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February 15, 2007
JOINT NASA STUDY
REVEALS LEAKS IN ANTARCTIC 'PLUMBING SYSTEM'
Scientists using NASA satellites
have discovered an extensive network of waterways beneath a fast-moving
Antarctic ice stream that provide clues as to how "leaks" in the
system impact sea level and the world's largest ice sheet. Antarctica
holds about 90 percent of the world's ice and 70 percent of the world's
reservoir of fresh water.
With data from NASA satellites, a team of scientists led by research
geophysicist Helen Fricker of the Scripps Institution of Oceanography,
La
Jolla, Calif., detected for the first time the subtle rise and fall of
the
surface of fast-moving ice streams as the lakes and channels nearly a
half-mile
of solid ice below filled and emptied. Results were presented Thursday
at the
annual meeting of the American Association for the Advancement of
Science
(AAAS) in San
Francisco.
The study will be published in the Feb. 16 issue of Science
magazine.
"This exciting discovery of large lakes exchanging water under the ice
sheet surface has radically altered our view of what is happening at
the base
of the ice sheet and how ice moves in that environment," said co-author
Robert Bindschadler, chief scientist of the Laboratory for Hydrospheric
and
Biospheric Sciences at NASA's Goddard Space Flight Center, Greenbelt,
Md.
"NASA’s state-of-the-art satellite instruments are so
sensitive we are
able to capture an unprecedented three-dimensional look at the system
beneath
the thick ice sheet and measure from space changes of a mere 3 feet in
its
surface elevation. That is like seeing an elevation change in the
thickness of
a paperback book from an airplane flying at 35,000 feet."
The surface of the ice sheet appears stable to the naked eye, but
because the
base of an ice stream is warmer, water melts from the basal ice to
flow,
filling the system’s “pipes" and lubricating flow
of the overlying ice.
This web of waterways acts as a vehicle for water to move and change
its
influence on the ice movement. Moving back and forth through the
system's
"pipes" from one lake to another, the water stimulates the speed of
the ice stream's flow a few feet per day, contributing to conditions
that cause
the ice sheet to either grow or decay. Movement in this system can
influence
sea level and ice melt worldwide.
"There's an urgency to learning more about ice sheets when you note
that
sea level rises and falls in direct response to changes in that
ice,” Fricker
said. “With this in mind, NASA's ICESat, Aqua and other
satellites are
providing a vital public service."
In recent years, scientists have discovered more than 145 subglacial
lakes, a
smaller number of which composes this "plumbing system" in the
Antarctic.
Bindschadler and Fricker; Ted Scambos of the National Snow and Ice Data
Center
in Boulder, Colo.; and Laurence Padman of Earth and Space Research in
Corvallis, Ore.; observed water discharging from these under-ice lakes
into the
ocean in coastal areas. Their research has delivered new insight into
how much
and how frequently these waterways “leak” water and
how many connect to the
ocean.
The study included observations of a subglacial lake the size of Lake Ontario
buried under an active area of west Antarctica that feeds into the Ross Ice Shelf. The research
team combined images from
the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument
aboard
NASA's Aqua satellite and data from the Geoscience Laser Altimeter
System
(GLAS) on NASA's Ice Cloud and Land Elevation Satellite (ICESat) to
unveil a
multi-dimensional view of changes in the elevation of the icy surface
above the
lake and surrounding areas during a three-year period. Those changes
suggest
the lake drained and that its water relocated elsewhere.
MODIS continuously takes measurements of broad-sweeping surface areas
at three
levels of detail, revealing the outline of under-ice lakes. ICESat's
GLAS
instrument uses laser altimetry technology to measure even the smallest
of
elevation changes in the landscape of an ice sheet. Together, data from
both
have been used to create a multi-year series of calibrated surface
reflectance
images, resulting in a new technique called satellite image
differencing that
emphasizes where surface slopes have changed.
For
more information and images,
visit:
http://www.nasa.gov/vision/earth/lookingatearth/antarctic_plumbing.html
For
more information about the
cryosphere:
http://neptune.gsfc.nasa.gov/csb/
ICESat
mission:
http://icesat.gsfc.nasa.gov/
Writer: Gretchen Cook-Anderson, NASA Goddard Space Flight Center
##
Contact:
Ed Campion
NASA Goddard Space Flight Center
301-286-0697
Edward.S.Campion@nasa.gov
This text is
derived from:
http://www.nasa.gov/home/hqnews/2007/feb/HQ_0742_antarctic_lakes.html
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