South Pole: Rock 'hotspot' causes ice sheet to sag

Scientists suspect a combination of unusually radioactive rocks and geothermal springs may be responsible. The warm bedrock is removing some 6mm a year from the underside of the 3km-thick ice sheet, producing a mass of meltwater that then flows away through sub-glacial rivers and lakes towards the continent's coastline. The roughly 100km-by-50km hotspot came to light when researchers examined radar images of the ice sheet at 88 degrees south. This revealed a startling sagging in the ice layers directly above the hotspot. Antarctica is in no danger of melting away as a result of this hotspot. In the grand scheme of things, the area affected and the amount of melting is simply too small to have a significant impact. But the knowledge adds to our understanding of the under-ice hydrology of the continent. There is a vast network of sub-glacial rivers and lakes in Antarctica and they influence the way the ice sheet moves above them. Any attempt to model how the frozen landscape might respond to future climate warming has to take account of this water system. The discovery also has a bearing on efforts to drill the most ancient ice on the continent. Scientists are currently looking for places where they could core an unbroken record of snowfall going back more than 1.5 million years. The air bubbles and dust trapped in this ice would provide key insights into the way Earth's atmosphere has changed through time.

But any drill site would have to avoid locations with enhanced basal heating because the melting will erase any climate record imprinted in the core.

The new study is the latest result to come out of the PolarGAP project.

This was initiated by the European Space Agency with the primary objective of acquiring gravity measurements at the South Pole.

Esa's satellites do not fly directly over the bottom of the world, meaning there is always a hole in their data.

To retrieve the missing gravity information, Antarctic scientists were asked to run an instrumented airplane back and forth across the pole

But they used the opportunity to sense also the magnetism in the bedrock, and to profile the height and structure of the ice.