Methane production controls in a young thermokarst lake formed by abrupt permafrost thaw

• Published in: Global Change Biology
• Main Authors: Pellerin, André, Lotem, Noam, Walter Anthony, Katey, Eliani Russak, Efrat, Hasson, Nicholas, Røy, Hans, Chanton, Jeffrey P., Sivan, Orit
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2022
• Subjects: Arctic; Talik; Trail Lake; permafrost; Thermokarst; Alaska
• Online Access: https://authors.library.caltech.edu/113757/; https://authors.library.caltech.edu/113757/4/Global%20Change%20Biology%20-%202022%20-%20Pellerin%20-%20Methane%20production%20controls%20in%20a%20young%20thermokarst%20lake%20formed%20by%20abrupt.pdf; https://authors.library.caltech.edu/113757/5/gcb16151-sup-0001-supinfo.docx; https://authors.library.caltech.edu/113757/6/gcb16151-sup-0002-data.xlsx; https://resolver.caltech.edu/CaltechAUTHORS:20220304-60918000

Methane (CH₄) release to the atmosphere from thawing permafrost contributes significantly to global CH₄ emissions. However, constraining the effects of thaw that control the production and emission of CH₄ is needed to anticipate future Arctic emissions. Here are presented robust rate measurements of CH₄ 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 CH₄ production, long term (CH₄ accumulation) 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 CH₄ production despite heterogeneous lithology in the surface ~1 m of sediment. To estimate the total CH₄ production, the CH₄ 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 CH₄ in the first meter was produced further below. Interestingly, labeled ¹⁴C incubations with 2-¹⁴C acetate and ¹⁴C CO₂ indicate that variations in the pathway used by microbes to produce CH₄ depends 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 CH₄ produced by microbial breakdown of organic matter in actively expanding thermokarst is emitted to the atmosphere, and that the majority of this CH₄ is produced in the deep sediment.