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Antarctic ice samples: What do they say about global warming?

Antarctic ice core samples, up to 150,000 years old, may help scientists estimate whether it will take 50 years - or 500 years - for the Ross Ice Shelf to collapse at the current rate of climate change.

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At one point bad weather even compelled logistics experts to prepare a plan to keep the 14-member team there through the Antarctic winter, four months of almost total darkness and temperatures that can drop to minus 60 C (minus 76 F).

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The weather improved, but the round-the-clock daylight of the Antarctic summer is grueling enough. Bertler, 42, who has spent nearly every summer there for 14 years, says its boundless frontiers can feel like a prison, though she has grown to love the exceptional landscape.

While on the island, the team's only form of communication was three satellite phones. Every person carried a GPS unit in case he or she got lost in the fog or storms.

The crew worked 10-hour shifts, read, occasionally skied cross-country. Some found it difficult to sleep in permanent daylight. "Everything becomes quite primal, in a way," Bertler said. "You're just thinking about your daily survival, being safe, and doing the work that you're there to do."

The team used a sophisticated drill to collect cylinders or cores of ice. To ensure the samples stayed cold enough to get safely to New Zealand, the team had to do something that seemed counterintuitive: import a freezer to Antarctica.

Still, the thousands of years of history collected in the ice cores almost melted away on the voyage home, when huge waves knocked out power to the freezer and swamped a backup generator. It was 36 hours before a technician could get on deck and restore power. But the ice stayed cold enough and reached the project's base in Wellington, the New Zealand capital, last month.

The cores consist of sandwich-like layers of ice, formed when annual snowfall compacts to a fraction of its original depth. Bertler said she believes most of the ice she has collected is less than 40,000 years old, although the final pieces near the rock bottom could be up to 150,000 years old.

The material Bertler thinks may be marine sediment came from 760 meters (2,500 feet) deep.

Richard Levy, a New Zealand scientist who specializes in past climates and who was not involved in Bertler's research, said the project provides a high level of detail about climate change over relatively short periods of time.

The layers of ice allow scientists to measure atmospheric gas levels on an almost annual basis going back thousands of years, he said. That complements rock-drilling work Levy and others have done in the Antarctic interior, which tracks climate change over longer time horizons of several million years, he said.

Bertler's project has taken about seven years to complete and cost about 11 million New Zealand dollars ($9.2 million), most of which has come from the New Zealand government. Scientists from Australia, Britain, China, Denmark, Germany, Italy, Sweden and the U.S. also are involved.

Tim Naish, a colleague of Bertler's who heads New Zealand's Antarctic Research Centre, said that if Bertler has indeed found recent marine sediment, it could be significant.

"It will provide insight into what happens when the Earth warms," he said.

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McGuirk reported from Scott Base, Antarctica.

Copyright 2013 The Associated Press.

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