Physical controls on the storage of methane in landfast sea ice

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Abstract

<p><strong>Abstract.</strong> We report on methane (CH<sub>4</sub>) dynamics in landfast sea ice, brine and under-ice seawater at Barrow in 2009. The CH<sub>4</sub> concentrations in under-ice water ranged from 25.9 to 116.4 nmol L<sup>&amp;minus;1</sup><sub>sw</sub>, indicating a supersaturation of 700 to 3100% relative to the atmosphere. In comparison, the CH<sub>4</sub> concentrations in sea ice ranged from 3.4 to 17.2 nmol L<sup>&amp;minus;1</sup><sub>ice</sub> and the deduced CH<sub>4</sub> concentrations in brine from 13.2 to 677.7 nmol L<sup>&amp;minus;1</sup><sub>brine</sub>. We investigated the processes underlying the difference in CH<sub>4</sub> concentrations between sea ice, brine and under-ice water and suggest that biological controls on the storage of CH<sub>4</sub> in ice were minor in comparison to the physical controls. Two physical processes regulated the storage of CH<sub>4</sub> in our landfast ice samples: bubble formation within the ice and sea ice permeability. Gas bubble formation due to brine concentration and solubility decrease favoured the accumulation of CH<sub>4</sub> in the ice at the beginning of ice growth. CH<sub>4</sub> retention in sea ice was then twice as efficient as that of salt; this also explains the overall higher CH<sub>4</sub> concentrations in brine than in the under-ice water. As sea ice thickened, gas bubble formation became less efficient, CH<sub>4</sub> was then mainly trapped in the dissolved state. The increase of sea ice permeability during ice melt marked the end of CH<sub>4</sub> storage.</p>

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Zhou, J., Tison, J. L., Carnat, G., Geilfus, N. X., & Delille, B. (2014). Physical controls on the storage of methane in landfast sea ice. Cryosphere, 8(3), 1019–1029. https://doi.org/10.5194/tc-8-1019-2014

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