TheLeeuwin Current is a warmocean current which flows southwards near the western coast ofAustralia. It roundsCape Leeuwin to enter the waters south of Australia where its influence extends as far asTasmania.
The existence of the current was first suggested byWilliam Saville-Kent in 1897. Saville-Kent noted the presence of warm tropical water offshore in theHoutman Abrolhos, making the water there in winter much warmer than inshore at the adjacent coast. The existence of the current was confirmed over the years, but not characterised and named until Cresswell and Golding did so in the 1980s.[1]
TheWest Australian Current and Southern Australian Countercurrent, which are produced by theWest Wind Drift on the southern Indian Ocean and at Tasmania, respectively, flow in the opposite direction, producing one of the most interesting oceanic current systems in the world.
The ‘core’ of the Leeuwin Current can generally be detected as a peak in the surface temperature with a strong temperature decrease further offshore. The surface temperature difference across the Current is about 1 °C atNorth West Cape, 2° to 3° at Fremantle and can be over 4° offAlbany in theGreat Australian Bight. The current frequently breaks out to sea, forming both clockwise and anti-clockwise eddies.
Its strength varies through the year; it is weakest during the summer months (winter in the northern hemisphere) from November to March when the winds tend to blow strongly from the south west northwards. The greatest flow is in the autumn and winter (March to November) when the opposing winds are weakest.Evaporation from the Leeuwin current during this period contributes greatly to the rainfall in thesouthwest region ofWestern Australia.
Typically the Leeuwin Current's speed and itseddies are about 1knot (50 cm/s), although speeds of 2 knots (1 m/s) are common, and the highest speed ever recorded by a drifting satellite-tracked buoy was 3.5 knots (6.5 km/h). The Leeuwin Current is shallow for a major current system, by global standards, being about 300 m deep, and lies on top of a northwardscountercurrent called the Leeuwin Undercurrent.
Because of the Leeuwin Current, thecontinental shelf waters of Western Australia are warmer in winter and cooler in summer than the corresponding regions off the other continents. The Leeuwin Current is also responsible for the presence of the most southerly true corals at theAbrolhos Islands and the transport of tropical marine species down the west coast and across into the Great Australian Bight.
The Leeuwin Current is influenced byEl Niño conditions, characterised by slightly lower sea temperatures along the Western Australian coast and a weaker Leeuwin Current, with corresponding effects upon rainfall patterns.
The Leeuwin Current is very different from the cooler, equatorward flowing currents found along coasts at equivalent latitudes such as the southwest African Coast (theBenguela Current); the long Chile-Peru Coast (theHumboldt Current), where upwelling of cool nutrient-rich waters from below the surface results in some of the most productive fisheries; theCalifornia Current, which brings foggy conditions to San Francisco; or the coolCanary current of North Africa.
