WASHINGTON - Antarctic glaciers that had been blocked behind the Larsen
B ice shelf have been flowing more rapidly into the Weddell Sea, following
the break-up of that shelf. Studies based on imagery from two satellites
reached similar conclusions, which will be published September 22 in the
journal Geophysical Research Letters.
Researchers from NASA’s Jet Propulsion Laboratory (JPL) in Pasadena,
California, the National Snow and Ice Data Center (NSIDC) in Boulder,
Colorado, and NASA’s Goddard Space Flight Center (GSFC) in Greenbelt,
Maryland, said the findings prove that ice shelves act as "brakes"
on the glaciers that flow into them. The results also suggest that climate
warming can lead to rapid sea level rise.
Large ice shelves in the Antarctic Peninsula disintegrated in 1995 and
2002, as a result of climate warming. Almost immediately after the 2002
Larsen B ice shelf collapse, researchers observed nearby glaciers flowing
up to eight times faster than they did prior to the break-up. The speed-up
also caused glacier elevations to drop, lowering them by up to 38 meters
[125 feet] in six months.
"Glaciers in the Antarctic Peninsula accelerated in response to the
removal of the Larsen B ice shelf," said Eric J. Rignot, a JPL researcher
who is lead author of one of the studies. "These two papers clearly
illustrate, for the first time, the relationship between ice shelf collapses
caused by climate warming and accelerated glacier flow." Rignot's
study used data from the European Space Agency's European Remote Sensing
Satellites (ERS) and the Canadian Space Agency's RADARSAT satellite.
"If anyone was waiting to find out whether Antarctica would respond
quickly to climate warming, I think the answer is yes," said Theodore
A. (Ted) Scambos, an NSIDC glaciologist who is lead author of the second
study. "We've seen 150 miles [240 kilometers] of coastline change
drastically in just 15 years." Scambos's paper used data from Landsat
7 and ICESat, a NASA laser altimetry mission launched in 2003. Landsat
7 is jointly run by NASA and the United States Geological Survey.
The Rignot and Scambos papers illustrate relationships between climate
change, ice shelf break-ups, and increased flow of ice from glaciers into
the oceans. Increased flow of land ice into the oceans contributes to
sea level rise. While the Larsen area glaciers are too small to affect
sea level significantly, they offer insight into what will happen when
climate change spreads to regions further south, where glaciers are much
larger.
Scambos and his colleagues used five Landsat 7 images of the Antarctic
Peninsula from before and after the Larsen B break-up. The images revealed
crevasses on the surfaces of glaciers, which were used as markers in a
computer-matching technique for tracking motion between image pairs. By
following the patterns of crevasses from one image to the next, the researchers
were able to calculate velocities of the glaciers.
The surfaces of glaciers dropped rapidly as the flow sped up, according
to ICESat measurements. "The thinning of these glaciers was so dramatic
that it was easily detected with ICESat, which can measure elevation changes
to within an inch or two [several centimeters]," said Christopher
A. Shuman, a GSFC researcher and a co-author on the Scambos paper.
The Scambos study examined the period right after the Larsen B ice shelf
collapse, to try to isolate the immediate effects of ice shelf loss on
the glaciers. Rignot's study used RADARSAT to take monthly measurements
that are ongoing.
RADARSAT radar sends out signals and tracks their return after they bounce
from snow and ice surfaces. Radar is not limited by clouds, while Landsat
images require clear skies. RADARSAT can therefore provide continuous
and broad velocity information of the ice.
According to Rignot's study, the Hektoria, Green, and Evans glaciers flowed
eight times faster in 2003 than they did in 2000. They slowed moderately
in late 2003. The Jorum and Crane glaciers accelerated two-fold in early
2003 and three-fold by the end of 2003. Adjacent glaciers where the shelves
remained intact showed no significant changes, according to both studies.
The studies were funded by NASA. The National Science Foundation, and
the Instituto Antartico Argentino.
**********
Notes for Journalists
Journalists (only) may obtain a pdf copy of these papers upon request
to Harvey Leifert: hleifert@agu.org. Please provide your name, name of
publication, phone, and email address. The papers and this press release
are not under embargo.
***
Title: "Accelerated ice discharge from the Antarctic Peninsula
following the collapse of the Larsen B ice shelf"
Authors:
E. Rignot, Jet Propulsion Laboratory, Pasadena, California, USA, and Centro
de Estudios Cientificos, Valdivia, Chile;
G. Casassa, Centro de Estudios Cientificos, Valdivia, Chile;
P. Gogineni, Radar Systems and Remote Sensing Laboratory, University of
Kansas, Lawrence, Kansas, USA;
W. Krabill, EG&G Services and NASA Goddard Space Flight Center, Laboratory
for Hydrospheric Processes, Wallops Flight Facility, Wallops Island, Virginia,
USA;
A. Rivera, Centro de Estudios Cientificos, Valdivia, Chile;
R. Thomas, EG&G Services and NASA Goddard Space Flight Center, Laboratory
for Hydrospheric Processes, Wallops Flight Facility, Wallops Island, Virginia,
USA, and Centro de Estudios Cientificos, Valdivia, Chile.
Citation: Rignot, E., G. Casassa, P. Gogineni, W. Krabill, A.
Rivera, and R. Thomas (2004), Accelerated ice discharge from the Antarctic
Peninsula following the collapse of the Larsen B ice shelf, Geophys. Res.
Lett., 31, L18401, doi:10.1029/2004GL020697.
Contact information for author:
Eric Rignot: +1 818-354-1640 or eric@pib.jpl.nasa.gov
***
Title: "Glacier acceleration and thinning after ice shelf
collapse in the Larsen B embayment, Antarctica"
Authors:
T. A. Scambos, National Snow and Ice Data Center, University of Colorado,
Boulder, Colorado, USA;
J. A. Bohlander, National Snow and Ice Data Center, University of Colorado,
Boulder, Colorado, USA;
C. A. Shuman, Oceans and Ice Branch, NASA Goddard Space Flight Center,
Greenbelt, Maryland, USA;
P. Skvarca, Division Glaciologia, Instituto Antartico Argentino, Buenos
Aires, Argentina.
Citation:
Scambos, T. A., J. A. Bohlander, C.A. Shuman, and P. Skvarca, Glacier
acceleration and thinning after ice shelf collapse in the Larsen B embayment,
Antarctica, Geophys. Res. Lett., 31, L18402, doi:10.1029/2004GL020670.
Contact information for authors:
Ted Scambos: +1 303-492-1113 or teds@icehouse.colorado.edu
Christopher Shuman: +1 301-614-5706 or Christopher.A.Shuman@nasa.gov
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