October 22nd, 2009
From Green Right Now Reports
New ground measurements made by the West Antarctic GPS Network project, composed of researchers from The University of Texas at Austin, The Ohio State University and The University of Memphis, suggest the rate of ice loss of the West Antarctic ice sheet has been slightly overestimated.
“Our work suggests that while West Antarctica is still losing significant amounts of ice, the loss appears to be slightly slower than some recent estimates,” Ian Dalziel, lead principal investigator for the project, said in a statement. “So the take home message is that Antarctica is contributing to rising sea levels. It is the rate that is unclear.”
In 2006, another team of researchers used data from the Gravity Recovery and Climate Experiment satellites to infer a significant loss of ice mass over West Antarctica from 2002 to 2005. Those satellites do not measure changes in ice loss directly but measure changes in gravity, which can be caused both by ice loss and vertical uplift of the bedrock underlying the ice.
Now, for the first time, researchers have directly measured the vertical motion of the bedrock at sites across West Antarctica using the Global Positioning System. The results should lead to more accurate estimates of ice mass loss.
Antarctica was once buried under a deeper and more extensive layer of ice during a period known as the Last Glacial Maximum. Starting about 20,000 years ago, the ice began slowly thinning and retreating. As the ice mass decreases, the bedrock immediately below the ice rises, an uplift known as postglacial rebound.
Postglacial rebound causes an increase in the gravitational attraction measured by satellites and could explain their inferred measurements of recent, rapid ice loss in West Antarctica. The new GPS measurements show West Antarctica is rebounding more slowly than previously thought. This means that the correction to the gravity signal from the rock contribution has been overestimated and the rate of ice loss is slower than previously believed.
The researchers do not yet know how large the overestimation was. A more definitive correction will be conducted by other researchers who specialize in interpreting satellite data. Previous estimates of postglacial rebound were made with theoretical models. Analysis of the direct GPS results into new models are expected to produce significant improvements in estimations of ice mass loss.
A team from The University of Texas at Austin’s Jackson School of Geosciences (Ian Dalziel, lead principal investigator), The Ohio State University’s School of Earth Sciences (Michael Bevis), and The University of Memphis’ Center for Earthquake Research and Information (Robert Smalley, Jr.) performed the project.
