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Subglacial Lakes and Water-systems

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Boreas
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« on: February 23, 2007, 07:28:16 am »


Space lasers find huge lakes under Antarctic ice
Discovery could help figure out how climate change impacts sea levels


WASHINGTON - Lasers beamed from space have detected what researchers have long suspected: big sloshing lakes of water underneath Antarctic ice. These lakes — more than 100 of them and some stretching across hundreds of square miles — fill and drain so dramatically that the movement can be seen by a satellite looking at the icy surface of the southern continent, glaciologists reported in Thursday's editions of the journal Science.



Global warming did not create these big pockets of water — they lie beneath some 2,300 feet of compressed snow and ice, too deep to be affected by temperature changes on the surface — but knowing how they behave is important to understanding the impact of climate change on the Antarctic ice sheet, said study co-author Helen Fricker.
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About 90 percent of the world's fresh water is locked in the thick ice cap that covers Antarctica; if just the smaller West Antarctic Ice Sheet melts, scientists estimate it could cause a 15-foot rise in world sea levels. Even a three-foot sea level rise could cause havoc in coastal and low-lying areas around the globe, according to a World Bank study released this week.

"Because climate is changing, we need to be able to predict what's going to happen to the Antarctic ice sheet," said Fricker, of the Scripps Institute of Oceanography and the University of California, San Diego.

"We need computer models to be faithful to the processes that are actually going on on the ice sheet," she said. At this point, computer models do not show how the subglacial water is moving around.

Satellite help

To detect the subglacial lakes, Fricker and her colleagues used data from NASA's ICESat, which sends laser pulses down from space to the Antarctic surface and back, much as sonar uses sound pulses to determine underwater features.

Previously researchers had to drill deep holes in the ice to determine what was going on underneath, a process that limited then to studying only small areas at a time. The satellite detected dips in the surface that moved around as the hidden lakes drained and filled beneath the surface glaciers, which are moving rivers of ice.

"The parts that are changing are changing so rapidly that they can't be anything else but (sub-surface) water," she said. "It's such a quick thing." "Quick" can be a relative term when talking about the movement around glaciers, which tend to move very slowly. But one lake that measured around 19 miles by 6 miles caused a 30 foot change in elevation at the surface when it drained over a period of about 30 months, Fricker said.

The ice above the lakes is moving as fast as six feet a day — "really ripping along" in the words of study co-author Robert Bindschadler of NASA's Goddard Space Flight Center. "It's the fast-moving ice that determines how the ice sheet responds to climate change on a short timescale," he said in a statement.

Water like 'grease on the wheel'



"We aren't yet able to predict what these ice streams are going to do. We're still learning about the controlling processes. Water is critical, because it's essentially the grease on the wheel. But we don't know the details yet," he said.

Fricker said the researchers were surprised by how fast things were moving. "We thought these changes took place over years and decades, but we are seeing large changes over months," she said. The project took observations from 2003 through 2006 of the Whillans and Mercer Ice Streams, two of the fast-moving glaciers that carry ice from the Antarctic interior to the floating ice sheet that covers parts of the Ross Sea.

Reuters and The Associated Press contributed to this report.


Sourced; MSNBC News Services, Feb. 16, 2007.
www.msnbc.msn.com/id/17172218

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Boreas
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« Reply #1 on: February 23, 2007, 07:34:25 am »



Subglacial Lake Vostok

by Michael Studinger,
Lamont-Doherty Earth Observatory

   

Lake Vostok lies in the heart of the Antarctic continent hidden beneath 4 kilometers of ice (see map). 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. The lake was named for the Russian research station that sits above its southern tip - a place where in 1983 the temperature fell below -129°F (-89°C), the coldest ever recorded temperature on Earth. More than 145 lakes have been identified beneath the thick Antarctic ice sheet. Most of these lakes, covered between 3-4 kilometers of ice, are several kilometers long (see map). One of these lakes, Lake Vostok , is an order of magnitude larger than all other known lakes (slide show).

http://www.ldeo.columbia.edu/~mstuding/vostok.html
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« Reply #2 on: February 23, 2007, 08:11:47 am »

West Antarctica's subglacial plumbing system mapped from space

Science study reveals extensive water system beneath fast-moving ice streams

A network of rapidly filling and emptying lakes lies beneath at least two of West Antarctica's ice streams, new research suggests. The findings will be published online by the journal Science, at the Science Express website, on Thursday, 15 February. Science is the journal of AAAS, the nonprofit science society.

More than 100 subglacial lakes have already been discovered, but the new ones are particularly interesting because they occur below fast-moving ice. Though it's too early to say exactly how this liquid water is affecting the rates of ice flow above, understanding the behavior of these fast-moving ice streams is essential for predicting how Antarctica may contribute to sea level rise.



Helen Fricker of the University of California San Diego's Scripps Institution of Oceanography and colleagues analyzed elevation data recorded by NASA's Ice Cloud and land Elevation Satellite (ICESat) collected over the lower parts of the Whillans and Mercer Ice Streams. These are two of the major, fast-moving glaciers that are carrying ice from the interior of the West Antarctic Ice Sheet to the floating Ross Ice Shelf.

"We've found that there are substantial subglacial lakes under ice that's moving a couple of meters per day. It's really ripping along. It's the fast-moving ice that determines how the ice sheet responds to climate change on a short timescale," said Robert Bindschadler of NASA Goddard Space Flight Center, one of the study's coauthors.

"We aren't yet able to predict what these ice streams are going to do. We're still learning about the controlling processes. Water is critical, because it's essentially the grease on the wheel. But we don't know the details yet," he said.

Glaciologists have known that water exists under ice streams, but the observation of a system of water storage reservoirs is unprecedented. The surprising thing about this discovery is the amount of water involved, and the pace at which it moves from one reservoir to another, according to lead author Helen Fricker.

"We didn't realize that the water under these ice streams was moving in such large quantities, and on such short time scales," Fricker said. "We thought these changes took place over years and decades, but we are seeing large changes over months."

The authors identified numerous spots that either rose or deflated from 2003 to 2006, likely because water flowed into or out of them. Water would be capable of this because it is highly pressurized under the weight of the overlying ice.

The three largest regions are between approximately 120 and 500 square kilometers, while the others are widely scattered and smaller. One of the large regions, referred to as Subglacial Lake Engelhardt, drained during the first 2.7 years of the ICESat mission, while another, Subglacial Lake Conway, steadily filled during the same period.

"I'm quite astonished that with this combination of satellite sensors we could sense the movement of large amounts of water like this. From 600 kilometers up in space, we were able to see small portions of the ice sheet rise and sink," Bindschadler said.

http://www.eurekalert.org/pub_releases/2007-02/aaft-was021407.php


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