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Deep, centuries-old water prevents Antarctic Ocean warming

Tuesday, May 31, 2016,15:48 IST By Metrovaartha A A A

Washington | The Antarctic Ocean has remained unaffected by climate change and global warming due to the deep, centuries-old water that is continually pulled to the surface, a new study has found.

The study from the University of Washington and the Massachusetts Institute of Technology (MIT) in the US resolves a scientific conundrum, and an inconsistent pattern of warming often seized on by climate deniers. Observations and climate models show that the unique currents around Antarctica continually pull deep, centuries-old water up to the surface – seawater that last touched Earth’s atmosphere before the machine age, and has never experienced fossil fuel-related climate change.

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, assistant professor at University of Washington. Gale-force westerly winds that constantly whip around Antarctica act to push surface water north, continually drawing up water from below.

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.

Other places in the oceans, like the west coast of the Americas and the equator, draw seawater up from a few hundred meters depth, but that doesn’t have the same effect. The Southern Ocean is unique because it’s bringing water up from several thousand meters, Armour said.

The water surfacing off Antarctica last saw Earth’s atmosphere centuries ago in the North Atlantic, then sank and followed circuitous paths through the world’s oceans before resurfacing off Antarctica, hundreds or even a thousand years later. Delayed warming of the Antarctic Ocean is commonly seen in global climate models.

However, the culprit had been wrongly identified as churning, frigid seas mixing extra heat downward. The old idea was that heat taken up at the surface would just mix downward, and that’s the reason for the slow warming, Armour said.

But the observations show that heat is actually being carried away from Antarctica, northward along the surface, he said. In the Atlantic, the northward flow of the ocean’s surface continues all the way to the Arctic.

Researchers used dyes in model simulations to show that seawater that has experienced the most climate change tends to clump up around the North Pole.

This is another reason why the Arctic’s ocean and sea ice are bearing the brunt of global warming, while Antarctica is largely oblivious, researches said.