Tabatha Thompson
Headquarters, Washington
202-358-3895
Ed Campion
Goddard Space Flight Center, Greenbelt, Md.
301-286-0697
RELEASE: 07-42
JOINT NASA STUDY REVEALS LEAKS IN ANTARCTIC 'PLUMBING SYSTEM'
WASHINGTON - 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 online about NASA and agency programs, visit:
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