Ice-loss moves the Earth 400km down

 

Earth's mantle under Antarctica is moving rapidly, changing the shape of the land at a rate that can be recorded by GPS, scientists say.

 

An international research team led by Newcastle University, UK, has explained for the first time why the upward motion of Earth's crust in the Northern Antarctic Peninsula is currently taking place so quickly.

 

Previous studies have shown the Earth is 'rebounding' due to the overlying ice sheet shrinking in response to climate change.

 

This movement of the land was understood to be due to an instantaneous, elastic response followed by a very slow uplift over thousands of years.

 

But Global Positioning System (GPS) data collected has shown that the land in this region is actually rising at a phenomenal rate of 15mm a year - much greater than can be accounted for by the present-day elastic response alone. And researchers have shown for the first time how the mantle below the Earth's crust in the Antarctic Peninsula is flowing much faster than expected, probably due to subtle changes in temperature or chemical composition.

 

This means it can flow more easily and so responds much more quickly to the lightening load hundreds of miles above it, changing the shape of the land.

 

"You would expect this rebound to happen over thousands of years and instead we have been able to measure it in just over a decade. You can almost see it happening which is just incredible," lead researcher, Grace Nield, from School of Civil Engineering and Geosciences at Newcastle, said.

 

"Because the mantle is 'runnier' below the Northern Antarctic Peninsula it responds much more quickly to what's happening on the surface. So as the glaciers thin and the load in that localised area reduces, the mantle pushes up the crust," said Nield.

 

Since 1995, several ice shelves in the Northern Antarctic Peninsula have collapsed and triggered ice-mass unloading, causing the solid Earth to 'bounce back'.

 

"The ice is pressing down on the Earth and as this weight reduces the crust bounces back. But what we found when we compared the ice loss to the uplift was that they didn't tally ? something else had to be happening to be pushing the solid Earth up at such a phenomenal rate," Nield said.

 

Collating data from seven GPS stations situated across the Northern Peninsula, the team found the rebound was so fast that the upper mantle viscosity - or resistance to flow - had to be at least ten times lower than previously thought for the region and much lower than the rest of Antarctica.

 

"Seeing this sort of deformation of the Earth at such a rate is unprecedented in Antarctica. What is particularly interesting here is that we can actually see the impact that glacier thinning is having on the rocks 250 miles (402km) down," Professor Peter Clarke, one of the authors of the paper, said.