Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Sediment wedge key to glacial environmental stability

A wedge of sediment, pushed up by glacial movement, may be a buffer against moderate sea level rise, pointing to ocean temperature rise as the key factor in glacial retreat, according to two papers published today (March 1) in Science Express.

"Sediment beneath ice shelves helps stabilize ice sheets against retreat in response to rise in relative sea level of at least several meters," says Richard Alley, the Evan Pugh professor of geosciences, Penn State. "Large sea level rise, such as the more than 325 feet at the end of the last ice age, may overwhelm the stabilizing feedback from sedimentation, but smaller sea-level changes are unlikely to do the same."

The researchers identified a sediment wedge beneath the Whillans Ice Stream in Antarctica using snowmobile-towed radar where ice from the Whillans Ice Stream in West Antarctica begins to float in the Ross Sea forming the Ross Ice Shelf. They report this research in Science Express in the article "Discovery of Till Deposition at the Grounding Line of Whillans Ice Stream."

The radar imaged a miles-long pile of sediments as thick as 100 feet deposited beneath the Ross Ice Shelf over the last 1000 years. The sediments are eroded out of the ground by the moving ice sheet that then drags them along and deposits them in a wedge-shaped delta.

"We found this miles-long pile of deposited sediment just where the ice stream goes afloat," says Sridhar Anandakrishnan, associate professor of geosciences, Penn State. "This showed us that sediment transport beneath the ice plays an important role in determining the size of this ice stream."

Antarctic glaciers form over the Antarctic land mass and glacial ice streams flow toward the oceans. When the edge of the glacier flows past the edge of land, that portion of the glacier begins to float and forms an ice shelf. Portions of ice shelves occasionally calve off and float into the oceans. Previous research suggested that rising sea level would push back the grounding line -- the line where grounded glacier and ice shelf meet -- shrinking the glaciers.

"Our results suggest that the grounding line is well above the point at which the ice floats and will tend to remain in the same location even though sea level changes, until sea level rises sufficiently to overcome the effect of the sediment wedge," says Anandakrishnan. "We determined the grounding line location from the drop in ice surface elevation, which was 33 feet over only about 2 miles."

According to the researchers, "the grounding-line position has probably been stable near the present position for a millennium."

Anandakrishnan and colleagues note that the wedge depicted by radar imaging closely matches wedges found beyond the floating Ross Sea on the ocean bottom. These wedges are those left at the glacial maximum and as the glaciers retreated to their present day location, indicating that this wedge formation is a natural part of ice stream movement. "The modern grounding line occurs where the bed falls away rather than where the ice thins," says Anandakrishnan.

The Science Express paper, "Effect of Sedimentation on Ice-Sheet Grounding-Line Stability," suggests reasons why the sediment wedge provides stability against the increase or decrease of a few meters or more of sea-level change.

The researchers used three different ice-flow models to first model the configuration approximating the Whillans Ice Stream and the adjacent Ross Ice Shelf assuming a flat glacial bed. After the ice streams stabilized, they instantaneously added a wedge of sediment similar to that located by the radar.

The response of these models to instantaneous sea-level rise, both with and without the sediment wedge, showed that without the sediment wedge, the ice shelf forms at the point where the ice thins; however, with the sediment wedge, the ice shelf forms where the bed falls away.

"In all three models, sea-level rise without a wedge causes grounding-line retreat," says Alley. "With the wedge, the ice over the wedge thickens to above flotation mass so that small increases in sea-level cause only small grounding line retreat which never reaches the point where the ice over the wedge floats."

However, large sea-level increase could push the grounding-line much farther back, allowing the ice above to float and the glacier as a whole to retreat. Further calculations indicate that a sea-level rise of more than 33 feet may be required to force the ice to retreat from the wedge.

"Our results, together with recent evidence that ice shelves respond sensitively to ocean-temperature changes and quickly propagate the response inland, point to greater importance of other environmental variables, and especially sub-ice-shelf temperatures," says Alley.

The researchers caution that sea level may be the primary control on the ice sheet if other variables that affect ice sheets more quickly, such as water temperature under ice shelves, remain stable.

"Common climatic forcing, including an increase in ocean temperatures, which can have very large and very rapid effects on ice sheets, is more likely to cause Antarctic glacial retreat," says Alley.

Floating ice shelves around Antarctica run aground on submerged islands. Friction from the islands helps hold back the ice behind. Warming of the water beneath the ice shelf of only one degree Fahrenheit increases the melt rate of the floating ice by almost 20 feet per year. The melting reduces friction with the islands, letting the ice flow faster. The resulting decrease in ice may be enough to allow the ice to float free of the sediment wedge, shrinking the ice sheet and raising sea level.

"Recent discoveries, including the changing lakes beneath the ice that flows into the Ross Ice Shelf, show that the great ice sheet still has many mysteries," says Alley. "Understanding these mysteries will be necessary to predict the behavior of the great ice sheet in a warming world."

Vicki Fong | EurekAlert!
Further information:

More articles from Earth Sciences:

nachricht Gas hydrate research: Advanced knowledge and new technologies
23.03.2018 | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ

nachricht New technologies and computing power to help strengthen population data
22.03.2018 | University of Southampton

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Space observation with radar to secure Germany's space infrastructure

Satellites in near-Earth orbit are at risk due to the steady increase in space debris. But their mission in the areas of telecommunications, navigation or weather forecasts is essential for society. Fraunhofer FHR therefore develops radar-based systems which allow the detection, tracking and cataloging of even the smallest particles of debris. Satellite operators who have access to our data are in a better position to plan evasive maneuvers and prevent destructive collisions. From April, 25-29 2018, Fraunhofer FHR and its partners will exhibit the complementary radar systems TIRA and GESTRA as well as the latest radar techniques for space observation across three stands at the ILA Berlin.

The "traffic situation" in space is very tense: the Earth is currently being orbited not only by countless satellites but also by a large volume of space...

Im Focus: Researchers Discover New Anti-Cancer Protein

An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.

The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

New solar solutions for sustainable buildings and cities

23.03.2018 | Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

Latest News

For graphite pellets, just add elbow grease

23.03.2018 | Materials Sciences

Unique communication strategy discovered in stem cell pathway controlling plant growth

23.03.2018 | Agricultural and Forestry Science

Sharpening the X-ray view of the nanocosm

23.03.2018 | Physics and Astronomy

Science & Research
Overview of more VideoLinks >>>