The icy coating on the Arctic Ocean has thinned dramatically
18th Nov 1999
A new underwater map of the Arctic ice cap has convinced scientists that the icy coating on the Arctic Ocean has thinned dramatically in the past few decades.
Although the comparison of two sets of submarine sonar maps of the underside of the ice -- one from 1958-1976 and another from the 1990s -- leaves little doubt that the ice is melting, environmental scientists still aren't sure why, or even if the thinning is unusual.
"Everyone wants to know if this is caused by global warming," says University of Washington oceanic physicist Drew Rothrock, "but we don't know. It's hard to say if the change we see is even out of the ordinary." Prior to 1958, scientists measured the ice thickness by walking out on the cap and drilling through the ice. But beginning in 1958, the U.S. Navy provided scientists with a view from below, on board nuclear submarines. "The sub is a much handier tool" than an ice drill, says University of Washington atmospheric scientist Greg Maykut, "You can cover a lot more area."
Although much of the Navy's data remains classified because it contains detailed locations of top-secret nuclear submarines, Rothrock, Maykut, and fellow University of Washington scientist Yanling Yu were able to gather enough unclassified archival data from 1958-76 to compare to the current ice thickness at 29 sites.
"The cover has thinned essentially everywhere," says Maykut, and declined from almost 3 meters thick to less than 2 meters in some locations. "Rothrock's work is the first confirmation that the ice is thinning," says geophysicist Terry Tucker of the Cold Region Research and Engineering Lab in Hanover, N.H.
Tucker notes that the small area covered by previous experiments made it difficult to prove that the average thickness of the shifting ice had changed.
Although everyone is guessing that the current melt is somehow related to recent observations of warm water flowing into the Arctic Ocean, no one is quite sure how the two are connected.
"They need more evidence that shows when the thinning occurs," says Tucker. To address that question, Rothrock has begun a 5-year study of soon-to-be-declassified Navy data. "That will help fill in the interim period" from 1976 to 1990, says Rothrock.
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