The Influence of Antarctic Sea Ice Distribution on the Southern Ocean Overturning Circulation for the Past 20,000 Years

Abstract

The changes invoked in the Southern Ocean physics are dynamically linked to Southern Hemisphere westerlies, ocean currents, and Antarctic sea ice distribution. Therefore, it is necessary to understand the response of the Southern Ocean dynamics to the Antarctic sea ice distribution on a basin scale. This modeling study employs a fully coupled Earth system model to investigate the effect of Antarctic Sea ice distribution on the Southern Ocean Overturning circulation during the past twenty thousand years before the present. The simulation shows that the Southern Ocean surface buoyancy flux influences the Southern Ocean overturning circulation. The results indicate that the formation and melting of Antarctic sea ice feedback affect the coverage of surface buoyancy flux over the Southern Ocean. The simulated sea ice boundary (ocean surface area covered with more than a 5% sea ice fraction) almost demarcates the boundary between the upper and lower meridional overturning cells in the Southern Ocean. The Antarctic quasi-permanent sea ice boundary (ocean surface area covered with more than eighty percent sea ice fraction) overlaps with the transition of surface buoyancy flux from positive (surface buoyancy gain) to negative (surface buoyancy loss). Moreover, similar to the Antarctic sea ice coverage, the negative surface buoyancy flux zone has displaced polewards for the past twenty thousand years except for about 14.1 thousand years. Our study highlights that the melting and formation of Antarctic sea ice modulates the Southern Ocean surface buoyancy flux, which affects the Southern Ocean Overturning circulation.