Colloquium Series Spring 2018

March 1, 2018 - 4:00pm

Thaw 102

Dr. Ben Gaglioti

Postdoctoral Research Scientist
Biology and Paleo Environment
Lamont-Doherty Earth Observatory

Columbia University

The Thin Brown Line: The Crucial Role of Peat in Protecting Permafrost in Arctic Alaska

Ongoing warming threatens to thaw Arctic permafrost and release its stored carbon, which could trigger a permafrost-carbon feedback that augments global warming. The effects of warming air temperatures on permafrost are complicated by the fact that across much of the Arctic and Subarctic a mat of living plants and decaying litter cover the ground and buffer underlying permafrost from air temperatures. For simplicity here, we refer to this organic mat as “peat”. Because this peat modifies heat flow between ground and air, the rate and magnitude of permafrost responses to changing climate - and hence the permafrost-carbon feedback - are partly slaved to the peat layer’s slower dynamics. To explore this relationship, we used radiocarbon (14C) age offsets within lake sediments in Alaskan watersheds underlain by yedoma deposits to track the changing responses of permafrost thaw to fluctuating climate as peat has accumulated over the last 14,000 years. As the peat layer built up, warming events became less effective at thawing permafrost and releasing ancient carbon. Consistent with this age-offset record, the geological record shows that early in post-glacial times when the peat cover was still thin and limited in extent, warm intervals triggered extensive thermokarst that resulted in rapid aggradation of floodplains. Today in contrast, hillslopes and floodplains remain stable despite rapid warming, probably because of the buffering effects of the extensive peat cover. Another natural experiment is provided by tundra fires like the 2007 Anaktuvuk River fire in Alaska that removed the peat cover from tundra underlain by continuous permafrost and resulted in widespread thermokarsting. Further support for peat’s critical role in protecting permafrost comes from the results of modeling how permafrost temperatures under different peat thicknesses respond to warming air temperature. Although post-industrial warming has not yet surpassed the buffering capacity of 14,000 years of peat buildup in Arctic Alaska, modeling suggests that a threshold could be crossed with further warming.