A image compiled from satellite data showing where the sea level has fallen as the eddies swirl off NSW.
Photo: CSIRO
A massive whirlpool has developed off the coast of NSW, dragging down the sea surface by almost a metre, diverting a mighty ocean current and chilling Sydney beachgoers.
The mysterious whirlpool is 200 kilometres across and 1000 metres deep, reaching the ocean floor, CSIRO oceanographers say. The centre is 100 kilometres from the coast and could stay there for several months.
And another eddy of similar proportions is sitting further off the coast.
CSIRO satellite oceanographer Dr David Griffin said that, while cold-water eddies regularly appeared off Sydney, scientists knew very little about what causes them or the influence they have in the Tasman Sea ecosystem.
"What we do know is that this is a very powerful natural feature which tends to push everything else aside - even the mighty East Australian Current," said Dr Griffin.
The sea level has dropped 70 centimetres at its centre while the water 400 metres below the surface is 6 degrees centigrade colder than normal.
The colder water has helped bring down the average water temperature at Sydney beaches by several degrees.
At the eddy's centre, cold water from 400m is raised about 200m. The sea surface, conversely, is lowered by 70cm. This dip in the surface of the ocean is invisible to the eye, but it can be accurately measured by satellites and a robotic Argo float deployed by the CSIRO.
The eddies are invisible to the human eye but would contribute to cooler beach swimming conditions, said Dr Griffin.
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