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.
Northern post-glacial lakes are significant, increasing sources of atmospheric carbon through ebullition (bubbling) of microbially-produced methane (CH4) from sediments. Ebullitive CH4flux correlates strongly with temperature, reflecting that solar radiation drives emissions. However, here we show that the slope of the temperature-CH4flux relationship differs spatially across two post-glacial lakes in Sweden. We compared these CH4emission patterns with sediment microbial (metagenomic and amplicon), isotopic, and geochemical data. The temperature-associated increase in CH4emissions was greater in lake middles—where methanogens were more abundant—than edges, and sediment communities were distinct between edges and middles. Microbial abundances, including those of CH4-cycling microorganisms and syntrophs, were predictive of porewater CH4concentrations. Results suggest that deeper lake regions, which currently emit less CH4than shallower edges, could add substantially to CH4emissions in a warmer Arctic and that CH4emission predictions may be improved by accounting for spatial variations in sediment microbiota.
more » « less- Award ID(s):
- 2022070
- NSF-PAR ID:
- 10305337
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Methane (CH4) release to the atmosphere from thawing permafrost contributes significantly to global CH4emissions. However, constraining the effects of thaw that control the production and emission of CH4is needed to anticipate future Arctic emissions. Here are presented robust rate measurements of CH4production and cycling in a region of rapidly degrading permafrost. Big Trail Lake, located in central Alaska, is a young, actively expanding thermokarst lake. The lake was investigated by taking two 1 m cores of sediment from different regions. Two independent methods of measuring microbial CH4 production, long term (CH4accumulation) and short term (14C tracer), produced similar average rates of 11 ± 3.5 and 9 ± 3.6 nmol cm−3 d−1, respectively. The rates had small variations between the different lithological units, indicating homogeneous CH4production despite heterogeneous lithology in the surface ~1 m of sediment. To estimate the total CH4production, the CH4production rates were multiplied through the 10–15 m deep talik (thaw bulb). This estimate suggests that CH4 production is higher than emission by a maximum factor of ~2, which is less than previous estimates. Stable and radioactive carbon isotope measurements showed that 50% of dissolved CH4in the first meter was produced further below. Interestingly, labeled14C incubations with 2‐14C acetate and14C CO2indicate that variations in the pathway used by microbes to produce CH4depends on the age and type of organic matter in the sediment, but did not appear to influence the rates at which CH4 was produced. This study demonstrates that at least half of the CH4produced by microbial breakdown of organic matter in actively expanding thermokarst is emitted to the atmosphere, and that the majority of this CH4is produced in the deep sediment.
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Abstract The ongoing global temperature rise enhances permafrost thaw in the Arctic, allowing Pleistocene‐aged frozen soil organic matter to become available for microbial degradation and production of greenhouse gases, particularly methane. Here, we examined the extent and mechanism of anaerobic oxidation of methane (AOM) in the sediments of four interior Alaska thermokarst lakes, which formed and continue to expand as a result of ice‐rich permafrost thaw. In cores of surface (~ 1 m) lake sediments we quantified methane production (methanogenesis) and AOM rates using anaerobic incubation experiments in low (4°C) and high (16°C) temperatures. Methanogenesis rates were measured by the accumulation of methane over ~ 90 d, whereas AOM rates were measured by adding labeled‐13CH4and measuring the produced dissolved inorganic13C. Our results demonstrate that while methanogenesis was vigorous in these anoxic sediments, AOM was lower by two orders of magnitude. In almost all sediment depths and temperatures, AOM rates remained less than 2% of the methanogenesis rates. Experimental evidence indicates that the AOM is strongly related to methanogens, as the addition of a methanogens' inhibitor prevented AOM. Variety of electron acceptor additions did not stimulate AOM, and methanotrophs were scarcely detected. These observations suggest that the AOM signals in the incubation experiments might be a result of enzymatic reversibility (“back‐flux”) during CH4production, rather than thermodynamically favorable AOM. Regardless of the mechanism, the quantitative results show that near surface (< 1‐m) thermokarst sediments in interior Alaska have little to no buffer mechanisms capable of attenuating methane production in a warming climate.
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Accelerated warming in the Arctic has led to concern regarding the amount of carbon emission potential from Arctic water bodies. Yet, aquatic carbon dioxide (CO 2 ) and methane (CH 4 ) flux measurements remain scarce, particularly at high resolution and over long periods of time. Effluxes of methane (CH 4 ) and carbon dioxide (CO 2 ) from Toolik Lake, a deep glacial lake in northern Alaska, were measured for the first time with the direct eddy covariance (EC) flux technique during six ice-free lake periods (2010–2015). CO 2 flux estimates from the lake (daily average efflux of 16.7 ± 5.3 mmol m −2 d −1 ) were in good agreement with earlier estimates from 1975–1989 using different methods. CH 4 effluxes in 2010–2015 (averaging 0.13 ± 0.06 mmol m −2 d −1 ) showed an interannual variation that was 4.1 times greater than median diel variations, but mean fluxes were almost one order of magnitude lower than earlier estimates obtained from single water samples in 1990 and 2011–2012. The overall global warming potential (GWP) of Toolik Lake is thus governed mostly by CO 2 effluxes, contributing 86–93% of the ice-free period GWP of 26–90 g CO 2,eq m −2 . Diel variation in fluxes was also important, with up to a 2-fold (CH 4 ) to 4-fold (CO 2 ) difference between the highest nighttime and lowest daytime effluxes. Within the summer ice-free period, on average, CH 4 fluxes increased 2-fold during the first half of the summer, then remained almost constant, whereas CO 2 effluxes remained almost constant over the entire summer, ending with a linear increase during the last 1–2 weeks of measurements. Due to the cold bottom temperatures of this 26 m deep lake, and the absence of ebullition and episodic flux events, Toolik Lake and other deep glacial lakes are likely not hot spots for greenhouse gas emissions, but they still contribute to the overall GWP of the Arctic.more » « less
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Abstract Lakes and reservoirs collectively contribute significant amounts of methane (CH4) to the global atmosphere. If CH4production were not at least partially balanced by consumption (oxidation) in most of these systems, they could potentially emit an order of magnitude or more CH4. The impacts of environmental drivers such as trophic status, temperature, and latitude on CH4production, CH4oxidation, and the balance of the two processes influence current and future patterns of freshwater CH4emissions. Using CH4production and oxidation rates measured with a common methodology (incubations) from over 60 different lakes and reservoirs, we provide novel evidence for lower sediment CH4oxidation efficiency at high sediment CH4production rates. We also show a strong positive correlation between sediment CH4production and lake trophic status. Our results suggest that less efficient CH4consumption at high CH4production rates could help explain greater surface emissions often observed in eutrophic lakes globally.
