HR: 0800h
AN: B31A-0205    [Abstracts]
TI: Thermokarst lake bubbling as a source of atmospheric methane (CH4) at rapid climate transitions during the last glacial period.
AU: * Walter, K M
EM: ftkmw1@uaf.edu
AF: Institute of Arctic Biology, University of Alaska, Fairbanks, Fairbanks, AK 99775 United States
AU: Edwards, M A
EM: Mary.Edwards3@btinternet.com
AF: University of Southampton, University Road University of Southampton, Southampton, S0171BJ United Kingdom
AU: Chapin, T
EM: terry.chapin@uaf.edu
AF: Institute of Arctic Biology, University of Alaska, Fairbanks, Fairbanks, AK 99775 United States
AU: Zimov, S
EM: sazimov@cher.sakha.ru
AF: Northeast Science Station, PO Box 18 Sakha Republic, Cherskii, 678830 Russian Federation
AB: We propose a new hypothesis to explain the prompt increases in atmospheric methane (CH4) concentration (AMC) that accompanied rapid interglacial climate warming during the last glacial age. Understanding sources of variation in AMC is important because CH4 is a greenhouse gas with strong potential to feed back onto rapid climate change. Until now, two main hypotheses have been advanced to explain millennial scale variations in AMC as recorded in ice cores: 1) The wetland hypothesis proposes that CH4 emission from wetlands existing at the end of the glacial periods increased in response to climate warming, and 2) the `clathrate gun hypothesis' assumes that catastrophic release of methane hydrates from sea floor sediments caused rapid increases in AMC. The wetlands hypothesis is poorly constrained by a lack of data on the extent of paleo-wetlands and by the discontinuity between the fast rates of AMC rise and the slower process of wetland expansion. We propose a third hypothesis: Permafrost degradation over extensive regions of Siberia, Asia, Europe and North America resulted in the formation of thermokarst (thaw) lakes, from which high rates of ebullition (bubbling) provided an additional source of CH4 to the atmosphere. Ebullition, a mechanism of gas transport seldom quantified, constitutes 96% of CH4 emissions from modern North Siberian thermokarst lakes. Rates of CH4 ebullition along thermokarst margins of lakes are up to two orders of magnitude higher than from non-thermokarst areas of lakes. Thermokarst activity releases organic matter from permafrost soils into anaerobic lake bottoms, enhancing methane production and emission from lakes. Recognition of modern North Siberian thermokarst lakes as an additional source of atmospheric CH4 increases the current estimate of the contribution of northern aquatic ecosystems to the global atmospheric CH4 budget by 21%. Through a synthesis of paleopedological records of permafrost and thaw lake distributions, and measurements of CH4 biogeochemistry in modern thermokarst lakes, we advance the hypothesis that expansion of thermokarst lakes at the onset of interstadials constituted a major feedback to global warming during the last glacial age.
DE: 3309 Climatology (1620)
DE: 1823 Frozen ground
DE: 1845 Limnology
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting