SST fronts in inverse estuaries, South Australia-indicators of reduced gulf-shlef exchange

Abstract

During the austral summer, the entrance to the South Australian gulfs exhibits sea surface temperature (SST) fronts of between 3 and 3.5°C that are clearly discernible on NOAA/AVHRR imagery. The surface fronts are formed by seasonal juxtaposition of relatively warm gulf and cooler bight water. Field surveys indicate that the SST fronts coexist with and overlay strong benthic temperature and salinity differentials of 74°C and 1.2-1.5, respectively. Density variation in the entrance to both gulfs exhibits a density minimum at all depths and suggests bottom convergence of density currents that effectively isolates gulf from shelf waters during the summer. Analysis of field temperature-salinity data, using the 1-atmosphere equation of state, indicates that the density minimum is formed by mutual compensation of the salinity and temperature dependent terms. The effect of the combined salinitytemperature dependent terms is less but not insignificant. The value of satellite SST imagery as a tool to signal periods of reduced communication between the gulfs and the shelf is revealed.