B028-02
Characterizing extreme thermokarst methane emissions in interior Alaska with implications for pan-Arctic source attribution

Tuesday, 8 December 2020: 19:04
Virtual
Clayton Elder1, David R Thompson2, Andrew K Thorpe2, Philip Hanke3, Nicholas Hasson4,5, David Olefeldt6,7, Katey M Walter Anthony3 and Charles E Miller2, (1)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (2)Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States, (3)University of Alaska Fairbanks, Water and Environmental Research Center, Fairbanks, AK, United States, (4)Fairbanks, Alaska, United States, (5)University of Alaska Fairbanks, Fairbanks, AK, United States, (6)University of Guelph, Guelph, ON, Canada, (7)University of Alberta, Department of Renewable Resources, Edmonton, AB, Canada
Recorded Presentation
Abstract:
Rapid warming of the Arctic has caused widespread permafrost thaw and collapse (thermokarst), threatening the stability of the vast permafrost carbon (C) reservoir. When thermokarst causes soil inundation, decomposition of previously frozen organic C can emit large quantities of methane (CH4), accelerating a warming feedback. Despite this impact on global climate, estimates of CH4 emissions from the northern permafrost domain are sparse and highly uncertain, ranging from 11 – 75 Tg CH4 yr-1. The Arctic’s inaccessibility and the challenge of scaling observations across space and time in complex landscapes are primary contributors to this uncertainty. This study estimated pan-arctic CH4 emissions attributable to thermokarst by coupling novel airborne imaging spectroscopy (NASA’s Next Generation Airborne Visible/Infrared Imaging Spectrometer, AVIRIS-NG), with ground-based observations of permafrost conditions and the magnitude and isotopic characteristics of CH4 fluxes. AVIRIS-NG detected millions of CH4 emission hotspots with high spatial resolution (5 m pixels) across a broad area (70,000 km2). Big Trail Lake in interior Alaska was identified via airborne remote sensing as a persistent CH4 hotspot and ground-based flux chamber measurements confirmed CH4 fluxes >5,000 mg CH4 m-2 d-1. Ground-based electrical resistance tomography revealed the presence of a talik directly beneath the CH4 hotspot. This, combined with preliminary 14C and 13C isotope analysis of the emitted CH4, reinforce the influence of thawing permafrost C in fueling extreme emissions. Hotspot metrics derived from the AVIRIS-NG surveys conducted in the Arctic Boreal Vulnerability Experiment (ABoVE) domain were then used to extrapolate observed CH4 hotspot fluxes across thermokarst areas in the pan-Arctic. We estimate thermokarst-related CH4 hotspots to represent 0.5 – 3.0 Tg CH4 y-1, or approximately 2 - 10% of annual pan-Arctic CH4 emissions. While this estimate carries large uncertainty, it offers a novel approach for attributing CH4 emissions to climate-sensitive thermokarst processes – a key factor for estimating emissions in the warmer future.
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