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A shift of thermokarst lakes from carbon sources to sinks during the Holocene epoch

Observations and modelling show that the deep thermokarst lakes that formed in Siberia and Alaska when the permafrost warmed in the Holocene epoch changed from climate-warming methane sources to climate-cooling carbon sinks about 5,000 years ago. The carbon budget of permafrost lakes With the onset...

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Published in:Nature (London) 2014-07, Vol.511 (7510), p.452-456
Main Authors: Anthony, K. M. Walter, Zimov, S. A., Grosse, G., Jones, M. C., Anthony, P. M., III, F. S. Chapin, Finlay, J. C., Mack, M. C., Davydov, S., Frenzel, P., Frolking, S.
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Language:English
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Summary:Observations and modelling show that the deep thermokarst lakes that formed in Siberia and Alaska when the permafrost warmed in the Holocene epoch changed from climate-warming methane sources to climate-cooling carbon sinks about 5,000 years ago. The carbon budget of permafrost lakes 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. Thermokarst lakes formed across vast regions of Siberia and Alaska during the last deglaciation and are thought to be a net source of atmospheric methane and carbon dioxide during the Holocene epoch 1 , 2 , 3 , 4 . However, the same thermokarst lakes can also sequester carbon 5 , and it remains uncertain whether carbon uptake by thermokarst lakes can offset their greenhouse gas emissions. Here we use field observations of Siberian permafrost exposures, radiocarbon dating and spatial analyses to quantify Holocene carbon stocks and fluxes in lake sediments overlying thawed Pleistocene-aged permafrost. We find that carbon accumulation in deep thermokarst-lake sediments since the last deglaciation is about 1.6 times larger than the mass of Pleistocene-aged permafrost carbon released as greenhouse gases when the lakes first formed. Although methane and carbon dioxide emissions following thaw lead to immediate radiative warming, carbon uptake in peat-rich sediments occurs over millennial timescales. We assess thermokarst-lake carbon feedbacks to climate with an atmospheric perturbation model and find that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5,000 years ago. High rates of Holocene c
ISSN:0028-0836
1476-4687
DOI:10.1038/nature13560