The collapse of a huge ice shelf in Antarctica in 2002 has no precedent in the past 11,000 years, according to a study that points the finger at global warming.
Measuring some 3,250 sq km in area and 220m thick, the Larsen B iceshelf broke away from the eastern Antarctic Peninsula in 2002, eventually disintegrating into giant icebergs.
By chance, a US-led team of geologists had gathered a rich harvest of data around the iceshelf just before the spectacular collapse, including six cores that had been drilled into marine sediment.
The cores contain the remains of plankton and algae imbedded in layers of minerals, and their radiocarbon and oxygen isotopes provide clues about ice cover and climate change over the millennia.
The researchers, reporting in Nature, the British science weekly, say that since the end of the last Ice Age, some 11,000 years ago, the iceshelf had been intact but had slowly thinned, by several dozen metres.
Its coup de grace came from a recent but decades-long rise in air temperature, they say.
"The modern collapse of the LIS-B [Larsen B iceshelf] is a unique event within the Holocene," they write.
"The LIS-B eventually thinned to the point where it succumbed to the prolonged period of regional warming now affecting the entire Antarctic Peninsula region."
The Holocene is the period of relatively balmy weather that followed the last Ice Age.
The research is the latest in a series of studies to sound the alarm about the effects of climate change in Antarctica, where the bulk of the world's freshwater is locked up.
The Antarctic Peninsula, which juts northwards out of West Antarctica, is considered a warming hot-spot.
Over the past half century, temperatures in the peninsula have risen by around two degrees Celsius.
In recent years, the peninsula has lost ice shelves totalling more than 12,500 sq km, equivalent to four times the area of Luxembourg.
Of the 244 glaciers that drain inland ice and feed these shelves, 87 per cent have fallen back since the mid-1950s, according to a British study published in April.
Global warming, also called the greenhouse effect, is caused by carbon gases mostly discharged by burning oil, gas and coal, that trap the Sun's heat.
But Earth's climate also goes through natural oscillations of warming and cooling, resulting in Ice Ages and the milder interglacial periods in between.
The new study does not say that global warming caused by human activity was responsible for the Larsen B's demise.
However, it refers to a steep rise in the temperatures over the past several decades, a phenomenon that climatologists concur was unleashed by fossil fuels.
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Discovering An Ecosystem Beneath A Collapsed Antarctic Ice Shelf
Washington DC (SPX) Jul 19, 2005
The chance discovery of a vast ecosystem beneath the collapsed Larsen Ice Shelf will allow scientists to explore the uncharted life below Antarctica's floating ice shelves and further probe the origins of life in extreme environments.
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