Surveys of Arctic ice can be tricky business
For the past 40 years, thanks to satellite measurements, scientists have known that sea ice coverage in the Arctic is shrinking. Global warming has reduced the extent of ice in the region in summer, when it is at its lowest, by nearly 13 percent a decade. That has led some researchers to predict that the Arctic could be ice-free in summers by the middle of the century.
But ice extent is only part of the story. Scientists want to know thickness, too, because together with extent, that tells them the total volume of ice in the Arctic.
Average thickness also has declined sharply, as melting of multiyear ice leaves a greater proportion of thinner, first-year ice. Winds and currents also can move older ice out of the Arctic at a higher rate.
Measuring the thickness of sea ice is trickier than measuring its extent. There’s a European satellite, Cryosat-2, that can do the job using radar to determine ice elevation and therefore thickness. But Cryosat-2 works best in winter; in summer, when the ice is melting, it has difficulty distinguishing between ice and open water.
To fill the data gap, some governments and other groups have conducted summer measurement campaigns from aircraft. The latest was undertaken in late July and August by researchers from the Alfred Wegener Institute, which is based in Bremerhaven, Germany.
Operating from Station Nord, a small Danish military and scientific outpost in Greenland, about 575 miles from the geographic North Pole, the researchers measured ice thickness in the Arctic Ocean and in the Fram Strait, which separates Greenland from the Norwegian archipelago of Svalbard. During the summer, Station Nord, a Danish military outpost in Greenland, becomes the site of dozens of scientific efforts to monitor the effects of global warming on the ice.
The Wegener Institute program, which is led by Thomas Krumpen, a seaice physicist, employs an electromagnetic device similar to a metal detector. It uses the difference in electrical conductivity between ice and seawater, coupled with precise elevation data measured by a laser scanner, to determine thickness.
The torpedo-shaped device, called the EM-Bird is suspended by a cable just 70 feet above the surface while the plane, a rebuilt and extensively modified DC-3, flies a few hundred feet higher.
But the low-altitude flights require a lot of planning, and good visibility is a must. So the Wegener team — which this summer included two pilots, an engineer, a mechanic and two scientists — spends a lot of time looking at weather forecasts and determining the best spot to take their measurements.
Warm weather across much of the Arctic this summer often led to lessthan-ideal flying conditions. Still, over a little more than two weeks, Krumpen’s team completed nine survey flights, including one that reached within about 150 miles of the North Pole.
“Given the weather situation, I’m actually pretty happy,” he said.
Preliminary analysis of the data shows that, although ice thickness varies considerably year to year, the downward trend continues.
Average thickness of undisturbed ice in the areas surveyed this summer was a little less than 5 feet, down from more than 7 feet in the mid-2000s.