Four ocean and coastal currents in the Australasian region are significant in shaping marine environmental conditions and our climate. Research in CSIRO and its partners seeks to better understand these currents and the role they play in our environment.
The Antarctic Circumpolar Current
The 20 000 kilometre Antarctic Circumpolar Current is considered the powerhouse for global climate. It connects the Atlantic, Pacific and Indian Oceans in an eastward flow equivalent to 150 times the combined flow of all the world’s rivers.
The Antarctic Circumpolar Current comprises a series of merging and separating jets acting as a buffer between different masses of water either side of two naturally occurring features, the sub-tropical front and the sub-Antarctic front. This region features high ocean nutrient production south of Australia.
The Leeuwin Current
Influenced from the Pacific Ocean by El Niño, the Leeuwin Current exerts a major influence on the distribution of marine life and Western Australia’s weather. It forms near the North West Shelf on Australia’s west coast.
As it travels south the current breaks into a series of southward and eastward flowing eddies and eventually dissipates in the Tasman Sea and Southern Ocean. It is the longest coastal current in the world, extending some 5 000 kilometres.
The Indonesian Throughflow
The Indonesian Throughflow is a system of currents that carries water westward from the Pacific to the Indian Ocean through the deep passages and straits of the Indonesian Archipelago. This is the only place in the world where warm, equatorial waters flow from one ocean to another.
This warm tropical water influences the character of the Leeuwin Current. Without these deep ocean passages between Australia and Asia, the ocean and climate conditions off Western Australia would be very different – more like the colder conditions and deserts found along the western coast of South America and south-west Africa.
Beyond Australia, the Indonesian Throughflow is a critical element in the global climate system because the heat it carries from the tropical Pacific to the Indian Ocean increases the energy available to the Asian and Australian monsoons.
Knowing how much heat and freshwater is transferred between oceans is relevant to understanding the extent to which ocean currents influence regional sea surface temperatures and rainfall. Understanding the way the upper ocean and atmosphere interact is the key to predicting variations in rainfall and other aspects of the climate.
The East Australian Current
The East Australian Current flows south along the east coast of Australia from near Queensland’s Fraser Island to Tasmania. It is an important feature of the Tasman Sea between Australia and New Zealand, which has been warming faster than other parts of the ocean.
This is caused by activity in the upper part of the atmosphere over Antarctica, where each spring the onset of daylight brings a set of chemical reactions that deplete ozone in the stratosphere.
This changes the circulation of the atmosphere which in turn alters the wind patterns that drive the ocean currents in the Pacific Ocean, known as the South Pacific Gyre. This strengthening of the South Pacific Gyre also causes a strengthening of the East Australian Current, so that the warm tropical waters from the Coral Sea region are forced further south, warming the Tasman Sea.