Role of methanotrophy in a high‐methane emitting thermokarst lake

This is the authors' abstract. We don't add key points for this paper.

Thermokarst (thaw) lakes are projected to be an increasing source of atmospheric methane (CH 4 ), a potent greenhouse gas, as climate warms and permafrost thaws. However, the magnitude of CH 4 cycling, particularly the role of aerobic CH 4 oxidation (methanotrophy), among thermokarst lakes, is not well constrained. This study assesses year‐round methanotrophic CH 4 oxidation in relation to total CH 4 emissions at Big Trail Lake, a young Interior Alaska thermokarst lake which formed in icy, Pleistocene‐aged Yedoma permafrost and which is characterized by large CH 4 emissions. By integrating field measurements, incubations, and modeling, we demonstrate that methanotrophy reduced dissolved gas emissions (i.e., diffusive fluxes) by 57–100% during the open water period. However, its impact on total annual lake emissions was much lower (12–19%) due to a paucity of oxygen in the ice‐covered water column during winter and high rates of ebullition that bypass methanotrophy in summer. Methanotrophy was most active during short shoulder seasons when snowmelt and autumnal turnover supplied oxygen to CH 4 ‐rich water columns, yet these periods were insufficient to significantly offset the annual CH 4 budget dominated by ebullition emissions. Model predictions for scenarios of shortened ice‐cover periods due to future warming suggest marginal increases in CH 4 emissions. This study highlights the limited role of methanotrophy against the backdrop of vast permafrost‐derived CH 4 lake emissions in a warming Arctic.