Building from beneath - ice-sheets in Antarctica flip glaciologist's ideas on their head

By Martin Leggett - 04 Mar 2011 12:40:1 GMT
Building from beneath - ice-sheets in Antarctica flip glaciologist's ideas on their head

Image Credit NSIDC

Intensive geophysical surveying of the East Antarctic high plateau, where the ice rears up some 14,000 feet, has revealed mammoth bulges of ice at their base - which may have been formed by extensive refreezing of sub-glacial waters. The two-year, six-nation study, which included scientists from Columbia University, is causing glaciologists to think again about the ways in which ice-sheets work - which could have consequences for Antarctica's response to rising temperatures.

Whilst the presence of these sub-glacial waters, thousands of feet beneath the glacial ice, has been known for a while, the impact of them in helping to form such massive structures, flips ideas of ice-sheet growth on their head. As much as half of the thickness of the ice-sheet above the Gamburtsev Mountains has come from these streams of melt-water, freezing as they flow upwards against them. Most scientists had assumed all of the thickness of these ice-sheets was due to the millennial accumulation of snow, that gets buried and compacted into ice.

The Antarctic ice-sheets form the largest body of freshwater on the planet, making up 60% of all water outside the oceans. Completely covering the continent of Antarctica, up to 200-feet of potential sea-level rise is locked up in their icy mass. Whilst any release of that, due global warming, is most likely to be measured in centuries, the processes by which these ice-sheets will respond to warming remain poorly understood.

Until recently, it was assumed that melting in East Antarctica would be limited, as this part of the continent has temperatures many tens of degrees below freezing. But with the discovery of under-ice streams and lakes, acting as potential lubricants, there is a worry that the ice-sheets could advance more rapidly into the sea.

These concerns have prompted this latest spurt of aerial-surveying - using laser-altimeters, magnetometers and gravity meters to dig deep into the ice-sheet's secrets. As well as aiming to better understand buried structures, scientists were also looking for the oldest ice-layers - these hold clues for climate changes as long as a million years ago.

What they found surprised them. A geophysicist at Columbia University, Robin Bell, said that they ''were worried they were an error in the data'', however, ''as they were seen on many lines, it became clear that they were real. We did not think that water moving through ancient river valleys beneath more than one mile of ice would change the basic structure of the ice-sheet.''