Wednesday, July 25, 2012

GPS can now measure ice melt, change in Greenland over months rather than years

Ohio State University: Researchers have found a way to use GPS to measure short-term changes in the rate of ice loss on Greenland - and reveal a surprising link between the ice and the atmosphere above it. The study, published in the early online edition of the Proceedings of the National Academy of Sciences, hints at the potential for GPS to detect many consequences of climate change, including ice loss, the uplift of bedrock, changes in air pressure - and perhaps even sea level rise.

The team, led by earth scientists at Ohio State University, 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 melted away from the continent in only 6 months.

They were able to make the measurement because the earth compresses or expands like a spring depending on the weight above it, letting them use the Greenland bedrock like a giant bathroom scale to weigh the ice atop it. As ice accumulates, the bedrock sinks, and as the ice melts away, the bedrock rises. Measurements revealed that Greenland sank by about 6 mm (about one quarter of an inch) over the winter of 2010, and the researchers determined that half of the sinking (3 mm, or one eighth of an inch) was actually due to high air pressure above the ice, and the other half was due to ice accumulation.

Further, they determined that the bedrock lifted 11 mm (less than half an inch) over the course the summer. Air pressure appeared to affect the bedrock less during this time, so that the bounce-back appears to be mostly due to ice loss.

This method has been used to study ice loss before, in Antarctica as well as Greenland. But previously, GPS could only detect changes over a period of several years, said project leader Michael Bevis, Ohio Eminent Scholar in Geodynamics and professor in the School of Earth Sciences at Ohio State. While shortening the detection time to six months is a substantial advance, Bevis thinks his team will soon do even better....

Composite photograph of a GNET GPS unit implanted in the southeastern Greenland bedrock. Image by Dana Caccamise, courtesy of Ohio State University

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