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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Between 1972 and now!
How did it change between 1972 and 1979 when all the other polar ice coverage data starts?
Amazing how they can suddenly find earlier data when it suits the narrative.
So excited you left out ‘get’.
I’m excited too. Hopefully, many other commentators will also get excited as they should with most of your finely excited posts. But I digress.
In Scotland they have recently ceased the plantation of grasses on sand dunes as a means to stop erosion. A sand dune ecosystem relies on wind changing the structure of the dunes. Similarly, what’s the problem with Antarctic ice sheets dynamically moving into a position relative to the natural systems around them. Changing glacier flows are a natural occurrence. Where does the now paradigm of glacial theory say ice sheets move in a never ending extension to the Oceans?
We’re all going to die…aaaargggaahhh!
“…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”
Since when could ice shelf extent be compared to Antarctic sea ice extent? Apples and pears, surely?
“… 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.”
No connection, of course. Because the shelf ice never goes to sea, but to Niburu.
Southern Hemisphere sea ice can extend to roughly 50 degrees south. Moreover, Antarctic sea ice does not extend southward to the pole; it can only fringe the continent.
Because of this geography, the Antarctic’s sea ice coverage is larger than the Arctic’s in winter, but smaller in the summer. Total Antarctic sea ice peaks in September—the end of Southern Hemisphere winter—historically rising to an extent of roughly 18 million square kilometers (about 6.9 million square miles). Ice extent reaches its minimum in February, when it dips to roughly 3 million square kilometers (about 1.2 million square miles).
This looks like an interesting glaciological study and should improve our understanding of the mechanics of accelerated glaciation. It also focuses on possible positive feedbacks and improving computer modeling of glaciation. Why not? Good science, I say. No mention of CAGW – simply observation of accelerated glaciation in this (small) area of West Antarctica. But I guess the alarmists will tout it as proof of some imminent tipping point, rather than consider the short time frame and small area of the study. The rest of this enormous continent is doing all sorts of growing, calving, shrinking, snowing, expanding, freezing, melting – has been for a gazillion years.
http://nsidc.org/cryosphere/seaice/characteristics/difference.html
The description given in the last table on the page above indicates that the variation in minimum and maximum extent is quite large for Antarctica. And also that the ice loss is greater in the Arctic by percent than the gain in the Antarctic. However given this discussion is about sea ice as opposed to talking about land ice wouldn’t it be expected that that sea ice increases as ice calving increases and this is a consistent mechanism with the rifts found in the Thwaites glacier? In other words, isn’t it a real indication of this process actually requiring comparison with land ice? It seems to have no context to me otherwise.
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!
The same phenomenon must have taken place countlessly from time immemorial.
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…)
Two added notes:
1) Isn’t this on / near the warming peninsula? That part of Antarctica to have a bunch of volcanoes and warming dirt under the ice? As the rest of Antarctica is getting colder, to have ice growing where it’s colder and breaking off a bit where the land is warming seems quite reasonable.
2) With the solar sleepy time the UV dropped. That let the air column shorten. I’ve observed a return of the stronger more blustery winds of the 1950s and ’60s (and potentially a bit more so). Now assuming this holds near Antarctica too (do we have wind data there?) that would lead to larger waves and a faster circumpolar current. I’d fully expect that to put more ‘tearing’ force on an ice shelf; and more up / down flexing fracturing the margins too. Do we have circumpolar current speed data anywhere? ( IMHO, the spike of cold water we saw in the last few years out into the central Pacific from S. America is evidence for a faster circumpolar current whacking into Drake Passage and sending the ‘excess’ up the coast of S. America. To the extent that is true, the Antarctic side of Drake Passage ought to be getting more currents and pressure too.)
So I think it’s an interesting observation on the ice sheet and land mooring at the margins, but think it’s more likely related to #1 and #2 above and unrelated to air temperatures.
I’m gunna get famous by inventing a new word for this hitherto unknown phenomenumenum.
I’m gunna call it “calving”..
For “ice shelves in the Antarctic peninsula are losing their grip and cracking a bit” read “warmist scaremongers everywhere are losing their grip and cracking a bit”
I seem to recall somewhere, a few years back, seeing a little bit of math about the size of this bay they are speaking about. I wish I could recall where….. However, it something along the lines of this region being 2% of the Antarctic peninsula, which was 2% of the entire continent. Can anyone verify that?
And if that is anywhere near close, can anyone tell me why focusing on .4% of the continent, equates to the entire continent, in the minds of AGW True Believers?
It’s great to see that they are prepared to go back to 1972 for Antarctica. Will the IPCC do it again for the Arctic or will they continue to delete records in any forthcoming report? In the meantime what’s the panic when over the period Antarctic sea ice has grown?
Proof of accelerating rising sea levels. Head for the hills!!!!! 😉
Even the Guardian is alarmed.
http://www.sciencedaily.com/releases/2007/12/071210094332.htm
But looking at this graph of Pine Island glacier velocity, at least from 2005, there seems to be a plateau in velocity. This would depend upon thermal activity under the glacier and more detail about this by the authors would be welcome.
Here is an overview of Pine Island glacier.
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.”
@-And, there’s only a 40 year historical context for these observations. I just can’t too excited about this. – Anthony
While the direct observation may only cover 40 years, the ice SHELVES (not sea ice) that are being observed CAN be dated and 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. In most previous interstadial cycles these ice masses would be expanding, not shrinking several thousand years after the maximum post-melt temperature.
Ice shelves losing their grip, eh.
Where’s Garfield when you need him?
This is really bad.
“West Antarctic Ice Shelves Tearing Apart at the Seams”.
I read this quickly as, “West Antarctic Ice Shelves Tearing Apart at the Scams”.
Somehow this seems to be more likely than the originally intended heading.
“Crack In The Antarctic!”
Dang! Drugs are everywhere now…. oh wait…. nevermind.
Ice breaks up floats in sea……… Titanic meet Iceberg!
Really, who pays for all this twaddle? Oh don’t ask, its you and me.
How was it changing before LANDSAT?
“Typically, the leading edge of an ice shelf….. ”
Ay, there’s the rub! As if it is known from our limited observation in time and space, what is “typical” in Antarctica and what is anomalous.