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Physical oceanography off the South Coast of Western Australia

Mondello, Nicholas (2017) Physical oceanography off the South Coast of Western Australia. Honours thesis, Murdoch University.

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Compared to neighbouring regions of ocean, the south coast of Western Australia (WA) has received relatively little scientific attention despite a range of Australian Commonwealth marine protected areas having been established in the region as of 2012. The ocean off the south coast of WA is characterised by a canyon-dense continental shelf edge including the Bremer Canyon, a shelf edge canyon of approximately 8 km width. There are also two main currents in the region, the eastward flowing Leeuwin Current (LC) situated above the continental shelf edge, and the westward flowing Flinders Current (FC) situated south of the continental shelf. The Blue-link Reanalysis (BRAN) ocean forecasting model simulates the currents, temperature and salinity around Australia at daily intervals from 1994 – 2016 with 1/10th degree resolution. It has been speculated that these currents may interact with the canyons along the shelf edge to induce oceanographic conditions conducive to increased pelagic productivity and ecological diversity.

This study was a two-part investigation of the physical oceanography off the south coast of WA with a focus on shelf edge dynamics near Bremer Canyon. It involved the use of the (BRAN) model and in situ data including conductivity, temperature and depth (CTD) profiles during January 2017 and temperature logger measurements from near Bremer Canyon between 2015 and 2017. The BRAN outputs were in close agreement with previous studies of the LC and FC and showed that the mixed layer depth (MLD) was shallowest (<50 m) in summer and deepest in winter (>200 m), in sync with seasonal heat flux. The CTD results were within one SD of the average BRAN profiles and MLD results for January. The volume transport of the LC and strong westerly wind events were dominant drivers of the temperature variation along the shelf edge during autumn and winter of 2015 as the warm LC water was forced downwards. In spring and summer, the volume transport of the LC was lowest (1.6 Sv) and other factors became dominating drivers of the shelf edge temperature variation including eddy kinetics and canyon-related processes. The BRAN outputs effectively simulated the mesoscale features examined in this study including the volume transport of the LC, westerly wind forced response and the influence of mesoscale eddies. These processes have the potential to influence the pelagic ecology through vertical mixing and upwelling.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
Supervisor(s): Beckley, Lynnath
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