SHEBA Breaks Free Of Arctic's Icy Embrace

"We've observed the ice, the atmosphere and the ocean over a full annual cycle covering the physical variables in all three systems. We've seen it all: melting, freezing, heating, cooling, ridges, cracks, leads, melt ponds and all kinds of different formations of ice and snow," said Richard Moritz, polar scientist with the University of Washington's Applied Physics Laboratory and director of the SHEBA project office based at the university. The Des Groseilliers is expected to anchor off Prudhoe Bay Oct. 14 or 15 to offload personnel and cargo.

Purposely frozen into the ice pack early last October, the Des Groseilliers became the heart of Ice Station SHEBA, short for the Surface Heat Budget of the Arctic Ocean. It is a $19.5 million research effort to gather data to improve Arctic climate models and, in turn, global forecasts of climate change, said Mike Ledbetter, director for NSF's Arctic System Science Program.

The Arctic ice pack undergoes profound changes every year. In winter, the ice pack is about the size of the continental United States; in summer, there is only half as much ice. Understanding what controls this annual freeze and meltdown is a key to predicting future climate change and assessing the toll of global warming, whether it's natural or human-caused.

Warming could, for instance, affect westerly winds and change weather patterns in the northern hemisphere, Ledbetter says. It certainly would affect the web of life in the Arctic that ranges from microscopic algae on the sea ice to 1,600-pound polar bears that roam the surface.

A better understanding of the consequences of global warming in the Arctic would be important as world governments debate options that range from doing nothing to taking drastic steps to curtail the production of greenhouse gases.

SHEBA documented how such things as clouds, snow, ice and the ocean interact and exchange energy over the course of a year. "The data collected is unprecedented and will be used for decades to improve climate predictions," Ledbetter said.

The ice station, funded by NSF with support from the Office of Naval Research and the Japanese government, was located on a floe that originally was 5 miles by 6 miles. The station consisted of a collection of plywood research huts, cold-weather tents, meteorological towers, automatic buoys and stands of instruments surrounding the Des Groseilliers. The icebreaker was used under an agreement between the Office of Naval Research, NSF and Canadian Department of Fisheries and Oceans.

Small planes able to land on the ice and U.S. icebreakers provided the means to rotate scientists and crew during the experiment. The number of scientists working on site ranged from 15 in mid-winter to about 35 last spring.

Data also was gathered by sensors on six spacecraft, by researchers using four different kinds of aircraft and by a submarine prowling beneath the ice cap. The work was done in collaboration with U.S. agencies such as Department of Energy, NASA and the Navy.

SHEBA was concerned with how the climate of the Arctic works, not with trying to determine if global warming is underway in the Arctic Ocean, Moritz said. Nevertheless, scientists were surprised in October 1997 that the water was much fresher than in measurements made in the same area 20 years ago. It was determined that the melting of the ice pack during the summer of 1997 caused the lower salinity. The findings were published in Geophysical Research Letters in May.

The ice where the station was established a year ago also was thinner than expected, Moritz says. Scientists had hoped to find ice of two to three meters in that area but despite searching some 50 miles farther north, settled on a floe that was between 1.6 and 1.8 meters thick. Going even farther north would have placed SHEBA beyond the limit of the Twin Otter aircraft used most of the year to reach the ice station from mainland Alaska.

Factors at work since last fall, including some effects from the El Nino event, produced a winter where the pack didn't thicken as much as seasoned ice experts had expected. Preliminary analyses of late summer measurements indicate that the floe lost more ice than it gained last winter.

Weather, ice and ocean conditions also combined in unexpected ways to move the floe farther and faster from its starting point than anyone predicted. Originally frozen in about 300 miles north of Prudhoe Bay, the floe was shoved along a meandering, 1,000-mile path ending up about 400 miles northwest of where it started.

Along with moving the ice floe, sometimes at a rate of 20 miles a day, the wind and ocean currents rearranged the station itself a number of times. During blizzard conditions in early April, for instance, the part of the camp with a 70-foot meteorological tower and seven huts migrated a quarter-mile away from the ship * overnight.

For more information, see: http://sheba.apl.washington.edu