Reduced net methane emissions due to microbial methane oxidation in a warmer Arctic

Methane emissions from organic-rich soils in the Arctic have been extensively studied due to their potential to increase the atmospheric methane burden as permafrost thaws(1-3). However, this methane source might have been overestimated without considering high-affinity methanotrophs (HAMs; methane-oxidizing bacteria) recently identified in Arctic mineral soils(4-7). Herein we find that integrating the dynamics of HAMs and methanogens into a biogeochemistry model(8-10) that includes permafrost soil organic carbon dynamics(3) leads to the upland methane sink doubling (similar to 5.5 Tg CH4 yr(-1)) north of 50 degrees N in simulations from 2000-2016. The increase is equivalent to at least half of the difference in net methane emissions estimated between process-based models and observation-based inversions(11,12), and the revised estimates better match site-level and regional observations(5,7,13-15). The new model projects doubled wetland methane emissions between 2017-2100 due to more accessible permafrost carbon(16-18). However, most of the increase in wetland emissions is offset by a concordant increase in the upland sink, leading to only an 18% increase in net methane emission (from 29 to 35 Tg CH4 yr(-1)). The projected net methane emissions may decrease further due to different physiological responses between HAMs and methanogens in response to increasing temperature(19,20).