Climate science: cold carbon storage.

Abstract

Lakes that form in thawing permafrost emit substantial amounts of greenhouse gases to the atmosphere. It emerges that large quantities of carbon can also be stored in sediments at the lake bottoms. See Letter p.452 With the onset of a warmer Holocene climate, permafrost degradation gave rise to numerous thermokarst lakes — lakes formed when meltwater accumulates in surface depressions over thawing permafrost — across large regions of Siberia, Alaska and northern Canada. These lakes are commonly regarded as a net source of atmospheric methane and carbon dioxide due to organic matter degradation. But the question arises, can carbon taken up by these lakes in the form of organic matter accumulation offset their greenhouse gas emissions? This study finds that carbon accumulation in deep thermokarst lake sediments increases the circumpolar peat carbon pool estimate for permafrost regions by more than half, and is larger than the mass of Pleistocene-aged permafrost carbon released as greenhouses gases when the lakes first formed. The authors suggest that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago.