cosust.2013.11.007 6 %X Coastal deltas are landforms that typically offer a wide variety of benefits to society including highly fertile soils for agricultural development, freshwater resources, and rich biodiversity. For these reasons, many deltas are densely populated, are important economic hubs, and have been transformed by human interventions such as agricultural intensification, modification of water and sediment fluxes, as well as urbanization and industrialization. Additionally, deltas are increasingly affected by the consequences of climate change including sea level rise, and by other natural hazards such as cyclones and storm surges. Five examples of major deltas (Rhine-Meuse, Ganges, Indus, Mekong, and Danube) illustrate the force of human interventions in shaping and transforming deltas and in inducing shifts between four different social-ecological system (SES) states: Holocene, modified Holocene, Anthropocene and ‘collapsed’. The three Asian deltas are rapidly changing but whereas SES in the Ganges and Indus deltas are in danger of tipping into a ‘collapsed’ state, SES in the Mekong delta, which is at the crossroads of various development pathways, could increase in resilience in the future. The Rhine-Meuse and Danube delta examples show that highly managed states may allow, under specific conditions, for interventions leading to increasingly resilient systems. However, little is known about the long-term effects of rapid human interventions in deltas. It is therefore critical to increase the knowledge-base related to SES dynamics and to better characterize social tipping points or turning points in order to avoid unacceptable changes. %0 Artikel %@ 1726-4170 %A Dähnke, K. %A Thamdrup, B. %D 2013 %J Biogeosciences %N 2118 %P 3079 - 3088 %R doi:10.5194/bg-10-3079-2013 %T Nitrogen isotope dynamics and fractionation during sedimentary denitrification in Boknis Eck, Baltic Sea %U http://dx.doi.org/10.5194/bg-10-3079-2013 5 %X The global marine nitrogen cycle is constrained by nitrogen fixation as a source of reactive nitrogen, and denitrification or anammox on the sink side. These processes with their respective isotope effects set the marine nitrate 15N-isotope value (δ15N) to a relatively constant average of 5‰. This value can be used to better assess the magnitude of these sources and sink terms, but the underlying assumption is that sedimentary denitrification and anammox, processes responsible for approximately one-third of global nitrogen removal, have little to no isotope effect on nitrate in the water column. We investigated the isotope fractionation in sediment incubations, measuring net denitrification and nitrogen and oxygen stable isotope fractionation in surface sediments from the coastal Baltic Sea (Boknis Eck, northern Germany), a site with seasonal hypoxia and dynamic nitrogen turnover. Sediment denitrification was fast, and regardless of current paradigms assuming little fractionation during sediment denitrification, we measured fractionation factors of 18.9‰ for nitrogen and 15.8‰ for oxygen in nitrate. While the input of nitrate to the water column remains speculative, these results challenge the current view of fractionation during sedimentary denitrification and imply that nitrogen budget calculations may need to consider this variability, as both preferential uptake of light nitrate and release of the remaining heavy fraction can significantly alter water column nitrate isotope values at the sediment–water interface. %0 Artikel %@ 0148-0227 %A Nagel, B. %A Emeis, K.-C. %A Flohr, A. %A Rixen, T. %A Schlarbaum, T. %A Mohrholz, V. %A Plas, A.van der %D 2013 %J Journal of Geophysical Research : Biogeosciences %N 1212 %P 361 - 371 %R doi:10.1002/jgrg.20040 %T N-cycling and balancing of the N-deficit generated in the oxygen minimum zone over the Namibian shelf - An isotope-based approach %U http://dx.doi.org/10.1002/jgrg.20040 1 %X The northern Benguela upwelling system is a nutrient-replete region with high plankton biomass production and a seasonally changing oxygen minimum zone. Nitrate:phosphate ratios in fresh upwelling water are low due to denitrification in the near-seafloor oxygen minimum zone and phosphate efflux from sediments. This makes the region a candidate for substantial dinitrogen fixation, for which evidence is scarce. Nutrient and oxygen data, N isotope data of nitrate, nitrogen isotope ratios of particulate matter, particulate organic carbon content, and suspended matter concentrations on a transect across the shelf and upper slope at 23°S illustrate N-cycling processes and are the basis for estimating the contribution of N-sources and N-sinks to the reactive nitrogen pool. It appears that N-removal due to denitrification exceeds N gain by N2 fixation and physical mixing processes by a factor of >6, although inorganic N:P ratios again increase as surface water is advected offshore. Nitrate and ammonium regeneration, nutrient assimilation with N:P < 16, shelf break mixing, atmospheric input, and N2 fixation all contribute to the restoration of inorganic N:P ratios back to Redfield conditions, but in seasonally changing proportions. The Benguela upwelling system thus is a nutrient source for the oceanic-mixed layer where N-sources and N-sinks are not in balance and Redfield conditions can only re-adjust by advection and mixing processes integrated over time. %0 Artikel %@ 1541-5856 %A Church, T. %A Rigaud, S. %A Baskaran, M. %A Kumar, A. %A Friedrich, J. %A Masque, P. %A Puigcorbe, V. %A Kim, G. %A Radakovitch, O. %A Hong, G. %A Choi, H. %A Stewart, G. %D 2012 %J Limnology and Oceanography: Methods %N 2091 %P 776 - 789 %R doi:10.4319/lom.2012.10.776 %T Intercalibration studies of 210Po and 210Pb in dissolved and particulate seawater samples %U http://dx.doi.org/10.4319/lom.2012.10.776 10 %X Documented is an intercalibration (IC) exercise for both 210Po and 210Pb in seawater aliquots distributed between up to eight international laboratories that followed individual protocols. Dissolved and particulate samples were provided by GEOTRACES during two IC cruises at baseline stations in the North Atlantic and North Pacific oceans. Included were surface and/or deep dissolved and particulate samples at each site, plus complete profiles analyzed by the laboratory of the lead author. An unspecified solid phase standard was also distributed with 210Po and 210Pb in secular equilibrium to confirm spike calibrations. The 210Po activities reported n = 8) for the standard were very similar with a relative standard deviation (RSD) of 3.6% and mean value indistinguishable from the certified value, confirming accurate calibration of Po spikes. For seawater samples, the agreement was strongly dependent for both nuclides on the activity of the samples. The agreement was relatively good for dissolved seawater samples (RSD = 9% to 29%, n = 4), moderate for the particulate samples (RSD = 12% to 80%, n = 8), and poor for particulate dip blanks (RSD = 50% to 200%, n = 8). Noted is the higher apparent affinity of 210Po versus 210Pb for polysulphone filter material. Some lack of reproducibility between labs may have been caused by unspecified differences in individual lab protocols and calculations. A minimum sample activity of 0.1 dpm for both nuclides is recommended for an adequate reproducible sample activity. It is suggested that a consistent set of procedures and calculations be used to optimize future 210Po and 210Pb analyses in seawater samples. %0 Artikel %@ 1726-4170 %A Dähnke, K. %A Moneta, A. %A Veuger, B. %A Soetaert, K. %A Middelburg, J.J. %D 2012 %J Biogeosciences %N 2118 %P 4059 - 4070 %R doi:10.5194/bg-9-4059-2012 %T Balance of assimilative and dissimilative nitrogen processes in a diatom-rich tidal flat sediment %U http://dx.doi.org/10.5194/bg-9-4059-2012 10 %X Tidal flat sediments are subject to repetitive mixing and resuspension events. In a short-term (24 h) 15N-labelling experiment, we investigated reactive nitrogen cycling in a tidal flat sediment following an experimentally induced resuspension event. We focused on (a) the relative importance of assimilatory versus dissimilatory processes and (b) the role of benthic microalgae therein. 15N-labelled substrate was added to homogenized sediment, and 15N was subsequently traced into sediment and dissolved inorganic nitrogen (DIN) pools. Integration of results in a N-cycle model allowed us to quantify the proportion of major assimilatory and dissimilatory processes in the sediment. Upon sediment disturbance, rates of dissimilatory processes like nitrification and denitrification were very high, but declined rapidly towards a steady state. Once this was reached, the balance between assimilation and dissimilation in this tidal mudflat was mainly dependent on the nitrogen source: nitrate was utilized almost exclusively dissimilatory via denitrification, whereas ammonium was rapidly assimilated, with about a quarter of this assimilation due to benthic microalgae (BMA). Benthic microalgae significantly affected the nitrogen recycling balance in sediments, because in the absence of BMA activity the recovering sediment turned from a net ammonium sink to a net source. The driving mechanisms for assimilation or dissimilation accordingly appear to be ruled to a large extent by external physical forcing, with the entire system being capable of rapid shifts following environmental changes. Assimilatory pathways gain importance under stable conditions, with a substantial contribution of BMA to total assimilation. %0 Artikel %@ 0036-8075 %A Teeling, H. %A Fuchs, B.M. %A Becher, D. %A Klockow, C. %A Gardebrecht, A. %A Bennke, C.M. %A Kassabgy, M. %A Huang, S. %A Mann, A.J. %A Waldmann, J. %A Weber, M. %A Klindworth, A. %A Otto, A. %A Lange, J. %A Bernhardt, J. %A Reinsch, C. %A Hecker, M. %A Peplies, J. %A Bockelmann, F.D. %A Callies, U. %A Gerdts, G. %A Wichels, A. %A Wiltshire, K.H. %A Gloeckner, F.O. %A Schweder, T. %A Amann, R. %D 2012 %J Science %N 1408 %P 608 - 611 %R doi:10.1126/science.1218344 %T Substrate-Controlled Succession of Marine Bacterioplankton Populations Induced by a Phytoplankton Bloom %U http://dx.doi.org/10.1126/science.1218344 6081 %X Phytoplankton blooms characterize temperate ocean margin zones in spring. We investigated the bacterioplankton response to a diatom bloom in the North Sea and observed a dynamic succession of populations at genus-level resolution. Taxonomically distinct expressions of carbohydrate-active enzymes (transporters; in particular, TonB-dependent transporters) and phosphate acquisition strategies were found, indicating that distinct populations of Bacteroidetes, Gammaproteobacteria, and Alphaproteobacteria are specialized for successive decomposition of algal-derived organic matter. Our results suggest that algal substrate availability provided a series of ecological niches in which specialized populations could bloom. This reveals how planktonic species, despite their seemingly homogeneous habitat, can evade extinction by direct competition. %0 Artikel %@ 0272-7714 %A Swaney, D.P. %A Humborg, C. %A Emeis, K. %A Kannen, A. %A Silvert, W. %A Tett, P. %A Pastres, R. %A Solidoro, C. %A Yamamuro, M. %A Henocque, Y. %A Nicholls, R. %D 2012 %J Estuarine, Coastal and Shelf Science %N 1123 %P 9 - 21 %R doi:10.1016/j.ecss.2011.04.010 %T Five critical questions of scale for the coastal zone %U http://dx.doi.org/10.1016/j.ecss.2011.04.010 %X Social and ecological systems around the world are becoming increasingly globalized. From the standpoint of understanding coastal ecosystem behavior, system boundaries are not sufficient to define causes of change. A flutter in the stock market in Tokyo or Hong Kong can affect salmon producers in Norway or farmers in Togo. The globalization of opportunistic species and the disempowerment of people trying to manage their own affairs on a local scale seem to coincide with the globalization of trade. Human-accelerated environmental change, including climate change, can exacerbate this sense of disenfranchisement. The structure and functioning of coastal ecosystems have been developed over thousands of years subject to environmental forces and constraints imposed mainly on local scales. However, phenomena that transcend these conventional scales have emerged with the explosion of human population, and especially with the rise of modern global culture. Here, we examine five broad questions of scale in the coastal zone: (1) How big are coastal ecosystems and why should we care? (2) Temporal scales of change in coastal waters and watersheds: Can we detect shifting baselines due to economic development and other drivers? (3) Are footprints more important than boundaries? (4) What makes a decision big? The tyranny of small decisions in coastal regions. (5) Scales of complexity in coastal waters: the simple, the complicated or the complex? These questions do not have straightforward answers. There is no single “scale” for coastal ecosystems; their multiscale nature complicates our understanding and management of them. Coastal ecosystems depend on their watersheds as well as spatially-diffuse “footprints” associated with modern trade and material flows. Change occurs both rapidly and slowly on human time scales, and observing and responding to changes in coastal environments is a fundamental challenge. Apparently small human decisions collectively have potentially enormous consequences for coastal environmental quality, and our success in managing the effects of these decisions will determine the quality of life in the coastal zone in the 21st century and beyond. Vigilant monitoring, creative synthesis of information, and continued research will be necessary to properly understand and govern our coastal environments into the future. %0 Artikel %@ 0272-7714 %A Kowalski, N. %A Dellwig, O. %A Beck, M. %A Grunwald, M. %A Duerselen, C.-D. %A Badewien, T.H. %A Brumsack, H.-J. %A Beusekom, J.E.E.van %A Boettcher, M.E. %D 2012 %J Estuarine, Coastal and Shelf Science %N 1123 %P 3 - 17 %R doi:10.1016/j.ecss.2011.03.011 %T A comparative study of manganese dynamics in the water column and sediments of intertidal systems of the North Sea %U http://dx.doi.org/10.1016/j.ecss.2011.03.011 %X The dynamics of the redox-sensitive trace metal manganese (Mn) and its response to biological activity were investigated in the water column and shallow pore waters of the German Wadden Sea (southern North Sea) in 2008 and 2009. Two systems, one from the southern (backbarrier area of Spiekeroog Island) and one from the eastern part (Sylt-Rømø Wadden Sea) of the German Bight were compared. The major aim was to examine to which extent biogeochemical findings are specific for a particular tidal basin or transferable to other basins of the German Wadden Sea. Although both study areas reveal hydrodynamical, sedimentological, and ecological differences, qualitatively pronounced similarities in Mn dynamics are observed. Thus, complex cycling of dissolved Mn with increasing values in spring and late summer due to elevated biological activity as well as a depletion period in early summer were observed in both study areas. This finding suggests a seasonal behaviour of Mn being generally representative for the tidal basins of the southern North Sea. Quantitative differences are significant as the backbarrier area of Spiekeroog Island shows much higher concentrations of dissolved Mn in the water column especially during spring. We suggest that this difference is due to a larger sediment area/water volume ratio in the Spiekeroog backbarrier area combined with a higher release of dissolved Mn from the tidal flat sediments as seen in pore water profiles from surface sediments. Site-specific differences are also seen in further tidal systems of the North Frisian Wadden Sea, which are characterised by individual hydrodynamical and sedimentological conditions. Several transects leading from offshore locations towards the coast also revealed a highly variable Mn level. Overall, the North Frisian Wadden Sea most likely represents a less important source for dissolved Mn than the East Frisian Wadden Sea. Furthermore, our data suggest that site-specific properties of the different tidal basins have to be considered in budget calculations for the entire Wadden Sea. %0 Artikel %@ 1616-7341 %A Petersen, W. %A Schroeder, F. %A Bockelmann, F.-D. %D 2011 %J Ocean Dynamics %N 1791 %P 1541 - 1554 %R doi:10.1007/s10236-011-0445-0 %T FerryBox - Application of continuous water quality observations along transects in the North Sea %U http://dx.doi.org/10.1007/s10236-011-0445-0 10 %X In 2002, the Helmholtz-Zentrum Geesthacht, Germany, started to use FerryBox-automated monitoring systems on Ships of Opportunity to continuously record standard oceanographic, biological and chemical in situ data in the North Sea. The present study summarises the operational experience gathered since the beginning of this deployment and reflects on the potential and limits of FerryBox systems as a monitoring tool. One part relates to the instrumental performance, constancy of shipping services, and the availability and quality of the recorded in situ data. The other considers integration of the FerryBox observations in scientific applications and routine monitoring campaigns. Examples are presented that highlight the added value of the recorded data for the study of both long- and short-term variability in water mass stability, plankton communities and surface water productivity in the North Sea. Through the assessment of technical and scientific performance, it is evident that FerryBoxes have become a valuable tool in marine research that helps to fill gaps in coastal and open ocean operational observation networks. %0 Artikel %@ 1726-4170 %A Schlarbaum, T. %A Daehnke, K. %A Emeis, K. %D 2011 %J Biogeosciences %N 2118 %P 3519 - 3530 %R doi:10.5194/bg-8-3519-2011 %T Dissolved and particulate reactive nitrogen in the Elbe River/NW Europe: a 2-yr N-isotope study %U http://dx.doi.org/10.5194/bg-8-3519-2011 12 %X Rivers collect and transport reactive nitrogen to coastal seas as nitrate, ammonium, dissolved organic nitrogen (DON), or particulate nitrogen. DON is an important component of reactive nitrogen in rivers and is suspected to contribute to coastal eutrophication, but little is known about seasonality of DON loads and turnover within rivers. We measured the concentrations and the isotope ratios 15N/14N of combined DON + NH4+ (δ15DON + NH4+), nitrate (δ15N − NO3−) and particulate nitrogen (δ15PN) in the non-tidal Elbe River (SE North Sea, NW Europe) over a period of 2 yr (June 2005 to December 2007) at monthly resolution. Combined DON + NH4+ concentrations ranged from 22 to 75 μM and comprised nearly 23% of total dissolved nitrogen in the Elbe River in annual mean; PN and nitrate concentrations ranged from 11 to 127 μM, and 33 to 422 μM, respectively. Combined PN and DON + NH4+ concentrations were, to a first approximation, inversely correlated to nitrate concentrations. δ15DON + NH4+, which varied between from 0.8‰ to 11.5‰, changed in parallel to δ15PN (range 6 to 10‰), and both were anti-correlated to δ15N − NO3− (range 6 to 23‰). Seasonal patterns of DON + NH4+ concentrations and δ15DON + NH4+ diverge from those expected from biological DON + NH4+ production in the river alone and suggest that the elution of organic fertilisers significantly affects the DON + NH4+ pool in the Elbe River. %0 Artikel %@ 1616-7341 %A Callies, U. %A Pluess, A. %A Kappenberg, J. %A Kapitza, H. %D 2011 %J Ocean Dynamics %N 1791 %P 2121 - 2139 %R doi:10.1007/s10236-011-0474-8 %T Particle tracking in the vicinity of Helgoland, North Sea: A model comparison %U http://dx.doi.org/10.1007/s10236-011-0474-8 12 %X Station Helgoland Roads in the south-eastern North Sea (German Bight) hosts one of the richest longterm time series of marine observations. Hydrodynamic transport simulations can help understand variability in the local data brought about by intermittent changes of water masses. The objective of our study is to estimate to which extent the outcome of such transport simulations depends on the choice of a specific hydrodynamic model. Our basic experiment consists of 3,377 Lagrangian simulations in time-reversed mode initialized every 7 h within the period Feb 2002–Oct 2004. Fifty-day backward simulations were performed based on hourly current fields from four different hydrodynamic models that are all well established but differ with regard to spatial resolution, dimensionality (2D or 3D), the origin of atmospheric forcing data, treatment of boundary conditions, presence or absence of baroclinic terms, and the numerical scheme. The particle-tracking algorithm is 2D; fields from 3D models were averaged vertically. Drift simulations were evaluated quantitatively in terms of the fraction of released particles that crossed each cell of a network of receptor regions centred at the island of Helgoland. We found substantial systematic differences between drift simulations based on each of the four hydrodynamic models. Sensitivity studies with regard to spatial resolution and the effects of baroclinic processes suggest that differences in model output cannot unambiguously be assigned to certain model properties or restrictions. Therefore, multi-model simulations are needed for a proper identification of uncertainties in long-term Lagrangian drift simulations. %0 Artikel %@ 0304-4203 %A Schlarbaum, T. %A Daehnke, K. %A Emeis, K. %D 2010 %J Marine Chemistry %N 1290 %P 91 - 107 %R doi:10.1016/j.marchem.2009.12.007 %T Turnover of combined dissolved organic nitrogen and ammonium in the Elbe estuary/NW Europe: Results of nitrogen isotope investigations %U http://dx.doi.org/10.1016/j.marchem.2009.12.007 1-4 %X Dissolved organic nitrogen (DON) is often the dominant form of reactive nitrogen transported from land to sea by rivers, but is considered to be largely recalcitrant and behaves conservatively in many estuaries. We measured the concentration and the isotope ratio δ15N of combined DON and ammonium (δ15DON + NH4+) in the Elbe River estuary (SE North Sea, NW Europe) by a combination of a modified persulfate digestion and the denitrifier method. Measurements were made on samples taken along the salinity gradient from 1 to 32 during different seasons, in order to gauge the effects of internal biological processes and external signatures (such as pollution). Combined DON and ammonium concentrations ranged from 20 to 60 µM, and δ15DON + NH4+ from 0 to 11‰. The results show that DON + NH4+ contributes < 20% to total reactive nitrogen in the river end member and rises to 50% in the outer estuary. By comparison with older data, the DON load in the Elbe River did not change since the 1980s, when nitrate and phosphate pollution was maximal. We find evidence that DON and/or ammonium or reactive components in DON are both consumed and produced in the estuary, indicated by changing isotope ratios and non-conservative mixing gradients. The estuarine turbidity maximum zone (TMZ) at salinities < 5, which today is a significant source of nitrate from nitrification, coincides with significantly decreased DON + NH4+ concentrations and δ15DON + NH4+ in all seasons sampled. Whether this is due to selective absorption/desorption of 15N enriched moieties onto particle surfaces, or to selective heterotrophic assimilation and nitrification is yet unclear, and the loss of DON + NH4+ does not balance the added nitrate. Because DON + NH4+ concentrations and δ15DON + NH4+ rise sharply seaward of the TMZ, we consider adsorption/desorption processes most likely. In the salinity gradient 5 to 30, DON + NH4+ behaves conservatively in both concentration and isotopic composition.