AUSTRALIA 
Cold water eddy threatens swimmers
Wednesday, 19 March, 2008
Swimmers jumping into a cold sea (Getty)
Scientists claim a water version of a tropical cyclone off Sydney is evidence that the ocean is not what it appears to be.
Rather than a constant, unchanging water mass, they say the sea is actually made up of eddies, which are believed to have a major impact on changes in ocean temperatures.
One such giant eddy - the size of Tasmania and spinning like a washing machine - is currently off the coast of Sydney.
Described as the undersea equivalent of an atmospheric cyclone, the eddy was first discovered in August last year near lord Howe Island.
Eddies can cause great variations in water temperature, and they are not uncommon - scientists say the ocean is full of them.
"We've known this for 30 or 40 years," said CSIRO oceanographer Dr Trevor McDougall. "Before that time we thought the currents were smooth and slowly varying but satellites told us that the oceans are full of eddies similar to how the atmosphere is full of weather systems."
Ocean temperatures plunging
The giant swirl measures a massive 300 kilometres across, and takes 10 days to do a full rotation.
Its western edge is now just 80 kilometres east of Sydney, and at its centre, cold water is welling up from a depth of 500 metres, causing the surface temperature to drop to as low as 14 degrees.
Forecasters have warned that a cold eddy can easily ruin a day at the beach - this time last year people were forced out of the water as ocean temperatures plunged.
CSIRO oceanographers say colder water can have a profound affect on biology.
"Cold water has a lot of nutrients in it and if that comes closer to the surface where there's light all of a sudden you get a lot of growth so everything that lives in the ocean is very dependant on everything thats coming to the sunshine," said CSIRO oceanographer Dr David Griffin.
But the experts don't know everything - at the moment they are working to discover how eddies develop.
Source: SBS
Rather than a constant, unchanging water mass, they say the sea is actually made up of eddies, which are believed to have a major impact on changes in ocean temperatures.
One such giant eddy - the size of Tasmania and spinning like a washing machine - is currently off the coast of Sydney.
Described as the undersea equivalent of an atmospheric cyclone, the eddy was first discovered in August last year near lord Howe Island.
Eddies can cause great variations in water temperature, and they are not uncommon - scientists say the ocean is full of them.
"We've known this for 30 or 40 years," said CSIRO oceanographer Dr Trevor McDougall. "Before that time we thought the currents were smooth and slowly varying but satellites told us that the oceans are full of eddies similar to how the atmosphere is full of weather systems."
Ocean temperatures plunging
The giant swirl measures a massive 300 kilometres across, and takes 10 days to do a full rotation.
Its western edge is now just 80 kilometres east of Sydney, and at its centre, cold water is welling up from a depth of 500 metres, causing the surface temperature to drop to as low as 14 degrees.
Forecasters have warned that a cold eddy can easily ruin a day at the beach - this time last year people were forced out of the water as ocean temperatures plunged.
CSIRO oceanographers say colder water can have a profound affect on biology.
"Cold water has a lot of nutrients in it and if that comes closer to the surface where there's light all of a sudden you get a lot of growth so everything that lives in the ocean is very dependant on everything thats coming to the sunshine," said CSIRO oceanographer Dr David Griffin.
But the experts don't know everything - at the moment they are working to discover how eddies develop.
Source: SBS
