Dynamics of Spencer Gulf: Effects of Evaporation, Heating and Tides

The importance of wind stress, freshwater (FWF) flux, net heat (NHF) flux, and tides to the circulation within Spencer Gulf (SG), South Australia, was investigated through a series of increasingly complex numerical experiments using ROMS. The dynamics of the circulation driven by thermohaline forcing and the effects of tides were investigated using simulations progressively forced with FWF, FWF and NHF and finally FWF, NHF and tides. All simulations show a cyclonic circulation within SG and with generally fresher water entering the gulf on the western side and relatively saltier water leaving the gulf on the eastern side near the bottom. The results also show that eddies are formed at the upper regions of the gulf due to baroclinic instability and propagate towards the shelf transporting salty water. For the NHF and FWF experiment, the cyclonic circulation is intensified during winter and very weak during summer. The combination of FWF and NHF is sufficient to block gulf-shelf exchange during summer and limit the generation of eddies to winter. The addition of tides leads to a 14 day spring-neap modulation of the circulation and formation of eddies. Tides also act to reduce the residual circulation and the salt exchange with the shelf, resulting in a large increase in the salinity in the upper region of SG. The observational and numerical results obtained here show that the pulses of high salinity waters previously observed in SG are indeed eddies. These results are new and in line with their Mediterranean cousins, we suggest the eddies here be named Speddies.

Carlos Teixeira - Universidade Federal do Ceara/ LABOMAR
John Middleton - SARDI Aquatic Sciences