Tiny Antarctic creatures hint at sea level rise

OSLO (Reuters) - Tiny marine creatures found on the seabed on opposite sides of the vast West Antarctic ice sheet give a strong hint of the risks of sea level rise caused by climate change, scientists said on Tuesday.

The discovery of very similar colonies of bryozoans, animals that anchor themselves to the seabed, in both the Ross and Weddell Seas are a clue that the ice sheet once thawed and the seas were once linked, they said.

West Antarctica holds enough ice to raise world sea levels by between 3.5 and 5 metres (11-16 ft) if the sheet collapsed. Some scientists believe it may have vanished during a natural warm period within the last few hundred thousand years.

"It was a very big surprise," said David Barnes, lead author of the study at the British Antarctic Survey, of the find of similar bryozoans 2,400 km (1,500 miles) apart in seas on either side of the West Antarctic ice sheet, which is 2 km thick.

"The most likely explanation of such similarity is that this ice sheet is much less stable than previously thought and has collapsed at some point in the recent past," he told Reuters.

"And if the West Antarctic ice shelf has been lost in recent times we have to re-think the possibility of loss in future with climate change," he said.

The bryozoans, sometimes called moss animals, are often microscopic as individuals but form colonies that can look like corals or some seaweeds. Those found were unlike others around the current coast of Antarctica.

WARM PAST

In a brief warm period about 125,000 years ago, world sea levels were about five metres higher than today and temperatures probably at least 4 degrees Celsius (7.4 F) warmer. There have been several similar warm periods in the past million years.

The U.N. panel of climate scientists said in a 2007 report that average world temperatures could rise by between 1.1 and 6.4 degrees C by 2100, mainly because of a build-up of greenhouse gases from burning fossil fuels.

Reviews of the panel have endorsed its main findings despite errors such as an exaggeration of the thaw of the Himalayas. Experts on Monday called for an overhaul of its management.

The Antarctic study, in the journal Global Change Biology, said that bryozoans were largely static and that their larvae, dispersed by currents, are short-lived and quickly sink.

With the huge ice sheet in the way, it was hard to explain how similar colonies could be in both the seas. But if the ice were destabilised it would open a passage through which currents might, over time, carry the larvae, Barnes said.

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(Editing by Jon Hemming)