Major Boundary Currents and Inter-basin Flows

The East Australian Current (EAC) is the major western boundary current of the South Pacific Gyre, flowing from the southern Coral Sea and along the northern NSW coast (Ridgway and Dunn 2003). It is Australia’s largest current with a variable annual transport. The core of the EAC is centred over the continental slope, although its coastal presence is felt through eddy encroachment over the shelf.

The EAC flows along Australia’s east coast in four stages: 1) the formation in the south Coral Sea; 2) the intensification of the current off northern NSW; 3) the separation stage from the coast (31-32ºS); and then 4) evolving into eddies and coastal fingers off southern NSW, eastern Victoria and to Tasmania. Recent work has shown that over the past 30 years the poleward transport of water within EAC eddies has increased significantly (especially from 2005 onwards). The primary inter-basin flow for this region is the Tasman Outflow, where the EAC penetrates into the Southern Ocean.

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

Fluxes: 

  • How do the mass, heat, and salt transports of the EAC and the coastal currents off NSW vary on seasonal, interannual, and multi-decadal timescale?
  • How does the EAC feed back into the climate system?
  • What are the temporal variations in the advective and air-sea components of the EAC heat flux contributions?
  • Can an index for the strengthening of the EAC be developed for use in correlating different parameters?
  • How do air-sea interactions with EAC warm core eddies influence the strength and path of East Coast Lows?

Drivers:

  • What is the cause of variations in current strength?
  • What forcing mechanisms drive the seasonal cycles of the EAC?
  • What is the relationship between boundary currents off NSW and modes of climate variability and change?

Dynamics:

  • What processes govern the EAC?
  • What processes govern the formation and propagation of eddies by the EAC?  How do these processes vary temporally, and how are they related to the mean EAC flow?
  • What processes govern the separation of the EAC?