Southern Australia Current System based on a gridded hydrography and a high-resolution model

Earl Duran, University of New South Wales, Climate Change Research Centre, CCRC, Sydney, NSW, Australia, Helen Elizabeth Phillips, Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia, Ryo Furue, JAMSTEC, Yokohama, Japan, Paul Spence, University of New South Wales, Climate Change Research Centre, Sydney, NSW, Australia and Nathaniel L. Bindoff, University of Tasmania, Institute for Marine and Antarctic Studies, Hobart, TAS, Australia
Abstract:
The boundary currents along Australia’s western and southern shelves have been described as the longest boundary current system in the world. While the poleward flowing Leeuwin Current has received much attention, the 3-dimensional structure and transport of the boundary current system south of Australia have not previously been presented.

We describe the annual-mean structure and transport budget of the Southern Australia Current System, and the coupling between currents. The system contains the shallow (<250 m) eastward Shelf Break Currents: a series of currents along the shelf break consisting of the Leeuwin Current Extension, South Australian Current and the Zeehan Current; and counter-flowing westward Flinders Current found both offshore of, and underneath, the Shelf Break Currents. We use a climatological hydrography gridded at high resolution and a high resolution oceanic general circulation model forced by an atmospheric climatology.

We find that the Shelf Break Currents are coupled horizontally to the offshore Flinders Current through onshore Ekman drift, and vertically to the slope Flinders Current through downwelling. The combined effect of the horizontal and vertical coupling is a conversion of a widespread northward Ekman drift into downwelling near the shelf break with little impact on the eastward transport of the SBC. In contrast, onshore flows feeding into the Flinders Current are largely converted into a westward increase in its westward transport.

The annual-mean circulation bears a remarkable similarity to the zonal overturning circulation in the Leeuwin Current System off Western Australia. There, near surface eastward flow merges with the poleward-flowing Leeuwin Current, downwells into the northward-flowing Leeuwin Undercurrent and moves offshore. The boundary current systems off western and southern Australia thus both provide pathways for heat and carbon dioxide to enter thermocline and intermediate depths of the Indian Ocean.

Back to: Boundary Currents and Shelf/Deep-Ocean Exchange IV Posters