11 June 2010, by Adele Rackley
The newest images of the Gamburtsev Subglacial Mountains (GSM) were presented at the International Polar Year conference in Oslo this week, showing the features of this enigmatic mountain range in unprecedented detail.
BAS scientists board the Twin Otter survey aircraft
Scientists from the British Antarctic Survey (BAS) were part of the seven-nation Antarctica's Gamburtsev Province project (AGAP), one of the most ambitious Antarctic missions of the International Polar Year.
The team used sophisticated radar, magnetic and gravity sensors to complete an airborne survey of 20% of this previously unexplored and incredibly inhospitable area.
The GSM was the birthplace of the vast East Antarctic Ice Sheet (EAIS), which now covers the main peaks to a depth of up to 3km. The EAIS covers 10 million km2 so understanding how this remote region is likely to respond to climate change and contribute to sea-level rise is very important.
Location of the Gamburtsev Mountains beneath the Antarctic ice sheet.
First identified by Soviet scientists in 1958, the GSM lie under the highest part of the EAIS, known as Dome A. The survey images clearly show the high-relief, alpine-style landscape of the GSM and the network of valleys branching across them. The profiles show that the valleys were carved by fluvial (river) as well as glacial activity.
'It's likely that the valleys were initially eroded by rivers, which points to the fact that the mountains were there long before the ice began to form, about 35 million years ago,' says Dr Kathryn Rose of BAS. 'As temperatures fell, glaciers formed on the highest peaks and followed the path of the existing darinage system,' she adds.
But the fact that the mountain peaks have not been eroded into plateaus suggests that the ice sheet could have formed relatively quickly.
Perspective view of GSM's peaks and valleys
As it accumulated, the ice sheet carved the imposing Lambert Rift that can be seen on the images at the edge of the GSM. This underlies a branch of the Lambert Glacier, the largest in the world, and is the site of the sheet's thickest ice, around 4.8km deep.
Amazingly, the radar also showed that liquid water is present under the ice. Scientists had to endure surface temperatures of around -30oC during the survey, but the temperature under the ice is as high as -2oC.
'This is because the ice acts like a blanket,' says BAS's Dr Tom Jordan. 'Geothermal heat is trapped and can't readily escape because of the thickness of the ice sheet.' The immense pressure of the ice above causes water to melt at lower temperatures than it does at the surface, so the water can exist as liquid at the base of the ice.
'One of the most exciting outcomes of the survey has been discovering new evidence for how subglacial water behaves.' Dr Tom Jordan, British Antarctic Survey
Studying the subglacial environment will help scientists understand the how the EAIS developed and how it's changing, as well as the dynamics of the Lambert Glacier. This will provide lots of clues about how the region's climate has changed – and how the ice has responded – over tens of thousands of years.
'One of the most exciting outcomes of the survey has been discovering new evidence for how subglacial water behaves,' says Jordan. The force of the ice above is moving the water around the valley systems, even pushing it upwards and into adjacent valleys. 'Meltwater from one place is moving through the system and seems to be freezing back onto the base of a different part of the ice sheet. This new process hasn't been taken into account in previous ice-sheet studies,' he adds.
Another key finding of the survey is that the mountains are not volcanic – there were none of the strong magnetic signatures that would indicate the presence of igneous rocks. Instead there were signs of ancient tectonic fabric – 'stripes' visible in the readings that indicate areas of rock that have been pushed together or slid past each other.
Today the GSM aren't close to the edge of a tectonic plate, so these readings provide important indications of their age: 'significantly more than 500 million years old,' says Jordan. 'The next step is to compare the data from the GSM with information from exposed rock near the coast, which have already been dated,' he says. 'That way we can refine our understanding of the age of the GSM itself.'
With GSM's tallest peaks now shown to be a mere 350m down, perhaps it won't be long before scientists come face to face with these mysterious mountains.
