BioEd Online

Almost all the glaciers that flow into the sea off the Antarctic Peninsula are retreating. The discovery comes from an analysis spanning more than half a century of aerial photographs and satellite images.

"Fifty years ago most glaciers were slowly growing in length, but the pattern is now reversed and they're shrinking," the British Antarctic Survey's Alison Cook told a press conference in London. Of 244 glaciers studied, 87% have shown a net retreat since photographic evidence was first collected in the 1940s, says Cook, who led the project.

The trend is probably linked to local climate changes on the peninsula, she explains, where temperatures have risen by around 2ºC over the past 50 years. This is much more than the average temperature increase seen in the rest of Antarctica.

The researchers are unsure whether glaciers are likely to be shrinking to the same extent across the rest of the continent. And they are also uncertain about the effects of the coastal glacier retreat. The ice blocks are typically about 2 kilometres wide and several dozen kilometres long. This is small compared to the peninsula's huge, floating ice shelves, which have likewise been disintegrating in recent years. The glacier melt is unlikely to raise sea levels much, or alter local salinity.

But if the glaciers retreat much further they may uncover bare rock, which could attract invasive species, the team says. "That would open up a whole load of new ground for colonization," says Cook's colleague David Vaughan.

Full picture

The survey, which is the most comprehensive of its kind thus far, was completed by researchers from the Cambridge-based British Antarctic Survey and the US Geological Survey, headquartered in Reston, Virginia. Together, they scrutinized some 2,000 images to chart the changing positions of the mouths of the 244 glaciers. The study included glaciers that flow directly into the sea on a westerly stretch of the Antarctic Peninsula, which points up towards South America.

The study also revealed that the mean rate of advance of glaciers in the 1940s and 1950s was slower than the current retreat. Widdowson Glacier, for example, has been receding by 1,100 metres each year for the past five years; in the 1940s it was advancing by just 200 metres annually.

Temperature is probably not the only cause, says Vaughan. During the late 1980s there seems to have been a 'blip', during which the glaciers' retreat was curtailed even though temperatures continued to rise. Vaughan suspects that changing ocean currents may be responsible.