Coastal upwelling along south-west Australia

In each of the main ocean basins, the surface circulation forms a gyre with poleward flow along the westward boundary of the basin and equatorward flow along the eastern margin. In addition, the eastern margins (off south America and south Africa, for example) are areas of high productivity due to upwelling. The exception to this rule is off the West Australian coast, where the Leeuwin Current transports water poleward from Exmouth to Cape Leeuwin and onto the
Great Australian Bight. Recent field data have shown that, particularly during the summer months there are several regions along the coast which are upwelling ‘hot spots’ and are due a variety of different processes. These include: (1) wind driven upwelling; (2) shelf break processes; and, (3) topographic effects due to islands and canyons (e.g. Rottnest Island). Wind-driven upwelling occurs when the southerly winds overcome alongshore pressure gradient particularly during the summer months. This results in surface layers moving offshore, colder
water upwelling onto the continental shelf, and the Leeuwin Current to migrate offshore. The main region for coastal upwelling is off the Capes region although wind driven upwelling exist along the whole coastline. At the shelf break, reversal of the shelf current system induces the formation of the shelf break ‘front’ resulting high production at the shelf break. The interaction between currents (shelf and/or deep currents) and topography results in upwelling within submarine canyons (e.g. Perth, Leeuwin) and in the lee of islands (e.g. Rottnest Island). These upwelling regions are documented through the use of field measurements obtained though moorings and ocean gliders as well as numerical modelling.