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Tuesday, June 7, 2016

Finishing Blows: Not Muhammad Ali's but Antarctica's Larsen B Ice Shelf

     "The biggest ice shelf collapse on record was set in motion years earlier than previously thought, new research reveals."

     "Analyzing declassified images from spy satellites, researchers discovered that the downhill flow of ice on Antarctica’s Larsen B ice shelf was already accelerating as early as the 1960s and ’70s. By the late 1980s, the average ice velocity at the front of the shelf was around 20 percent faster than in the preceding decades, the researchers report in a paper to be published in Geophysical Research Letters."

     "Rising temperatures since the 1950s probably quickened the ice flow, which in turn put more strain on the ice and further weakened the shelf, says study coauthor Hongxing Liu, a geographer at the University of Cincinnati. Previous work had suggested that the ice shelf’s downward slide began only a few years before a Rhode Island-sized region of ice disintegrated into thousands of icebergs in 2002."

     "The new data will help scientists more confidently predict how Antarctic ice will fare in the coming decades, says Penn State glaciologist Richard Alley, who was not involved in the work. The early response of Larsen B to warming “is consistent with this ice shelf system being sensitive, and gives a target for future modeling studies to learn how sensitive, and for what reasons,” he says."

     "Ice shelves such as Larsen B line Antarctica’s coast and slow the flow of the continent’s glaciers and ice sheets into the sea. Rising temperatures are shrinking Antarctica’s ice, with several ice shelves on track to disappear completely within 100 years.Tracking the long-term decline of ice shelves is tricky, though. Scientific satellite images are sparse prior to the 1990s and next to nonexistent before the 1980s."

     Liu and others turned to another group that peered at Antarctica, a U.S. intelligence agency called the National Reconnaissance Office. In 1963, the agency photographed the continent as part of an intelligence-gathering mission. While these images were declassified in 1995, the photos were too distorted by effects such as the camera used and Earth’s curvature to use for ice flow measurements.  

     "Making the photographs usable required identifying stationary landmarks for reference, a difficult task on a continent covered with shifting white ice. Comparing the spy photos with later scientific images, Liu and colleagues identified 44 potential landmarks. Then, using the locations as anchor points, the researchers unwarped the images. Along with additional satellite images taken in 1979 and the 1980s, the modified images allowed the researchers to track Larsen B’s ice flow over time."

     "The ice on Larsen B’s front flowed at around 400 meters per year on average between 1963 and 1986, calculations using images from those years indicate. From 1986 to 1988, the average was 490 meters per year. That speed boost suggests that the ice flow accelerated between the 1963 to 1986 satellite images. Several glaciers that feed into Larsen B underwent similar accelerations, the researchers found."

     Larsen B’s early acceleration hints that the ice shelf was already weakening well before the 1990s, says Ted Scambos, a polar scientist at the National Snow and Ice Data Center in Boulder, Colorado, USA, who was not involved in the study. 

     Previous studies suggested that balmy surface temperatures caused Larsen B’s demise by forming meltwater pools 

on top of the ice shelf that forced open cracks in the ice. The new satellite data suggest that this fracturing was a finishing blow*

 following long-term weakening by forces such as relatively warm seawater eroding the ice shelf’s underside, Scambos said.

      I wonder what else is to be revealed in older aerial photographs and Landsat images of Antarctica and other areas. . .

Unwarpedly, ;-)

*My dad was such a Muhammad Ali fan and I wanted to pay homage to the man; Dad and Mom were in Atlanta in 1996 for the Olympics. It was a very special opening ceremony. . .


  1. Pardon my ignorance, but the notion of 'spy photos' of Antarctica has me wondering: Penguin insurrection? What?

  2. Either penguin insurrections or missile bases, I imagine. . .

  3. Photoreconnaissance satellites are usually placed into polar orbits so they can cover the whole globe (as opposed to equatorial orbits for geosynchronous satellites, or inclined orbits for most other purposes). The antarctic isn't of much military interest, but there's a lot of submarine and other naval and commercial activity in the north polar area.

  4. So, perhaps spy satellites aren't watching penguins, but maybe penguins are watching the satellites?

    1. Thanks, jan. The thought of penguins falling over in unison made me smile.

      My friend's dad, at 99, used to do the same thing looking at things in the sky, dust himself off, and say "It happens all the time."

    2. I almost did the same thing watching the Int'l Space Station pass overhead a few months ago.

    3. Penguins and us--not so many differences. . .

  5. Replies
    1. Weighing in:
      nihonium: does nothing for me
      moscovium: smack of a cool mossy cove in the Caribbean
      tennessine: Tennis, anyone?
      oganesson: Oh Gee! Naming an element after President Ford's press secretary is long overdue.

      The freezer shelf that holds my ice trays is busted. I believe there is a climate change occurring in all my appliances, especially my oven.


    2. Nihonium won out over Japonium or Rikenium (for the RIKEN Institute), as discussed here in January.

    3. Ah, yes, jan! The element names have been a long time coming. . .

      Lego, your knowledge of a breadth of topics is a wonder. Especially Ford's press secretary.

  6. Replies
    1. That's a new one for me. "Front Opening Unified Pod." Replacement for the SMIF ("Standard Mechanical InterFace").

      "Foup" is how our 2-year old pronounced "soup", so, of course, it's how my wife and I still do.

  7. So, slow day at work, I'm reading a fascinating article about microbial dark matter, when I come across a reference to the Erta Ale lava lakes, in Ethiopia, and my immediate reaction is, "why hasn't Steph told us about that?"

    1. Oh, I want to know more about Erte Ale! Triple junctions are pretty wild and unknown tectonic features . .I asked Zoë for a full report if she goes there this summer. Thanks for the link, jan.

  8. It's a disturbance in Saturn's F ring, but it reminds me of an LP after my brother dropped the needle on it. I can hear that click go by 33-1/3 times a minute...

  9. New post on "Larger Super-Eruptions at Yellowstone National Park 8 to 12 Million Years Ago" is now up.