June 3, 2009

New Research Into Origins Of Antarctic Ice Sheet

New research by scientists in Britain and China reveals evidence of how the East Antarctic ice sheet initially formed.

The work provides a snapshot of terrain that has lain hidden miles beneath the ice for millions of years, when rivers ran through mountain valleys that were oddly similar to the modern European Alps.

The scientists used radar to map an area of the Gamburtsev mountains, believed to be where the ice originated. The region would have been cold enough to support the formation of the first glacier.

The researchers said their findings provide important insight into 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 Fausto Ferraccioli, a scientist with the British Antarctic Survey, during an interview with BBC News.

Ferraccioli, who is involved in a separate international project to study the region, said the elevation and location of the Gamburtsev Mountains made them an "ideal place" for the formation of the first ice.

The findings of Sun Bo from China's Polar Research Institute, the study's leader, and his team provide additional insight into the evolution of the ice sheet.

Dr. Sun and his colleagues traveled 767 miles by tractor train from a research station at the periphery of East Antarctica to the summit of Dome A of the Gamburtsev range. The team then drove around with radar equipment attached to the tractor, meticulously surveying an approximately 400 square mile glacial region.

The radar showed a landscape that, 14 million years ago, resembled the European Alps.

"This is true scientific exploration," Martin Siegert of Edinburgh University, who was also involved in the study, told BBC News.

"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."

Radio waves are very powerful for this type of research. When they reach the interface between rock and ice they bounce back due to differences in electrical properties between the two substances.

"You just measure the two-way travel time as they go down and come back up again," said Siegert.

"Then you can convert that to ice thickness, because you know the velocity at which [the radio waves] are traveling."

Dr. Siegert said the team was "very lucky" to obtain such a clear image of the underlying landscape, which included an entire valley system with mountains at the edge of region and a 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.

Using ancient climate patterns, scientists had 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 nearly 2 miles thick.

"You need a mean annual temperature of about 3C for the glaciers to form the way they did."

"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," said Dr. Siegert, adding that the findings provide 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," Siegert said.

"And what we can say about this place in the middle of the Antarctic is that nothing has changed."

However, he cautioned that if levels of atmospheric CO2 continue to increase, they will approach the same levels that existed "before there was persistent ice sheet in Antarctica," in about 1,000 years.

"This puts the ice sheet into the context of global climate and what conditions are needed to grow an ice sheet," he said.

"The worrying thing is that we seem to be going back to carbon dioxide concentrations consistent with there being a lot less ice around."

The study was published Wednesday by the British journal Nature.


On the Net: