Temperature inversions at intermediate depths in the Antarctic Intermediate waters of the South-western Pacific

Abstract

Deep (about 1000 m) marked temperature inversions and/or salinity reversals found in conductivity- temperature-depth profiles in the south-western Pacific for 1985 to 1987 are shown to arise from confluences of different branches of the Antarctic Intermediate Water (AAIW). Salinity reversals lead to the presence of several intermediate-depth salinity minima instead of the simple broad minimum in the vertical usually described as characterizing the presence of AAIW in this area. The anomalies are found at particular locations, often near ridges and rises. Significantly differing thermohaline properties acquired by the branches from mixing over separate travel paths apparently allows the formation of temperature inversions by isentropic penetrations. Some perturbations are dynamically caused in that at least one branch of AAIW is transported in association with strong surface currents with deep influence. Other confluences are caused by topographic control on AAIW flows moving independently of surface currents. Perturbations south of the Subtropical Convergence are related to the initial formation of the AAIW, but these are not of major interest in this analysis, being well known and simply explained. Locations of perturbations correspond in some areas to flow patterns of intermediate waters inferred by researchers using historical data, and they indicate other areas where the flow patterns need more investigation. Some comments are made on East Australian Current outflows from the Tasman and Coral Seas that have considerable influence on the flow of branches of the AAIW. Other remarks are made concerning the peculiarities of the temperature-salinity regime of the Tasman Front, which inhibits the formation of temperature inversions at depth. In general, the medium- and fine-scale structure in the central Tasman is that of the stepped type, with intrusive type in other areas.