On Antarctic Intermediate Water Mass Formation in Ocean General Circulation Models

Antarctic Intermediate Water is formed at the high mid-latitudes of the Southern Ocean. In many ocean general circulation model simulations with coarse resolution and a z-coordinate, a mid-depth salinity minimum characteristic of this intermediate water is reproduced. However, for the real ocean it remains unclear which are the dominant processes in the formation of this water mass and which are the source regions for contributing surface waters. To elucidate such processes and quantify intermediate water formation rates, two experiments with an ocean general circulation model were conducted. In one experiment, the traditional parameterization of horizontal and vertical mixing was applied, while the second model included the Gent-McWilliams parameterization for an eddy-induced transport velocity. In the latter application, the production and meridional export of intermediate water was found to be larger than in the first experiment. Furthermore, mid-latitude convective mixing, which had been argued to be the main intermediate water mass formation mechanism was found to be not as important as in previous model results. Passive tracer experiments indicated that diapycnal mixing and circumpolar subduction might also play important roles as water mass formation processes in this particular ocean circulation model.