Multi-decadal Ocean Change

Multi-decadal change in circulation can arise from long-term changes to wind stress curl in the South Pacific and Southern Ocean that act to drive the East Australian Current (EAC) and Flinders Current (FC), respectively. In the context of the latter, changes in the wind-stress curl can also affect the degree of downwelling found in the central Great Australian Bight (GAB). Intensification of the Indonesian through-flow can also enhance the Leeuwin Current and the shelf circulation in the GAB during winter. The frequency of El NiƱo events appears to have increased over the last century and if continued could see greater upwelling off the southern shelves.

Possible causes of decadal change in the circulation can be quite speculative. Indeed beyond the routine monitoring there are real problems in identifying definitive causes and effects and region specific questions for decadal periods which might be answered in South Australia. One of the problems is that the southern shelves are characterised by extremes in the seasonal variation in cross-shelf exchange and hydrographic properties. These extremes act to mask any long-term changes that might be present.