The Leeuwin Current is a tropical current, consisting of warm, low salinity water that affects Western Australia’s coastal waters and wildlife. Currents are part of a large sub circular current system called a gyre. The currents in the Southern hemisphere gyres circulate in an anti-clockwise direction (Skinner, Porter & Botkin, 1999, p.249). There is a current in each of the major oceans that generally flow northwards along the western coast of continents. However, the Leeuwin Current flows southwards along the coast, before turning eastwards at Cape Leeuwin and then into the Great Australian Bight where its physical and chemical influences reach as far as Tasmania (http://www.marine.csiro.au/Leafletsfolder/44leuwin/44.html). In this essay some of these consequences on the physico-chemical environment will be examined and the possible causes of the Leeuwin Current will be looked at.
The Leeuwin Current has important consequences on both the climate and marine biota off the coast of Western Australia. The first part of this essay will study these effects and introduce the concept of low nutrients, low salinity and high water clarity. The Leeuwin Current originates from tropical regions, making it relatively warm in addition to the distinctive lack of large-scale upwelling (http://www.per.marine.csiro.au/public/oceanography/regional/currents.html). Upwelling is the process by which subsurface waters flow upward and replace the water moving away (Skinner, et al, 1999). This process and other factors that cause the Leeuwin Current and its distinctive attributes will be analysed in later parts of this essay.
One of the most important influences that the Leeuwin Current has on marine ecosystems is the water temperature. Continental shelf waters off the coast of Western Australia are some four degrees warmer than other continents of the same latitude (http://www.per.marine.csiro.au/public/oceanography/regional/currents.html). This...