Publication Date:
2014-07-22
Description:
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. However, the same thermokarst lakes can also sequester carbon, 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 carbon accumulation in 20 lake sediments (47 +/- 10 grams of carbon per square metre per year; mean +/- standard error) were driven by thermokarst erosion and deposition of terrestrial organic matter, by nutrient release from thawing permafrost that stimulated lake productivity and by slow decomposition in cold, anoxic lake bottoms. When lakes eventually drained, permafrost formation rapidly sequestered sediment carbon. Our estimate of about 160 petagrams of Holocene organic carbon in deep lake basins of Siberia and Alaska increases the circumpolar peat carbon pool estimate for permafrost regions by over 50 per cent (ref. 6). The carbon in perennially frozen drained lake sediments may become vulnerable to mineralization as permafrost disappears, potentially negating the climate stabilization provided by thermokarst lakes during the late Holocene.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Anthony, K M Walter -- Zimov, S A -- Grosse, G -- Jones, M C -- Anthony, P M -- Chapin, F S 3rd -- Finlay, J C -- Mack, M C -- Davydov, S -- Frenzel, P -- Frolking, S -- England -- Nature. 2014 Jul 24;511(7510):452-6. doi: 10.1038/nature13560. Epub 2014 Jul 16.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Water and Environmental Research Center, University of Alaska, Fairbanks, Alaska 99775-5860, USA. ; Northeast Scientific Station, Pacific Institute for Geography, Far-East Branch, Russian Academy of Sciences, Cherskii 678830, Russia. ; 1] Geophysical Institute, University of Alaska, Fairbanks, Alaska 99775-7320, USA [2] Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam 14473, Germany. ; 1] Water and Environmental Research Center, University of Alaska, Fairbanks, Alaska 99775-5860, USA [2] US Geological Survey, Reston, Virginia 20192, USA. ; Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775-7000, USA. ; Department of Ecology, Evolution and Behavior, University of Minnesota, Saint Paul, Minnesota 55108, USA. ; Department of Biology, University of Florida, Gainesville, Florida 32611, USA. ; Max Planck Institute for Terrestrial Microbiology, Marburg 35043, Germany. ; Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire 03824-3525, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25043014" target="_blank"〉PubMed〈/a〉
Keywords:
Alaska
;
Atmosphere/chemistry
;
Canada
;
Carbon Dioxide/analysis
;
*Carbon Sequestration
;
Climate
;
Freezing
;
Geologic Sediments/chemistry
;
Greenhouse Effect
;
History, Ancient
;
Lakes/*chemistry
;
Methane/analysis
;
Siberia
;
Soil/chemistry
;
Temperature
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
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