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
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A few years ago, there was talk about volcanic activity up and down that region of west Antarctica.
Sea ice has little to do with shelf ice, so the comparison is meaningless.
I remember very long-period ocean waves (“infragravity waves”) being implicated in the collapse of Antarctic ice shelves like with the Wilkins Ice Shelf breakup events in 2008. Worrying about CO₂ ain’t gonna save these shelves.
But it may indicate the Southern Ocean might be a good place to test those future ocean-based renewable-energy wave generators, as besides dragging out “climate change” as a project justification, they can claim the need to intercept all that energy before the ice shelves collapse yielding a 3 meter (+0.01/-3.01) sea level rise. Hansen would be pleased.
…ice shelves in the Antarctic peninsula are losing their grip and cracking a bit.
Proof that Antarctic ice shelves are therefore a suitable proxy for CAGW cultists…
They mentioned acceleration of the ice flow which would indicate increased snowfall.If the average temp in Antarctica is -40 c then logic dictates it’s not melting ,I would suggest that our Beautiful Planet with it’s EVER CHANGING CLIMATE is F——-G with their tiny brains.Climate Change is Natural get over it.
izen says:
March 28, 2012 at 2:29 am
…so the context is of large ice shelves which have been stable features at least throught the Holocene starting to collapse, long after the post-glacial Holocene maximum.
No, they’re not starting to collapse. They’ve become detached, most likely due to volcanic warming. It’s now autumn in the Southern Hemisphere — in a few months the rifts should be frozen over again.
In most previous interstadial cycles these ice masses would be expanding, not shrinking several thousand years after the maximum post-melt temperature.
Ahem — what is it about “recent volcanic ground warming” that you didn’t understand?
As I see it, the ice that slides off the continent into the sea has two options. It can either break off and float away and melt, or it can keep on expanding Northwards. Do they have any evidence that it has done the later in the last 10,000 years, if so I think we should be told.
“no comprehensive record of this pattern existed.”
So they don’t know if what they describe is common nor unusual.
sea ice in Antarctica is growing.
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So the article is about land ice and Anthony mentions sea ice. Is anyone here confused by the distinction?
Maybe land ice moving faster means the Antarctic is getting warmer. Maybe more land ice melting is making it easier for seawater to freeze and make more sea ice?
“Losing its grip”
Johnny Weissmuller played Tarzan in several movies, swinging from the vines with bravado. Later, he had the misfortune of dementia and was put into a care home. One evening he made a leap from a balcony to swing on a chandelier, but failed. Unkind newspaper headlines next day were “Tarzan Loses His Grip”.
It’s not my fault.
Sorry, I thought this was a page about cracks about the Antarctic.
Kelvin Vaughan says: March 28, 2012 at 1:19 am
Carol says: March 28, 2012 at 12:33 am
We’re all going to die…aaaargggaahhh!
It’s ok we don’t really exist we just think we do!
In that vein, ‘What you don’t think can’t hurt you’. Firesign Theatre
Lazy Teen says:
“So the article is about land ice and Anthony mentions sea ice. Is anyone here confused by the distinction?”
You mean: is anyone else confused…
These should be added to that article to give background information..
With all that potential water vapor locked up in ice, on the north and south poles does anyone else think that this could mean a dry spell for some areas this year?
H.R. says:
March 28, 2012 at 2:24 am
Whoa, Anthony!
Careful what you’re doing to people who read your posts early in the morning before they’ve had enough coffee to get going.
First thing that I see on WUWT at 5:00 am is “Crack In The Antacrtic” and I think “Wow! Drugs are everywhere nowadays.”
Of course reading further… well, as Emily Litella would say, “Nevermind.”
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Yeah, I know what you mean. I read “Crack In The Antarctic” and thought OH MY a large earthquake was cracking the Antarctic glacier. Something akin to what is being seen in Africa.
Death of a Continent, Birth of an Ocean
Africa’s Afar region gives glimpses of geology in action
Exciting stuff! Well at least if you like Geology. I though this was something similar instead it is just the usual Greenie twisting of facts.
Now, as I understand it, an ice shelf is ice that is anchored to land and extends out over the water. It would seem to me that if the ice thickness were to increase, it would reach a point that the end would be too heavy (because it is not supported by land) and there would be a break. So, cracking of an ice shelf could be because it has gained too much weight. I am no scientist, so I would appreciate it if someone would correct me if I am wrong.
How has the resolution of the imagery changed since 1972, and can that have an impact on the visibility of surface features? The resolution of the sensors has improved dramatically since 1972. The Landsat 2, launched in 1975, had 80 meter resolution from its multispectral camera system. (http://landsat.usgs.gov/about_landsat2.php) Landsat 7 (since 1999) has multiple sensors with 30 meter resolution. (http://landsat.usgs.gov/about_landsat7.php)
Just looking at those pictures above, I am not sure they can really tell us anything, given the difference in visible surface features.
Ben
First, you know the climate changes or it doesn’t.
If you know it does change then it must either get colder or warmer and get more or less precipitation. Therefore, any reasonable thinker would understand the ice will change.
LazyTeenager says:
March 28, 2012 at 4:15 am
This crackin the Pine Island Glacier was first noticed 12 years ago. It has hardly changed at all since that time.
They just keep flying over it, again and again, and sounding the alarm as if it were new.
First satellite picture of it from 2000.
ftp://sidads.colorado.edu/pub/DATASETS/ICESHELVES/pine/aster_pig_20001212_ov_nobox.jpg
Earth Observatory article talking about it showing pictures from 2001.
http://earthobservatory.nasa.gov/IOTD/view.php?id=76437
In fact, the current 2012 images show the crack is not as wide as it was 12 years ago.
Otter said “…can anyone tell me why focusing on .4% of the continent…”
Sorry to troll you sir, but 2% of 2% is 0.04% – ya lost a zero there.
Pip pip.
Yes, over a period of 30-35 years the trend of the Antartic sea ice is growing. But if we might say that the global temperature is not rising anymore since 2008….then we have to be honnest and say also that the Antartic sea ice is not growing anymore since then ! More “warming-like people” can possibly say that the Antartic sea ice is declining since 2008…and there is no argument in the observations to contradict them !
Most glaciologists, including Vaughan, say that warmer ocean water is the primary cause of thinning.
Silly me. Here I’d always thought that glaciers moved over *land* — and a combination of sublimation and a dearth of snowfall was the primary cause of glaciers thinning.
Was this a not-so-subtle allusion to that 1965 geology sci-fi “Crack in the World”? http://www.imdb.com/title/tt0059065/
Behold the dangers of ‘green’ energy…