Major Boundary Currents and Inter-basin Flows

The summer time (February 2008) SST for the SA-IMOS region. Arrows denote estimated surface velocities (courtesy David Griffin, CSIRO).
The summer time (February 2008) SST for the SA-IMOS region.

The slope region of Australia‚Äôs southern shelves hosts the Flinders Current (FC) 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 (LC), the bottom boundary layer of the FC 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 LC enters the Great Australian Bight (GAB) as a shelf current and extends as far as the Eyre Peninsula. To the south east, the mean winter winds drive this shelf boundary current into Bass Strait and along the west coast of Tasmania. During summer, the coastal winds often reverse to the northwest and the influence of the eastward LC is smaller. The episodic south-easterly winds can drive shelf flows to the northwest and west in the GAB. 

The following high-level science questions will guide the South Australia IMOS observing strategy in this area:

a) Limited observations and modelling studies indicate that the FC does exist and is likely much stronger in the west.  Is this the case and how well connected is it to the Tasman Outflow, and Leeuwin Undercurrent? This might be answered by additional CTD sampling and moorings off the southern tip of Tasmania and in the GAB. Sea gliders could be used to map the CTD structure down to 1,000 m.

b) Evidence exists for summer downwelling in the central GAB. Can this be confirmed using repeated CTD sampling, glider data and associated model development?

c) Does the ACW exist? Long time series of temperature observations at the KI National reference station are needed.

d) What is the importance of mesoscale eddies in the central and eastern GAB? Data assimilating hydrodynamic models are needed.