By Mike CherneyThe Daily Northwestern
A new study suggests that an iceberg near Antarctica was split apart by a wave that originated more than 8,300 miles away.
The study, led by Douglas MacAyeal of the University of Chicago and Emile Okal, a Northwestern geological sciences professor, investigated the mysterious October 2005 breakup of the iceberg B15A, which was 60 miles long and nearly 19 miles wide. Satellite images showed that the iceberg had broken into half a dozen pieces under mild conditions.
The scientists suggested that a wave generated by a storm near Alaska caused the breaking up – or calving – of the iceberg, an example of how weather happening in one area of the globe can affect another. The study was published in the October issue of Geophysical Research Letters.
It’s one of the first times that a sea swell from the northern hemisphere has been documented breaking up an iceberg in the southern hemisphere. Before now, scientists had studied storms in the northern and southern hemisphere separately.
“The implication is that these two systems may be related and could be joined together,” Okal said. “This means that systems which we were really not sure were linked together may very well be.”
Seismometers that the scientists had placed on the iceberg recorded the wave several days after the Alaskan storm. The team also checked seismometers placed on islands in the wave’s path to confirm that the wave actually did originate near Alaska.
Mac Cathles, a graduate student in geophysical sciences at the University of Chicago who also worked on the study, said waves from distant storms could explain why the breakup of icebergs seems to have been synchronized in the past.
“It proposes a possible answer, not definitive proof,” he said.
The study also could shed light on global warming’s effect on the Antarctic ice sheets. Some scientists who study global warming have long said that the phenomenon could cause an increase in storms. If there are more storms worldwide, then more icebergs eventually could get broken up by the waves that the storms produce.
In the past, significant iceberg breakup has been associated with climate change, according to the study, so an increase today in the rate of iceberg breakup could indicate that the climate is changing. But Okal said that scientists do not have enough evidence to determine the exact rate of breakup.
“If, in the future, we had some evidence for the rate at which these things take place, any change in the rate can be attributable to the change in climate, but it’s not going to change the climate,” he said.
The team originally had not planned to study the effect of distant sea swells on iceberg calving. The seismometers initially were deployed to investigate strange harmonic tremors that occur within icebergs that scientists think could be related to calving. Only after B15A had broken up did the scientists arrange to make a special flight from an isolated Antarctic research station to retrieve the seismometers.
“They flew out to the iceberg, which was an all-day trip,” MacAyeal said, according to a press release. “It was a superhuman effort, because they had to virtually fill the aircraft cabin with barrels of fuel, land several times, throw the fuel barrels out, pump the fuel into the wing tank, and then continue on.”
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