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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We need to separate cause from effect here. The cause of West Antarctic glacier retreat might be AGW, it might be ocean cycles, it might be something else.
But as a practical matter we are not interested in causes, we are interested in effects.
What are the effects of West Antarctic glacier retreat?
More ocean exposed to the atmosphere and more ocean heat loss. Resulting in a temporary rise in atmospheric temperatures, while the ocean and the climate cools (almost all the climate’s heat is in the oceans).
I think one consequence is increasing SH sea ice, which is a powerful negative feedback – ice has a higher albedo than open ocean.
In all likleyhood increasing sea ice will net out with decreasing land origin icesheets, but wouldn’t discount a negative feedback over 1 and net cooling as the effect over a decade or 2.
E.M.Smith says:
March 28, 2012 at 1:24 am
Golly, ice shelves break up. I’m shocked…
(Last thing I’d want to see is ice shelves extending and never breaking, if that ever happens, we’re headed for Iceball Earth again…)
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How about what the ocean currents are doing there??
Warmer/colder?
This is not global warming…..this is a design flaw
That is about the stupidest place to put a peninsula and expect ice to be stable…………
“Typically, the leading edge of an ice shelf moves forward steadily over time”
These guys need to get with the glacier guys and coordinate their talking points…………
Tragic? Why tragic? Ice shelves grow, they crack and fall away, and grow again. Normal. When they grow and DON’T sheave off, then we’ve got a problem — it’s called an oncoming ice age.
It should be comforting to know that the ice is going through its normal cycles.
I’d say that it’s something more than just the ice shelves that is cracked here.
Reference this link to sciencedaily
“Jimbo says:
March 28, 2012 at 2:15 am
http://www.sciencedaily.com/releases/2007/12/071210094332.htm”
I noted this statement in the article
“Greenland ‘s ice sheet contains at least 10 percent of the world’s freshwater AND it has been losing more than 24 cubic miles (100 cubic kilometers) of ice annually for the last five years and 2007 was a record year for glacial melting there.”
Per Wikipedia the Greenland ice sheet amounts to a mere “If the entire 2,850,000 cubic kilometres (683,751 cu mi) of ice were to melt, it would lead to a global sea level rise of 7.2 m (23.6 ft). – yes 2,850,000 cubic kilometers. I am not a matematician but I can divide 100 cubic kilometers into 2,850,000 cubic kilometers and arrive at 28,500 years. Too early to worry about a 7.2 m sea level rise. Furthermore the record melt was in 2007 so each year 2008-2011 saw less melt!!!??? What a load of propaganda.
izen
perhaps it is because the Holocene is estimated to be one of the three warmest interglacials in the past 3 million years.
Bill
Sparks says:
March 28, 2012 at 4:44 am
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?
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It is a heck of a lot more complicated than that. Some glaciers are melting, some are increasing in size. list of the specific glaciers that are growing Greenpeace or WWF will be only to happy to list those that are shrinking.
Also you have the flip to the cool cycle of NASA: PDO flip to cool phase confirmed
The Arctic Oscillation Index goes strongly negative
Queensland Government:Rainfall probabilities based on the ‘phases’ of the Southern Oscillation Index—Consistently negative SOI phase
NOAA: Southern Oscillation Index (It looks to be headed negative in the graph)
More general discussions:
The North Atlantic Oscillation
Global Patterns – Arctic & North Atlantic Oscillations (AO & NAO)
It is astonishing to see the cavalier attitude displayed by so many commentators on this thread. A casual reader might get the impression that this is some sort of table top exercise, being played by sophomores in a science lab.
This study is one of many, all part of a vast mosaic, which, when taken collectively, contributes to a picture of a changing polar picture, As the study shows, this change is observable from satellites. These observations should not be dismissed out-of-hand. While it may be difficult for the lay person to understand the full context of change in the polar regions, given that most of us don’t have access to all of the other studies, we can (if we chose) rely on summaries provided by experts in the field, and other relevant bodies such as the IPCC.
Two questions: 1) how large is the ice extent supposed to be in the the antarctic and 2) When if ever is it acceptable for these ice masses to crack or fracture? If you can define what the normal state for what Antarctic ice should be right now then we can compare it to these “changes” that we see occurring.
It’s as if Warmers believe the earth is in some kind of unchanging stasis where only the actions of mankind upset some a perfect delicate balance that snowballs into certain catastrophe. Oh wait, that is what they believe.
The faster a glacier grows out onto the sea surface, the bigger and more frequent are the lumps that fall off. That’s what “growing” means.
Hugh Pepper says:
“While it may be difficult for the lay person to understand…”
Hugh Pepper is a dopey “lay person” who has no clue about anything scientific. If I am wrong, Pepper needs to post his verifiable CV here. But the fact is that Hugh Pepper is a complete scientific illiterate who gets his talking points from alarmist echo chambers.
Prove me wrong, Pepper. Post your CV.
Gross exaggeration! 2% of 2% is 0.04%. >:(
The Arctic sea ice is always referenced from 1979 (+/-), with the implicit statement that prior to 1979 the ice extent was always (!) similar to 1979. The Antarctic sea ice graph should make a comparison to the same period of time, which means that the current ice extent is now about one quarter of a million km2 greater than currently shown.
An overlay graph with a similar start-point would make a good comparison of what is going on.
Dave Bradley says:
March 28, 2012 at 5:05 am
It’s not supported by land, but that does not mean it is not supported. It is still supported by water.
On the other hand, as the amount of sea ice gets bigger, it will have more surface area, which means that winds and currents will pull on it more strongly. In other words, the bigger it gets, the easier it is to break free.
By extrapolating out from this one data point, we can safely conclude…
IT’S WORSE THAN WE THOUGHT!
~More Soylent Green!
Shouldn’t that be “sheer”? (I.e., as in cut-off margins. I think that’s what they mean, not that the margins are steep (shear).)
[Moderator’s Offer: Let me know when you want this comment deleted. -REP]
Can’t improve on this! Very well said!
ftp://ftp.aviso.oceanobs.com/pub/oceano/AVISO
Sea level has been plummeting for four years, and is lower than it was in 2003 when EU’s Envisat satellite was launched. This is solid proof that Greenland and Antarctica are melting down at unprecedented rates and flooding the oceans with negative water.
“Until then, researchers have a front seat to an unparalleled physical spectacle. “It’s a really unique opportunity to understand how continents break apart,” says Tim Wright, a remote-sensing expert at the University of Leeds in England.”
Brings a whole new meaning to “watching paint dry!”
Before getting too excited about this, here are a couple of things to keep in mind:
1. The breaking off of ice shelves is a cyclical process. A year or so ago, there was a great clip of time lapse images that showed how the shelf ice breaks off periodically, reforms, and then does it all over again, with no real net, long-term change.
2. This is the Antarctic Peninsula, not the main ice sheet, and, as the authors point out, most of the melting comes from warmer ocean water around the peninsula, not from changes in air temp.
3. Because of (1) and (2) above and the tiny amount of ice involved relative to the huge ice sheet, ice shelf activity is a pretty poor place to judge what’s happening climatically.
4. It’s very clear that the Antarctic ice sheet is not melting–in fact it’s growing. The average annual temp on the ice sheet is about -58 degrees F so to get any significant melting you would have to raise the temp 58 + 32 = 90 degrees just to get to the melting point and it would take a temp rise of around 100 degrees to melt much ice. No sea live rise worries here!
Quick question – are we using the same satellites in 2011 as we had in 72/73? No.
They’re comparing pictures from Landsat 1 (72-78), with pictures from Landsat 7.
Landsat 1 only had a 79m resolution (about 260ft), while Landsat 7 has a 30m resolution (about 98ft).
So while we may have satellite images covering a period of 40 years, we still can’t see a crack in the ice today till it reaches about 98ft wide.
Some of the observable changes might be because we’ve made advances in imaging – a “crack” seen today may not have been seen in 72/73. The ice only LOOKS smoother back then because of the resolution.
If it’s negative water, shouldn’t that be “melting up” instead of down? Just for consistency, like …
;p
Hugh Pepper says: “These observations should not be dismissed out-of-hand.”
Why not? So ice moved. That is what the ice sheets are supposed to do. Just think how deep the ice would be on Antarctica if it didn’t.
“That could be tragic…”
Tragic? Really Anthony, that’s a bit over the top don’t you think? It is sea ice and won’;t make a bit of difference if it breaks off or not as far as sea levels go. The only danger is icebergs and I haven’t heard of them causing too many problems since the Titanic hit one.
This is just more scaremongering by the watermelons.
@Hugh Pepper,
Glaciers only flow if more ice is being added to them. If they are now flowing so fast as to be buckling and breaking sea ice from the force of their flow, as you see in those images, that means ice on Antarctica is increasing. Which is exactly what the satellites show, and completely contrary to the unsupported nonsense in the source article.
“Just think how deep the ice would be on Antarctica if it didn’t.”
By the time the top of the glacier reached the stratosphere, it would stop. Pretty hard to get more snow on top at that level.