WARMER WORLD MAY SPLIT ANTARTICA

AS ANTARCTICA melts, seaways will open up across the western side of the continent, linking marine communities that have long been isolated from one another.

That's according to David Vaughan of the British Antarctic Survey in Cambridge, UK, and colleagues, who have worked out where these seaways opened up during Antarctica's warmer past — and where they are likely to form again if melting continues. Without its icy cover, much of west Antarctica would lie beneath sea level, partly because the ice has weighed down the continent. If, when Earth’s climate was wamier, Antarctica lost significant quantities of ice, areas of the ice sheet may have become thin and buoyant enough to float above the rocky continent. Seawater would then have flooded beneath the ice and created narrow channels across the continent between chunks of rock that retained their icy caps. Vaughan suspects that the channels would have been visible from the air, as the floating ice would quickly have broken up.

The team used radar data to measure the depth of Antarctica’s rock and the thickness of the ice sheet resting above it, and used this to work out which icy areas will be first to thin to the point that they would detach from the rock below. They identified a number of routes that are likely to have opened up across west Antarctica in the past (see map, below).

To find evidence for their theory, Vaughan's team turned to the animals living in the seas around Antarctica. They focused on bryozoans, marine filter feeders which spend their adult lives attached to rocks but move around as larvae. Communities on either side of the west Antarctic Peninsula share significantly more species in common than would be expected given the thousands of kilometres of coastline that separates them. This suggests there were once oceanic shortcuts across the peninsula itself, roughly where the team suspected the seaways to have been (Geochemistry, Geophysics, Geosystems, DOI: 10.1029/2o11GCoo3688).

“This is a great use of careful, fundamental science to extract important information from subtle clues,” says Richard Alley of Penn State University in University Park.

Vaughan says the bryozoan data cannot tell us when the seaways last opened. Genetic  testing of animals living at each end of the routes could help put a date on it, which in turn would tell us how likely the channels are to reopen and how vulnerable the west Antarctic ice sheet is to climate change. However, although parts of the sheet are already disappearing, Vaughan estimates that with the current rate of ice loss, even the most easily opened seaway is unlikely to reappear for around 900 years.

SOURCE : NEW SCIENTIST MAGAZINE NOVEMBER 2011