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Researchers are traveling around the globe – from the poles to the tropics—to try and gain a better understanding of the worlds climate change. They are particularly interested in finding out to what extent the warming we see today is due to human production of greenhouse gases, such as carbon dioxide, which trap heat in the atmosphere. In the Antarctic Peninsula, average annual air temperature has increased about 5 degrees Fahrenheit in the past half-century, a huge rise. As a result, many of the peninsula's ice shelves are shrinking. Ice shelves are floating platforms of ice hundreds or even thousands of feet thick that extend many miles from the continent. For example, in just a few short years, almost half of the third-largest ice shelf in Antarctica—the Larsen Ice Shelf—has disappeared. The northernmost segment--called Larsen A--has completely melted since the mid 1990's. And the much larger middle segment—Larsen B—shrank rapidly through the late 1990's, then lost most of its remaining mass in February 2002 when a chuck the size of the state of Rhode Island (about 1,250 square miles of ice) broke off and disintegrated.
Is melting of this magnitude an unprecedented event in recent geologic time? The National Science Foundation's Office of Polar Programs is supporting researchers like Scott Ishman, a paleobiologist and assistant professor of geology at Southern Illinois University Carbondale, to try to answer this question by determining the history of the Larsen Ice Shelf during the 12,000 years that have passed since the end of the last great ice age. Part of Ishman's research has involved collecting water and sediment samples from sites recently covered by Larsen B. Ishman and his team is working with geology undergraduate Phillip Szymcek to identify foraminifera (called "forams" for short)—single-celled marine creatures found throughout the world's oceans—in the samples.
There are thousands of species of forams but what groups occur in a given area depends upon the water temperature, salinity, and oxygen content; the nutrient density; and the type of sea-floor sediment. By learning what environmental conditions living foram groups require, scientists finding the same groups in the fossil record can tell what a region's environment was like in the past and can better interpret what's happening with the climate today.
Foram samples collected in May 2000 suggest that Larsen A may have melted once before, between 9,000 and 6,000 years ago, when the earth in general was warmer. The team also found evidence of ancient algae blooms, a surface phenomenon that indicates the presence of open water in the past. However at this time, no evidence collected shows any indication that Larsen B has been anything but stable since the ice ages—until now. No remnants of algae blooms were found in cores taken from the sea floor in this area. Based on their studies thus far, Ishman and his colleagues have concluded that the collapse of the Larsen Ice Shelf appears to be due entirely to atmospheric warming. Thumbnail">
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