Sur­veys of Arctic ice can be tricky busi­ness

The Columbus Dispatch - - Front Page - By Henry Foun­tain

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.

Newspapers in English

Newspapers from USA

© PressReader. All rights reserved.