| Summary: | Methane (CHâ‚„) release to the atmosphere from thawing permafrost contributes significantly to global CHâ‚„ emissions. However, constraining the effects of thaw that control the production and emission of CHâ‚„ is needed to anticipate future Arctic emissions. Here are presented robust rate measurements of CHâ‚„ production 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 CHâ‚„ production, long term (CHâ‚„ accumulation) and short term (¹â´C tracer), produced similar average rates of 11 ± 3.5 and 9 ± 3.6 nmol cmâ»Â³ dâ»Â¹, respectively. The rates had small variations between the different lithological units, indicating homogeneous CHâ‚„ production despite heterogeneous lithology in the surface ~1 m of sediment. To estimate the total CHâ‚„ production, the CHâ‚„ production 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 CHâ‚„ in the first meter was produced further below. Interestingly, labeled ¹â´C incubations with 2-¹â´C acetate and ¹â´C COâ‚‚ indicate that variations in the pathway used by microbes to produce CHâ‚„ depends on the age and type of organic matter in the sediment, but did not appear to influence the rates at which CHâ‚„ was produced. This study demonstrates that at least half of the CHâ‚„ produced by microbial breakdown of organic matter in actively expanding thermokarst is emitted to the atmosphere, and that the majority of this CHâ‚„ is produced in the deep sediment. © 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd. This is an open access article under the terms of the Creative Commons ...
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