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Dead whales tell tales of sea ice decline.

By delving deep into whaling records going back to the 1930s, an Australian scientist has discovered evidence of a major decline in the amount of sea ice surrounding Antarctica.

The ice-covered sea around Antarctica measures about twice the size of the United States, and oceanographers regard it as a climatic canary in a coal mine--a sensitive measure of changing conditions.

Because satellite records of sea ice only go back to the 1970s, climate scientists have no direct means of assessing long-term changes in the amount of polar sea ice. Whaling data, however, can provide a roundabout technique for studying the ice, reports William K. de la Mare of the Australian Antarctic Division in Tasmania in the Sept. 4 Nature.

The International Whaling Commission has 1.5 million records of whale catches since the 1930s. They include the date, the ship's position, and the species captured. De la Mare surmised that he could use these data to track sea ice because many whales congregate around the ice's edge, an area rich in food.

For the period 1930 through 1950, de la Mare finds that the sea ice boundary remained stable, averaging around 61.5 [degrees] S. During the early 1950s, the positions of the southernmost catches started drifting south, indicating a reduction in sea ice coverage.

Between 1957 and 1971, whalers moved farther north because they had depleted populations of large whales. In the early 1970s, whalers returned to the south to pursue the smaller minke whales, which accumulate at the sea ice edge.

De la Mare found a big change in whaling reports between the 1940s and the 1970s. During the later period, ships made their southernmost catches on average 2.8 [degrees] farther south than in the earlier period.

"This suggests a decline in the area of sea ice of some 25 percent," which equals a loss of 5.65 million square kilometers of sea ice, says de la Mare.

Some sea ice researchers remain unconvinced. "I find it hard to believe," says H. Jay Zwally of NASAs Goddard Space Flight Center in Greenbelt, Md. Zwally notes that whalers pursued different prey in the 1970s than they did earlier, perhaps explaining some of the change. Furthermore, de la Mare lacks data for the critical interval during the late 1950s and 1960s, when whalers worked away from the ice edge.

De la Mare counters that changes in whaling practice cannot explain the observed southward shift. The ultimate cause of the sea ice decline, he says, remains uncertain. Some computer climate models predict that greenhouse warming should increase the amount of Antarctic sea ice, although other models indicate a decline.
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Title Annotation:whaling records suggest a 25% decline in Antarctica sea ice between the 1940s and 1970s
Author:Monastersky, Richard
Publication:Science News
Article Type:Brief Article
Date:Sep 6, 1997
Words:439
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