Professor predicts recent, future iceberg calvings

The University scientist who predicted the recent calving of two large icebergs in Antarctica now predicts that even more will follow in coming months, thanks largely to the violent actions of the giant iceberg he calls “Godzilla.”

Douglas MacAyeal, Professor in Geophysical Sciences, had been trying for the last several years to obtain funding for an Antarctic expedition that would enable him to place instruments on a section of the Ross Ice Shelf that he could see was beginning to crack away. That section of ice broke away last month, creating an iceberg almost as large as Connecticut. But now this Godzilla, officially known as iceberg B15, threatens to crash back into the Ross Ice Shelf, creating still more icebergs.

“I’d say that there is a 50-50 chance of a ‘berg’ as big or bigger than B15 to be calved once the spring sea-ice thaw sets in around next October, and B15 starts to bash the western side of the Ross Ice Shelf,” MacAyeal said. “The ice shelf there is more overextended and more due for calving than the original location where B15 calved from.”

This next calving event could occur anytime between now and December, said MacAyeal, who would like to be there when it happens.

“If Godzilla is slow, we might be able to fly into McMurdo Station when it opens late next September or early October, go out with helicopters, put global positioning instruments on the Ross Ice Shelf and catch it calving when the big guy comes by and whacks it,” he said.

MacAyeal’s computer models indicate that this summer B15 could drift into the shipping lanes that serve McMurdo Station, now approximately 250 miles away. McMurdo is Antarctica’s largest community, housing approximately 1,100 researchers and support personnel during the warmer months from October to February.

The calving of iceberg B15 was followed a week later by the calving of B17, just as MacAyeal had predicted. This smaller iceberg, which MacAyeal calls “Bambi,” measures approximately 960 square miles––more than four times the size of Chicago.

Such events happen only every 50 to 100 years, MacAyeal said, so it is too early to tell whether the newest icebergs are a sign of global warming or business as usual.

“We’ve only had satellites looking at the Antarctic since the late ’60s or early ’70s. This happens to be the beginning of our experience with icebergs,” he said.

MacAyeal was able to confirm the calving of B15 and track the calving of B17 by analyzing satellite images provided by Matthew Lazzara of the University of Wisconsin-Madison’s Antarctic Meteor-ological Research Center. MacAyeal was acting on a tip from contacts at the National Science Foundation, which sponsors U.S. polar research in Antarctica.

MacAyeal and Lazzara began working together just weeks before the calving of B15, after discovering a mutual interest in A38, a much smaller iceberg that broke off the Ronne Ice Shelf in 1998. For a year and a half, Lazzara said, he and his Wisconsin colleagues had casually followed the progress of A38 through satellite images. Then MacAyeal gave a lecture at Wisconsin during which he presented a computer animation of A38’s motion as it was jostled by ocean tides.

“We had the satellite observations to complement Doug’s modeling work,” Lazzara said. “Our hobby has turned into a serious research activity.”

The world’s first weather satellite was launched April 1, 1960. Today, a variety of satellites are in position to monitor B15 with photographs, infrared images and two types of radar.

“This once-in-a-lifetime event has been fascinating to watch via modern satellite technology, and in nearly real time, too,” Lazzara said.

Scientists rarely get to study rapidly changing glacial phenomena, MacAyeal noted.

“People use the metaphor, ‘It’s glacially slow.’ You know, ‘Walk for your lives; the glaciers are coming!’ Well, finally, we have something happening in the glacial world, and it’s happening on a daily basis,” he said.

To view animated simulations of iceberg B15 as it is jostled by ocean tides off the coast of Antarctica, see http://www-news.uchicago.edu/releases/photos/icebergs. MacAyeal developed the simulations in collaboration with Benjamin Kerman of the College and graduate student Theodore Gotis. It was Kerman’s interest in working with MacAyeal following a class on Ice Age Earth that got the latter researching icebergs.

“I thought that working on icebergs would be the least likely project to come to any kind of interesting results,” MacAyeal said. “One thing led to another, and I’m saying this is surprisingly important.”