Do deep ocean currents explain why Antarctica isn't melting?

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The waters surrounding Antarctica are believed to be among the last places on Earth to be seemingly unaffected by global warming. But why the southern pole's waters have been unaffected, unlike those in the Arctic, has puzzled climate scientists and oceanographers.

Now researchers believe they have solved the conundrum.

They say ocean currents dragging frigid water from the deep may explain why the Antarctic seas have remained the same temperature, while much of the rest of the world has warmed.

Scientists at the University of Washington and the Massachusetts Institute of Technology (MIT) have explained the inconsistent pattern of warming in the journal Nature Geoscience, which is often seized on by climate deniers as proof global warming is not man-made.

Observations and climate models show the unique currents around Antarctica continually pull up deep, centuries-old water to the surface.

This seawater last touched Earth's atmosphere before the machine age and so has not been warmed by the atmosphere since fossil fuels began contributing to greenhouse gases.

'With rising carbon dioxide you would expect more warming at both poles, but we only see it at one of the poles, so something else must be going on,' said lead author Kyle Armour, an assistant professor of oceanography and of atmospheric sciences at the University of Washington.

'We show that it's for really simple reasons, and ocean currents are the hero here.'

Gale-force westerly winds that constantly whip around Antarctica act to push surface water north, cause water from up to two miles (3.2km) below to be pulled up to the surface.

The Southern Ocean's water comes from such great depths - and from sources that are so distant - that it will take centuries before the water reaching the surface has experienced modern global warming.

While in other waters, such as the west coast of the Americas and the equator, seawater is drawn up from a few hundred metres below the surface, the action of the currents does not have the same effect.

'The Southern Ocean is unique because it's bringing water up from several thousand metres,' Dr Armour said.

'It's really deep, old water that's coming up to the surface, all around the continent. You have a lot of water coming to the surface, and that water hasn't seen the atmosphere for hundreds of years.'

The water surfacing off Antarctica last reached Earth's atmosphere centuries ago in the North Atlantic.