Major Boundary Currents and Inter-basin Flows
The slope region of Australia’s southern shelves hosts the Flinders Current that appears to be fed in the east by the Tasman Outflow, a remnant of the East Australian Current (EAC). As with the EAC and Leeuwin Current, the bottom boundary layer of the Flinders Current is upwelling favourable so that the onshore exchange of nutrients will be enhanced. In common with these other boundary currents, it also flows with the shelf slope on the right, so that upwelling through canyons can also occur.
During winter, the Leeuwin Current enters the Great Australian Bight as a shelf current and extends as far as the Eyre Peninsula (Cirano and Middleton 2004). To the south east, the mean winter winds extend the current into Bass Strait and also along the west coast of Tasmania. Evidence suggests that the shelf currents during winter and Leeuwin Current off Perth, are both modulated by 4 to 7 year ENSO events that can affect the alongshore transport of marine biota from Cape Leeuwin to South Australia, although this has yet to be quantified. During summer El Nino events colder more nutrient rich water is available to the shelf ecosystems. The boundary currents may also be subject to the Antarctic Circumpolar Wave with temperature changes along Australia’s southern shelves of up to 1C, although its impact on boundary circulation is unknown.
Key Science Questions
- Are internal waves significant and are they a source of shelf-slope boundary mixing?
East Australian Current system
- What is the temporal and spatial variability and nature of the Flinders Current/Leeuwin Current and coastal shelf boundary currents including effects of seasonal and ENSO forcing?
- What is the connectivity of the boundary currents to those off Western Australia and the Tasman Outflow both from a physical viewpoint and from the perspective of the transport of marine biota, pathogens and invasive species?
Antarctic Circumpolar Current
- Is the Antarctic Circumpolar Wave detectable and significant?