Clues About Weather Hidden in Ice
SHEBA ICE STATION, ARCTIC OCEAN
It's windy and well below zero when five bundled explorers head for what, until yesterday, was "SHEBA International Airport." The 1,200-foot ice runway had been the landing strip for a Twin Otter airplane whose resupply flights to Dead Horse, Alaska, are the lifeline for this research outpost on top of the world.Skip to next paragraph
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But no more.
The white airstrip is now traversed by a dark crack that's 10 feet wide at some parts and stretches as far as the eye can see.
The rift typifies the changes in Arctic ice, a key theme for the SHEBA project, a 13-month effort to measure the changes in heat in the Arctic Ocean area in unprecedented detail. By understanding more about how heat is transferred from ice to sea to sky in this frosty region, researchers back on the mainland - who use supercomputers to mimic Earth's climate - will be better able to calculate global warming and its effects on the rest of the planet. The stability of the ice - how much it moves and its thickness - is a key component of understanding the transfer of heat.
The fissure we're snowmobiling out to see this afternoon opened overnight, just before a video crew from "Good Morning, America" was scheduled to fly back to Dead Horse. The plane got off the ice thanks to a hastily built plywood bridge. Now, the ice station's logistics team has set about building a new runway elsewhere.
Hassle and blessing
While the new crack causes trouble for the logistics crew, it's also a great subject of study for this pack of scientists.
To a newcomer to the Arctic, walking across the ice-floe runway to the crack feels no different that walking down a country road after a freeze and light snowfall. The floe seems stable. But there's subtle evidence all around that it's not so steady.
For one thing, the massive chunk of ice on which this expedition is based has slowly roamed in a figure-eight pattern around a 30-mile by 12-mile area of ocean in the past month.
Other evidence of instability, such as the crack we're investigating, is more dramatic.
The forces that cause the ice to crack or join are the focus of Jacqueline Richter-Menge's work here at the SHEBA ice station. "My main interest is in the ice cover itself. That's what controls the heat balance between the ocean and atmosphere," she says. "Ice thickness controls the interaction."
To measure thickness, she has put 100 stakes around the floe to measure changes in ice thickness and snow depth. Nearly 2 meters tall, these wooden stakes are the epitome of Ace- Hardware simplicity in an era of supercomputer science.
At each spot, Dr. Richter-Menge and the rest of the ice team drill through the ice and lower a metal rod attached to a steel wire into the ocean below. Then they let the wire freeze into the ice. Periodically, they use a portable generator and jumper cables to heat the wire, which melts the ice around it. Then they lift rod until it's snug against the floe's bottom and measure the distance it moved.
Pulling together many threads
The multifaceted nature of the SHEBA project is evident in the placement of the team's instruments.
At the ship-side ice camp, the US Army Corps of Engineers has set up instruments near the oceanography team, which is measuring heat flow in ocean, and near meteorological teams that are measuring heat flow in the atmosphere.
Correlating that kind of data is vital to understanding the forces that cause ice to break up and come crushing together.
One notion researchers here want to test holds that ice ridges form when the wind pushes one floe into another. Then, the crunch comes, raising ice rubble into a ridge, much as mountains form when massive plates in Earth's crust collide. When the winds subside, the floe rebounds, opening cracks where the rubble once was.
The crack we stand near exhibits all the right signs of compression and relaxation. Now, the winds are picking up, and we hear a periodic "crunch" as the rift starts to close.
By getting a better look at the factors that speed or retard the breakup of ice, which allows the exposed ocean to absorb more of the sun's radiation, the team hopes to hand climate modelers several more pieces of the ocean-atmosphere-climate puzzle they're trying to solve.