Scientists Seek Explanations for Antarctic Icebergs

Imagine if the state of Connecticut somehow splintered from the continental United States, then floated south and rammed into Long Island, knocking a chunk of the New York appendage into the Atlantic.

Granted, that’s not likely to happen, but convert those land masses to ice and you have the approximate scenario of what most likely occurred last week on the western coast of Antarctica.

A Connecticut-sized iceberg, known as B-15, peeled off the Ross Ice Shelf in March and has been knocking around the continent’s coastline ever since. Although clouds prevented satellites from capturing the moment, Doug MacAyeal, an iceberg specialist at the University of Chicago, is almost positive B-15 was responsible for knocking a smaller iceberg, known as B-20, from the shelf.

“B-20 was ready to calve and it needed a little shove from some outside stimulus,” he says, “like the spank a doctor gives to a newborn to get it to begin breathing.”

Trigger Uncertain

All this banging around by the iceberg known as “Godzilla” (B-15 weighed about 2 billion tons and measured about 4,250 square miles before breaking up into five pieces) has led to cluttered waters around the Ross Ice Shelf. In addition to B-20, which extends for about 350 square miles, B-15 triggered another large iceberg, B-17, to calve late last March. MacAyeal predicts there are more to come.

Is global warming also a factor? Scientists aren’t yet sure.

“There has definitely been an increased amount of calving,” says Bob Bindschadler of NASA’s Goddard Space Flight Center. “Whether that is something that is part of a natural variability or due to rising water temperatures we can’t really say. But it does beg the question: What is causing the increase?”

Throughout history, people have documented intimidating encounters with icebergs. There was the Titanic’s fateful collision with a 60-foot iceberg in 1912. That chunk of ice from the north tore through the ship’s hull and doomed 1,503 passengers to a chilling death. And in 1956, crewmen aboard a U.S. Navy icebreaker near the Ross Ice Shelf reported citing a floating chunk that supposedly measured an incredible 208 by 60 miles.

But it wasn’t until the early 1970s that scientists gained access to pictures of icebergs forming through images snapped by military and research satellites. These bird’s-eye images are what captured the near disappearance of Antarctica’s Wordie Ice Shelf between 1974 and 1989 and the even more dramatic collapse of the Larsen Ice Shelf in just 50 days in 1994.

Although satellites haven’t captured much iceberg activity at the Ross Ice Shelf before this year, Stan Jacobs of Columbia University’s Lamont-Doherty Earth Observatory has pieced together early descriptions of the shelf since it was first discovered in 1841. These records, he says, suggest it may have been long due to shed some icebergs.

“Early records at the beginning of the century show the region to be much further south than it is now,” Jacobs says. “It may have gone 75 to 90 years without a large calving event.”

Continent in Motion

Antarctica is a slow-moving continent that produces icebergs as part of a natural process. At the interior of the continent, the weight of piles of ice — sometimes a mile thick — continually push downward and outward. At the continent’s edges, the ice forms shelves and eventually falls off into the sea.

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