Sea-Ice Melt Driven by Ice-Ocean Stresses on the Mesoscale

The seasonal ice zone around both the Arctic and the Antarctic coasts is typically characterized by warm and salty waters underlying a cold and fresh layer that insulates sea-ice floating at the surface from vertical heat fluxes. Here, we explore how a mesoscale eddy field rubbing against ice at the surface can, through Ekman-induced vertical motion, bring warm waters up to the surface and partially melt the ice. We dub this the "Eddy-Ice-Pumping" (EIP) mechanism. When sea-ice is relatively motionless, underlying mesoscale eddies experience a surface drag that generates Ekman upwelling in anticyclones and downwelling in cyclones. An eddy composite analysis of a Southern Ocean eddying channel model, capturing the interaction of the mesoscale with sea-ice, shows that within the compact ice zone, the mixed layer depth (MLD) is shallow in anticyclones (similar to 20 m) due to sea-ice melt and deep in cyclones (similar to 50-200m) due to brine rejection. "EIP" warms the core of anticyclones without significantly affecting the temperature of cyclones, producing a net upward vertical heat flux that reduces the mean sea-ice thickness by 10% and shoals the MLD by 60% over the course of winter and spring. In the following months, the sea-ice thickness recovers with an overshoot, due to strong negative feedbacks associated with atmospheric cooling and salt stratification. Consequently, the effect of "EIP" does not accumulate over the years, but modulates the seasonal cycle of ice within the compact ice zone.