Climate-cooling Arctic lakes soak up greenhouse gases
Thermokarst lakes, which form when ice-rich permafrost thaws, have long been considered major sources of carbon dioxide and methane to the atmosphere. However, new research led by University of Alaska Fairbanks (UAF) and USGS scientists indicates that arctic thermokarst lakes stabilize climate change by storing more greenhouse gases than they emit into the atmosphere. Countering a widely-held view that thawing permafrost accelerates atmospheric warming, new research published in Nature suggests arctic thermokarst lakes are ‘net climate coolers’ when observed over longer, millennial, time scales.
Incorporating published data from the circumpolar arctic, new field observations of Siberian permafrost and thermokarst features, radiocarbon dating, atmospheric modeling, and spatial analyses, the research shows how thawing permafrost is impacting climate change and greenhouse gas emissions.
Thermokarst lakes occur in the Arctic and cold mountain regions when ice-rich permafrost thaws and creates surface depressions that fill with melted freshwater, converting what was previously frozen land into lakes. New research indicates that these lakes initially formed in ice-rich regions of North Siberia and Alaska after the atmospheric warming associated with deglaciation (predominantly forming between approximately 15,000 and 10,000 years ago), and were large sources of methane to the atmosphere. As peat began accumulating rapidly in partially drained and fully drained lake basins, which also led to permafrost re-aggradation, the lakes started acting as carbon sinks. Roughly 5,000 years ago more carbon was being taken up by the peat in these lake basins than emitted as carbon dioxide and methane, turning these lakes into a net carbon sink on a global scale. Thus, while methane and carbon dioxide emissions following thaw led to immediate radiative warming, net carbon uptake in peat-rich sediments that occurs over millennial timescales ultimately leads these lakes to have a net cooling effect.
Because roughly 30% of global permafrost carbon is concentrated within 7% of the permafrost region in Alaska, Canada, and Siberia, this study’s findings renew scientific interest in how carbon uptake by thermokarst lakes offsets greenhouse gas emissions. Through its data collection, the study expanded the circumpolar peat carbon pool estimate for permafrost regions by more than 50%.
This paper, published in Nature, is available at: https://pubs.er.usgs.gov/publication/70157138.