Ice-shelf rifts could threaten glaciers, says Antarctic expert

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Ice-shelf rifts could threaten glaciers, says Antarctic expert

Like ice-sheet experts the world over, Rice University oceanographer John Anderson is waiting to see what will become of dramatic rifts that could signal trouble for two Antarctic ice shelves.

Anderson, a veteran of 24 research expeditions to the Antarctic, said the lesser publicized of the two breaks — a crack in the Pine Island ice shelf on the Amundsen Sea — is the more troubling because of its critical location.

The more dramatic break in the Larsen C fracture, which is about 70 miles long, could produce an iceberg approximately the size of Delaware and has received increasing publicity following reports that it grew by as much as 11 miles in December.

“Ice shelves are floating structures that act like corks to keep Antarctic glaciers bottled up on land,” said Anderson, Rice’s W. Maurice Ewing Professor of Oceanography and professor of Earth science.

“Just as melting ice cubes don’t increase the level of water in a glass, melting ice shelves do not increase sea level. However, the breakup of ice shelves does allow glaciers and ice streams to flow much more rapidly, and these do contribute to sea-level rise.”

For instance, glaciers that were once behind the Larsen B ice shelf today flow as much as 10 times faster into the Weddell Sea than they did prior to the breakup of that ice shelf in 2002.

The rift in the Pine Island ice shelf was discovered by scientists who were measuring a 2013 break in the shelf that produced a Chicago-sized iceberg. While berg-forming rifts are common in all ice shelves, the breaks usually form at the sides of the shelves. Both the 2013 and 2015 breaks began in the middle of the Pine Island ice shelf.

“The most likely explanation is that the shelf is being eaten away from below by warmer water from the nearby ocean,” Anderson said. “There’s ample evidence that ice sheets have collapsed in exactly this way during warming periods in Earth’s distant past.”

Because the Pine Island glacier, which stands behind the Pine Island ice shelf, is one of the five-largest ice streams in Antarctica, Anderson said a breakup of the Pine Island ice shelf would have more far-reaching consequences than a Larsen C breakup.

“The Pine Island glacier and its nearby twin, the Thwaites Glacier, are two of the primary outlets for the Western Antarctic Ice Sheet,” Anderson said.

“That ice is as much as 2,000 meters thick, but it sits on ground that is below sea level and is therefore believed to be particularly vulnerable to runaway melting, should the seaward ice shelves break apart.”

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News source: Rice University.
Figure legend: This Knowridge.com image is credited to NASA/John Sonntag