The Mean Summertime Circulation along Australia's Southern Shelves: A Numerical Study

Abstract

For the first time, a high-resolution regional model is developed for the slope and shelf circulation within the Great Australian Bight and for the Gulfs region of South Australia. The results indicate the extent, nature, and dynamical interaction of a variety of circulation features that are most likely to be important for the region. In particular, the positive wind stress curl south of Australia leads to an equatorward Sverdrup transport in the deep ocean, westward Flinders Current along the slope, and upwelling of the (600 m) deep permanent thermocline. The wind stress curl also leads to a seaward topographic Sverdrup transport within the wide sloping shelf of the bight and results in an anticyclonic gyre that is intensified off the Eyre Peninsula and reduced in magnitude by the joint effect of baroclinicity and topographic relief. In the western half of the bight, the seaward surface Ekman and topographic transports are shown to converge with the onshore component of the Flinders Current leading to a ridge in sea level, eastward current over the shelf break, and downwelling to 100 m or so. The shelfbreak circulation is similar farther east but is driven by the anticyclonic gyre within the bight and a trough in sea level along the shelf slope: the latter results from the geostrophic adjustment to density anomalies that arise from wintertime downwelling and the Flinders Current. Limited hydrographic, satellite, and current meter data support the existence of an eastward shelfbreak current. Off the Gulfs and Robe regions, the wind-forced coastal currents are to the northwest and both the model and observations indicate that upwelling occurs to depths of up to 150 m.