New finding: Arctic melting caused by change in ocean circulation

And this one is NOT a hoax. GRL is a most prestigious publication

Global warming over the past decade or so isn't all about coal, gasoline and other greenhouse gases, space scientists said Tuesday. Melting Arctic Ocean sea ice may have been caused by a reversal in the ocean's circulation that had been going on for about a decade, scientists from NASA and the University of Colorado said. Whether that reversal in direction was caused in large part by warmth generated by greenhouse gas is a question for another day.

The scientists used both deep-sea pressure gauges and NASA's twin satellites, the Gravity Recovery and Climate Experiment, to measure tiny changes in the weight of columns of water from the surface to the ocean bottom, between 2002 and 2006. The two GRACE satellites travel in tandem and monitor tiny hair's-breadth changes in Earth's gravity field caused by the movement of water. Meanwhile, the pressure gauges on the sea floor directly measure water pressure there. "The close agreement between the North Pole pressure gauges and GRACE data demonstrates GRACE's potential for tracking world ocean circulation," said CU-Boulder physics Professor John Wahr, who co-authored the study that appears in the current issue of Geophysical Research Letters.

The weight of a column of water in the ocean is influenced by such things as the height of the ocean's surface and its salinity. A saltier ocean is heavier and circulates differently than one with less salt. The scientists found a 10-millibar decrease in water pressure at the bottom of the Ocean at the North Pole between 2002 and 2006. That is equal to removing the weight of four inches of water from the ocean, Wahr said. That much drop in water pressure suggests that the Arctic Ocean changed back to a clockwise circulation, the scientists said. The Arctic Ocean had been circulating clockwise prior to 1990, but had been turning counterclockwise in the 1990s.

The change was sparked by a weakened Arctic Oscillation, which reduced the amount of salt in the upper ocean near the North Pole. That slightly decreased the weight of a column of water, changing the water's circulation direction. "Our study confirms that many changes seen in upper Arctic Ocean circulation in the 1990s were mostly decadal in nature, rather than trends caused by global warming," said project leader James Morrison of the University of Washington's Polar Science Center Applied Physics Laboratory.

The Arctic Oscillation was fairly stable until about 1970, but has varied on an approximate 10-year time scale since then. It was turning strongly counterclockwise in the 1990s, during which time the Arctic Ocean lost a lot of its ice, prompting many scientists to view the changes as evidence of an ongoing climate shift. The fact that it can change every decade or so indicates how short-term the oscillations can be, Morrison said.

In fact, the Arctic Ocean circulation seemed to have shifted again in the winter of 2006-07, commensurate with the lowest ice expanse in recorded history. While there is no direct connection between global warming and the Arctic Oscillation, most climate models predict the oscillation will become more strongly counterclockwise in the future, Morrison said. "The events of the 1990s may well be a preview of how the Arctic will respond over longer periods of time in a warming world," he said

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