Oceanic response to interactive momentum flux over Southern Hemisphere sea ice

Abstract

The Southern Ocean (SO) winds affect the global ocean circulation via their direct atmosphere-to-ocean wind-stirring effects remotely driving the North Atlantic (NA) overturning. In this study, an indirect atmosphere-sea ice-ocean buoyancy-driven effects under the SO winds are investigated in the framework of a coupled sea ice-ocean general circulation model. Over the SO sea ice, an interactive momentum flux (IMF) forcing is introduced to investigate the effect of the strength of the sea ice-atmosphere coupling on the long-term ocean circulation. To estimate the robustness of the oceanic response to the IMF parameterization, it is applied to three fundamentally different reference experiments. By allowing the strength of the momentum flux between atmosphere and sea ice to vary in response to the simulated sea ice conditions, the IMF enhances wind-driven sea ice divergence to increase the fraction of leads and polynyas, which intensifies convection. The ensuing increase in dense water formation along Antarctica increases the amount pf Antarctic Bottom Water being formed, which intensifies the Southern Hemisphere (SH) overturning and indirectly weakens the NA overturning. As a result of these hemispheric changes, the meridional density gradient across the Antarctic Circumpolar Current (ACC) increases, leading to an increase in the ACC. This study shows that the SH atmosphere-sea ice-ocean system can play an active, primary role in the global ocean circulation and provides insights on the possible linkage between the SH winds, the SH overturning, and the NA overturning via buoyancy-driven effects associated with SO sea ice. Copyright 2009 by the American Geophysical Union.