Antarctic ice shelf breaks apart

An Antarctic ice shelf that was 200 metres thick and had a surface area of 3,250 square kilometres has broken apart in less than a month.

This is the largest single event in a series of retreats by ice shelves in the peninsula over the last 30 years

US National Snow and Ice Data Center

UK scientists say the Larsen B shelf on the eastern side of the Antarctic Peninsula has fragmented into small icebergs.

Researchers from the British Antarctic Survey (Bas) predicted in 1998 that several ice shelves around the peninsula were doomed because of rising temperatures in the region - but the speed with which the Larsen B has gone has shocked them.

"We knew what was left would collapse eventually, but the speed of it is staggering," said Dr David Vaughan, a glaciologist at the Bas in Cambridge.

"[It is hard] to believe that 500 billion tonnes of ice sheet has disintegrated in less than a month."

Faster flow

The climate on the peninsula has changed rapidly in the last 50 years. The region has experienced a 2.5-degree-Celsius rise in average temperatures - an increase greater than for any location in the Southern Hemisphere.

However, the picture generally in Antarctica is a complicated one with temperatures in the interior actually falling over the same period. There is also some evidence that the retreat of the West Antarctic Ice Sheet, on the other side of the peninsula to the Larsen B shelf, has halted.

The Larsen B was one of five ice shelves - huge masses of ice that are floating extensions of the ice sheets covering the land - that had been steadily shrinking because of climate change, Dr Vaughan said.

But the break up of the ice mass would not raise sea levels because the ice was already floating, he added. Sea levels would only be affected if the land ice behind it now began to flow more rapidly into the sea.

Gather data

The UK scientists were first alerted to the Larsen B collapse by US colleagues studying images from the American space agency's Modis satellite.

The area is now littered with small icebergs

The British Antarctic Survey then dispatched its research ship RRS James Clark Ross to the area to obtain photographs and samples.

Scientists hope the data gathered on site will help them determine when such an event last happened and which ice shelves are threatened in future.

The US-based National Snow and Ice Data Center (NSIDC) said on Tuesday: "This is the largest single event in a series of retreats by ice shelves in the peninsula over the last 30 years.

"The retreats are attributed to a strong climate warming in the region."

Future predictions

"We know that the climate in this area has been relatively stable for at least 1,800 years, but now it is starting to change," Dr Vaughan told the BBC.

"Has it been kicked off by (human induced) global warming or is it something a bit more natural?

"For glaciologists this is fascinating because we can see the processes at work and we can predict with more certainty what is going to happen in the rest of Antarctica.

"As far as global implications are concerned, there are few as far as the present event is concerned."

Locally, however, Dr Vaughan said there would be ecological changes as organisms moved into the seabed area no longer covered by ice.

Big berg

US scientists also reported on Tuesday that an iceberg more than nine times larger than Singapore had broken off Antarctica.

This image of B-22 was taken on 11 March

The National Ice Center said the berg, named B-22, broke free from an ice tongue in the Amundsen Sea, an area of Antarctica south of the Pacific Ocean.

It is more than 64 kilometres (40 miles) wide and 85 kilometres (53 miles) long, and covers an area of about 5,500 square kilometres.

Icebergs are named for the section of Antarctica where they are first sighted. The B designation covers the Amundsen and eastern Ross seas and the 22 indicates it is the 22nd iceberg sighted there by the US National Ice Center.