Andrea Thompson, livescience.com Yahoo News 3 Jun 09;
Antarctica is a massive block of ice today, but it used to more simply be a range of glacier-topped mountains like those found in Alaska and the Alps.
The strange continent's thick ice sheets formed tens of millions of years ago against an Alpine-style backbone of mountains during a period of significant climate change, a new study finds.
The Antarctic continent now is covered almost entirely by ice that averages about a mile (1.6 kilometers) thick.
Scientists have known for some time that the Antarctic Ice Sheet formed around 14 million years ago, "but we didn't know how it formed," said study team member Martin Siegert of the University of Edinburgh in Scotland.
Specifically, researchers had little idea of the topography that lies underneath the thick layers of ice, which would provide clues to the history of ice on the southernmost continent, as well as inform models of how current ice flow might be impacted by climate change.
So little was known about the landforms beneath the Antarctic ice, in fact, that scientists had more information about the geography of the surface of Mars than at the Earth's own South Pole.
At a site called Dome A (the highest ice feature in Antarctica), only one Soviet traverse in 1957-58 and one radar flight in the 1970s had looked for topography below the ice. These studies showed that a mountain range, dubbed the Gamburtsev mountains, sat beneath the ice, but little detail was known about them or the rest of the sub-ice topography.
That changed with a detailed radar survey conducted in 2004-05 and 2007-08 by Chinese glaciologists over an 11.5 square mile (30 square kilometer) section of the region.
The radar study, detailed in the June 4 issue of the journal Nature, showed the Gamburtsev mountains in greater detail.
Antarctic Alps
The topographical features show a landscape carved out by small glaciers, much like the European Alps.
The climate required to allow these glaciers to form and flow started around 34 million years ago, at the end of the Eocene epoch. Small changes in Earth's orbit likely drove the glaciers to advance and recede (just at these glaciers that once covered North America did).
The glaciers carved out valleys that had already been worn in by river flow, changing the topography. Once the expansive ice sheets that now cover the continent began to form, they preserved these landforms in frigid perpetuity.
More radar surveys of Antarctica are already underway and Siegert said these should gives scientists a much better picture of what is hiding under all that ice.
Knowing what topographical features sit below the ice helps scientists better model how the ice flows around those features.
"It allows us to understand how ice flows in Antarctica," Siegert said. "The topography has a major influence on the ice flow of Antarctica."
With a better understanding of ice flow, scientists can better model how Antarctica's ice will respond to changes in Earth's climate, which have already affected ice shelves in parts of Antarctica.
The work was funded by the National Natural Science Foundation of China, the International Polar Year program CHINARE, and the UK Natural Environment Research Council.
Origin of Antarctic ice revealed
Victoria Gill, BBC News 3 Jun 09;
Incredible peaks and valleys, buried beneath ice for 14 million years, have revealed evidence of how the East Antarctic ice sheet first formed.
Scientists used radar to map an area of the Gamburtsev mountains - believed to be the point of origin of the ice.
The region would have been cold enough for the first glacier to form.
Writing in the journal Nature, the researchers say their findings provide important clues about how the ice sheet will behave as our climate changes.
"This is the largest reservoir of ice on Earth, and the most poorly understood place on our planet," said the British Antarctic Survey's Fausto Ferraccioli, a scientist involved in a separate international project to study the region.
He explained that the elevation and location of the Gamburtsev Mountains - in the centre of the ice sheet - made them an "ideal place" for the formation of the very first ice.
Icy unknown
Sun Bo from the Polar Research Institute of China, who led this study, has now provided further insight into the evolution of the ice sheet.
He and his colleagues travelled 1,235km (767 miles) by tractor train from a research station at the edge of East Antarctica, to the summit of Dome A of the Gamburtsev range, near the centre.
Dr Sun's team then attached radar equipment to the tractor and drove around, meticulously surveying a 30km by 30km square of the glacial region.
Their radar revealed a landscape that, 14 million years ago, looked similar to the European Alps.
"This is true scientific exploration," said Martin Siegert, head of the school of geosciences at Edinburgh University, who was also involved in the study.
"There's nothing to guide you really. Peering down at the ice sheet beneath your feet, you just don't know what's under there."
And for this type of exploration, the use of radio waves is very powerful.
When the waves reach the interface between ice and rock they bounce back, because of the difference in electrical properties between the two.
"You just measure the two-way travel time as they go down and come back up again," explained Dr Siegert. "Then you can convert that to ice thickness, because you know the velocity at which [the radio waves] are travelling."
Dr Siegert said the research team was "very lucky" to see such a clear image of the underlying landscape. They discovered a whole valley system - with mountains at the edge of the survey region and the valley in the middle.
"That's perfect, because it allows us to work out how the valley would have worked when it was filled with ice, and how the water would have flowed when there was no ice there at all," said Dr Siegert.
Frozen in time
By looking at ancient climate patterns, scientists have previously estimated that the East Antarctic ice sheet formed around 14 million years ago, burying and preserving the Gamburtsev mountain landscape under ice that is now up to 3km thick.
"You need a mean annual temperature of about 3C for the glaciers to form the way they did," Dr Siegert told BBC News.
"The mean annual temperature in this region now is -60 C. So we believe that these mountains are relics of [glacial erosion] in Antarctica before the ice sheet was in place."
He added that the findings provided an insight into the stability of the ice.
"It is a critical part of our Earth's system," said Dr Ferraccioli. "If the whole ice sheet collapsed, sea levels would rise by 60m."
"There's been a lot of climate change over the last 14 million years," Dr Siegert said. "And what we can say about this place in the middle of the Antarctic is that nothing has changed."
But, he warned, if levels of atmospheric carbon dioxide continued to rise, in around 1,000 years they will approach the same levels that existed "before there was persistent ice sheet in Antarctica".
"This puts the ice sheet into the context of global climate and what conditions are needed to grow an ice sheet," explained Dr Siegert. "The worrying thing is that we seem to be going back to carbon dioxide concentrations consistent with there being a lot less ice around."
How Antarctica grew its ice – and lost its hanging gardens
Catherine Brahic, New Scientist 3 Jun 09;
Up to 3000 metres beneath the ice, at the coldest point on Earth, towering peaks, hanging valleys and deep gorges have been frozen in ice for 14 million years. Now the first detailed view of this frozen landscape is revealing how the world's biggest chunk of ice – the Antarctic ice sheet – was born.
The radar images suggest that Antarctica "grew" its ice cap in three stages, carving out the rock below in distinct ways as glaciers expanded, retracted, and flowed downstream.
The images were collected between 2004 and 2008 by researchers who drove huge trains of caterpillar tractors in tight lines over Dome A, a plateau of ice at the heart of Antarctica. The tractors carried radars that pinged down through the ice and sent back profiles of the frozen rock landscape below.
Dome A, the highest point on the continent, is also one of the coldest places on Earth, with temperatures as low as -90 °C. Far beneath its frozen surface lie the Gamburtsev mountains, where glaciologists believe the Antarctic ice sheet was born. Its distance to the ocean and high altitude would have made it the coolest spot on the continent 34 million years ago, when the ice began to grow.
Stranger than Mars
Because Dome A is so remote and so cold, and because kilometres of ice separate the surface from the mountain tops, we know more about the surface of Mars than we do about the Gamburtsev. Until recently, only a single radar flight some 30 years ago had probed the chain.
In the past few years glaciologists have used planes and tractors to map out the iced mountains more fully. Earlier this year, the British Antarctic Survey revealed images of the mountains' profile. Now, a Chinese, Japanese and UK team have published results detailing the 900-square-kilometre area beneath Dome A.
By studying the images, the researchers have determined how the ice cap formed. First, some 34 million years ago, small mountain-top glaciers developed. They froze and thawed with variations in Earth's orbit, sometimes filling the range's main valley and its tributaries, sometimes disappearing entirely. These variations would have created distinct, high-altitude cirques, hanging valleys and deepened the main valley.
Isotope records from the deep ocean show that global temperatures dropped by up to 8 °C about 14 million years ago. This froze the ice to the rock, and it will have moved very little since then, preserving the landscape below.
Rocks are not all that will have been frozen in time and space. Martin Siegert of the University of Edinburgh, UK, says it is very likely that there are bits of frozen vegetation down there too – far out of reach. "It would have looked much like Patagonia today, with quite lush forests and small valley glaciers cutting into the alpine topography," he says.
Journal reference: Nature (DOI: 10.1038/nature08024)
Ghost alps of Antarctica are glimpsed after 14 million years
Yahoo News 3 Jun 09;
PARIS (AFP) – Millions of years ago, rivers ran in Antarctica through craggy mountain valleys that were strangely similar to the European Alps of today, Chinese and British scientists reported on Wednesday.
In a study published by the British journal Nature, they gave a snapshot of terrain that for aeons has lain hidden beneath ice up to several kilometres (nearly two miles) thick.
The imaging comes from a gruelling effort by Chinese glaciologists to probe the mysterious realm beneath the East Antarctic heights, one of the most forbidding places in the world.
In 2004-5 and again in 2007-8, the team hauled deep-penetrating ground radar around a box-shaped sector, measuring 30 kilometers (18 miles) by 30 kilometres, at a point called Dome Argus, or Dome A.
Dome A lies at 4,093 metres (13,302 feet) above sea level and has an average annual temperature of -58.4 degrees Celsius (-73 degrees Fahrenheit).
Beneath it is an ice sheet between 1,649 and 3,135 metres 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.
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 the process of 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 three degrees C (37 degrees F), they estimate.
The second cooling spurt came some 14 million years ago, characterised by a plunge in temperatures of around six to seven degrees C (10.8-12.6 degrees F), reaching up to eight degrees C (14.4 degrees F) in the Transantarctic Mountains, the spine that divides East from West Antarctica.
