- HOUSTON -- In visits last year to Antarctica, Rice University geologists
found evidence that put one of their concerns on ice.
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- They found that one threat from the roster
of suspects that could cause the collapse of the West Antarctic Ice Sheet,
the most unstable part of the region, seems less of a threat. A collapse
would raise the world's sea level and threaten to flood coastal areas.
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- John Anderson, professor of geology and
geophysics, and graduate student Stephanie Shipp have been studying how
the West Antarctic Ice Sheet slides across the bed of rock or sediment
beneath it, a mechanism believed to be one that could lead to breakdown
of the ice sheet. The sliding allows it to accelerate, become thinner and
eventually float off the sea floor. This phenomenon is known as ice sheet
collapse.
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- To test the plausibility of this mechanism,
Rice geologists have been examining the geological record of the ice sheet's
behavior during the past 20,000 years.
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- "The evidence we have today shows
that this was not an important mechanism in the past," Anderson says.
"The evidence suggests that the recent retreat of the ice sheet has
been slower and more continuous than previously thought. So this portion
of the ice sheet appears to be more stable than some previous models predicted."
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- Using sophisticated instruments such
as side-scan sonar, the Rice team of scientists imaged the sea floor on
which the ice sheet formerly rested. These records show a variety of glacial
landforms that formed beneath the ice sheet, such as giant lineations or
ridges that extend for miles across the sea floor and mark the former route
of the advancing ice sheet. Other features were formed in the wake of the
retreating ice sheet and indicate that it never actually floated off the
bed or collapsed.
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- Anderson's and Shipp's results were presented
at a September meeting of glaciologists, oceanographers, meteorologists
and geophysicists interested in the fate of the ice sheet. The results
will be published in a spring issue of the Geological Society of America
Bulletin.
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- Anderson has made 20 visits to Antarctica
over the past 28 years to study the structure, movement and erosion of
this icy continent.
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- There is a large range of uncertainty
in trying to predict how much the ice sheets will contribute to sea level
rise over the next century as Earth's climate warms. Reports published
by an international government panel estimate a rise in sea level by 2100
that varies in range from 20 centimeters, which is minimal and the present
rate, to 96 centimeters. The West Antarctic Ice Sheet is believed to be
the most likely source of this rise, but there is still debate concerning
the ice sheet's stability and those mechanisms that could cause the ice
sheet to melt.
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- If this extreme prediction comes true,
Anderson says, Texas's Galveston Island would not survive, South Louisiana
would be flooded, and Bangladesh would be under water. To date, research
has focused on the Ross Sea, where 50 percent of the ice sheet drainage
into the ocean occurs.
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- To get a more accurate prediction of
future behavior of the ice sheet, scientists look at a variety of complex
factors, including temperature, precipitation, the ice sheet system, and
climate change and its direct impact on surface oceans. The most predictable
impact of global warming is that of expansion of the oceans as surface
waters become warmer. Scientists also want to understand those complexities
over a 100-200 year scenario.
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- Other mechanisms that have been tied
to a rapid retreat of the ice include melting under the ice from warm ocean
currents.
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- "The undermelting now seems to take
on greater importance," Anderson says, "now that the ice sliding
across a bed of deforming sediment is played down by our results."
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- In visits to Antarctica this year, Anderson
and his team of graduate and undergraduate students will focus on other
factors that could lead to collapse. They will head to Pine Island Bay
in the Antarctic Peninsula region, an area of the ice sheet that currently
is retreating rapidly. The area has been dubbed the "weak underbelly
of the ice sheet" by some glaciologists. The Rice team will try to
determine the recent retreat history of the ice sheet from the bay to see
if evidence exists there for a collapse.
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- Editors: For more information about Antarctica
visit <http://www.glacier.rice.edu/http://www.glacier.rice.edu/.
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