Giant hole melted in northern ice cap

Scientists suspect event may be a symptom of global warming

September 22, 2006|By Frank D. Roylance | Frank D. Roylance,Sun reporter

Something unusual is going on in the Beaufort Sea, a remote part of the Arctic Ocean north of Alaska. Over the past six weeks, a huge "lake" bigger than the state of Indiana has melted out of the sea ice.

Within the past week, this "polynya" - a Russian word for any open water surrounded by sea ice - finally melted through a part of the ice that separated it from the open ocean, forming a kind of bay in the planet's northern ice cap.

"The reason we're tracking it is because we had never seen anything like that before," said Mark C. Serreze, senior research scientist at the National Snow and Ice Data Center in Boulder, Colo.

Polynyas occur every year in certain parts of the Arctic where warm currents and persistent winds clear swaths of sea ice.

But this one, covering 38,000 square miles, is unique in the memory of scientists who watch the Arctic ice closely because they see it as a bellwether for the effects of global warming. They've found that the area of the summer ice cap has been shrinking for at least three decades, and it's getting thinner, too.

Last year, scientists at NASA and the NSIDC reported the most extensive summer meltdown of Arctic sea ice on record and an acceleration in the rate of its long-term decline.

In a new study reported last week, NASA researcher Josefino Comiso found that the Arctic's winter ice is also in decline, and at an accelerating rate.

The ice cap is critical because it helps regulate the planet's temperature. Its bright surface reflects 80 percent of the solar energy that strikes it, sending it back into space.

Climatologists say a smaller ice cap will reflect less solar energy and expose more open water, which is darker and absorbs 90 percent of the solar energy that falls on it. It heats up, holds more of that heat from year to year, and makes it harder for ice to form again in the fall and winter.

So Arctic temperatures rise. From January through August 2005, they were 3.6 to 5.4 degrees Fahrenheit warmer than the long-term average across most of the region.

As of Tuesday, NSIDC reported that the summer sea ice this year had shrunk to the fourth-smallest September minimum on record. Some refreezing has begun, but parts of the polynya were continuing to melt, so the final totals are uncertain.

If current rates of summer melting continue, NSIDC researchers have said, the Arctic Ocean could be completely ice-free in summer before the end of this century.

Serreze stopped short of blaming this summer's giant polynya on global warming. "To be honest, it's hard to draw a direct link. The sea ice is inherently quite variable," he said. "But to get a big patch of open water out there in the multi-year ice, which is thinning and loosening up, it's not a surprising event in the context of global warming."

Precisely what caused this polynya to open up when and where it did will remain a mystery until scientists can investigate further.

For climatologist Claire L. Parkinson, a senior scientist at the NASA Goddard Space Flight Center in Greenbelt, what's significant is not the polynya, but the appearance of so much open water.

"The fact of decreasing ice coverage is certainly a concern," she said. And "it's certainly thought to be related to the warming of the Arctic region which has been occurring for these past three decades."

Smaller polynyas open up every year in other parts of the Arctic, where steady winds and warm ocean currents part the ice. Their predictability attracts many species of animals who rely on them for sustenance, especially in winter, said Ian Stirling, a research scientist with the Canadian Wildlife Service.

Sunlight on the open water encourages algae blooms. That provides the foundation for a food chain used by crustaceans, fish and whales. And the marine bounty attracts birds, walruses and seals, which are in turn hunted by polar bears.

"The location of bird colonies in most areas of the high Arctic are determined by the distribution of recurring polynyas along the coastline," Stirling said.

For biologists, the largest and most important recurring lake is the North Water Polynya. Located in the strait between Ellesmere Island and Greenland, the water is kept open even in winter by persistent northwest winds.

Polynyas can also attract whales - some of whom stay too long and are fatally trapped as the ice refreezes, an event Greenlanders call "sassats."

In October 1988, three gray whales got trapped in a small polynya as it refroze off the North Slope of Alaska, five miles from the nearest open water. They were eventually rescued by a Russian ice breaker, a spectacle that attracted worldwide media attention.

Stirling said arctic whales have already begun their annual migration westward from their summer feeding grounds in the Beaufort Sea along the coast of Alaska toward their wintering grounds in the Bering Sea.

"It's possible a few might head through that area [of the giant polynya]," he said. But it's unlikely they'll get stuck there.

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