[1] In this study, we present evidence that Antarctic and Arctic sea ice act as sink for atmospheric CO 2 during periods of snowmelt and surface flooding. The CO 2 flux measured directly at the flooded sea ice surface (F flood ) constituted a net CO 2 sink of À1.1 6 0.9 mmol C m À2 d À1 (mean 6 1 SD), which was an order of magnitude higher than the flux measured at the snow-air surface (F snow ) and bare ice surface (F ice ). The F snow /F flood ratio decreased with increasing water equivalent of snow and superimposed-ice, suggesting that the properties of snow and superimposed-ice formation affect the magnitude of the CO 2 flux. The F snow /F flood ratio ranged from 0.1 to 0.5, illustrating that 50-90% of the potential flux at the flooded surface was reduced due to the presence of snow/superimposed-ice. Hence, snow cover properties and superimposed-ice play an important role in the CO 2 fluxes across the sea ice-snow-atmosphere interface.Citation: Nomura, D., M.A. Granskog, P.Assmy, D. Simizu, and G. Hashida (2013), Arctic and Antarctic sea ice acts as a sinkfor atmospheric CO 2 during periods of snowmelt and surface flooding,

Mass loss from the Antarctic ice sheet, Earth’s largest freshwater reservoir, results directly in global sea-level rise and Southern Ocean freshening. Observational and modeling studies have demonstrated that ice shelf basal melting, resulting from the inflow of warm water onto the Antarctic continental shelf, plays a key role in the ice sheet’s mass balance. In recent decades, warm ocean-cryosphere interaction in the Amundsen and Bellingshausen seas has received a great deal of attention. However, except for Totten Ice Shelf, East Antarctic ice shelves typically have cold ice cavities with low basal melt rates. Here we present direct observational evidence of high basal melt rates (7–16 m yr −1 ) beneath an East Antarctic ice shelf, Shirase Glacier Tongue, driven by southward-flowing warm water guided by a deep continuous trough extending to the continental slope. The strength of the alongshore wind controls the thickness of the inflowing warm water layer and the rate of basal melting.

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