Researchers from the US have found a way to use GPS to measure short-term changes in the rate of ice loss in Greenland.
The team from Ohio State University planted more than 50 GPS stations into the ground surrounding Greenland’s ice sheet and used them to measure how the rock rose and fell under the changing mass of the ice as if it were a weighing scale.
This method had only previously been used to study ice loss over a period of several years but the team shortened this to six months by planting enough GPS stations close together in a network around the ice.
‘Within the next year or so, we should be able to process the GPS data within a month of its being collected and then we can monitor abrupt changes in ice mass only a month or two after they occur,’ said project leader Michael Bevis in a statement.
Using this technique, the researchers pinpointed a period in 2010 when high temperatures caused the natural ice flow out to sea to suddenly accelerate and 100 billion tons of ice to melt away in only six months.
They positioned the GPS antennas that formed the Greenland GPS Network (GNET) on poles anchored into bare rock, and were able to record how the landmass fell as ice accumulated and rose as it melted.
GNET’s measurements were so detailed that the researchers were able to determine what portion of bedrock motion was due to the ice melting away and what portion was due to seasonal swings in air pressure above the ice.
‘It surprises most meteorologists that there is such a strong seasonal signal in surface pressure in Greenland,’ said Bevis. ‘But it amazes almost everyone to learn that seasonal changes in air mass push on the bedrock just as strongly as seasonal changes in ice mass. It is highly counterintuitive, but true.’
By correlating daily displacements of the GPS stations with daily changes in surface pressure fields produced by numerical weather models, the researchers were able to isolate the movement due to air pressure and make more accurate measurements of ice mass.
The team is now investigating the possibility of detecting changes in sea level rise via GPS units planted at coastlines and in small ocean islands.