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Thursday, January 28, 2021

Super current gives clues

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Australian scientists have identified a huge underwater current they say is the missing link in a "global conveyor belt" that connects the world's oceans and regulates climate around the planet

Research confirms that a current sweeping past Tasmania, south of the Australian mainland, towards the South Atlantic is a previously undetected component of the “engine room” of the global climate system.

Ken Ridgway, a scientist with the Commonwealth Science and Industrial Research Organisation, the Australian Government’s scientific body, said yesterday the current – called the Tasman Outflow and found at a depth of 800m to 1000m – might play an important role in the conveyor belt’s response to climate change.

The missing deep ocean pathway, known as a “supergyre”, links the three ocean basins of the Southern Hemisphere: the Indian, Pacific and Atlantic. Research by a CSIRO team has confirmed that the waters south of Tasmania form a “choke point”, connecting the main “circulation cells” in the three oceans. Mr Ridgway said it had long been known that a system of currents north of Australia, called the Indonesian Throughflow, drained water from the Pacific into the Indian Ocean through the Indonesian archipelago – a process that influenced rainfall in Australia.

“Now we can see that they [deep ocean pathway currents] move south of Tasmania as well, another important link [between the Pacific and Indian oceans],” he said.

In each ocean, water flows around anti-clockwise pathways, known as “gyres”, which are the size of ocean basins. The gyres distribute nutrients from the deep ocean, generating life on the continental shelves and slopes. They also drive the circulation of the world’s oceans, creating currents and eddies, and helping to balance the climate system by transferring ocean heat away from the tropics towards the polar region.

The newly discovered Tasman Outflow, which sweeps out of the Tasman Sea, is classed as a “supergyre”, connecting gyres in the three oceans.

The research team analysed thousands of temperature and salinity data samples collected between 1950 and 2002 by research ships, robotic ocean monitors and satellites in the region between 60 degrees south, just north of the Antarctic Circle, and the Equator. They identified linkages between the gyres and established that the supergyre transfers water to all three ocean basins.

Mr Ridgway and his fellow author, Jeff Dunn, said identification of the supergyre would enable scientists to explain more accurately how the ocean governed global climate.

“Recognising the scales and patterns of these sub-surface water masses means they can be incorporated into the powerful models used by scientists to project how climate may change,” they said.

The vast Southern Ocean, which swirls around Antarctica, has been identified in recent years as the main “lung” of global climate, absorbing one-third of all carbon dioxide taken in by the world’s oceans.

The best known of all ocean currents is the North Atlantic loop of the Great Ocean Conveyer, which brings warm water from the Equator to northern Europe, ensuring that area enjoys relatively mild weather. Scientists said if the conveyor collapsed, northern Europe would be plunged into an ice age.

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