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



(Copyright 2011 by The Associated Press. All Rights Reserved.)