'Ice Bumps' Reveal History Of Antarctic Melting

Scientists say they now have a better idea of exactly where and when the margin of Antarctica started melting.

They've traced the changing shapes of bumps on the ice surface that mark locations where glaciers are anchored in place.

Half a century ago, few of these frozen moorings, or "pinning points", showed much change.

Since 2000, however, more than a third have reduced in size, emphasizing the acceleration in melting.

The research is published in the journal Nature and underscores once again the increasing contribution that ice losses from the continent will make to future sea-level rise around the globe.

The study's focus was the ice shelves that fringe 75% per cent of Antarctica's coastline.

The shelves are the floating fronts of glaciers that have pushed out into the surrounding ocean.

Many of them - especially in the west of the continent - are being assaulted by warm water and are thinning as a consequence.

That's bad news because they are regarded as a key braking mechanism, slowing the movement of ice off the continent.

In places where the seafloor is shallow - where there's an underwater hill, for example - the shelves can get caught in place, holding back the glacier ice to their rear.

The pinning points are reasonably obvious to a passing satellite because they produce a lump at the shelf surface where the flowing ice has had to ride over them.

What the Edinburgh University team did was analyse through time how these bumps had changed shape.

The idea was to see if the bumps got smaller, which would imply the shelves were thinning - that they were melting; that their braking force was getting weaker._BBC