From the University of Texas at Austin, a press release to tell us the ice shelves in the Antarctic peninsula are losing their grip and cracking a bit. That could be tragic, except, well, sea ice in Antarctica is growing.
And, there’s only a 40 year historical context for these observations. I just can’t too excited about this. – Anthony
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West Antarctic Ice Shelves Tearing Apart at the Seams
Posted on March 26, 2012
Rifts along the northern shear margin of Pine Island Glacier (upper right of image). Credit: Michael Studinger, NASA’s Operation IceBridge.
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.
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.
“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.”
Location of Amundsen Sea Embayment
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.
The article, titled “Widespread rifting and retreat of ice-shelf margins in the eastern Amundsen Sea Embayment between 1972 and 2011”, appears in issue #209 of Journal of Glaciology.
West Antarctic Ice Shelves – Then and Now
(click to download high resolution version):
Pairs of Landsat satellite images showing changes in ice shelf margins in the eastern Amundsen Sea Embayment in West Antarctica between 1972 and 2011. The striping visible in the 2011 images is due to an unrepaired malfunction in the Landsat-7 platform that occurred in 2003.
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UPDATE: Gail Combs adds this background info in comments:
Velocities of Pine Island and Thwaites Glaciers, West Antarctica, From ERS-1 SAR images
ABSTRACT:
Average velocities of Pine Island and Thwaites Glaciers were measured for the time periods between 1992 and 1994 by tracking ice-surface patterns. Velocities of the central flow of the Pine Island Glacier range from 1.5 km/yr above the grounding line (separating the grounded from the floating parts of a glacier) to 2.8 km/yr near the terminus; velocities of the central Thwaites Glacier range from 2.2 km/yr above the grounding line to 3.4 km/yr at the limit of measurements on the tongue. Both glaciers show an increase in velocity of about 1 km/yr where they cross their grounding lines. The velocities derived from ERS-1 images are higher than those previously derived from Landsat images, perhaps reflecting acceleration of the glaciers. Both glaciers are exceptionally fast. The high velocities may be due to high precipitation rates over West Antarctica and the lack of a major buttressing ice shelf.
Keywords: ERS-SAR images, Pine Island Glacier, Thwaites Glacier, glacier velocity, glacier tongue, glacier terminus
Antarctic volcanoes identified as a possible culprit in glacier melting
…”This is the first time we have seen a volcano beneath the ice sheet punch a hole through the ice sheet” in Antarctica, Vaughan said.
Volcanic heat could still be melting ice to water and contributing to thinning and speeding up of the Pine Island glacier, which passes nearby, but Vaughan said he doubted that it could be affecting other glaciers in western Antarctica, which have also thinned in recent years. Most glaciologists, including Vaughan, say that warmer ocean water is the primary cause of thinning.
Volcanically, Antarctica is a fairly quiet place. But sometime around 325 B.C., the researchers said, a hidden and still active volcano erupted, puncturing several hundred yards of ice above it. Ash and shards from the volcano carried through the air and settled onto the surrounding landscape. That layer is now out of sight, hidden beneath the snows that fell during the next 2,300 years…..
http://www.nytimes.com/2008/01/20/world/europe/20iht-climate.4.9358350.html
Amplified acceleration. Huh? Redundant much?
The ice shelves are cantilever structures buoyed by the ocean. The greater the moment arm the greater the tendency to crack. This is basic engineering. Helllllllooooooooo!
How does one differentiate East Antarctica from West Antarctica. I can figure North and South. I guess it must be through Longitude.
This is all good. I, for one, can’t wait to vacation there. Under the swaying palms. Me and my Corona.
Move along now; nothing to see here.
I have a photo that Svend Hendriksen sent me, that was of that earlier ice shelf (not Larsen B) that collapsed on the Antarctic peninsula. Svend pointed out an ajacent area of shelf, that had collapsed 50 years earlier and grown back but now lower level than the surroundings, which had another 50 years of snow deposits.
So 40 years of observations, isn’t nearly long enough to find out what is standard operating procedure for these ice shelves.
And how many times do I have to say that the whole Pacific and Atlantic oceans go sloshing through that gap from the AP to Cape horn twice a day, back and forth. and the article does say they are FLOATING ice shelves, so when the sea goes up and down, they behave with their usual concrete like lack of tensile strength, and would be expected to crack with all that water driving underneath.
SteveSadlov says:
March 28, 2012 at 9:55 am
The ice shelves are cantilever structures buoyed by the ocean. The greater the moment arm the greater the tendency to crack. This is basic engineering. Helllllllooooooooo!
Exactly.
Maybe I’m being a bit obtuse, but how come there’s a WEST Antarctica?
West of what? Doesn’t the joint cover every longitude?
And is there an East Antarctica?
If so, what’s it east of?
Please don’t say West Antarctica.
A little climate trivia: One cubic inch, foot, yard, or meter of water at 70 degrees and sea level contains about 3250 times more specific heat than an of equal volume of adjacent dry air.
glaciers accelerating forward are a sign of glacier GROWTH
Just curious, but I wonder what kind of effect those major tsunamis had on these floating parts of the glaciers. Sumatra, Chile, and Japan tsunamis were quite large. Maybe not much considering distance, but just curious.
Obviously, our electricity generation is releasing the evil voo-doo molecules that cause this problem, & others much like it. Keep in mind that lower case letters (in ASCII & UTF-8) have a great many more 1s than upper case, thus consume far more electricity. SO TYPING IN ALL CAPS IS THE GREEN THING TO DO.
I hate ice. Good riddance.
Smokey says:
March 28, 2012 at 7:26 am
Now, I wouldn’t normally step in here to defend a warmist, but please don’t be mean to Hugs Pepper. I’m sure if you ask Dr. Pepper, he’ll tell you he has a PC, not a CV (or a Mac, for that matter).
Brian D said on March 28, 2012 at 12:24 pm:
Review previous WUWT post on long-period ocean waves. If storms in the North Pacific Ocean can disturb those Antarctic ice shelves, tsunamis in the area could contribute damage, although each would only be a one-time pulse instead of an ongoing phenomenon. But as tsunamis are known for a drop in water level before hitting, which would leave ice shelves that are firmly attached to the ice on the land briefly suspended under tension with insufficient buoyancy to counter their weight, the effect could be considerable.
As mentioned, it’s ice floating but gaining mass from snow, As the mass increases, the support on the seaward side decreases. It’s bound to break sometime.
DaveE.
This article appears to be based on observations, not on model output. Be thankful for small favors!
If we continue making careful observations for a couple hundred years, we may have some idea what “normal” is. Gotta start somewhere!
Frank: Yep, we only need to watch for a full glacial/interglacial cycle so we will know the cycle. (But what if it is quantum and we change it by observations! OH NOES!!!)
Graphite says:
March 28, 2012 at 11:28 am
Graphite,
It is a bit late to get a grip on Antarctica. Rumor has it that it’s cracking up.
Just kidding. Go here:
http://geology.com/world/antarctica-map.jpg
The general east/west thing would be established by the zero longitude line. As it so happens in Antarctica there is a mountain range, labeled on the maps as the Transantarctic Mountains – very nice photos here:
http://www.transantarcticmountains.com/
This range sort of – but not quite, runs along the virtual cartographic line and so the human thing to do is to apply the concept of east/west in a fuzzy sort of way, as shown in the map.
Hope that helps.
The CAGW sausage factory rolls on. It’s wurst than we thought!
[Moderator’s Offer: Let me know when you want this comment deleted. -REP]
Brilliant! 🙂
REP – perhaps I should let you know I wanted to turn off the italics at the end of the first line!
“we can (if we chose) rely on summaries provided by experts in the field, and other relevant bodies such as the IPCC”
Perfecty acceptable concept; however if you take away the facts and the climistas’ pre-determined computer models, what do you have?
Answer: Not much, other than a vaguely interesting minor climate phenomenom in the current inter-glacial period.
As for the IPCC, let’s be nice and call this organisation as being great, apart from being totally conflicted and grant addicted.
Hugh Pepper, I assume you work for a government or quasi-government organisation, so immediately your comments are conflicted because you are paid to toe the official party line, which is: ” Scare the crap out of them, so we can stiff them with more taxes.” – Do that and the grant addiction machine will work for you.
I’m just glad we didn’t get pix of Al Gore skinny-dipping on his recent trip.
Hoser said on March 28, 2012 at 5:09 pm:
Another crack in the Antarctic?
It would have been photographic evidence of Global Shrinkage.
And, if Gore had an intern or massage therapist with him, it might have been photographic evidence he’d changed his position on offshore drilling.