The Wilkins Ice Shelf in Antarctic set to collapse after ice bridge breaks

7 April 2009

An ice bridge connecting an Antarctic island to the mainland and holding an ice shelf half the size of Scotland in place has broken for the first time in recorded history.

Wilkins ice shelf

The Wilkins Ice Shelf breaking up

The break-up of the bridge raises the possibility of the whole ice shelf disintegrating and is further evidence of the effect of global warming on the continent, say researchers.

The Wilkins Ice Shelf - on the western side of the Antarctic Peninsula - has been retreating since the 1990s. Now Charcot Island is a real island for the first time in history.

Last year, the European Space Agency's Envisat satellite captured images showing the collapse of a 520 square mile section of the ice shelf. The collapse left the shelf hanging by a thread.

Cracks revealed

Last week, Envisat images revealed cracks in the 500 metre wide bridge and scientists were bracing themselves for the inevitable.

We know that [the Wilkins Ice Shelf] has been completely or very stable since the 1930s and then it started to retreat in the late 1990s. But we suspect that it's been stable for a very much longer period than that.

- Professor David Vaughan, British Antarctic Survey

Researchers think the bridge helped hold the rest of the ice shelf in place and say that now the bridge no longer exists, ice can move freely into the open ocean. If the shelf now breaks up, it will be the biggest collapse on record, dwarfing the break-up of the Larson B ice shelf in 2002. The Larson B ice shelf covered 770 square miles, whereas the Wilkins Ice Shelf covers an area nearly 10 times bigger - 6,200 square miles.

In January this year Professor David Vaughan of the British Antarctic Survey visited the Wilkins Ice Shelf to place GPS monitoring equipment on the ice. Data from the equipment and data from ESA satellites meant the break-up of the ice shelf could be analysed far more effectively than any previous break-up.

Professor Vaughan told BBC News, "We know that [the Wilkins Ice Shelf] has been completely or very stable since the 1930s and then it started to retreat in the late 1990s. But we suspect that it's been stable for a very much longer period than that."

"The fact that it's retreating and now has lost connection with one of its islands is really a strong indication that the warming on the Antarctic is having an effect on yet another ice shelf," he added.

Wilkins ice shelf

Wilkins ice shelf

The Wilkins Ice Shelf is the largest of 10 ice shelves to have receded or collapsed in recent years. Scientists say the rising temperatures in the region are likely to be responsible. The polar regions are the fastest warming regions on the planet, with temperatures in Antarctica rising 3°C in the last 50 years.

However, with the Antarctic summer coming to an end and sea ice starting to form, the ice shelf could become locked in place until next summer. But when warmer temperatures return, icebergs are likely to drift into the open ocean eventually leading to the total break-up of the ice shelf.

Sediment cores taken from the seabed suggest that Antarctic ice shelves have been in place for 10,000 years.

Ice shelves float on the sea and can be hundreds of metres thick. Collapsing ice shelves do not affect sea levels. But with no ice shelf to limit their progress, sea-terminating glaciers can slide more rapidly towards the sea, adding water to the oceans and contributing to sea-level rise.

Experts from 175 countries are at a meeting in Bonn, Germany to negotiate a new climate treaty ahead of the United Nations Climate Change Conference in Copenhagen, which runs from 7 to 18 December of 2009.