Leeuwin Current

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Leeuwin Current is a warm ocean current which flows southwards near the western coast of Australia. It rounds Cape Leeuwin to enter the waters south of Australia where its influence extends as far as Tasmania. The West Australian Current and Southern Australian Countercurrent, which are produced by the West Wind Drift on 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 southward-flowing Leeuwin Current (warmest water shown in red/orange, with red arrows) and the cool Capes Current (shown in blue, with blue arrows) represent the summer situation.

Its strength varies through the year, it is weakest during the summer months from November to March when the winds tend to blow strongly from the south west northwards. The time of 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 the south west region of Western Australia.

Typically the Leeuwin Current current's speed and its eddies are about 1 knot (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. The Leeuwin Current is shallow for a major current system, by global standards, being about 300 m deep, and lies on top of a northwards countercurrent called the Leeuwin Undercurrent.

The Leeuwin Current is very different from the cooler, northward flowing currents found along coasts at equivalent latitudes such as the southwest African Coast (the Benguela Current); the long Chile-Peru Coast (the Humboldt Current), where upwelling of cool nutrient-rich waters from below the surface results in some of the most productive fisheries; the Californian current, which brings foggy conditions to San Francisco; or the cool Canaries current of North Africa.

Because of the Leeuwin Current, the continental 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 the Abrolhos Islands and the transport of tropical marine species down the west coast and across into the Great Australian Bight.

Data from two satellite instruments is used in constructing this image of the Leeuwin Current. Sea surface temperature information comes from the US NOAA 14 satellite while the surface current velocity is derived from sea level measurements made by the satellite-borne altimeter. Sea level data from the US/French Topex/Poseidon and European ERS altimeters are combined

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 at North West Cape, 2° to 3° at Fremantle and can be over 4° off Albany in the Great Australian Bight. The current frequently breaks out to sea, forming both clockwise and anti-clockwise eddies.

[CSIRO Marine Research]

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