This collaborative project is a modeling study of thermobaric instability in the ocean, and its effect on deep convection in the Southern Ocean. Thermobaric instability refers to the fact that the compressibility of sea water is a non-linear function of pressure, so that a colder and fresher layer overlying a warmer and a saltier layer may be statically stable, but become unstable if it is disturbed. That this is theoretically possible has been known for a long time, but only recently has it been considered as an effect that could actually occur in the Southern Ocean, specifically as the potential explanation of the episodic occurrence of polynyas (sizable areas of open water within the sea-ice pack) in the Weddell Sea. This evaluation of the impact of thermobaricity on deep ocean convection will be based on a numerical Large Eddy Simulation (LES) model capable of simulating directly the convection plumes and large scale oceanic flow features that would be expected with intense thermobaric overturn. Based on preliminary results of an LES model initialized and forced by conditions observed during previous oceanographic cruises to the Weddell Sea, this proposed work will combine a carefully structured series of model runs with observations to identify critical overturning processes.