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abstracts
The response of permafrost to last interglacial warming constrains projections of future thaw
Alberto Reyes, Duane Froese, Britta Jensen
Numerical models predict that 21st century warming will result in thinning and disappearance of permafrost over much of the northern hemisphere, leading to positive warming feedback through decomposition of thawed organic carbon and release of CO2 and CH4. However, it is difficult to evaluate projections of permafrost degradation, and the associated release of greenhouse gases, because there is little understanding of the magnitude of permafrost degradation during past warmer-than-present intervals. We document the response of permafrost to warming during the last interglaciation, focusing on the unglaciated region of Yukon Territory and Alaska, where numerous distal tephra provide excellent chronostratigraphic control. Multiple exposures in Alaska and Yukon show consistent stratigraphic relations between Old Crow tephra (131±11 kyr) and prominent deposits of last interglacial organic material, which represent widespread ground thaw and thermokarst development during the last interglaciation. However, thaw was limited to the uppermost several metres of permafrost, and relict pre-last interglacial ice wedges are present in at least three exposures separated by over 700 km. These relict ice wedges indicate that the antiquity and resilience of discontinuous permafrost is regional in nature. However, the ubiquity and magnitude of last interglacial thermokarst suggest that terrain effects associated with current permafrost degradation foreshadow more widespread and severe shallow thaw under modest future warming scenarios. The response of permafrost to last interglacial warming suggests that carbon sequestered in near-surface permafrost is likely highly vulnerable to 21st century warming, but deeper permafrost and its associated carbon reservoirs are probably more stable than previously thought.
Alberto Reyes, Department of Earth and Atmospheric Sciences, University of Alberta,Earth Sciences Bldg. 1-26, T6G 2E3, Canada, areyes@ualberta.ca
Duane Froese, University of Alberta, Department of Earth and Atmospheric Sciences, Canada
Britta Jensen, University of Alberta, Department of Earth and Atmospheric Sciences, Canada
Session: F1: Climate Forcings
Download Talk:
> YSM09_OralA_Reyes.pdf
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