Observations before, during and after this swift, forceful event were collected and analyzed by a team led by Ian Joughin of the University of Washington in Seattle and Sarah Das of the Woods Hole Oceanographic Institution in Woods Hole, Mass. Their first-of-a-kind observations confirm the structure of the Greenland Ice Sheet plumbing, and go further to show that summertime melt indeed contributes to the speed up of ice loss. They also conclude, however, that summertime melt is not as critical a factor as other causes of ice loss. Research by Joughin and colleagues, published April 17 in Science Express, was funded in part by NASA and the National Science Foundation.
Scientists know that Greenland is losing ice. Much of Greenland's ice sheet is slow moving, creeping toward the ocean where the ice can calve off as icebergs. The landscape is also dumps ice into the ocean through outlet glaciers – rivers of ice that channel through valleys of bedrock and move at least 10 times faster than the ice sheet. Whether or not summertime melt has a significant influence on the speed of these flows has been an endless topic of debate among scientists – until now.
"For years people have said that the increasing length and intensity of the melt season in Greenland could yield an increase in ice discharge," said Joughin, lead author on the paper in Science. "Greater melt in future summers would cause ice to flow faster toward the coast and draw down more of the ice sheet."
Scientists have used computer models to show how melt could contribute to the observed speed up of the ice sheet. Meltwater travels through cracks in the ice down to the base of the mile-thick ice sheet where it forms a lubricating layer between the ice and the land. The fluid layer then makes it easier for the ice to slip away toward the ocean. The effect, however, had never been observed in Greenland on a large-scale, a fact that motivated Joughin and colleagues to get a closer look.
In 2006, Joughin embarked on an expedition by airplane to locate lakes on the ice sheet that they had identified in advance using NASA's Moderate-resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra and Aqua satellites. The team selected two lakes full of meltwater and set up Global Positioning System (GPS) equipment to measure ground movement in a limited area but over frequent intervals, every two days. They also collected data from the NASA-launched and Canadian-owned satellite RADARSAT, which could provide similar movement information over an area hundreds of miles wide, but could make those measurements only every 24 days. When combined, these data helped the researchers identify relative changes in ice movements across the entire ice sheet.
They found that the influence of the violent draining of the lakes had a short-lived influence on the local movement of the ice sheet. Speedup during periods of summer were widespread across Greenland, suggesting that the ice sheet's plumbing is composed of a drainage network that quickly distributes the lubricating meltwater throughout the base of the ice sheet, as opposed to the water remaining confined to a single isolated crack.
As for the relative speed of movement across Greenland, the researchers found that the slow-moving ice sheet saw seasonal increases in speed ranging from 50 to 100 percent. Despite the speed up, the ice sheet makes a relatively small contribution to ice loss compared to the already fast-moving outlet glaciers. The fast-moving outlet glaciers, however, are not affected as much by seasonal melt, which accounts for a speed increase of up to 15 percent and in many cases much less. "If you're really going to get a lot of ice out of Greenland, that would have to occur through outlet glaciers, but those are not being affected very much by seasonal melt," Joughin said. "The outlet glaciers are more affected by the removal of their shelves and grounded ice in their fjords, which decreases resistance to ice flow."
Lynn Chandler | EurekAlert!
NASA examines Peru's deadly rainfall
24.03.2017 | NASA/Goddard Space Flight Center
Steep rise of the Bernese Alps
24.03.2017 | Universität Bern
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Earth Sciences
24.03.2017 | Health and Medicine
24.03.2017 | Earth Sciences