The Impact of Southern Ocean Sea Ice in a Global Ocean Model

Most of the Southern Ocean (SO) is marginally stably stratified and thus prone to enhanced convection and possibly bottom-water formation whenever the upper ocean is cooled or made more saline by ice formation. Sea ice modifies the heat and freshwater fluxes, which in turn constitute a critical surface condition in this sensitive region of intense vertical exchange. The authors investigate the effect of SO sea ice in modifying these fluxes in a global, coarse-resolution, primitive-equation ocean general circulation model, which has been coupled to a comprehensive dynamic–thermodynamic sea ice model. Specifically, the long-term impact of a series of modifications in the formulation of the sea ice model and its forcing on quantities such as the overturning circulation, the deep ocean water-mass characteristics, the sea ice thickness, the strength of convection, as well as the strength of the major volume transports are investigated. The results indicate that the rate of Antarctic bottom-water formation is strongly coupled to the local sea ice processes in the SO, which in turn vary sensitively depending on their model formulation and their forcing from the atmosphere. The largest impacts arise from the effect of brine release due to sea ice formation and that of employing more variable winds over SO sea ice.