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Antarctic Ice
Sheet's Hidden Lakes Speed Ice Flow Into Ocean, May Disrupt Climate
NASA 03.05.07
Just as explorers once searched
the vast reaches of Africa's Nile River for clues to its behavior and ultimate
source, modern-day scientists are searching Antarctica for its hidden lakes and
waterways that can barely be detected at the surface of the ice sheet. In a new
study, researchers have unearthed how water from this vast subglacial system
contributes to the formation of ice streams, and how it plays a crucial role in
transporting ice from the remote interior of Antarctica toward the surrounding
ocean. Water flowing from this network of under-ice lakes, they say, ultimately
affects climate and global sea level.
Combined RADARSAT and ICESat
images show the Recovery Glacier Ice Stream (arrows) and location of four new
subglacial lakes (A, B, C and D) that lie at the head of the stream.
Credit: NASA
A research team led by
geophysicists Robin Bell and Michael Studinger from the Lamont-Doherty Earth
Observatory of Columbia University in New York City, discovered four large,
subglacial lakes miles beneath the Antarctic ice sheet's surface. The team was
able to link these lakes for the first time to a fast flowing ice stream above
and establish that within this 170-mile wide area the lakes contribute to the
creation of a major ice stream. The team, which includes scientists from NASA,
the University of New Hampshire, Durham, and the University of Washington,
Seattle, published their results in the Feb. 22 issue of Nature.
"This connection of major
subglacial lakes to the accelerated pace of ice movement deep in Antarctica’s
interior is a key piece of the ice sheet stability puzzle," said co-author
Christopher Shuman, a physical scientist in the Cryospheric Science Branch at
NASA's Goddard Space Flight Center, Greenbelt, Md. "Given the remoteness of
the area, we could not have put the picture together without multiple types of
satellite data."
Ice streams are large,
fast-flowing features within ice sheets that transport land-based ice and
meltwater to the ocean. One such stream, the Recovery Glacier ice stream,
annually drains the equivalent of eight percent of the huge East Antarctic Ice
Sheet, an area larger than the continental United States. The associated
Recovery drainage basin, virtually unexplored since an American-led Antarctic
ice sheet research trek over 40 years ago, funnels an estimated 35 billion tons
of ice into the Weddell Sea annually.
The scientists used a remote
sensing technology called interferometric synthetic aperture radar from the
Canadian Space Agency’s RADARSAT instrument to measure the speed of the ice
flow. They also used visible imagery from sensors aboard NASA’s Terra and Aqua
satellites and high-resolution laser data from NASA's Ice Cloud and Land
Elevation Satellite to capture small changes in the landscape characteristics of
the ice stream indicating the presence of subglacial lakes beneath the ice.
Not only did the scientists find
four new lakes, they discovered that the lakes coincide with the origin of
tributaries of the Recovery Glacier ice stream. Upstream of the lakes, the ice
sheet moves at just a few feet a year; downstream the flow increases to a third
of a mile each year. The research team concluded that the lakes provide a
reservoir of water that lubricates the bed of the stream, which speeds the flow
of ice, and prevents the base of the sheet from freezing to the bedrock.
Lake Vostok lies in the heart of
the Antarctic continent hidden beneath miles of ice. As big as Lake Ontario in
North America, Lake Vostok is one of the world's biggest freshwater lakes. Lake
Vostok has been covered by the vast Antarctic ice sheet for up to 25 million
years. Credit: Columbia University, Lamont-Doherty Earth Observatory
"It's almost as if the lakes
are capturing the geothermal energy from the entire basin and releasing it to
the ice stream," said lead author Bell, a senior research scientist at the
Lamont-Doherty Earth Observatory. "They power the engines that drive ice
sheet collapse. The more we learn about the lakes, the more we realize how
important they are to ice sheet stability."
The team's work also suggests
that subglacial lakes play a role in sea-level rise as well as regional and
global climate change. "Here we found that meltwater at the base of the ice
sheet speeds the flow of Recovery ice to the oceans. In turn, that contributes
to higher sea levels worldwide," said Shuman. "Floods have been known
to originate from the interior of the ice sheet in the past, possibly from
systems like these subglacial lakes. These sudden outbursts of fresh water could
potentially interfere with nearby ocean currents that redistribute heat around
the globe and could disrupt the Earth's climate system."
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