Modeling the impediment of methane ebullition bubbles by seasonal lake ice

[摘要] Microbial methane (CH₄) ebullition (bubbling) from anoxic lakesediments comprises a globally significant flux to the atmosphere, butebullition bubbles in temperate and polar lakes can be trapped by winter icecover and later released during spring thaw. This "ice-bubble storage"(IBS) constitutes a novel mode of CH₄ emission. Before bubbles areencapsulated by downward-growing ice, some of their CH₄ dissolves intothe lake water, where it may be subject to oxidation. We present fieldcharacterization and a model of the annual CH₄ cycle in GoldstreamLake, a thermokarst (thaw) lake in interior Alaska. We find that summertimeebullition dominates annual CH₄ emissions to the atmosphere. Eightypercent of CH₄ in bubbles trapped by ice dissolves into the lake watercolumn in winter, and about half of that is oxidized. The ice growth rateand the magnitude of the CH₄ ebullition flux are important controllingfactors of bubble dissolution. Seven percent of annual ebullition CH₄is trapped as IBS and later emitted as ice melts. In a future warmerclimate, there will likely be less seasonal ice cover, less IBS, lessCH₄ dissolution from trapped bubbles, and greater CH₄ emissionsfrom northern lakes.

[学科分类] 地球化学与岩石