Bottoms-up Antarctic ice growth discovered

[March 04, 2011]  WASHINGTON (AP) -- When it comes to ice, scientists are giving a whole new meaning to the phrase "bottoms up." Those massive ice sheets in Antarctica don't just grow on top when snow falls, they also grow from the bottom up, according to new research published Thursday.

Ice melts at the bottom of ice sheets, and the water helps the sheets slide across the ground below. But the water can refreeze to the bottom of the sheets and push them up, the researchers report in the online edition of the journal Science.

The base of a massive ice plateau on the East Antarctic ice sheet called Dome A is about 24 percent refrozen water, according to the team headed by Robin Bell, a geophysicist at Columbia University's Lamont-Doherty Earth Observatory.

"The ice sheets are not simple layer cake structures. Water moves around underneath the ice sheet and deforms" it, Bell explained.

Fausto Ferraccioli, a scientist with the British Antarctic Survey and co-author of the report, added that knowing how the ice is formed is critical in the search for the oldest ice and also in understanding how the ice moves.

Ted Scambos, a glaciologist at the National Snow and Ice Data Center at the University of Colorado, Boulder, called the finding "totally new, at least at this scale."

"This is orders of magnitude larger than refreezing was imagined to be, and the concept that it could uplift the ice cap is completely new," said Scambos, who was not part of the research project.

In the past, deposits of refrozen water were only seen where there are lakes under the ice, said glacier researcher Sasha Carter of the Scripps Institution of Oceanography in San Diego.

"Now it appears they are widespread in the East Antarctic interior," said Carter, who was not part of the research team.

The researchers discovered the refrozen ice during field work in 2008 and 2009, using radar that can see through the ice.

At first, "we thought they looked like beehives and were worried they were an error in the data," Bell said. But as they found more and more of the refrozen ice pieces it became clear that they were real.

Because the ice moves, it is essential to understand changes to the base, especially in response to climate changes, researchers say. The world's climate has been warming over the last century or so and the impacts are being first noted at the poles. Ice cores, long sections of ice drilled from glaciers, are often used to study past climates.

Bell suggested that the refreezing process "may push really old ice closer to the surface and make it easier to find."

However, Jeff Severinghaus, a geologist at Scripps Institution who was not involved in the study, said it could either mean older ice is better preserved or, it could make it harder to interpret the record, "if it's shuffled like a deck of cards."

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Online: http://www.sciencemag.org/

[Associated Press; By RANDOLPH E. SCHMID]

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