Featured Research

from universities, journals, and other organizations

Sediment Wedge Key To Glacial Environmental Stability

Date:
March 6, 2007
Source:
Penn State
Summary:
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 in Science Express.

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 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."

Researchers on the "Discovery of Till Deposition" paper include Anandakrishnan; Alley; Ginny Catania, research associate, Institute of Geophysics, University of Texas, Austin; and Huw Horgan, graduate student in geosciences, Penn State. Researchers on the "Effect of Sedimentation" paper include Alley; Anandakrishnan; Todd K. Dupont, assistant professor of earth and environmental sciences,University of Illinois at Chicago; Byron Parizek, assistant professor of physics, College of New Jersey; and David Pollard, senior research associate, geosciences, Penn State.

The National Science Foundation and the Gary Comer Science and Education Foundation supported portions of this work.


Story Source:

The above story is based on materials provided by Penn State. Note: Materials may be edited for content and length.


Cite This Page:

Penn State. "Sediment Wedge Key To Glacial Environmental Stability." ScienceDaily. ScienceDaily, 6 March 2007. <www.sciencedaily.com/releases/2007/03/070302082800.htm>.
Penn State. (2007, March 6). Sediment Wedge Key To Glacial Environmental Stability. ScienceDaily. Retrieved April 23, 2014 from www.sciencedaily.com/releases/2007/03/070302082800.htm
Penn State. "Sediment Wedge Key To Glacial Environmental Stability." ScienceDaily. www.sciencedaily.com/releases/2007/03/070302082800.htm (accessed April 23, 2014).

Share This



More Earth & Climate News

Wednesday, April 23, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

California Drought Is Good News for Gold Prospectors

California Drought Is Good News for Gold Prospectors

AFP (Apr. 22, 2014) — For months California has suffered from a historic drought. The lack of water is worrying for farmers and ranchers, but for gold diggers it’s a stroke of good fortune. With water levels low, normally inaccessible areas are exposed. Duration: 01:57 Video provided by AFP
Powered by NewsLook.com
Raw: MN Lakes Still Frozen Before Fishing Opener

Raw: MN Lakes Still Frozen Before Fishing Opener

AP (Apr. 22, 2014) — With only three weeks until Minnesota's fishing opener, many are wondering if the ice will be gone. Some of the Northland lakes are still covered by up to three feet of ice, causing concern that just like last year, the lakes won't be ready. (April 22) Video provided by AP
Powered by NewsLook.com
Scientists Warn Of Likely El Niño Event This Year

Scientists Warn Of Likely El Niño Event This Year

Newsy (Apr. 22, 2014) — With Pacific ocean water already showing signs of warming, the NOAA says there's about a 66 percent chance the event will begin before November. Video provided by Newsy
Powered by NewsLook.com
Is North Korea Planning Nuclear Test #4?

Is North Korea Planning Nuclear Test #4?

Newsy (Apr. 22, 2014) — South Korean officials say North Korea is preparing to conduct another nuclear test, but is Pyongyang just bluffing this time? Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins