AUSTRALIAN researchers have discovered that vast, pancake-shaped bodies of cool water, about 40 kilometres in diameter, are spinning out of Bass Strait into the Tasman Sea, and then turning east to head for the Indian Ocean.
The phenomenon happens at a stately pace, with perhaps one giant disc of water each year making it as far as the southern coast of Western Australia, after a journey of several years.
”At first we thought maybe there was a malfunction in the instruments,” said Mark Baird, an oceanographer and senior research fellow at the University of Technology, Sydney.
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”But there was no malfunction, we had just run into a ‘wall’ or water that was relatively sharp, and undiluted by the water around it. We were able to establish that it was a disc shape, a few hundred metres high and about 40 kilometres across.”
Dr Baird and fellow researcher Ken Ridgway from the CSIRO, were analysing data from a deep-diving ocean glider, a torpedo-like machine that dives a kilometre under the sea and then rises back to the surface, measuring water temperature and salinity.
Dozens of the gliders are deployed in the oceans of Australia’s coast and further afield, building up a detailed picture of ocean currents.
The glider in question had been dispatched on a routine mission to take measurements from the edge of the East Australian Current, a flow featured in the film Finding Nemo. The current brings warm water from the Coral Sea off northern Queensland down to the Tasman Sea.
But, off the coast of NSW, it also forms eddies that can scoop up the pancakes of colder water from the south and send them slowly spinning west for the full length of continental Australia.
While it has been known for many years that large bodies of cool and warm water can remain undiluted for long periods, the findings published this week in the journal Geophysical Research Letters show for the first time that such bodies of water can survive for years and travel for thousands of kilometres.
”There was a general perception that water like this from Bass Strait disappears or diffuses into the Tasman Sea,” Dr Baird said. ”It was really surprising, to be honest, because it was a totally unexpected finding. Now we know that it gets caught by these eddies and remains intact for long periods.”
The research may have applications for the fishing industry, but it could also help scientists to understand the ocean currents that play a key role in regulating weather and climate.