Permafrost thaw liberates frozen organic carbon, which is decomposed into carbon dioxide (CO2) and methane (CH4). The release of these greenhouse gases (GHGs) forms a positive feedback to atmospheric CO2 and CH4 concentrations and accelerates climate change1,2. Current studies report a minor importance of CH4 production in water-saturated (anoxic) permafrost soils3,4,5,6 and a stronger permafrost carbon–climate feedback from drained (oxic) soils1,7. Here we show through seven-year laboratory incubations that equal amounts of CO2 and CH4 are formed in thawing permafrost under anoxic conditions after stable CH4-producing microbial communities have established. Less permafrost carbon was mineralized under anoxic conditions but more CO2–carbon equivalents (CO2–Ce) were formed than under oxic conditions when the higher global warming potential (GWP) of CH4 is taken into account8. A model of organic carbon decomposition, calibrated with the observed decomposition data, predicts a higher loss of permafrost carbon under oxic conditions (113 ± 58 g CO2–C kgC−1 (kgC, kilograms of carbon)) by 2100, but a twice as high production of CO2–Ce (241 ± 138 g CO2–Ce kgC−1) under anoxic conditions. These findings challenge the view of a stronger permafrost carbon-climate feedback from drained soils1,7 and emphasize the importance of CH4 production in thawing permafrost on climate-relevant timescales.
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We acknowledge the financial support through the Cluster of Excellence 'CliSAP' (EXC177), Universität Hamburg, funded through the German Research Foundation, the CarboPerm project funded by the German Ministry for Research and Education (03G0836A) to C.K., C.B. and E.-M.P. and the Helmholtz Gemeinschaft by funding the Helmholtz Young Investigators Group of S.L. (VH-NG-919). We also thank G. Hugelius for valuable discussions, D. Wagner and S. Zubrzycki for providing samples, B. Schwinge for laboratory assistance, W. Schneider and G. Stoof for help during the field campaigns and the German and Russian colleagues from the Alfred Wegener Institute in Potsdam, the Lena Delta Reserve in Tiksi and the Tiksi Hydrobase for logistical support.
The authors declare no competing interests.
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Knoblauch, C., Beer, C., Liebner, S. et al. Methane production as key to the greenhouse gas budget of thawing permafrost. Nature Clim Change 8, 309–312 (2018). https://doi.org/10.1038/s41558-018-0095-z
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