Abstract: The importance of winds, fresh water (FWF) and net heat (NHF) fluxes and tides to the circulation within Spencer Gulf (SG), South Australia, was investigated through a series of increasingly complex numerical experiments using the ROMS model. The local effects of the wind-stress were determined by forcing with 10-day periodic up-gulf and cross-gulf winds. When driven by an up-gulf periodic wind, the barotropic circulation consists of strong down-wind currents on the coastal regions of the gulf and a return flow with up-wind currents in the deep central SG. When forced by a cross-gulf periodic wind, a strongly cyclonic (anti-cyclonic) circulation is found when the winds are to the east (west). The effects of remote wind forcing were examined using a 10-day periodic CSW paddle at the western model boundary and the circulation within the gulf was found to be very small. The inclusion of stratification significantly changes the wind-driven circulation by enhancing or reducing the circulation depending on the wind direction. The dynamics of the circulation driven by thermohaline forcing and the effects of tides were investigated using a series of simulations progressively forced with FWF, FWF and NHF and finally FWF, NHF and tides. All simulations show a cyclonic circulation within SG and generally with fresher water entering the gulf on the western side and relative 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.

My PhD has been done at  University of New South Wales, and at South Australia Research and Development  Institute  (SARDI Aquatic Centre). .

Supervisor: Dr. John Middleton

Finished in August, 2010.

Link to my thesis (3.4 Mb)