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East Antarctic Ice Sheet stayed frozen for 14 million years

Wednesday, Dec 16, 2015,13:59 IST By Metrovaartha A A A

Washington | The East Antarctic Ice Sheet (EAIS) has remained frozen for the past 14 million years, according to researchers who used an innovative technique to date one of Antarctica’s ancient lake deposits. Antarctica was once lush with plants and lakes.

Finding out how long the continent has been a barren, cold desert of ice can give clues as to how Antarctica responded to the effects of past climates and can also indicate what to expect in the future as Earth’s atmospheric concentration of carbon dioxide grows, researchers said.

The research at the University of Pennsylvania adds new support for the idea that the EAIS did not experience significant melting even during the Pliocene, a period from 3 to 5 million years ago, when carbon dioxide concentrations rivalled what they are today.

The Pliocene is sometimes thought to be an analogue to what Earth will be like if global warming continues, said Jane K Willenbring, an assistant professor at the university.

This gives us some hope that the East Antarctic Ice Sheet could be stable in today’s and future climate conditions, said Willenbring. Studies from the past few years suggest that sea level will likely rise a few metres as that ice melts.

However, the East Antarctic Ice Sheet is 20 times more massive. If it melted, the ensuing sea level rise would be even more catastrophic than the western peninsula’s dissolution.

Some scientists believe the ice sheet experienced significant melting during the relatively warmer conditions of the Pliocene, while others think it has remained almost entirely frozen for the last 14 million years.

Researchers hoped to help clarify the history of the EAIS. They travelled to Antarctica’s Friis Hills in the central Dry Valleys of the eastern portion of the continent.

About a foot beneath the surface are sediment deposits from an ancient lake which is known from animal fossils to have been freshwater. Earlier dating established that the volcanic ash deposits at the bottom of the ancient lake are 20 million years old.

To see if any melting had occurred in the interim, they analysed radioactive isotopes of beryllium known as beryllium-10, which form in the atmosphere when cosmic rays collide with oxygen and nitrogen atoms.

After estimating an initial level of initial concentration of beryllium-10 in their lake samples, the researchers were able to estimate the age of the sediments to be between 14 and 17.5 million years ago.

This means that the sediment is definitely older than the time when a lot of people think that Antarctica might have been quite deglaciated, Willenbring said.

By offering support for the idea that the EAIS has been largely stable during the last 14 million years, the research offers some hope that a massive collapse of the ice sheet, and associated sea level rise of tens of meters, may not be imminent.

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