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.

中文翻译：

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Mackenzie三角洲一个小北极湖中2年间溶解的甲烷及其碳同位素（δ13C，Δ14C）的连续动力学

在开阔水域，北极的季节性冰雪覆盖的多年冻土湖向大气中排放甲烷。但是，尽管在冰化过程中可能有大量甲烷排放到大气中，但仍未彻底解决导致冰循环下的甲烷的过程。我们使用传感器和水采样套件研究了一个小（0.2公顷）的麦肯齐河三角洲湖泊中的年度溶解甲烷动态，这些传感器和水采样套件分别在多个水柱深度分别自主和连续两年地收集了湖水样本。湖泊的物理和生物地球化学特性（温度；光；溶解氧，锰，铁和溶解甲烷（包括稳定碳和放射性碳同位素）的浓度）揭示了年度模式。在电子受体（氧气，锰和铁氧化物）耗尽或无法从水柱中进入后，冰下溶解的甲烷浓度会升高。溶解甲烷的放射性碳时代表明，碳源是最近分解的碳，而不是融化的古老永冻土。溶解于冰下的甲烷的来源包括来自沉积物的扩散通量，并且可能包括水柱的甲烷生成和/或冰下的水动力控制。结冰后，水柱仅部分混合，使一半冬天提取的溶解甲烷被微生物氧化。尽管深度氧化，地表水还是大气中甲烷的来源。冰层融化（75 mmol CH 溶解甲烷的放射性碳时代表明，碳源是最近分解的碳，而不是融化的古老永冻土。溶解于冰下的甲烷的来源包括来自沉积物的扩散通量，并且可能包括水柱的甲烷生成和/或冰下的水动力控制。结冰后，水柱仅部分混合，使一半冬季提取的溶解甲烷被微生物氧化。尽管深度氧化，地表水还是大气中甲烷的来源。冰层融化（75 mmol CH 溶解甲烷的放射性碳时代表明，碳源是最近分解的碳，而不是融化的古老永冻土。溶解于冰下的甲烷的来源包括来自沉积物的扩散通量，并且可能包括水柱的甲烷生成和/或冰下的水动力控制。结冰后，水柱仅部分混合，使一半冬天提取的溶解甲烷被微生物氧化。尽管深度氧化，地表水还是大气中甲烷的来源。冰层融化（75 mmol CH 溶解于冰下的甲烷的来源包括来自沉积物的扩散通量，并且可能包括水柱的甲烷生成和/或冰下的水动力控制。结冰后，水柱仅部分混合，使一半冬天提取的溶解甲烷被微生物氧化。尽管深度氧化，地表水还是大气中甲烷的来源。冰层融化（75 mmol CH 溶解于冰下的甲烷的来源包括来自沉积物的扩散通量，并且可能包括水柱的甲烷生成和/或冰下的水动力控制。结冰后，水柱仅部分混合，使一半冬季提取的溶解甲烷被微生物氧化。尽管深度氧化，地表水还是大气中甲烷的来源。冰层融化（75 mmol CH₄ m ^-2  d ^-1）和7月中旬的一次混合事件中，可能是由暴风雨事件驱动的。这项研究表明，精细的时间采样对于了解季节性冰雪覆盖的湖泊中溶解的甲烷过程的重要性。