Greenland’s more than 200 major outlet glaciers are constantly on the move - many of them at some of the fastest speeds ever recorded. Thanks to the work of the Greenland Ice Mapping Project (GIMP), scientists and glaciologists have a wealth of data dating back to 2000 to help analyze the movement of these outlet glaciers and the potential consequences of these movements.
“We have found lots of things looking through the data,” says Ian Joughin, Principal Investigator for the Greenland Ice Mapping Project and Senior Principal Engineer at the Applied Physics Laboratory at the University of Washington. “For example, we recently published data about Jakobshavn Glacier in Greenland hitting the fastest glacier speeds ever recorded. We’re producing a time series of velocities of all the major outlet glaciers in Greenland. We’ve shown that there is a huge variability in the flow in Greenland. There are numerous investigators downloading these data to try to figure out what’s going on.”
The Greenland Ice Mapping Project is part of NASA’s Making Earth System Data Records for Use in Research Environments, or Making Earth System Data Records for Use in Research Environments (MEaSUREs) Program. MEaSUREs projects produce coherent, consistent data records that are archived and distributed by EOSDIS Distributed Active Archive Centers (DAACs). Data from the Greenland Ice Mapping Project is archived and distributed through the National Snow and Ice Data Center Distributed Active Archive Center (NSIDC DAAC). “MEaSUREs is not a science analysis program, but more of a data production program,” Joughin says. “The idea is to get the data to the user community so we can leverage the entire scientific community’s resources.”
Satellites have collected data about changes in Greenland’s ice cover since 1979, including NASA’s Ice, Cloud,and land Elevation Satellite (ICESat) mission (2003-2010) and the upcoming ICESat-2 mission (scheduled for launch in 2017). These satellite observations are supplemented with airborne data collection campaigns, such as NASA’s ongoing Operation IceBridge. Data from ICESat and IceBridge show that Greenland’s ice sheet has thickened toward the center of the island, but has significantly thinned around the coasts, especially at outlet glaciers like Jakobshavn, which are retreating rapidly. In fact, researchers recently observed summer glacier speeds that are more than four times the speeds recorded in the 1990s. “The velocity data are tremendously helpful for understanding what’s causing the thinning and trying to understand why the glaciers are speeding up,” Joughin says.
Joughin notes that the increased velocities of glaciers were not anticipated a decade or two ago. “In Greenland and Antarctica, we’ve had satellites looking at these areas since the 1990s and we’ve been seeing speed-up on both ice sheets,” he says. “I couldn’t correlate one glacier to the next, but the overall pattern of speed-up is happening on both ice sheets.”
One major consequence of this more rapid movement is an increase in the amount of ice flowing into the surrounding oceans. This added fresh water could lead to changes in ocean currents, sea life, and, of course, sea level. Joughin is quick to point out that there still is a lot of uncertainty about how much or how rapidly this flux of ice will affect global sea levels.
The Greenland Ice Mapping Project velocity data are derived from synthetic aperture radar (SAR) measurements from a number of international missions, including Canada’s RADARSAT-1 and RADARSAT-2, Japan’s “Daichi” Advanced Land Observing Satellite (ALOS-1), and Germany’s TerraSAR-X. These SAR systems, however, were not designed for the express purpose of mapping sea ice.
This will change with the launch of the joint NASA-Indian Space Research Organisation Synthetic Aperture Radar (NISAR) mission, which currently is scheduled for 2020. One of the primary science objectives of NISAR is to measure the flow of ice sheets.
Until NISAR launches, Joughin and his team are providing an invaluable baseline data set of the Greenland ice sheet and glacier velocities. Thanks to a recent five-year extension, the Greenland Ice Mapping Project will continue to provide these data to NASA’s NSIDC DAAC.
“When I first started working on ice sheets, someone said that if you’re mapping speeds of ice sheets, when you’ve mapped them once you’re done, because they don’t change all that rapidly,” Joughin says. “Now, we’re finding that they’re changing all over the place.”