Summer sea surface temperature fronts and elevated chlorophyll-a in the entrance to Spencer Gulf, South Australia

Historical and recent oceanographic cruise data, MODIS chlorophyll-a satellite data, and an analytical model are used to examine SST fronts in the entrance to Spencer Gulf, South Australia. The fronts (2–3 °C) due to the contrast between warm Spencer Gulf waters and cooler waters of the continental shelf are readily observable on satellite imagery. Three water masses: cool, fresh upwelled shelf water; warm, salty Great Australian Bight water; and very warm and salty Spencer Gulf bottom water occupy the area. In consequence a summer density minimum is formed at the entrance to Spencer Gulf. The analytical model predicts that this thermohaline structure sets up an ageostrophic circulation, which favours upwelling in the central portion of the entrance. This is confirmed by the satellite data which show an increased chlorophyll-a concentration in the vicinity of the upwelling.

► Data from three cruises indicate a summer density minimum in the mouth of Spencer Gulf, South Australia.
► This dynamic structure leads to a unique upwelling system in the form of a stationary tropical cyclone.
► MODIS satellite and cruise observations confirm the summer production of chlorophyll-a in this region.