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 (14CCH420 079 ± 1227 years BP, mean ± standard error (s.e.m.) years) to deeper taliks (thaw bulbs) compared to younger14CCH4in new lakes (14CCH48526 ± 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.
Methane in Gas Shows from Boreholes in Epigenetic Permafrost of Siberian Arctic
The gas shows in the permafrost zone represent a hazard for exploration, form the surface features, and are improperly estimated in the global methane budget. They contain methane of either surficial or deep-Earth origin accumulated earlier in the form of gas or gas hydrates in lithological traps in permafrost. From these traps, it rises through conduits, which have tectonic origin or are associated with permafrost degradation. We report methane fluxes from 20-m to 30-m deep boreholes, which are the artificial conduits for gas from permafrost in Siberia. The dynamics of degassing the traps was studied using static chambers, and compared to the concentration of methane in permafrost as analyzed by the headspace method and gas chromatography. More than 53 g of CH4 could be released to the atmosphere at rates exceeding 9 g of CH4 m−2 s−1 from a trap in epigenetic permafrost disconnected from traditional geological sources over a period from a few hours to several days. The amount of methane released from a borehole exceeded the amount of the gas that was enclosed in large volumes of permafrost within a diameter up to 5 meters around the borehole. Such gas shows could be by mistake assumed as permanent gas seeps, which leads to the overestimation of the role of permafrost in global warming.
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- Award ID(s):
- 1442262
- NSF-PAR ID:
- 10087813
- Date Published:
- Journal Name:
- Geosciences
- Volume:
- 9
- Issue:
- 2
- ISSN:
- 2076-3263
- Page Range / eLocation ID:
- 67
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
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This research demonstrates a new measurement and scaling approach to constrain the estimates of methane (CH4) fluxes emitted from permafrost thaw (thermokarst) lakes. Permafrost is estimated to store about 20% of the total terrestrial carbon (C) stock. Permafrost thawing releases C in part as CH4, however, there are large uncertainties in the global CH4 budget that limit the accuracy of climate change projections. Estimating how much C is released from permafrost is critical to overcome this knowledge gap. Lake CH4 fluxes are estimated by combining direct observations, geophysical mapping and satellite remote sensing along with a scaling strategy based on lake expansion rate. This research contributes to advance the understanding of CH4 fluxes from thermokarst lakes and improve atmospheric C models.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/geosciences9020067
