Australia is heavily influenced by four major ocean currents (Figure 6.4):
- The East Australian Current flows southward along the east coast of Australia from near Fraser Island in Queensland to Tasmania. It is an important feature of the Tasman Sea between Australia and New Zealand, and generates large eddies that peel off the main current as it moves south.
- The Leeuwin Current forms near the North West Shelf and breaks into a series of eddies as it travels south along Australia's west coast, eventually dissipating in the Tasman Sea and Southern Ocean. It is the longest coastal current in the world and has a major influence on the weather in Western Australia and the distribution of marine life.
- The Indonesian Throughflow is a system of currents that carries water westward from the Pacific Ocean to the Indian Ocean through the Indonesian Archipelago. Beyond Australia, the throughflow is a critical element in the global climate system because the heat it carries from the tropical Pacific Ocean into the Indian Ocean affects regional sea surface temperatures and rainfall, including the Asian and Australian monsoons.
- The 20 000-kilometre-long Antarctic Circumpolar Current is considered to be the powerhouse for global climate. It connects the Atlantic, Pacific and Indian oceans with an eastward flow equivalent to 150 times the combined flow of all the world's rivers. The current comprises merging and separating jets between different masses of water—the subtropical front and the subantarctic front. This turbulent region, well south of Australia, is characterised by high ocean nutrient levels and primary production, and typically hosts large aggregations of krill, migratory fish, birds and marine mammals.
Together, these four major currents have a driving influence on the conditions and biodiversity in our oceans and coastal environments, and on Australia's climate.
Along with the major ocean basin currents and the continental currents, there are a number of smaller and more complex current systems. All these ocean features can change from season to season, and may be more or less extensive and energetic, depending on climate factors that influence the oceans at the scale of the whole ocean basin.