Rivers of fast-flowing water are gushing beneath the West Antarctica ice sheet in an extensive arterial system of rapidly filling and emptying lakes, new satellite images have revealed.
Researchers had predicted that the western ice sheet would contain subglacial water stores, but the unprecedented scale of the network and the speed of the water has surprised them. Crucially, the lakes occur below fast-moving ice streams, which could have major implications for glacial melt rates and associated sea-level rises.
"We've found substantial lakes under ice that's moving a couple of metres a day. It's really ripping along," says Robert Binschadler of NASA's Goddard Space Flight Center in Maryland, US, who carried out the study with colleagues. He presented the research at a meeting of the American Association for the Advancement of Science in San Francisco, California, US.
The linked reservoir system was discovered beneath the Whillans and Mercer ice streams - fast-flowing channels of ice that are major feeders of the continent's largest ice shelf, the Ross Ice Shelf. It may be that the ice streams themselves are eroding the ground beneath, making such water reservoirs more likely, Binschadler told New Scientist.
Fast-flowing ice streams are important predictors for climate change. Data from the streams can be used to calculate how Antarctic ice - which comprises 90% of the world's ice stores - will survive increases in temperature, and to help determine sea-level rises.
It is thought that the vast network of moving water will help lubricate the ice, carrying it from the relative protection of the sheet's interior to the floating edge, which could exacerbate melting.
In just the three years from 2003 to 2006, laser pulses bounced down from NASA's ICESat (Ice, Cloud, and land Elevation Satellite) mission discovered numerous areas of ice that either rose or sank due to highly pressurised water flooding into or out of subglacial lakes beneath.
The three most massive subglacial lakes measure up to 500 square kilometres. One of these - Subglacial Lake Engelhardt - drained a volume of 2 cubic kilometres in that period, while another - Subglacial Lake Conway - steadily filled by 1.2 cubic kilometres over the same timeframe.
"We didn't realise that the water under these ice streams was moving in such large quantities and on such short time scales. We thought these changes took place over years and decades, but we are seeing large changes over months," says Helen Fricker at the University of California San Diego's Scripps Institution of Oceanography in the US, who led the study.
During the period studied, the team saw a net gain in subglacial water, although it is too early to draw conclusions about how this will affect the stability of the ice sheet, Fricker says.
More than 150 subglacial lakes have been discovered, most through drilling narrow holes in the ice, which is limited and labour intensive (see Hidden Antarctica: Terra incognita).
The new satellite technique - taken from 600 kilometres above the Earth's surface - gives a far more comprehensive view of the ice sheet. "It is the most complete picture to date of what is going on beneath fast-flowing ice," Bindschadler says.
Journal reference: Sciencexpress (doi: 10.1126/science.1136897)
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