Permafrost Thaw and Stabilization in the Arctic’s Distant Past

Science Advances, April 28

Past permafrost thaw extended into the high Arctic between 1.5 and 0.5 million years ago, and underwent cycles of thawing and re-freezing in regions where permafrost is stable today. However, for the past 400,000 years, extensive permafrost thaw has been limited to the sub-Arctic. This shift toward more stable permafrost in the Arctic can be linked to more persistent Arctic Ocean sea ice cover in this period. This study’s reconstruction of permafrost thaws across sub-Arctic regions about 400,000 years ago and earlier was not accompanied by dramatic increases in atmospheric greenhouse gas concentrations. This suggests that either greenhouse gas concentrations during these inter-glacials were relatively insensitive to permafrost thaw, or were offset by carbon uptake elsewhere. It also implies relatively long-term sequestration of stored carbon in the permafrost. Understanding permafrost dynamics and carbon cycling is fundamental when evaluating the potential contribution of permafrost-carbon climate feedback to anticipated warming.

https://tc.copernicus.org/articles/15/1501/2021/