Friday, October 14, 2011

Young and thin instead of old and bulky: A report on changes in Arctic sea ice

Alfred Wegener Institute News has a detailed story about their research vessel's recent voyage: In the central Arctic the proportion of old, thick sea ice has declined significantly. Instead, the ice cover now largely consists of thin, one-year-old floes. This is one of the results that scientists of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association brought back from the 26th Arctic expedition of the research vessel Polarstern.

The ship arrived at its home port of Bremerhaven at about 7 o’clock this morning. Prior to that it had covered more than 11,800 nautical miles on its 16-week research voyage and accommodated around 130 scientists from six countries on the three legs. The last stage took them through the central Arctic Ocean and the Polarstern also reached the North Pole. One of the most important research questions was: Did sea ice melt to a greater extent this summer, making it thinner than in past years?

To answer it, the sea ice physicists headed by Dr. Marcel Nicolaus and Dr. Stefan Hendricks employed a measuring instrument called “EM Bird”. This nearly four-metre-long, torpedo-shaped probe is flown over the ice with a helicopter and measures the ice thickness by means of an electromagnetic induction method. In this way the sea ice physicists created an ice thickness profile of the central Arctic over a total distance of more than 2,500 flown kilometres. Their conclusion is: at sites where the sea ice was mainly composed of old, thicker ice floes in the past decades there is now primarily one-year-old ice with an average thickness of 90 centimetres. Only in the Canadian Basin and near the Severnaya Zemlya island group in northern Siberia did the sea ice physicists encounter significant amounts of several-year-old ice. As a rule, this old ice is between two and five metres thick.

Compared to their measurements from 2007, when the extent of the sea ice had diminished to a record minimum of 4.3 million square kilometres, the researchers have not yet found any differences, however. “The ice has not recovered. This summer it appears to have melted to exactly the same degree as in 2007. Yes, it is exactly as thin as in the record year,” says Hendricks....

Ingo Arndt took this dramatic shot of the Polarstern and its mooring chain. From the website of the Alfred Wegener Institute for Polar and Marine Research

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