Permafrost contains more nitrogen than previously assumed
As a result of global warming, permafrost regions around the world are thawing now. As they do, climate-relevant greenhouse gases containing carbon (carbon dioxide, methane) and nitrogen (nitrous oxide) can be released from the soil and into the atmosphere. Accordingly, having data on the stored amounts of both elements that are as accurate as possible is essential to making good climate forecasts. Whereas substantial research has been conducted on the carbon reservoirs in permafrost, we still know comparatively little about nitrogen. A team of experts led by the Alfred Wegener Institute with participation of the Helmholtz-Zentrum Hereon has now determined the size of the nitrogen reservoir and calculated how much of it could be released as climate change progresses. The team’s findings have just been released in the journal Nature Communications.
Due to climate change, the permafrost regions are now warming at roughly four times the average global rate. Consequently, soils that have been frozen since the last ice age (ca. 100,000 to 12,000 years ago) are now experiencing widespread thawing, releasing big amounts of dead plant matter. As a result, a previously inaccessible pool of organic material is slowly but surely becoming “bioavailable” and can be used by microorganisms. As this biomass is used, large amounts of carbon are released into the atmosphere as greenhouse gases, accelerating global warming.
Impact on climate change
On the 2019 Lena Expedition (CACOON Sea) Photo: Hereon/ Tina Sanders
“Especially because of the carbon, permafrost is a particular focus of climate research. In this regard, numerous studies offer a scientifically sound picture of the status quo,” says Dr Jens Strauss, first author of the study and head of the Permafrost Biogeochemistry working group at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI). “In contrast, we have very few data on the amount of nitrogen stored in the soil, which is also highly relevant for the climate. Our study is the first to determine just how much nitrogen the permafrost actually contains down to considerable depths.”
The international team, consisting of researchers from Germany, Finland, the US, Canada and China focussed on Yedoma permafrost, a type of permafrost that is predominantly found in eastern Siberia and Alaska. Because of its high ice content, Yedoma is considered to be especially climate-sensitive. When it warms, it can collapse and rapidly thaw to depths of several metres. As a result, it can activate significantly more organic material than other types of permafrost. In the course of the study, Jens Strauss and his team analysed more than 2,200 soil samples from Siberia and Alaska, determined the nitrogen concentration, and subsequently calculated the size of the total pool.
Nitrogen and nitrous oxide
“According to our findings, the Yedoma region contains 41.2 metric gigatons of nitrogen. As such, the reservoir is considerably larger than indicated by previous estimates,” Strauss explains. “Of those 41.2 gigatons, 37 gigatons – or roughly 90 percent – are still frozen and not bioavailable. But this will change as climate change continues. Based on our calculations, in a future scenario with continuing high anthropogenic greenhouse-gas emissions, between 4 and 16 gigatons of nitrogen could be thawed and activated in Yedoma by the year 2100.”
The consequences of this surprisingly high amount for the climate chiefly depend on the microorganisms in the soil. “The newly bioavailable nitrogen could promote plant growth, since plants need nitrogen. And if the plants could access this nitrogen, they could absorb CO2 from the atmosphere, which means the effect on the climate would be positive for a certain time,” says Strauss. “But this microbial decomposition could also release large amounts of N2O into the atmosphere. This nitrous oxide – better known as laughing gas – is also a greenhouse gas 300 times as potent as CO2, which means it can seriously affect the climate. That’s why we’ll need further studies to determine just what will happen to this newly activated nitrogen pool.”
Dr Tina Sanders, scientist at the Hereon Institute for Carbon Cycles, Department "Aquatic Material Cycles" adds: "However, part of the released nitrogen is also washed out into the rivers and thus reaches the Arctic Ocean. The increased input of nitrogen will change productivity and further the food chain. What effect this will have on the ecosystem, we still have to investigate in the future."
- Original publication Jens Strauss, Christina Biasi, Tina Sanders, Benjamin W. Abbott, Thomas Schneider von Deimling, Carolina Voigt, Matthias Winkel, Maija E. Marushchak, Dan Kou, Matthias Fuchs, Marcus A. Horn, Loeka L. Jongejans, Susanne Liebner, Jan Nitzbon, Lutz Schirrmeister, Katey Walter Anthony, Yuanhe Yang, Sebastian Zubrzycki, Sebastian Laboor, Claire Treat and Guido Grosse: A globally relevant stock of soil nitrogen in the Yedoma permafrost domain. Nature Communications (2022).
- Website Institute of Carbon Cycles
- Website Coastal Pollution Toolbox On the Hereon page of the Coastal Pollution Toolbox, there is a detailed description of nitrogen release, turn-over, and transport in the permafrost region. We want to understand the consequences of the release on the ecosystem and how the input to the Arctic Ocean changes.
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