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Seaweed and carbon storage

Researchers revealed: Seaweed forests are significant contributors to oceanic carbon storage

A groundbreaking study by an international team of researchers, including two scientists at Helmholtz-Zentrum Hereon, has revealed the role of seaweed for oceanic carbon storage. Their research estimates that the world’s seaweed forests transport 56 million tons of carbon (between 10 to 170 million tons) to deep ocean sinks each year. Between 4 and 44 million tons of this carbon could remain sequestered in these deep sinks for at least a hundred years. This discovery, published in the prestigious journal Nature Geoscience .

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Seaweed play an even more important role as scientist thought. Photo: Daniel Carlson

It highlights a considerable contribution of macroalgae to oceanic carbon sinks. The study also suggests that large-scale shifts in seaweed forest distribution and abundance, including past and ongoing losses, would affect the carbon sink capacity.

These results provide further impetus for conservation and restoration efforts and emissions reductions to safeguard our seaweed forests and the ecosystem services that they provide.

Seaweed forests, primarily composed of large brown macroalgae like kelps and rockweeds, are among the most extensive and productive vegetated coastal ecosystem on the planet and are hotspots of marine biodiversity. These ocean forests can grow as rapidly as forests on land and are efficient in capturing carbon, which they store in their biomass. Part of this biomass can be transported to deep ocean sinks.

Outstanding science

The study, led by Dr Karen Filbee-Dexter at the Norwegian Institute of Marine Research and the University of Western Australia, reveals that seaweed forests export about 15 percent of their captured carbon into deep ocean waters each year, where part of it can remain trapped for centuries. The study estimates that seaweed-carbon export below 200 m depth totaled 3 to 4 percent of the ocean carbon sink. The findings underscore the need to include macroalgae in the depictions of the global ocean carbon budget, which still ignores the contribution of marine vegetation.

The international team used global ocean models to track the fate of seaweed carbon from the coast to the deep ocean. The transport time for macroalgae to the deep ocean was compared to their degradation rate to estimate the fraction that would reach the deep sinks. The team identified hotspots of carbon export globally, for example in areas with extensive seaweed forests or coastal areas with canyons or narrow continental shelves that are close to the deep sea. The coastal ocean represents an important global carbon sink and is a focus for interventions to mitigate climate change and meet the Paris Agreement targets while supporting biodiversity. “Hopefully our findings will help motivate efforts to reduce emissions as well as the negative impacts of human activities in the coastal zone to ensure the longevity of seaweed forests and their contributions to carbon sequestration and marine biodiversity,” said Dr Daniel Carlson, coauthor on the study.

Further information

Original publication Website Norwegian Institute of Marine Research Website University of Western Australia Website Hereon Institute of Coastal Ocean Dynamics


Dr Daniel Carlson


Helmholtz-Zentrum Hereon I Institute of Coastal Ocean Dynamics

Phone: +49 (0)4152 87-1860

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Christoph Wöhrle

Press Officer

Helmholtz-Zentrum Hereon I Communication and Media

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