The Roles of Orbital and Meltwater Climate Forcings on the Southern Ocean Dynamics during the Last Deglaciation

The last deglacial climate evolution, from 19 to 9 thousand years before the present, represents the vital role of feedback in the Earth’s climate system. The Southern Ocean played a fundamental role by exchanging nutrients and carbon-rich deep ocean water with the surface during the last deglaciation. This study employs a fully coupled Earth system model to investigate the evolution of Southern Ocean dynamics and the roles of changes in orbital and meltwater forcings during the last deglaciation. The simulation supports that the Southern Ocean upwelling was primarily driven by windstress. The results show that the melting and formation of Antarctic sea ice feedback influenced Southern Ocean surface buoyancy flux. The increase in Antarctic sea ice melt-induced freshwater flux resulted in a steepened north-south surface salinity gradient in the Southern Ocean, which enhanced the upwelling. The single-forcing experiments indicate that the deglacial changes in orbital insolation influenced the Southern Ocean upwelling. The experiments also highlight the dominant role of Northern Hemisphere meltwater discharge in the upper and lower branch of the Meridional Overturning Circulation. Furthermore, orbital forcing shows lesser deglacial Antarctic sea ice retreat than the Northern Hemisphere meltwater forcing, which follows the bipolar seesaw mechanism.