Abstract
[Truncated abstract] The shelf circulation off Ningaloo Reef near the North West Cape of Western Australia is driven by complex interactions between the relatively persistent, poleward pressuregradient driven Leeuwin Current (LC) and local wind-driven currents that episodically reverse the coastal flow equatorward. These transient wind-driven equatorward currents can generate coastal upwelling, and are thought to play a significant role in bringing cool, nutrient rich water to the surface waters off Ningaloo Reef. In this thesis, a combination of field experiments and numerical modelling are used to investigate the detailed shelf dynamics off Ningaloo Reef, in particular: (1) to characterize flow structures and transient coastal upwelling, (2) to determine the major mechanisms driving the along-shelf flow, the cross-shelf advection and the coastal cooling.
A field experiment was conducted in the austral summer (Nov-Dec 2009), which
included the deployment of four cross-shelf moorings in the northern region of the Ningaloo Peninsula. The observations revealed several equatorward flow reversals accompanied by cooling of the coastal waters adjacent to Ningaloo, and several transient upwelling events when the surface Ekman layer offshore transport was replenished by subsurface onshore transport. Based on these observations, we also developed and evaluated two Regional Ocean Model System (ROMS) sub-models: (1) a coarser model of north-western Australia forced by a global operational ocean model and (2) a nested fine-scale model of the Ningaloo region forced by the coarse model. The observations showed no significant reduction of upwelling velocity in the presence of the relatively strong poleward pressure gradient. Analysis of the coastal heat budget revealed that coastal cooling events were primarily driven by coastal upwelling, whereas warming of coastal waters during wind relaxation events resulted mostly from along-shelf advection of warm water from the north. As a consequence, the coastal cooling process on the Ningaloo shelf is much weaker than that of other upwelling systems.
A field experiment was conducted in the austral summer (Nov-Dec 2009), which
included the deployment of four cross-shelf moorings in the northern region of the Ningaloo Peninsula. The observations revealed several equatorward flow reversals accompanied by cooling of the coastal waters adjacent to Ningaloo, and several transient upwelling events when the surface Ekman layer offshore transport was replenished by subsurface onshore transport. Based on these observations, we also developed and evaluated two Regional Ocean Model System (ROMS) sub-models: (1) a coarser model of north-western Australia forced by a global operational ocean model and (2) a nested fine-scale model of the Ningaloo region forced by the coarse model. The observations showed no significant reduction of upwelling velocity in the presence of the relatively strong poleward pressure gradient. Analysis of the coastal heat budget revealed that coastal cooling events were primarily driven by coastal upwelling, whereas warming of coastal waters during wind relaxation events resulted mostly from along-shelf advection of warm water from the north. As a consequence, the coastal cooling process on the Ningaloo shelf is much weaker than that of other upwelling systems.
| Original language | English |
|---|---|
| Qualification | Doctor of Philosophy |
| Publication status | Unpublished - 2014 |