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On thin ice: As Arctic Ocean warms, a scramble to understand its weather

Increasing summer ice melt in the Arctic Ocean could shift global weather patterns and make polar waters more navigable. But scientists say forecasting Arctic ice and weather remains a massive challenge.

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In 2007, when the summer melt season ended in mid-September, the extent of summer ice reached its lowest point in the satellite record, which goes back to 1979.

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The '07 record didn't last long. In 2012, the melt-back of summer ice broke the '07 record – in the middle of the melt season. By the end of the season the extent of summer sea ice was 18 percent below the 2007 figure. The surviving ice patch – some 1.4 million square miles of it – had anchored one edge to the northern coasts of Greenland and Canada's Arctic Archipelago, leaving several hundred miles of open water between its seaward edges and the remaining Arctic coastlines of North America, Europe, and Asia.

The extent of melting in 2007 "caught pretty much everybody by surprise, because the retreat of the ice cover that summer was quite extreme," says Martin Jeffries, program officer and science advisor to the Office of Naval Research's Arctic and Global Prediction Program.

Despite the initial shock, however, the record melts of '07 and '12 arrived in the context of a persistent decline in summer sea ice throughout the 24-year satellite record.

The potential for a significant increase in maritime traffic in the Arctic basin each summer demands a better understanding of the ice cover and the factors that affect it in order to improve predictions.

Summer storms, for instance, can have a profound effect on the ice. Last summer provided a textbook example. A storm dubbed the Great Arctic Cyclone of 2012 moved into the central Arctic Ocean from Siberia Aug. 4 – the most powerful August storm on record for the Arctic Ocean. The storm packed winds of more than 30 miles an hour in some areas of the Arctic Ocean above the Pacific and lingered over the ocean for a few days before petering out.

For 10 days, the pace of ice loss accelerated, reducing the extent of summer ice by nearly 60,000 square miles. The heaviest losses appeared from the Beaufort Sea above Canada and Alaska west to the East Siberian Sea.

A team led by the University of Washington's Jinlun Zhang, a researcher with the university's Applied Physics Laboratory, analyzed the storm's impact via modeling studies.

From Aug. 6 to Aug. 8, the researchers say the ice underwent an "unprecedented" loss of volume of 12.9 percent.

The mechanism? Wind from the storm essentially turned already-thin pack ice into a giant Mix Master as it blew across the pack's rough surface. As floating pack ice slowly moved, the ice's rough underside stirred to the surface relatively warm water typically held at bay by an upper layer of colder water. The warmed water melted the ice from below, the study indicates.

Thin pack ice is vulnerable to wind and waves, which break it into smaller floes that are more easily carried off by the winds.

In the end, the loss of ice the storm triggered amounted to only 4.4 percent of the season's total loss, so the season's decline would have set a record even without the storm, the researchers say.

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