CO2 and CH4 emissions to the atmosphere in the Arctic do not come from historical old sources

A recent study conducted by the Vrije Universiteit Amsterdam, with the participation of Alberto Borges of the Chemical Oceanography Unit (FOCUS) of ULiège, shows that the rivers and lakes of the Eastern Siberian Arctic tundra emit carbon dioxide (CO₂) and methane (CH₄) to the atmosphere from the degradation of contemporary organic matter and not ancient organic matter from permafrost, as previously thought. A situation that is likely to worsen as temperatures rise. This study was published in the journal Nature Communications.

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ermafrost refers to soil that remains frozen for at least two years and is found in high latitudes, mainly in the Arctic and Antarctic regions. Over millenia, organic carbon from the plants that grow each summer on its surface has accumulated in this frozen soil, making it one of the largest reservoirs of carbon in the form of soil in the world today. Scientists estimate that permafrost contains almost the double of the carbon in our atmosphere, which when it melts can be converted by bacteria into the powerful greenhouse gases carbon dioxide (CO₂) and methane (CH₄).

The carbon stock in the permafrost has remained largely frozen for millennia but is becoming increasingly vulnerable to melting as average air temperatures rise. And it is the Eastern Siberian Arctic region that is experiencing the largest increases (2.7°C between 1971 and 2017 - estimated +7°C by 2100). A quarter of the carbon in the Arctic permafrost in Siberia and Alaska is contained in one of the 'oldest' layers called the Yedoma, sediments that are more than 50,000 years old. Yedoma carbon is particularly vulnerable to melting due to rising temperatures in the Arctic because of its high water content," explains Alberto Borges, Researcher at the Chemical Oceanography Laboratory (FOCUS Researh unit/Faculty of Science). The contribution of this melting to atmospheric emissions of CO₂ and CH₄ from ponds, lakes and rivers remained unknown. It was therefore important to know whether the current emissions of CO₂ and CH4 from the tundra were due to the degradation of modern or ancient organic matter.»

The recent study published in Nature Communications, in which Alberto Borges participated, has provided estimates of carbon mobilization from Yedoma to the continental waters of the Siberian tundra and radiocarbon (¹⁴C, allowing dating) measurements of organic matter, CO₂ and CH₄. This study shows that more than 80% of the CO₂ and CH₄ emissions due to permafrost melting in this region come from contemporary carbon and not from Yedoma, as the scientific community thought until now. "The radiocarbon signatures of dissolved CO₂ and CH₄ were younger than the mobilized organic carbon, suggesting that the mobilization of carbon from Yedoma by melting will not necessarily result in its immediate emission to the atmosphere," says the researcher, who points out that methane warming in the atmosphere is 34 times more powerful than that of CO₂ over a period of 100 years (at equal amounts).

Since most emissions will most likely come from the melting of the "young" carbon in the coming years, we may not have to worry about the substantial increase in climate change due to old permafrost. However, the Arctic will remain a huge source of carbon emissions, as carbon that was soil or plant matter only a few hundred years ago is escaping into the atmosphere. This situation is likely to get worse as warmer temperatures lengthen the growing seasons of the Arctic summer.

Scientific reference

Dean J.F., O.H. Meisel, M.M. Roscoe, L.B. Marchesini, M.H. Garnett, H. Lenderink, R. van Logtestijn, A.V. Borges, S. Bouillon, T. Lambert, T. Röckmann, T. Maximov, R. Petrov, S. Karsanaev, R. Aerts, J. van Huissteden, A.J. Dolman (2020) East Siberian Arctic inland waters emit mostly contemporary carbon, Nature Communications, 11(1627):1-10