The role of the Southern Ocean/sea ice interaction in global climate change

The seasonal sea ice field of the Southern Ocean strongly modulates climate through its insulating effect and high albedo. Consequently, it plays a significant role in global climate and must be adequately parameterized for inclusion in large-scale circulation models attempting to predict the nature of global change. Recent field studies and modeling work show that the ice field is highly sensitive to the static stability and vertical fluxes in the Southern Ocean water column. Given the marginal stability and strong fluxes of the present-day water column, relatively small changes in the ocean/atmosphere may lead to significant changes in the stability or fluxes and thus the nature of the sea ice cover. These interactions link the local- and regional-scale processes to the global-scale processes, forming a Southern Ocean/climate feedback loop. The local-scale processes operate at sub-grid scales in most climate models; therefore the results of a local process-oriented model are reviewed to examine the nature of the local-regional interactions which are critical to this system. The model scalings indicate the direction and magnitude of change of the key external parameters which will drive the system toward a more stable or more unstable state. They also allow a computationally efficient means of monitoring the key elements of the ocean/sea ice system in large-scale models. The main external parameters include: (1) depth of the pycnocline; (2) ratio of heat to salt through the pycnocline; (3) strength of the pycnocline; and (4) magnitude of atmospheric cooling. The divergence of the ice field also plays an important role. Consideration of the influence of the local-regional interactions in light of anticipated changes in these variables given an assumed global warming suggest that the Southern Ocean may become less stable (initially) leading to a reduced sea ice cover and enhanced deep water ventilation