Permafrost is thawing worldwide as a result of global warming. In this way, climate-impacting greenhouse gases with carbon (carbon dioxide, methane) and nitrogen (laughing gas) can escape from the soil into the atmosphere.
A research team has determined the size of the nitrogen reservoir in the permafrost and calculated how much of it could be released as a result of climate change. The results now presented as part of a study were developed in several projects funded by the BMBF.
As a result of climate change, permafrost regions are currently warming up around four times faster than the global average. That is why the ground that has been frozen since the last cold period (approx. 100,000 to 12,000 years ago) is thawing over large areas and releasing vast amounts of dead plant remains. As a result, a previously inaccessible pool of organic material gradually becomes available for microorganisms to decompose. With the degradation of biomass, large amounts of carbon are released into the atmosphere as greenhouse gases and accelerate global warming.
2,200 soil samples evaluated in the Yedoma permafrost
“Permafrost is particularly in the focus of climate research because of the carbon. Numerous studies have already provided a reliable scientific picture,” says study lead author Dr. Jens Strauss, head of the Permafrost Biogeochemistry working group at the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (AWI). “On the other hand, there are hardly any reliable figures for the nitrogen stored in the permafrost, which is also highly relevant for the climate. With our work, we have now determined for the first time how much nitrogen is actually contained in the permafrost down to greater depths.”
The international team with researchers from Germany, Finland, the USA, Canada and China focused on the Yedoma permafrost, a soil variant that is particularly widespread in eastern Siberia and Alaska. Yedoma is considered to be particularly climate-sensitive due to its high ice content. If it warms up, it can collapse over a large area, thaw rapidly to a depth of many meters and thus activate significantly more organic material than other permafrost soils. As part of the study, Jens Strauss and his team analyzed more than 2,200 soil samples from Siberia and Alaska, determined the nitrogen content and calculated the size of the entire pool.
According to the results, the Yedoma region contains a total of 41.2 gigatonnes of nitrogen. The reservoir is thus significantly larger than previous estimates suggested. Of these, 37 gigatonnes – around 90 percent – are currently frozen. “But that will change as a result of climate change. We have calculated that in a future scenario with continued high greenhouse gas emissions by humanity by the year 2100, between 4 and a maximum of 16 gigatons of nitrogen could thaw in the Yedoma and thus be activated,” says Strauss.
Nitrous oxide is a greenhouse gas 300 times more potent than CO2
What consequences this surprisingly high amount would have for the climate depends crucially on the microorganisms in the soil. The nitrogen then available could boost plant growth. The plants, when they get to the nitrogen, could then produce CO2 bind from the atmosphere. “So the effect on the climate would be positive for a certain period of time,” says Strauss. “However, microbial degradation could also release large amounts of nitrous oxide into the atmosphere, a greenhouse gas 300 times stronger than CO2 . That has a significant impact on the climate.” Therefore, further studies would have to show what exactly will happen to the activated nitrogen pool.
Arctic in transition
In the German-British “Changing Arctic Ocean” research program, 220 scientists investigated the impact of climate change on the Arctic Ocean in a total of 16 projects from 2018 to 2021. The research program was funded by the Federal Ministry of Education and Research (BMBF) and the British Natural Environment Research Council (NERC). The results on nitrogen deposits presented in the current permafrost study are based, among other things, on data from the “Arctic in Transition” projects CACOON and ICEPAC. In addition, data from the BMBF-funded projects KoPf and CarboPerm were included.