Oceanographic processes in the Perth Canyon and their impact on productivity

• Main Author: Rennie, Susan Jane
• Format: Thesis
• Language: English
• Published: Curtin University 2005
• Subjects: submarine canyons; Leeuwin Current; oceanography; Balaenoptera musculus
• Online Access: https://hdl.handle.net/20.500.11937/1904

Submarine canyons are important to continental shelf ecosystems. They have a strong influence on shelf circulation and the distribution of biota. The Perth Canyon is a long, deep canyon on the Western Australian coastline that has attracted attention as a feeding area for pygmy blue whales (Balaenoptera musculus brevicauda). Despite existing on a highly oligotrophic coast, the Perth Canyon has the ability to support sufficient krill to feed these massive mammals. The aim of this study was to examine the physical processes within the Perth Canyon, and consider how these could affect productivity. Research areas included the interaction of the Leeuwin Current and Leeuwin Undercurrent with the canyon, the circulation within the canyon, the effect of wind forcing and the occurrence of upwelling. The oceanography of the Western Australian coast including seasonal productivity changes was also examined. This study utilised numerical modelling and collection of field data to develop a thorough understanding of the Perth Canyon. The numerical model ROMS (Regional Ocean Modelling System) was used to simulate a long stretch of coastline in which the Perth Canyon was centrally located. The model forced the Leeuwin Current and Undercurrent using density gradients, and the seasonal Capes Current was then generated by applying a surface wind stress. The simulations showed that primarily the Leeuwin Undercurrent interacted with the canyon. Eddies continually formed within the canyon, which enhanced vertical transport and could contribute to entrapment of passive drifters. The addition of wind had no discernible effect on canyon circulation although vertical velocities increased everywhere and shallow upwelling occurred along the shelf. The field data comprised moored temperature loggers, field cruises, and sundry data from satellite imagery, weather stations and whale observations.The temperature loggers, located on the canyon rim, indicated the range of processes that affect the canyon region. These processes included ...