Scientists Rule Out a Threat of Antarctic Collapse

CONTACT: Lia Unrau

PHONE: (713)
831-4793

E-MAIL: unrau@rice.edu

SCIENTISTS RULE OUT ONE THREAT

OF ANTARCTIC
COLLAPSE

In visits last year to Antarctica,
Rice University geologists found evidence that put one of their concerns on
ice.

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.

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.

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.

“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.”

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.

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.

Anderson has made 20 visits to Antarctica over the past 28
years to study the structure, movement and erosion of this icy
continent.

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.

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.

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.

Other mechanisms that have been tied to a rapid retreat of the
ice include melting under the ice from warm ocean currents.

“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.”

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/.