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New maps of the bedrock beneath Greenland’s ice
sheet (right) have found long, deep canyons that are likely to cause
ocean-feeding glaciers (left) to retreat faster and farther inland than
previously thought.
Image Credit: NASA
Scientists at NASA and the University of California, Irvine (UCI), have found
that canyons under Greenland's ocean-feeding glaciers are deeper and longer than
previously thought, increasing the amount of Greenland's estimated contribution
to future sea level rise.
"The glaciers of Greenland are likely to retreat faster and farther inland
than anticipated, and for much longer, according to this very different
topography we have discovered,” said Mathieu Morlighem, a UCI associate project
scientist who is lead author of the new research paper. The results were
published Sunday in the journal Nature Geoscience.
Ice loss from Greenland has accelerated during the last few decades. However,
older ice sheet models predicted the speedup would be temporary because the
glaciers would soon melt back onto higher ground and stabilize. The models
projected that Greenland's contribution to global sea level rise would therefore
be limited.
Morlighem's new topography shows southern Greenland's ragged, crumbling
coastline is scored by more than 100 canyons beneath glaciers that empty into
the ocean. Many canyons are well below sea level as far as 60 miles (100
kilometers) inland. Higher ground, where glaciers could stabilize, is much
farther from the coastline than previously thought. The finding calls into
question the idea that the recent accelerated ice loss will be short lived.
Buried under the Greenland Ice Sheet, the subcontinent's bedrock topography
has been estimated using soundings from ice-penetrating radar. However, the wet
and fractured ice along the southern coastline cluttered the radar soundings so
that large swaths of the bed remained invisible. To overcome that problem,
Morlighem and his colleagues devised an advanced technique to create a more
accurate map. The technique makes the best use of several kinds of data: ice
thickness measurements derived from airborne radar; satellite radar
interferometry data on the speed and direction of ice movement: and estimates of
snowfall and surface melt to the sea. By combining the different types of data,
they were able to map the bed topography along Greenland's margins with
unprecedented precision and detail.
"We have been able to make a quantum leap in our knowledge of bed topography
beneath ice sheets in the last decade, thanks to the advent of missions like
NASA's Operation IceBridge in combination with satellite data on the speed these
ice sheets are flowing," said coauthor Eric Rignot of UCI and NASA's Jet
Propulsion Laboratory (JPL), Pasadena, California.
The same research team reported new findings on glacial melt in West
Antarctica last week.
"Together the papers illustrate clearly the globe’s ice sheets will
contribute far more to sea level rise than current projections show,” said
Rignot.
The study used synthetic aperture radar data collected in 2008-2009 by the
Japanese Advanced Land Observing System Phased Array type L-band Synthetic
Aperture Radar (ALOS PALSAR), the Canadian RADARSAT-1, the German TerraSAR-X,
and the European Envisat Advanced Synthetic Aperture Radar (ASAR). Ice thinning
rates were derived from NASA's Airborne Topographic Mapper and ICESat data, and
ice thickness data came from NASA's Operation IceBridge airborne campaigns.
An animation of the newly mapped bed topography is available at:
The California Institute of Technology, Pasadena, manages JPL for NASA.
NASA monitors Earth's vital signs from land, air and space with a fleet of
satellites and ambitious airborne and ground-based observation campaigns. NASA
develops new ways to observe and study Earth's interconnected natural systems
with long-term data records and computer analysis tools to better see how our
planet is changing. The agency shares this unique knowledge with the global
community and works with institutions in the United States and around the world
that contribute to understanding and protecting our home planet.
For more information about NASA's Earth science activities in 2014,
visit:
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Guillermo Gonzalo Sánchez Achutegui
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