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.

Jacobs and MacAyeal suspect simple ice pile-up at the Ross Ice Shelf might be the reason behind the recent giant bergs like Godzilla. But others say that global warming can’t be ruled out.

A recent study by the National Oceanic and Atmospheric Administration showed ocean temperatures have increased by an average of half a degree Fahrenheit near the surface and a tenth of a degree at deep levels since the 1950s. Bindschadler suspects this warmer ocean water sloshing at the undersides of Antarctica’s ice shelves might increase their melting.

“How effectively the water can get underneath, we don’t know,” he says. “But the more it does, the more it will form icebergs.”

Other scientists worry an increase in temperature could speed the flow of ice streams on the continent. Ice streams are the vast channels of slow-moving ice traveling from the continent’s center to its edges.

Evidence of warming is more certain at the Antarctic Peninsula where temperatures have risen by about 2 ½ degrees over the past 50 years. Following that warming, a spate of icebergs split off in the 1980s and 1990s.

“The ice flows feeding the shelves aren’t speeding up, so if the shelves continue disintegrating, they could become sort of an endangered species, if you will,” says Bindschadler.

But, as Jacobs points out, the local warming at the peninsula might be part of a natural fluctuation in temperature.

Blocking Traffic

Whether or not global warming is making Antarctica’s ice shelves less stable may remain uncertain for now. What is more certain is the potential trouble the recent pile-up of icebergs holds for resupply ships traveling to the McMurdo Station, the logistics hub for the U.S. Antarctic programs.

Winter is now easing from the southern continent and McMurdo hosts only a skeletal crew of about 250 through the austral winter. But in coming months, more than 1,000 researchers, construction workers and other personnel are due to arrive for the coming summer season.

The resupply ships, which carry everything from food to vehicles to construction materials, are vital for keeping not only McMurdo, but every U.S. station, including the South Pole station, in operation.

Although the icebergs, themselves, are unlikely to block the ships, they could cause ice buildup known as ice plates, to form between them and the coast during the next winter season. And, like large icebergs, ice plates are known to stick around for many seasons. That could cause an icy lockout of McMurdo by the station’s next delivery date in 2002.

“You could still access the station by air,” says Scambos. “But trying to run McMurdo with only air support is a different proposition. You’d probably have to scale back the entire program and almost mothball the bases in the meantime.”