Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

While stability far from assured, Greenland perhaps not headed down too slippery a slope

21.04.2008
Lubricating meltwater that makes its way from the surface down to where a glacier meets bedrock turns out to be only a minor reason why Greenland's outlet glaciers accelerated their race to the sea 50 to 100 percent in the 1990s and early 2000s, according to University of Washington's Ian Joughin and Woods Hole Oceanographic Institution's Sarah Das. The two are lead co-authors of two papers posted this week on Science magazine's Science Express.

The report also shows that surface meltwater is reaching bedrock farther inland under the Greenland Ice Sheet, something scientists had speculated was happening but had little evidence.

"Considered together, the new findings indicate that while surface melt plays a substantial role in ice sheet dynamics, it may not produce large instabilities leading to sea level rise," says Joughin, a glaciologist with the UW's Applied Physics Laboratory. Joughin goes on to stress that "there are still other mechanisms that are contributing to the current ice loss and likely will increase this loss as climate warms."

Outlet glaciers are rapid flows of ice that start in the Greenland Ice Sheet and extend all the way to the ocean, where their fronts break apart in the water as icebergs, a process called calving. While most of the ice sheet moves less than one tenth a mile a year, some outlet glaciers gallop along at 7.5 miles a year, making outlet glaciers a concern because of their more immediate potential to cause sea level rise.

If surface meltwater lubrication at the intersection of ice and bedrock was playing a major role in speeding up the outlet glaciers, one could imagine how global warming, which would create ever more meltwater at the surface, could cause Greenland's ice to shrink much more rapidly than expected – even catastrophically. Glacial ice is second only to the oceans as the largest reservoir of water on the planet and 10 percent of the Earth's glacial ice is found in Greenland.

It turns out, however, that when considered over an entire year, surface meltwater was responsible for only a few percent of the movement of the six outlet glaciers monitored, says Joughin, lead author of "Seasonal Speedup along the Western Flank of the Greenland Ice Sheet." Even in the summer it appears to contribute at most 15 percent, and often considerably less, to the total annual movement of these fast-moving outlet glaciers.

Calculations were made both by digitally comparing pairs of images acquired at different times from the Canadian RADARSAT satellite and by ground-based GPS measurements in a project funded by the National Science Foundation and National Aeronautics and Space Administration.

But while surface meltwater plays an inconsequential role in the movement of outlet glaciers, meltwater is responsible for 50 to 100 percent of the summer speed up for the large stretches near the edge of the ice sheet where there are no major outlet glaciers, a finding consistent with, but somewhat larger than, earlier observations.

"What Joughin, Das and their co-authors confirm is that iceflow speed up with meltwater is a widespread occurrence, not restricted to the one site where previously observed. But, they also show that the really fast-moving ice doesn't speed up very much with this. So we can expect the ice sheet in a warming world to shrink somewhat faster than previously expected, but this mechanism will not cause greatly faster shrinkage," says Richard Alley, professor of geosciences at Pennsylvania State University, who is not connected with the papers.

So what's behind the speed up of Greenland's outlet glaciers" Joughin says he thinks what's considerably more significant is when outlet glaciers lose large areas of ice at their seaward ends through increased calving, which may be affected by warmer temperatures. He's studied glaciers such as Jakobshavn Isbrae, one of Greenland's fastest-moving glaciers, and says that as ice calves and icebergs float away it is like removing a dam, allowing ice farther uphill to stream through to the ocean more quickly. At present, iceberg calving accounts for approximately 50 percent of the ice loss of Greenland, much of which is balanced by snowfall each winter. Several other studies recently have shown that the loss from calving is increasing, contributing at present rates to a rise in sea level of 1 to 2 inches per century.

"We don't yet know what warming temperatures means for increased calving of icebergs from the fronts of these outlet glaciers," Joughin says.

Until now scientists have only speculated if, and how, surface meltwater might make it to bedrock from high atop the Greenland Ice Sheet, which is a half-mile or more thick in places. The paper "Fracture Propagation to the Base of the Greenland Ice Sheet During Supraglacial Lake Drainage," with Woods Hole Oceanographic Institution's glaciologist Das as lead author, presents evidence of how a lake that disappeared from the surface of the inland ice sheet generated so much pressure and cracking that the water made it to bedrock in spite of more than half a mile of ice.

The glacial lake described in the paper was 2 to 2 ½ miles at its widest point and 40 feet deep. Researchers installed monitoring instruments and, 10 days after leaving the area, a large fracture developed, a crack spanning nearly the full length of the lake. The lake drained in 90 minutes with a fury comparable to that of Niagara Falls. (The researchers were ever so glad they hadn't been on the lake in their 10-foot boat with its 5-horsepower engine and don't plan future instrument deployments when the lakes are full of water. They'll get them in place only when the lakes are dry.)

Measurements after the event suggest there's an efficient drainage system under the ice sheet that dispersed the meltwater widely. The draining of multiple lakes each could explain the observed net regional summer ice speedup, the authors write.

Along with Das and Joughin other authors on the two papers are Matt King, Newcastle University, UK; Ben Smith, Ian Howat (now at Ohio State) and Twila Moon of the UW's Applied Physics Laboratory; Mark Behn and Dan Lizarralde of Woods Hole Oceanographic Institution; and Maya Bhatia, Massachusetts Institute of Technology/WHOI Joint Program.

Sandra Hines | EurekAlert!
Further information:
http://www.washington.edu

More articles from Earth Sciences:

nachricht From volcano's slope, NASA instrument looks sky high and to the future
27.04.2017 | NASA/Goddard Space Flight Center

nachricht Penn researchers quantify the changes that lightning inspires in rock
27.04.2017 | University of Pennsylvania

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Bare bones: Making bones transparent

27.04.2017 | Life Sciences

Study offers new theoretical approach to describing non-equilibrium phase transitions

27.04.2017 | Physics and Astronomy

From volcano's slope, NASA instrument looks sky high and to the future

27.04.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>