WATER CIRCULATION IN THE GULF OF CARPENTARIA

The water circulation in the Gulf of Carpentaria was modeled numerically, and the predictions of tides and tidal currents compare very satisfactorily with observations at 9 mooring sites from a five month long field study in 1986-1987. In summer, before the occurrence of tropical cyclones, the Gulf is temperature stratified with a sharp thermocline on which ride internal waves up to 20 m peak to trough. When this thermocline is present, the low-frequency circulation shows both barotropic and baroclinic components. Under tropical cyclones, the water column becomes well-mixed vertically but the water circulation is three-dimensional, with a Gulf-wide gyre in the surface waters with a return flow in the bottom waters. The wind generates seasonal sea level fluctuations of about 0.5 m in the southern region of the Gulf and these create vast salt flats. The salt flats are only tidally inundated in summer when estuarine outwelling occurs. Tidal currents and wind-driven currents interact non-linearly to produce a barotropic coastal boundary layer. There is little mixing between estuarine and offshore waters. Large-scale coastal outwelling occurs in summer when this coastally trapped water, presumably nutrient-enriched by estuarine outwelling all along the coast of the Gulf, is ejected offshore at one point in the southernmost region of the Gulf. Estuarine outwelling, coastal outwelling and coastal trapping may have profound biological implications.