Antarctic boulders help sea level predictions
Boulders (large rocks) emerging from thinning ice in the West Antarctic Ice Sheet (WAIS) may help improve predictions of likely sea level rises resulting from climate change. Data from rocks found on the remote Amundsen Sea Embayment show that ice thinning, which has progressed at a rate of around 4cm each year for some 14000 years, has accelerated by a factor of 40 to 1.6m per year since the 1990s.
Scientists from the British Antarctic Survey, along with other UK and German researchers, analysed boulders left behind by retreating glaciers. The researchers looked for the build-up of certain isotopes in the rocks caused by exposure to cosmic rays. Levels of these isotopes help scientists determine when the glacier thinned, leaving the boulder exposed on the surface and able to absorb cosmic radiation.
Analysing the rocks helps scientists to develop a long-term picture of the region's glaciers. Putting the recent ice sheet changes in context will help them determine whether the accelerated ice thinning is part of a natural ice retreat underway since the last glacial period (around 20,000 years ago), or the result of climate change. The new findings can also be used to improve computer models used to predict future changes in the ice.
The Amundsen Sea Embayment is the focus of intense international scientific attention, because it is changing faster than any other part of the WAIS. It has also received little previous scientific attention because it is so remote. Loss of the Amundsen Sea Embayment part of the WAIS, which is unstable, could lead to a sea level rise of 1.5m. This new research suggests that the current rate of ice-sheet thinning cannot have been sustained for more than a few decades.
Collapse of the entire WAIS would lead to a 5m rise in global sea levels. Most scientists think that a complete collapse is unlikely within the next few centuries, but even the loss of one sector of the ice sheet could mean that current predictions about potential sea level rises are too low.