Reduced Sea Ice Production Due to Upwelled Oceanic Heat Flux in Prydz Bay, East Antarctica

The coastal shelf region of East Antarctica is hypothesized to be shielded from the offshore heat of Circumpolar Deep Water (CDW) due to the dynamic barrier of the Antarctic Slope Front. Yet modified CDW (mCDW) intrudes into the coastal environment in key locations, with impacts on dense shelf water formation and ocean/ice shelf interaction that remain largely unquantified. Using moored measurements and conductivity-temperature-depth-instrumented seal hydrographic data collected in Prydz Bay, East Antarctica, we find buoyancy-driven upwelling of mCDW into the subsurface (similar to 50 m) layer of the southeastern embayment. Wintertime convection extends as deep as 300 m, entraining heat of the upwelled mCDW to the surface. Accumulated sensible heat supply to the surface through deep convection during June-July reduces the potential sea ice production by 45% in the Davis Polynya, demonstrating that stronger/warmer mCDW intrusions onto the shelf will likely reduce the shelf water density and threaten Antarctic Bottom Water formation. Plain Language Summary Sea ice formation in key coastal polynyas (areas of open water or newly formed thin ice in the middle of the extensive pack ice) around Antarctica is critical to Antarctic Bottom Water (AABW) production. The intrusion of warm, modified Circumpolar Deep Water (mCDW) onto the continental shelf in East Antarctica conveys heat toward the shelf region at intermediate depth, capable of impacting sea ice formation in coastal polynyas. Here we use moored measurements and conductivity-temperature-depth-instrumented seal hydrographic data to shed new light on the interaction between sea ice formation and the heat flux from these mCDW intrusions. Due to the buoyancy contrast with the cold, dense shelf water, the warmer mCDW upwells to shallower depths in the coastal regions. When the winter freezing season begins, surface cooling and brine rejection due to sea ice formation drive convection, deepening the mixed layer and entraining heat of the upwelled mCDW to the surface, which results in a negative feedback that reduces sea ice production. The processes identified in this study have strong implications for AABW production, given the projected increase of mCDW intrusions in the future.