THE UPPER AND LOWER LIMBS OF THE SOUTHERN OCEAN OVERTURNING CIRCULATION
Bernadette Marie SLOYAN(Department Physical Oceanography, WoodsHole Oceanographic Insitution)
Previous studies of the Southern Ocean meridional overturningcirculation suggest a large northward transportof Antarctic Bottom Water and Lower Circumpolar Deep water that is closed by southward flow of upper deep water below 1500m. In the Indian and Pacific Oceans the deep overturning cell is essentially isolated from the thermocline and intermediate waters of the subtropical gyres.In the Southern Ocean upper deep water outcrops south of theAntarctic Circumpolar Current where air-sea fluxes modify its properties to that of Antarctic Surface water and convert Antarctic Surface Water to Subantarctic Mode and AntarcticIntermediate water. These studies suggest that diapycnal fluxes due to interior ocean mixing process close the deep and upper overturning circulations.
Fine-scale mixing observation suggest that interior mixing is often quite weak. However, enhanced mixing found over rough or isolated topographyand in topographically restricted submarine canyons has renewed interest in the possibility that intense mixing at specific site in the ocean dominate the net diapycnal transport. The 2-dbar WOCE hydrographic Program (WHP) data in the Southern Ocean are used to calculate the buoyancy frequency, whose variability provides an estimate of the order of magnitude of diapycnal mixing. These calculations provide a indication of the spatial variability of mixing withinthe Southern Ocean. The diapycnal mixing is a key element of the Southern Ocean overturning circulation.