The Gascoyne continental shelf is located along the north-central coastline of Western Australia between latitudes 21° and 28°S. This study presents CTD and ADCP data together with concurrent wind and satellite imagery, to provide a description of the summer surface circulation pattern along the continental margin, and the hydrography present in the upper 1km of ocean, between latitudes 21° and 35°S. It also discusses the outcome of a numerical modelling study that examined the physical factors contributing to a bifurcation event persistently observed in satellite imagery at Point Cloates. The region comprises a complex system of four surface water types and current systems. The Leeuwin Current dominated the surface flow, transporting lower salinity, warmer water poleward along the shelf-break, and causing downwelling. Its signature ‘aged’ from a warm (24.7°C), lower salinity (34.6) water in the north to a cooler (21.9°C), more saline (35.2) water in the south, as a result of 2-4Sv geostrophic inflow of offshore waters. The structure and strength of the current altered with changing bottom topographies. The Ningaloo Current flowed along the northernmost inner coast of the Gascoyne shelf, carrying upwelled water and re-circulated Leeuwin Current water from the south. Bifurcation of the Ningaloo Current was seen south of the coastal promontory at Point Cloates. Numerical modelling demonstrated a combination of southerly winds and coastal and bottom topography off Point Cloates to be responsible for the recirculation, and indicated that the strength of southerly winds affect recirculation. Hypersaline Shark Bay outflow influenced shelf waters at the Bay’s mouth and to the south of the Bay. The Capes Current, a wind-driven current from south of the study region was identified as a cooler, more saline water mass flowing northward. Results of the hydrography study show five different water masses present in the upper-ocean. Their orientations were affected by the geopotential gradient driven Leeuwin Current/Undercurrent system at the continental margin. The Leeuwin Undercurrent was found at the shelf-slope, carrying (>252 μM/L) Subantarctic Mode Water at a depth of 400m
| Identifer | oai:union.ndltd.org:ADTP/221158 |
| Date | January 2005 |
| Creators | Woo, Lai Mun |
| Publisher | University of Western Australia. Centre for Water Research |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Lai Mun Woo, http://www.itpo.uwa.edu.au/UWA-Computer-And-Software-Use-Regulations.html |
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