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Climate Hustle

West Antarctic Ice Shelves Tearing Apart at the Seams

Posted on 7 May 2012 by John Hartz

This is a reprint of a news release posted by the Jackson School of Geosciences of the Universtiy of Texas at Austin on March 26, 2012.


A new study examining nearly 40 years of satellite imagery has revealed that the floating ice shelves of a critical portion of West Antarctica are steadily losing their grip on adjacent bay walls, potentially amplifying an already accelerating loss of ice to the sea.

Map of Amundsen Sea Ebayment

Location of Amundsen Sea Embayment 

The most extensive record yet of the evolution of the floating ice shelves in the eastern Amundsen Sea Embayment in West Antarctica shows that their margins, where they grip onto rocky bay walls or slower ice masses, are fracturing and retreating inland. As that grip continues to loosen, these already-thinning ice shelves will be even less able to hold back grounded ice upstream, according to glaciologists at The University of Texas at Austin’s Institute for Geophysics (UTIG).

Reporting in the Journal of Glaciology, the UTIG team found that the extent of ice shelves in the Amundsen Sea Embayment changed substantially between the beginning of the Landsat satellite record in 1972 and late 2011. These changes were especially rapid during the past decade. The affected ice shelves include the floating extensions of the rapidly thinning Thwaites and Pine Island Glaciers.

NASA Photo of Pnie Island Glacier in the WAIS

Rifts along the northern shear margin of Pine Island Glacier (upper right of image). Credit: Michael Studinger, NASA's Operation IceBridge

 “Typically, the leading edge of an ice shelf moves forward steadily over time, retreating episodically when an iceberg calves off, but that is not what happened along the shear margins,” says Joseph MacGregor, research scientist associate and lead author of the study. An iceberg is said to calve when it breaks off and floats out to sea.

“Anyone can examine this region in Google Earth and see a snapshot of the same satellite data we used, but only through examination of the whole satellite record is it possible to distinguish long-term change from cyclical calving,” says MacGregor.

The shear margins that bound these ice shelves laterally are now heavily rifted, resembling a cracked mirror in satellite imagery until the detached icebergs finally drift out to the open sea. The calving front then retreats along these disintegrating margins. The pattern of marginal rifting and retreat is hypothesized to be a symptom, rather than a trigger, of the recent glacier acceleration in this region, but this pattern could generate additional acceleration.

 “As a glacier goes afloat, becoming an ice shelf, its flow is resisted partly by the margins, which are the bay walls or the seams where two glaciers merge,” explains Ginny Catania, assistant professor at UTIG and co-author of the study. “An accelerating glacier can tear away from its margins, creating rifts that negate the margins’ resistance to ice flow and causing additional acceleration.”

The UTIG team found that the largest relative glacier accelerations occurred within and upstream of the increasingly rifted margins.

The observed style of slow-but-steady disintegration along ice-shelf margins has been neglected in most computer models of this critical region of West Antarctica, partly because it involves fracture, but also because no comprehensive record of this pattern existed. The authors conclude that several rifts present in the ice shelves suggest that they are poised to shrink further.

This research is sponsored in part by the National Science Foundation.

Source paper:

Joseph A. MacGregor, Ginny A. Catania, Michael S. Markowski, Alan G. Andrews

“Widespread rifting and retreat of ice-shelf margins in the eastern Amundsen Sea Embayment between 1972 and 2011”, issue #209 of Journal of Glaciology.

before and after

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Comments 1 to 8:

  1. And now the good news...

    Things aren't quite as bad in Greenland:

    Although, as the articles says, the end result is the same, it just might take longer.
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  2. The MacGregor et al (2012) is an excellent paper. We saw a pattern of widespread thinning and retreat and the disintegration of Antarctic Peninsula ice shelves. Now we are seeing the same processes in the Amundsen Sea. As ice shelves thin they are less buttressed, more prone to rifting and can accelerate due to the reduced backforces, which leads to acceleration. Smith Glacier is the main glacier feeding Crosson Ice Shelf
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  3. Deniers often say that the Antarctic ice cannot melt because the air is too cold. From Mspelto's reference:

    "The thinning has been noted as widespread around most of Anarctic Ice Shelves in a paper this week from Pritchard et al (2012). This paper from an international team from British Antarctic Survey, Utrecht University, Scripps Institution of Oceanography and Earth & Space Research has identified the losses are principally the result of increased basal melting from intrusion at depth of warm water. In the Smith Glacier area there is no significant surface melting, so basal melting must be the source.

    My emphasis. Warm water from higher latitudes is melting the ice in the Antarctic.
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  4. "Warm water from higher latitudes is melting the ice in the Antarctic."

    I suppose some people at research stations are making coffee, but I think the Southern Ocean produces some very strong currents of cold deep Antarctic water and is replenished in part by water advected from mid-depth Pacific waters. Mid depth Pacific water is warmed by water forced down by the strong trade winds of La Niña.

    Oh well, by now you've had a flash: "Lower latitudes! I meant lower!" ;)
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  5. Another paper, another area, same topic:

    Press release AWI (Alfred Wegener Institute for Polar and Marine Research)

    Hartmut H. Hellmer, Frank Kauker, Ralph Timmermann, Jürgen Determann, Jamie Rae: Twenty-first-century warming of a large Antarctic ice shelf cavity by a redirected coastal current. Nature 10 May 2012, Vol 485, page 225. DOI: 10.1038/nature11064 [, Abstract]
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  6. ajki:

    Thank you for bringing this new paper to everyone's attention. I will proceed to transform the news release into an SkS article. The graphics that are provided by the Alfred Wegener Institute for Polar and Marine Research are extremely well done.
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  7. More troubling news about the stability of the West Antarctic Ice Sheet...

    “Scientists at the University of Liverpool have found that genetic information on the Antarctic octopus supports studies indicating that the West Antarctic Ice Sheet could have collapsed during its history, possibly as recently as 200,000 years ago.

    Source: “Antarctic octopuses 10,000km apart “genetically similar”, University News, University of Liverpool, May 9, 2012
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  8. Here's the journal reference for the information contained in my post #7:

    J. M. Strugnell, P. C. Watts, P. J. Smith, A. L. Allcock. "Persistent genetic signatures of historic climatic events in an Antarctic octopus", Molecular Ecology, 2012; DOI: 10.1111/j.1365-294X.2012.05572.x
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