A team of scientists at Columbia University concluded that a southward shift in wind patterns 17,000 years ago as the northern hemisphere warmed led to the release of natural CO2 from the depths of the Southern Ocean near Antarctica.

'The faster the ocean turns over, the more deep water rises to the surface to release CO2,' said lead author Robert Anderson, a geochemist at Columbia's Lamont-doherty Earth Observatory, said in the study published Thursday in Science magazine.

Similar shifts in wind patterns have occurred over the past 40 years in the Southern Ocean, which could intensify manmade warming, Mr Anderson said.

Many scientists believe the end of the Ice Age was triggered by a change in the Earth's orbit that caused the northern hemisphere to receive more sunlight and warm up.

Two years ago, a scientist at the National Oceanic and Atmospheric Administration proposed that the orbital change caused warm westerly winds to shift from north to south.

The winds caused heavy mixing in the Southern Ocean which pumped CO2 into the atmosphere, according to this theory. Mr Anderson and his team tested it by studying the sediments at the bottom of the Southern Sea to measure the rate at which the deep water was welling up to the surface.

What they found were spikes in plankton growth between 17,000 and 10,000 years ago. That would be consistent with a higher turnover of deep water in the Southern Ocean, which would release not only CO2 but also nutrients on which plankton thrive.

JR Toggweiler, the NOAA scientists who first postulated the shift in wind patterns, told Science the study 'really starts to lock up how the CO2 changed globally' at the end of the Ice Age.

At least one climate model supports the theory, but others do not, Science said. Mr Anderson said further research into changes in the Southern Ocean was needed, as well as improvement in modeling. -- AFp