Thermal structure above the Perth Canyon reveals Leeuwin Current, Undercurrent and weather influences and the potential for upwelling
Susan J. Rennie A , Robert D. McCauley A C and Charitha B. Pattiaratchi BA Centre for Marine Science and Technology, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia.
B Centre for Water Research, Mailstop MO15, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia.
C Corresponding author. Email: r.mccauley@cmst.curtin.edu.au
Marine and Freshwater Research 57(8) 849-861 https://doi.org/10.1071/MF05247
Submitted: 13 December 2005 Accepted: 11 September 2006 Published: 28 November 2006
Abstract
The Perth Canyon is a focal feeding area for pygmy blue whales on the Western Australian coast. Studies aimed at elaborating oceanographic mechanisms within the canyon were conducted between 2002 and 2005. Strings of temperature loggers set around the canyon rim were used to examine the water column’s response to climatological forcing, current meanders, upwelling and downwelling. Six moorings were positioned on a plateau in 500 m of water on the northern canyon rim, and one was positioned at the canyon head. Loggers were positioned to sample the whole water column, including the Leeuwin Current and Undercurrent. Moorings revealed spatial temperature differences between the plateau and canyon head. Observed temperature features ranged temporally from seasonal to <1 day. Seasonal changes in water temperature agreed with published Leeuwin Current studies: for example, mixed layer and stratification changes were apparent. Other observed temperature changes were related to Leeuwin Current movement and wind forcing such as the summer sea breeze and winter storms. Storms induced mixing, re-stratification, downwelling and upwelling as the wind changed direction and strength. Changes lasting a day were associated with diurnal sea breezes, internal waves and possibly solitary waves. Bottom loggers indicated that upwelling and downwelling events each occurred up to 20% of the time.
Extra keywords: stratification, submarine canyons, temperature measurement.
Acknowledgments
Funding for this study was provided by the WAXA (Western Australian Exercise Area) Blue Whale Project, which Australian Defence Forces funded in order to study the pygmy blue whales and their habitat. Paul Pettorini and the crew of the fishing vessel ‘Reliance II’ were crucial for mooring deployment and recovery. The Centre for Whale Research assisted with mooring deployments. The Australian Bureau of Meteorology supplied the meteorological data from the Rottnest Island station. Satellite SST images were accessed from the Western Australian Department of Land Information through the Land Online website at www.landonline.com.au, with additional SST images obtained from POET at http://poet.jpl.nasa.gov.
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