Major Boundary Currents and Inter-basin Flows

The south-eastern Indian Ocean has a complex structure of major currents that have direct impacts on marine ecosystems and climate in Northern and Western Australia. The Indonesian Throughflow is a critical “choke-point” in the distribution of heat on a global scale, and hence has an impact on global and regional climate.

Further south, the Leeuwin Current is an anomalous eastern boundary current that brings warm, lower salinity tropical waters southward along the west coast of Australia modulating the marine ecosystem. The other boundary current systems include the Holloway Current, the seasonal south-westward flow along the northwest coast of Australia; the Leeuwin Undercurrent, the continuation of the Tasman Outflow and the Flinders Current. Sustained regional observations are required to describe, understand and model the interplay of variability and change in regional currents and the cascade of scales from ocean-basins to local ecosystems.

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

  • What is the nature of ENSO signals propagating along the NW, west, and SW coasts of Australia? How much energy is transmitted from the Pacific versus generated by forcing in the Indian Ocean?
  • What are the relative roles of local and remote forcing driving the seasonal, inter-annual, and decadal variability of the Leeuwin Current, its eddy fields and its relationship to the Indonesian Throughflow?
  • What is the role of topography in the generation of Leeuwin Current eddies?
  • What are the mechanisms by which the Leeuwin Current and its mesoscale eddies drive the alongshore, cross-shelf exchanges?
  • What drives the upper ocean heat and freshwater balances in the ocean boundary current systems off WA?
  • What are drivers of the extreme Leeuwin Current strength and marine heat wave (Ningaloo Nino) off the coast of WA 
  • What is the predictability of Ningaloo Nino and other climate extreme events in WA?
  • What offshore mechanisms dominate the supply of nutrient to surface waters over the continental shelf, in the Leeuwin Current and offshore?