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Continuous Dynamics of Dissolved Methane Over 2 Years and its Carbon Isotopes (δ13C, Δ14C) in a Small Arctic Lake in the Mackenzie Delta
Seasonally ice‐covered permafrost lakes in the Arctic emit methane to the atmosphere during periods of open‐water. However, processes contributing to methane cycling under‐ice have not been thoroughly addressed despite the potential for significant methane emission to the atmosphere at ice‐out. We s...
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| Published in: | Journal of geophysical research. Biogeosciences 2021-03, Vol.126 (3), p.n/a |
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| Main Authors: | , , , , , , |
| Format: | Article |
| Language: | English |
| Subjects: | |
| Citations: | Items that this one cites Items that cite this one |
| Online Access: | Get full text |
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| Summary: | Seasonally ice‐covered permafrost lakes in the Arctic emit methane to the atmosphere during periods of open‐water. However, processes contributing to methane cycling under‐ice have not been thoroughly addressed despite the potential for significant methane emission to the atmosphere at ice‐out. We studied annual dissolved methane dynamics within a small (0.2 ha) Mackenzie River Delta lake using sensor and water sampling packages that autonomously and continuously collected lake water samples, respectively, for two years at multiple water column depths. Lake physical and biogeochemical properties (temperature; light; concentrations of dissolved oxygen, manganese, iron, and dissolved methane, including stable carbon, and radiocarbon isotopes) revealed annual patterns. Dissolved methane concentrations increase under‐ice after electron acceptors (oxygen, manganese, and iron oxides) are depleted or inaccessible from the water column. The radiocarbon age of dissolved methane suggests a source from recently decomposed carbon as opposed to thawed ancient permafrost. Sources of dissolved methane under‐ice include a diffusive flux from the sediments and may include water column methanogenesis and/or under‐ice hydrodynamic controls. Following ice‐out, the water column only partially mixes allowing half of the winter‐derived dissolved methane to be microbially oxidized. Despite oxidation at depth, surface water was a source of methane to the atmosphere. The greatest diffusive fluxes to the atmosphere occurred following ice‐out (75 mmol CH4 m−2 d−1) and during a mixing episode in mid‐July, likely driven by a storm event. This study demonstrates the importance of fine‐scale temporal sampling to understand dissolved methane processes in seasonally ice‐covered lakes.
Plain Language Summary
Atmospheric greenhouse gases, such as methane, contribute to climate change. Methane is naturally released to the atmosphere from Arctic lakes where it is formed by methane‐producing microorganisms. We observed changes to dissolved methane concentrations in an Arctic lake in the Mackenzie River Delta during the entire year, using autonomous and continuous samplers to collect water over a 2‐year period at multiple depths. Methane was produced by microbial decomposition of recently deceased plant material (i.e., macrophytes) that sank to the lake floor or remained in the water column. Dissolved methane concentrations increased at a constant rate when ice covered the lake, then immediately |
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| ISSN: | 2169-8953 2169-8961 |
| DOI: | 10.1029/2020JG006038 |