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

• Published in: Environmental Research Letters
• Main Authors: K M Walter Anthony, P Lindgren, P Hanke, M Engram, P Anthony, R P Daanen, A Bondurant, A K Liljedahl, J Lenz, G Grosse, B M Jones, L Brosius, S R James, B J Minsley, N J Pastick, J Munk, J P Chanton, C E Miller, F J Meyer
• Format: Article in Journal/Newspaper
• Language: English
• Published: IOP Publishing 2021
• Subjects: abrupt thaw; permafrost; thermokarst lakes; methane; ebullition; lake change; Environmental technology. Sanitary engineering; TD1-1066; Environmental sciences; GE1-350; Science; Q; Physics; QC1-999; New Lakes; Thermokarst; Alaska
• Online Access: https://doi.org/10.1088/1748-9326/abc848; https://doaj.org/article/a5f744c85ac8478b9d77f06769b66536

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.