glenc
17-02-2007, 06:28 AM
Giant "blisters" containing water that rapidly expand and contract have been mapped beneath the Antarctic ice sheet. Fed by a complex network of rivers, the subglacial reservoirs force the overlying ice to rise and fall.
By tracking these changes with Nasa's Ice Cloud and land Elevation Satellite (ICESat) scientists were able to map the extent of the subglacial plumbing.
The results, published in the journal Science, show that some areas fell by up to 9m (30ft) over just two years.
"We didn't realise that the water under these ice streams was moving in such large quantities, and on such short time scales," said Dr Helen Fricker of the Scripps Institution of Oceanography, University of California, and one of the authors of the paper.
"We thought these changes took place over years and decades, but we are seeing large changes over months."
The results are important for understanding how the Antarctic Ice sheet, which contains nearly 90% of the world's ice, may respond to global warming and how much it may contribute to sea level rise...
Ebb and flow
Using elevation data from Nasa's ICESat, cross-checked with other Nasa satellites, the team was able to map the rise and fall of the overlying ice, and hence areas where water pooled or flowed away.
Launched in 2003, ICESat can measure changes in elevation as small as 1.5cm (0.6ins) from its orbit 645km (400 miles) above the Earth.
The study revealed a complex network of ponds and rivers, the largest of which occurred under the Whillans ice stream and covered an area of 500 sq km (190 sq miles).
It also showed that water was constantly moving between different reservoirs.
For example, a feature known as Lake Englehardt took just under three years to empty two cubic kilometres (2 trillion litres) of water.
In the same period, Lake Conway filled with an additional 1.2 cubic kilometres (1.2 trillion litres) of water.
Not all of the water was the same as some escaped to the ocean or was refrozen on to the base of the glacier.
Observations like these were only possible using the new satellite technique.
"Until now, we've had just a few glimpses into what's going on down there," said Professor Bindschadler.
"This is the most complete picture to date what's going on beneath fast flowing ice."
The findings were presented at the American Association for the Advancement of Science (AAAS) annual meeting here in San Francisco, US.
http://news.bbc.co.uk/2/hi/science/nature/6364577.stm
By tracking these changes with Nasa's Ice Cloud and land Elevation Satellite (ICESat) scientists were able to map the extent of the subglacial plumbing.
The results, published in the journal Science, show that some areas fell by up to 9m (30ft) over just two years.
"We didn't realise that the water under these ice streams was moving in such large quantities, and on such short time scales," said Dr Helen Fricker of the Scripps Institution of Oceanography, University of California, and one of the authors of the paper.
"We thought these changes took place over years and decades, but we are seeing large changes over months."
The results are important for understanding how the Antarctic Ice sheet, which contains nearly 90% of the world's ice, may respond to global warming and how much it may contribute to sea level rise...
Ebb and flow
Using elevation data from Nasa's ICESat, cross-checked with other Nasa satellites, the team was able to map the rise and fall of the overlying ice, and hence areas where water pooled or flowed away.
Launched in 2003, ICESat can measure changes in elevation as small as 1.5cm (0.6ins) from its orbit 645km (400 miles) above the Earth.
The study revealed a complex network of ponds and rivers, the largest of which occurred under the Whillans ice stream and covered an area of 500 sq km (190 sq miles).
It also showed that water was constantly moving between different reservoirs.
For example, a feature known as Lake Englehardt took just under three years to empty two cubic kilometres (2 trillion litres) of water.
In the same period, Lake Conway filled with an additional 1.2 cubic kilometres (1.2 trillion litres) of water.
Not all of the water was the same as some escaped to the ocean or was refrozen on to the base of the glacier.
Observations like these were only possible using the new satellite technique.
"Until now, we've had just a few glimpses into what's going on down there," said Professor Bindschadler.
"This is the most complete picture to date what's going on beneath fast flowing ice."
The findings were presented at the American Association for the Advancement of Science (AAAS) annual meeting here in San Francisco, US.
http://news.bbc.co.uk/2/hi/science/nature/6364577.stm