Freshening of deep Antarctic waters worries experts

So-called Antarctic bottom water helps power the great ocean conveyor belt, a system of currents spanning the Southern, Pacific, Indian and Atlantic Oceans that shifts heat around the globe.

"The main reason we're paying attention to this is because it is one of the switches in the climate system and we need to know if we are about to flip that switch or not," said Rintoul of Australia's government-backed research arm the CSIRO.

"If that freshening trend continues for long enough, eventually the water near Antarctica would be too light, too buoyant to sink and that limb of the global-scale circulation would shut down," he said on Friday.

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