Continental Shelf and Coastal Processes

Satellite images of SST (a, upper panels) and chlorophyll (b, lower panels) showing surface enrichment in the circled area south of Fraser Island (Source: Scarla Weeks, UQ)
Satellite images of SST (a, upper panels) and chlorophyll (b, lower panels)

The South Equatorial Current is filamented by the topography as it meets the Queensland shelf, arriving as jets that eventually join up on the western boundary to form the poleward East Australian Current (EAC) or equatorward Gulf of Papua Current (GPC). Embedded within these jets are large eddies that can be cyclonic or anti-cyclonic. As eddies move toward the shelf, their momentum also squeezes waters from depth up onto the shelf and can produce a cross shelf flow that results in warm surface Coral Sea waters impinging on the shelf but also drives cooler water from depth along the seafloor toward the shelf.

Surveys of seabed communities throughout the Great Barrier Reef (GBR) Marine Park have revealed several regions on the shelf where marine plants are unusually abundant. These regions are likely to have persistent upwelling of nutrients from deeper layers in the Coral Sea. Several physical mechanisms appear responsible.

The blocking action of the dense offshore reef matrix in the Pompey-Swains section of the GBR results in anomalous tides that are 5-6 times greater than elsewhere along the east coast. Along most of its length, the offshore reef matrix is separated from the coast by a shallow lagoon of variable width and depth that deepens with latitude below 18°S. The GBR currents have been the subject of more hydrodynamic model solutions than any other marine area in Australia and knowledge of the shelf currents in this topographically complex domain continues to evolve as new solutions are implemented.

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

Boundary Current/shelf interactions

  • What is the influence of the EAC on eddy dynamics in the lee of the Swain Reefs?
  • What is the influence of the EAC on formation of the Fraser Island Gyre?
  • What is the influence of the EAC on longshore flow on the shelf south of Fraser Island?

Upwelling and Downwelling

  • What are the determinants of persistent upwelling regions in Queensland?
  • What are the dynamics (seasonal, interannual) of regional upwelling areas?
  • Are different upwelling regions in phase or independent?
  • Do upwelling dynamics in any region correlate with the sign of the SOI?

Shelf Currents

  • What is the influence of the EAC on longshore flow in the GBR Lagoon?
  • What is the influence of the EAC on cross-shelf transport in the GBR Lagoon?
  • What is the influence of the EAC on longshore and cross-shelf flow on the SEQ shelf

Wave Processes

  • What is the tidal regime and how does it influence shelf processes?
  • What is the importance of coastally trapped waves in driving shelf circulation?
  • How will changes in global wind fields alter wave climate, and associated sediment mobilisation?