Glaciers in West Antarctica are shrinking at a rate
substantially higher than observed in the 1990s. They are
losing 60 percent more ice into the Amundsen Sea than they
accumulate from inland snowfall.
The study was conducted by a science team from NASA, U.S.
universities and from the Centro de Estudios Científicos in
Chile. It is based on satellite data and comprehensive
measurements made in 2002 by a science team aboard a Chilean
P-3 aircraft equipped with NASA sensors. Science Express
published the findings today.
The ice loss from the measured glaciers corresponds to an
annual sea-level rise of .008 inches (.2 millimeters) or more
than 10 percent of the total global increase of about .07
inches (1.8 millimeters) per year.
For a balanced glacial system, the amount of glacier ice
melting or flowing into the sea roughly equals the ice formed
from snow accumulations further inland. The scientists report
the Amundsen Sea glaciers are not in balance.
Bob Thomas, a science team member with EG&G Services at the
NASA Goddard Space Flight Center’s Wallops Flight Facility,
Wallops Island, Va., commented that as the glaciers flow to
the ocean, they become afloat to form ice shelves. “The ice
shelves act like a cork and slow down the flow of the
glacier,” Thomas said.
“Ice shelves in the Amundsen Sea appear to be thinning,
offering less resistance to their tributary glaciers. Our
measurements show an increase in glacier thinning rates that
affects not only the mouth of the glacier, but also 60 miles
(100 kilometers) to 190 miles (300 kilometers) inland,”
Thomas said.
The scientists noted the earth underneath the ice is further
below sea level than had been assumed, so the ice is thicker
than once thought. This increases the amount of ice each
glacier can discharge into the ocean as its speed increases.
It makes it easier for the thinning glacier to float free
from its bed, and thus further ‘loosen the cork’,” Thomas
said.
Thomas pointed out the observed increases in velocities and
thinning rates apply to only a short time period, so it is
too early to tell if the accelerated thinning is part of a
natural cycle or is a sign of a longer-term change.
“Continued observation is important,” he said.
“The rates of glacier change remain relatively small at
present,” said Eric Rignot, a study participant from NASA’s
Jet Propulsion Laboratory, Pasadena, Calif. “But the
potential exists for these glaciers to increase global sea
level by more than one meter. The time scale over which this
will take place depends on how much faster the glaciers can
flow, which we do not know at present,” he said.
Thomas said in the last 10 years the ability to accurately
measure glaciers worldwide has greatly improved. Measurements
from aircraft and satellites like NASA’s Ice, Cloud and Land
Elevation Satellite (ICESat), launched in 2003, have greatly
improved accuracy.
To access the study on Science Express, the Web site of the
journal Science, visit.
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