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Antarctica's amazing disappearing, reappearing ice shelf

It comes and goes, say boffins

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The Ross Ice Shelf in Antarctica has melted and reformed many times in geologically recent history, scientists have found.

A research team has spent the last few weeks drilling 600 metres down into the giant ice slab to extract and analyse samples from the seabed below the ice, the BBC reports.

The long term goal of the project is to find out how stable the massive shelf of ice (which is the size of France) is. The clues are in the kinds of sediment they are finding, and they have already established that the shelf is far from a permanent feature.

"When the ice sheet is there, the sediments you get under it are very rubbly. They are the sort of sediments that you would see at the front of [glaciers]," New Zealand Institute of Geological and Nuclear Sciences palaeoclimatologist Dr Tim Naish told the news organisation.

"When the ice lifts a bit so water can flow underneath, and it becomes an ice shelf, you still get those rubbly bits but you also get sediments that tell you water was around, that water was flowing back and forth.

"When the ice shelf disappears and you've got completely open water, then you've got a completely different situation where you have high biological productivity and a lot of microfossils preserved."

The behaviour of the ice shelf is important for at least two reasons.

The shelf acts to buttress the huge Western Antarctica ice sheet. Researchers think if the ice shelf collapses, the loss of ice from the continent of Antarctica would speed up as the glacial flow would have nothing to impede its journey to the ocean.

By dating the sediments, the researchers are also keen to find out if there is a relationship between the coming and going of the ice shelf and fluctuations in the climate. This could help to predict future behaviour of the shelf, and therefore of the ice sheets themselves, and could be vital in predicting future sea-level changes.

Earlier research has shown that fluctuations in the ice shelves are connected with a wobble of the Earth in its orbit around the sun. These so called Milankovitch cycles come approximately every 23,000, 41,000 and 100,000 years.

The team notes that in the past the atmospheric concentrations of carbon dioxide had not risen above 300 parts per million, as they have today. The researchers speculate that this additional carbon in the atmosphere might make a difference to the behaviour of the shelves during the natural Milankovitch cycles. ®

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