Decadal-scale hotspot methane ebullition within lakes following abrupt permafrost thaw

• Published in: Environmental Research Letters
• Main Authors: Walter Anthony, K M, Lindgren, P, Hanke, P, Engram, M, Anthony, P, Daanen, R P, Bondurant, A, Liljedahl, A K, Lenz, J, Grosse, G, Jones, B M, Brosius, L, James, S R, Minsley, B J, Pastick, N J, Munk, J, Chanton, J P, Miller, C E, Meyer, F J
• Other Authors: U.S. National Science Foundation, Jet Propulsion Laboratory
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: IOP Publishing 2021
• Subjects: permafrost; Thermokarst; Alaska
• Online Access: http://dx.doi.org/10.1088/1748-9326/abc848; https://iopscience.iop.org/article/10.1088/1748-9326/abc848; https://iopscience.iop.org/article/10.1088/1748-9326/abc848/pdf

Abstract Thermokarst lakes accelerate deep permafrost thaw and the mobilization of previously frozen soil organic carbon. This leads to microbial decomposition and large releases of carbon dioxide (CO 2 ) and methane (CH 4 ) that enhance climate warming. However, the time scale of permafrost-carbon emissions following thaw is not well known but is important for understanding how abrupt permafrost thaw impacts climate feedback. We combined field measurements and radiocarbon dating of CH 4 ebullition with (a) an assessment of lake area changes delineated from high-resolution (1–2.5 m) optical imagery and (b) geophysical measurements of thaw bulbs (taliks) to determine the spatiotemporal dynamics of hotspot-seep CH 4 ebullition in interior Alaska thermokarst lakes. Hotspot seeps are characterized as point-sources of high ebullition that release 14 C-depleted CH 4 from deep (up to tens of meters) within lake thaw bulbs year-round. Thermokarst lakes, initiated by a variety of factors, doubled in number and increased 37.5% in area from 1949 to 2009 as climate warmed. Approximately 80% of contemporary CH 4 hotspot seeps were associated with this recent thermokarst activity, occurring where 60 years of abrupt thaw took place as a result of new and expanded lake areas. Hotspot occurrence diminished with distance from thermokarst lake margins. We attribute older 14 C ages of CH 4 released from hotspot seeps in older, expanding thermokarst lakes ( 14 C CH4 20 079 ± 1227 years BP, mean ± standard error (s.e.m.) years) to deeper taliks (thaw bulbs) compared to younger 14 C CH4 in new lakes ( 14 C CH4 8526 ± 741 years BP) with shallower taliks. We find that smaller, non-hotspot ebullition seeps have younger 14 C ages (expanding lakes 7473 ± 1762 years; new lakes 4742 ± 803 years) and that their emissions span a larger historic range. These observations provide a first-order constraint on the magnitude and decadal-scale duration of CH 4 -hotspot seep emissions following formation of thermokarst lakes as climate warms.