Using vibrations from ocean waves to measure ice-sheet mass

The Economist : Predicting sea-level rise due to melting ice sheets is complicated because of the difficulty in measuring the changing masses of the ice. Currently the mass is measured with laser topography and gravitational fluctuations, but those methods are limited by cost and resolution. Now Aurélien Mordret of MIT and his colleagues have developed a technique that uses seismometers to measure the vibrations created by ocean waves striking near ice sheets. The vibrations travel at different speeds depending on the compression of the rocky crust from the ice above. Mordret and his team predicted that the vibration speeds they would measure during the winter, when Greenland’s ice sheet is largest, would be different from those measured in the summer, when the sheet is smallest. Using seven monitoring stations throughout 2012 and 2013, the researchers found that their calculations were in line with measurements made using other techniques. Mordret says that expanding the network of seismometer stations in Greenland and elsewhere could give a much clearer picture of changes in ice-sheet mass.