Articles | Volume 11, issue 23
Research article
08 Dec 2014
Research article |  | 08 Dec 2014

Modeling the impediment of methane ebullition bubbles by seasonal lake ice

S. Greene, K. M. Walter Anthony, D. Archer, A. Sepulveda-Jauregui, and K. Martinez-Cruz

Abstract. Microbial methane (CH4) ebullition (bubbling) from anoxic lake sediments comprises a globally significant flux to the atmosphere, but ebullition bubbles in temperate and polar lakes can be trapped by winter ice cover and later released during spring thaw. This "ice-bubble storage" (IBS) constitutes a novel mode of CH4 emission. Before bubbles are encapsulated by downward-growing ice, some of their CH4 dissolves into the lake water, where it may be subject to oxidation. We present field characterization and a model of the annual CH4 cycle in Goldstream Lake, a thermokarst (thaw) lake in interior Alaska. We find that summertime ebullition dominates annual CH4 emissions to the atmosphere. Eighty percent of CH4 in bubbles trapped by ice dissolves into the lake water column in winter, and about half of that is oxidized. The ice growth rate and the magnitude of the CH4 ebullition flux are important controlling factors of bubble dissolution. Seven percent of annual ebullition CH4 is trapped as IBS and later emitted as ice melts. In a future warmer climate, there will likely be less seasonal ice cover, less IBS, less CH4 dissolution from trapped bubbles, and greater CH4 emissions from northern lakes.

Short summary
Methane (CH4) bubbles emitted from the anoxic sediments of northern lakes constitute a significant methane flux to the atmosphere, but entrapment by seasonal lake ice impedes bubble release to the atmosphere. Using numerical modeling and field measurement of a lake in Alaska, we found that 80% of CH4 in ice-trapped bubbles dissolves into the water column. Microbes consume half of that CH4. Emission by bubbling is greatest in summer but continues in winter through some open holes in lake ice.
Final-revised paper