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1. Panarctic lakes exerted a small positive feedback on early Holocene warming due to deglacial release of methane

   https://doi.org/10.1038/s43247-023-00930-2  

   Brosius, L. S.; Walter Anthony, K. M.; Treat, C. C.; Jones, M. C.; Dyonisius, M.; Grosse, G. (December 2023, Communications Earth & Environment)

   Abstract Climate-driven permafrost thaw can release ancient carbon to the atmosphere, begetting further warming in a positive feedback loop. Polar ice core data and young radiocarbon ages of dissolved methane in thermokarst lakes have challenged the importance of this feedback, but field studies did not adequately account for older methane released from permafrost through bubbling. We synthesized panarctic isotope and emissions datasets to derive integrated ages of panarctic lake methane fluxes. Methane age in modern thermokarst lakes (3132 ± 731 years before present) reflects remobilization of ancient carbon. Thermokarst-lake methane emissions fit within the constraints imposed by polar ice core data. Younger, albeit ultimately larger sources of methane from glacial lakes, estimated here, lagged those from thermokarst lakes. Our results imply that panarctic lake methane release was a small positive feedback to climate warming, comprising up to 17% of total northern hemisphere sources during the deglacial period. 

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

   https://doi.org/10.1088/1748-9326/abc848  

   Walter Anthony, K. M.; Lindgren, P.; Hanke, P.; Engram, M.; Anthony, P.; Daanen, R. P.; Bondurant, A.; Liljedahl, A. K.; Lenz, J.; Grosse, G.; et al (February 2021, Environmental Research Letters)

   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 (CO₂) and methane (CH₄) 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 CH₄ebullition 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 CH₄ebullition in interior Alaska thermokarst lakes. Hotspot seeps are characterized as point-sources of high ebullition that release¹⁴C-depleted CH₄from 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 CH₄hotspot 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 older¹⁴C ages of CH₄released from hotspot seeps in older, expanding thermokarst lakes (¹⁴C_CH420 079 ± 1227 years BP, mean ± standard error (s.e.m.) years) to deeper taliks (thaw bulbs) compared to younger¹⁴C_CH4in new lakes (¹⁴C_CH48526 ± 741 years BP) with shallower taliks. We find that smaller, non-hotspot ebullition seeps have younger¹⁴C 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 CH₄-hotspot seep emissions following formation of thermokarst lakes as climate warms. 

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3. Influence of permafrost thaw on an extreme geologic methane seep

   https://doi.org/10.1002/ppp.2114  

   Sullivan, Taylor D.; Parsekian, Andrew D.; Sharp, Janelle; Hanke, Philip J.; Thalasso, Frederic; Shapley, Mark; Engram, Melanie; Walter Anthony, Katey (May 2021, Permafrost and Periglacial Processes)

   Abstract The occurrence and magnitude of natural fossil methane (CH₄) emissions in the Arctic are poorly known. Emission of geologic CH₄, a potent greenhouse gas, originating beneath permafrost is of particular interest due to the potential for positive feedback to climate warming, whereby accelerated permafrost thaw releases permafrost‐trapped CH₄in a future warmer climate. The development of through‐going taliks in Arctic lakes overlying hydrocarbon reservoirs is one mechanism of releasing geologically sourced, subpermafrost CH₄. Here we use novel gas flux measurements, geophysical observations of the subsurface, shallow sediment coring, high‐resolution bathymetry measurements, and lake water chemistry measurements to produce a synoptic survey of the gas vent system in Esieh Lake, a northwest Alaska lake with exceedingly large geologic CH₄seep emissions. We find that microbially produced fossil CH₄is being vented though a narrow thaw conduit below Esieh Lake through pockmarks on the lake bottom. This is one of the highest flux geologic CH₄seep fields known in the terrestrial environment and potentially the highest flux single methane seep. The poleward retreat of continuous permafrost may have implications for more subcap CH₄release with increased permafrost thaw. 

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4. Characteristics of methane emissions from alpine thermokarst lakes on the Tibetan Plateau

   https://doi.org/10.1038/s41467-023-38907-6  

   Yang, Guibiao; Zheng, Zhihu; Abbott, Benjamin W.; Olefeldt, David; Knoblauch, Christian; Song, Yutong; Kang, Luyao; Qin, Shuqi; Peng, Yunfeng; Yang, Yuanhe (December 2023, Nature Communications)

   Abstract Understanding methane (CH₄) emission from thermokarst lakes is crucial for predicting the impacts of abrupt thaw on the permafrost carbon-climate feedback. However, observational evidence, especially from high-altitude permafrost regions, is still scarce. Here, by combining field surveys, radio- and stable-carbon isotopic analyses, and metagenomic sequencing, we present multiple characteristics of CH₄emissions from 120 thermokarst lakes in 30 clusters along a 1100 km transect on the Tibetan Plateau. We find that thermokarst lakes have high CH₄emissions during the ice-free period (13.4 ± 1.5 mmol m⁻²d⁻¹; mean ± standard error) across this alpine permafrost region. Ebullition constitutes 84% of CH₄emissions, which are fueled primarily by young carbon decomposition through the hydrogenotrophic pathway. The relative abundances of methanogenic genes correspond to the observed CH₄fluxes. Overall, multiple parameters obtained in this study provide benchmarks for better predicting the strength of permafrost carbon-climate feedback in high-altitude permafrost regions. 

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5. Assessing the Potential for Mobilization of Old Soil Carbon After Permafrost Thaw: A Synthesis of ¹⁴ C Measurements From the Northern Permafrost Region

   https://doi.org/10.1029/2020GB006672  

   Estop‐Aragonés, Cristian; Olefeldt, David; Abbott, Benjamin W.; Chanton, Jeffrey P.; Czimczik, Claudia I.; Dean, Joshua F.; Egan, Jocelyn E.; Gandois, Laure; Garnett, Mark H.; Hartley, Iain P.; et al (September 2020, Global Biogeochemical Cycles)

   Abstract The magnitude of future emissions of greenhouse gases from the northern permafrost region depends crucially on the mineralization of soil organic carbon (SOC) that has accumulated over millennia in these perennially frozen soils. Many recent studies have used radiocarbon (¹⁴C) to quantify the release of this “old” SOC as CO₂or CH₄to the atmosphere or as dissolved and particulate organic carbon (DOC and POC) to surface waters. We compiled ~1,900¹⁴C measurements from 51 sites in the northern permafrost region to assess the vulnerability of thawing SOC in tundra, forest, peatland, lake, and river ecosystems. We found that growing season soil¹⁴C‐CO₂emissions generally had a modern (post‐1950s) signature, but that well‐drained, oxic soils had increased CO₂emissions derived from older sources following recent thaw. The age of CO₂and CH₄emitted from lakes depended primarily on the age and quantity of SOC in sediments and on the mode of emission, and indicated substantial losses of previously frozen SOC from actively expanding thermokarst lakes. Increased fluvial export of aged DOC and POC occurred from sites where permafrost thaw caused soil thermal erosion. There was limited evidence supporting release of previously frozen SOC as CO₂, CH₄, and DOC from thawing peatlands with anoxic soils. This synthesis thus suggests widespread but not universal release of permafrost SOC following thaw. We show that different definitions of “old” sources among studies hamper the comparison of vulnerability of permafrost SOC across ecosystems and disturbances. We also highlight opportunities for future¹⁴C studies in the permafrost region. 

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