A topography of the surveyed section of the Gamburtsev Mountains, buried several kilometres below the ice. Dark red represents the highest elevations and blue the lowest.
Credit: Nature/Polar Research Institute of China/University of Edinburgh
PARIS: Millions of years ago, rivers ran in Antarctica through craggy mountain valleys that were strangely similar to the European Alps of today, say experts.
In a study published this week in the British journal Nature, they gave a snapshot of terrain that for aeons has lain hidden beneath ice up to three kilometres thick.
The imaging comes from a gruelling effort by Chinese and British glaciologists to probe the mysterious realm beneath the East Antarctic heights, one of the most forbidding places on the planet.
Dome A
In 2004/05 and again in 2007/08, the team, led by experts at the Polar Research Institute of China and Martin Siegert with the University of Edinburgh, hauled deep-penetrating ground radar around a box-shaped sector, measuring 30 km by 30 km, at a point called Dome Argus, or Dome A.
Dome A lies at 4,093 m above sea level and has an average annual temperature of -58.4ºC. Beneath it is an ice sheet between 1,649 and 3,135 m thick that smothers the Gamburtsev Mountains, a range named after a Soviet geophysicist, Grigoriy Gamburtsev, who detected the peaks in 1958.
The radar reflections revealed "classic Alpine topography" similar to Europe's Alps, showing that once there were river valleys that cut their way through the mountains. Later, these valleys were gouged and deepened by glaciers.
"The landscape has probably been preserved beneath the ice sheet for around 14 million years," says the paper.
Creating a polar cap
The research chimes with deep-sea isotope records that give insights into how Earth got its polar caps. These suggest there was a period of global cooling, called the Eocene, between 52 and 34 million years ago.
Then came two progressively sharper periods of cooling, linked to a fall in levels of naturally-produced greenhouse gases in the atmosphere – the same gases that, man-made, are today blamed for warming.
Changes in Earth's orbit and the formation of the frigid current that flows around Antarctica contributed to placing the continent in a deep freeze.
The first of the big chills came at the start of what is called the Oligocene period, around 34 million years ago, when glaciers first started to form in Antarctica.
The Gamburtsev Mountains, because of their high altitude, were probably one of the places where glaciation first began, the scientists believe. At the time, there would have been a mean summer temperature of 3ºC, they estimate.
The second cooling spurt came some 14 million years ago, characterised by a plunge in temperatures of 6ºC to 7ºC, reaching up to 8ºC in the Transantarctic Mountains, the spine that divides East from West Antarctica.
