Mysterious ocean feature found in Tasman Sea

By AAP with AG Staff February 24, 2012
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Massive spinning discs of water from the Bass Strait are travelling great distances in the East Australian Current.

AN UNSUAL WATER feature, described as a 40km-wide disc, has been detected travelling south of Australia in the Tasman Sea, around Tasmania and possibly as far as the Indian Ocean.

New deep-diving ocean gliders have discovered the 200m-deep formation in ocean eddies formed by the East Australian Current. Scientists from the CSIRO and the University of Technology Sydney (UTS) report the discovery in the journal Geophysical Research letters.

The finding is being hailed a success for the $200,000 gliders – robotic probes which can collect data from a depth of 1000m and are part of a $230-million marine observation program.

Undiluted from the Bass Strait

Salty water from the Bass Strait is getting trapped in the EAC and travelling hundreds of kilometres (Credit: CSIRO)

“In this case, we have seen for the first time a 200m-tall, 40km-wide disc formed from water that originated in Bass Strait and that amazingly remains undiluted as it travels hundreds of kilometres,” says Dr Mark Baird a scientist at UTS. “This new discovery is a clear example of the benefits arising from a significantly enhanced technical ability to explore our oceans.”

Scientists have known that salty waters from the Bass Strait (between Tasmania and the Australian mainland) flow into the Tasman Sea north-east of Flinders Island and sink to depths of 400-800m, a feature known as the Bass Strait Cascade. But now they think the water could travel thousands of kilometres beyond that (see diagram above).

Tasman Sea oceanography

“East of Tasmania we found bodies of water entrained in the ocean eddies that were originally formed six months previously in Bass Strait,” CSIRO scientist Ken Ridgway says. “Further measurements show that at least some of this Bass Strait water makes the journey past southern Tasmania and possibly thousands of kilometres into the Indian Ocean.”

Deployed in 2010 and 2011, the gliders were programmed to observe the East Australian Current and ocean eddies up to 200km wide that form off NSW. The scientists say the discovery will help the study of food chains and climate change in Australia’s oceans.