NASA Scientists Reveal a New Mode of Ice Loss in Greenland

A new NASA study published in Geophysical Research Letters reveals that during Greenland’s hottest summers on record, 2010 and 2012, the ice in Rink Glacier on the island’s west coast didn’t just melt faster than usual, it slid through the glacier’s interior in a gigantic wave, like a warmed freezer pop sliding out of its plastic casing. The wave persisted for four months, with ice from upstream continuing to move down to replace the missing mass for at least four more months.

This long pulse of mass loss, called a solitary wave, is a new discovery that may increase the potential for sustained ice loss in Greenland as the climate continues to warm, with implications for the future rate of sea level rise.

The study by three scientists from NASA’s Jet Propulsion Laboratory in Pasadena, California, was the first to precisely track a glacier’s loss of mass from melting ice using the horizontal motion of a GPS sensor. They used data from a single sensor in the Greenland GPS Network (GNET), sited on bedrock next to Rink Glacier. A paper on the research is published online in the journal Geophysical Research Letters.

Rink is one of Greenland’s major outlets to the ocean, draining about 11 billion tons (gigatons) of ice per year in the early 2000s — roughly the weight of 30,000 Empire State Buildings. In the intensely hot summer of 2012, however, it lost an additional 6.7 gigatons of mass in the form of a solitary wave. Previously observed melting processes can’t explain that much mass loss.

The wave moved through the flowing glacier during the months of June through September at a speed of about 2.5 miles (4 kilometers) a month for the first three months, increasing to 7.5 miles (12 kilometers) during September. The amount of mass in motion was 1.7 gigatons, plus or minus about half a gigaton, per month. Rink Glacier typically flows at a speed of a mile or two (a few kilometers) a year.

The wave could not have been detected by the usual methods of monitoring Greenland’s ice loss, such as measuring the thinning of glaciers with airborne radar. “You could literally be standing there and you would not see any indication of the wave,” said JPL scientist Eric Larour, a coauthor of the new paper. “You would not see cracks or other unique surface features.”

The researchers saw the same wave pattern in the GPS data for 2010, the second hottest summer on record in Greenland. Although they did not quantify the exact size and speed of the 2010 wave, the patterns of motion in the GPS data indicate that it must have been smaller than the 2012 wave but similar in speed.