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Cyclone Of The Deep Sits Off Sydney


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Cyclone of the deep sits off Sydney

The marine equivalent of a cyclone is sitting off Sydney's coast, causing a massive whirlpool which is turning the ocean green and spewing chilly water towards beaches.

A 200 kilometre-wide cyclonic eddy has pulled the sea's surface down by 70 centimetres and sucked cold deep ocean water onto Australia's eastern continental shelf.

The whirlpool is 1000 metres deep, reaching the ocean floor, CSIRO oceanographers say.

The centre is 100 kilometres off the coast and could stay there for several months.

Satellites can measure the drop in ocean surface caused by the eddy's pull, clearly showing how it is pushing aside the powerful East Australian Current running off our coast.

Another eddy of similar proportions is sitting further off the coast.

The eddies were like underwater cyclones, and the latitude of the coast near Sydney put it right in the marine cyclone belt, CSIRO oceanographer David Griffin said.

"This eddy is a particularly strong one - it's caused cold water to slop up onto the continental shelf and in places that water's available to come to the surface," he said.

"It's not happening right now off Sydney, but earlier this summer people will recall very cold beach temperatures - that was associated with the early phase of this eddy.

"It doesn't seem to be impacting beach temperatures at the moment, but that doesn't mean it won't happen again."

A run of warm water temperatures last September was due to an eddy spinning the other way, Dr Griffin said.

He said the current cyclonic eddy could chill water at the edge of the continental shelf from 18 degrees to 14 degrees.

"It has a big impact on ocean ecology - the cold water coming up has a lot of nutrients and when that's combined with sun, the phytoplankton grows like crazy," he said.

"That's why the water goes green, you can see that from a boat."


Steady eddy spares bathers big chill

IT IS 150 kilometres wide, rotating, and lies just off Sydney.

Scientists say a giant ocean eddy swirling in the Tasman Sea is compelling evidence that the ocean is not the constant, unchanging water mass it has long appeared.

A water version of an atmospheric cyclone, the eddy formed near Lord Howe Island in August and drifted east until Christmas when it stopped off NSW's continental shelf.

Rotating clockwise every 10 days, its western edge is now 80 kilometres east of Sydney. At its centre, 150 kilometres offshore, the ocean level is a metre below the surrounding Tasman Sea. Its rotation dredges up cold water from 500 metres below.

The existence of such eddies so close to Sydney was unknown before the 1990s, David Griffin, a CSIRO oceanographer, said yesterday. Fishermen and yachtsmen knew their ships were drifting in strong currents. "We knew things were happening that were making big changes to ocean temperatures," he said.

But until the development of satellite technology dedicated to monitoring ocean levels, the link with eddies was a mystery.

After reviewing data collected over the past 15 years, Dr Griffin said it now seemed the eddies were common. "It seems in most years we get one."

A giant eddy which reached the NSW coast in January last year sent water temperatures plunging six degrees. "It ruined a lot of summer holidays," he said.

The latest eddy, "as big as Tasmania" at its peak last month, is unlikely to bother swimmers. It is on the wane and "just spinning in place".

Yet another, even more powerful system 250 kilometres wide has now formed between Lord Howe Island and northern NSW.

The sea covers four-fifths of the world, and plays a vital role in driving the weather. But Dr Griffin said there was a lot to learn about the impact of eddies.


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