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Arctic freshening not due to ice melt after all, says NASA

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Concern that the Arctic Ocean is becoming massively less salty due to its ice cap melting - which could have knock-on consequences for the planet's climate - is unfounded, NASA scientists have said.

For years, researchers have seen falling salinity readings in the Canadian half of the Arctic Ocean. This has led them to theorise that large amounts of fresh water were being added due to permanent disappearance of ice. In itself this might not mean a lot - sea levels would be unaffected, as the Arctic ice floats atop the sea - but it had been feared that addition of so much fresh water could impact the oceanic "conveyor belt" which moves heat around the planet, with major consequences for the climate.

As long ago as 1999, Greenpeace were saying things like this:

Calculations suggest that most, if not all, of the fresh water added to the Beaufort Sea came from melting Beaufort sea ice in the summer of 1997, and imply that much of the ice of the Beaufort Sea was much thinner (perhaps more than a meter thinner) at the end of the melt season in 1997 than it was during the end of the melt season in 1975.

But the hippies were wrong. Analysis of data from specialised NASA satellites monitoring the Arctic ice has disproven this.

"Changes in the volume and extent of Arctic sea ice in recent years have focused attention on melting ice," says Ron Kwok of NASA's Jet Propulsion Laboratory, which runs the Grace and ICESat spacecraft. "The Grace and ICESat data allow us to now examine the impacts of widespread changes in ocean circulation."

According to Kwok and his colleagues, analysing readings from the satellites overhead, new freshwater in the Beaufort Sea comes not from melted ice but from rivers in Russia. Formerly this freshwater would have stayed largely in the Russian side of the Arctic, but a shift in circulation has occurred.

According to a JPL statement:

The team attributes the redistribution to an eastward shift in the path of Russian runoff through the Arctic Ocean, which is tied to an increase in the strength of the Northern Hemisphere's west-to-east atmospheric circulation, known as the Arctic Oscillation. The resulting counterclockwise winds changed the direction of ocean circulation, diverting upper-ocean freshwater from Russian rivers away from the Arctic's Eurasian Basin, between Russia and Greenland, to the Beaufort Sea in the Canada Basin bordered by the United States and Canada. The stronger Arctic Oscillation is associated with two decades of reduced atmospheric pressure over the Russian side of the Arctic.

The shift has meant that the Beaufort Sea in particular is the freshest it has been in 50 years of recordkeeping - but only a "tiny fraction" of that results from melting ice, according to the NASA scientists. Taken as a whole the Arctic has got no fresher, it's merely that freshwater which was always present has shifted in the past two decades from the seldom visited Russian side to the Canadian, where many climate scientists are found.

"Climate models need to more accurately represent the Arctic Oscillation's low pressure and counterclockwise circulation on the Russian side of the Arctic Ocean," says oceanographer Jamie Morison, lead author of a paper on the new satellite research published yesterday by Nature. ®

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