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baking

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Re: Thwaites Glacier Discussion
« Reply #250 on: March 26, 2020, 09:44:43 PM »
It appears to me that the very western group of icebergs (the ones that were split by the undersea mountain some months ago) seem to be immobile (lower right corner of your animation). Are they all grounded now or do they just queue up behind one or two grounded icebergs?
Of course it is impossible to be 100% certain, since we lack detailed bathymetry of that area, but certainly from watching it for the past 6 months and looking at older GIFs made by other folks, the underwater peaks seem to concentrated in a small area to the North (right) of the red line of latitude.  All the other ones are backed up behind the grounded ones.

baking

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Re: Thwaites Glacier Discussion
« Reply #251 on: April 05, 2020, 01:06:30 PM »
It's very late in the season and the surrounding water is almost all iced up so I'm not expecting much additional movement right now, but this 6-day GIF shows some motion at the end of Thwaites Tongue relative to the rest of the Tongue.

The most likely explanation is that strong winds out of the Southeast shifted sea ice bringing along a portion of the end of the Tongue.

baking

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Re: Thwaites Glacier Discussion
« Reply #252 on: April 11, 2020, 05:43:24 AM »
I've been meaning to make an update on iceberg B22-A for a while now.  It seemed to be moving a little extra in the past two months and the a good sized chunk of the Western fractured in early April.

I've included a one year GIF that shows a significant Northern movement.  It may not seem like much, but the iceberg has been grounded there since 2002 and that much movement in one year has to be a significant change.  The fracture has not yet floated away clear, but it has continued to separate gradually since throughout early April.

I also include an overlay with the bathymetry showing B22-A is likely pinned between an underwater peak in the East and some shallow in the West.  I think the biggest worry might be if the iceberg rotated nearly 90 degrees and was able to move away from one of its grounding points.

The big picture concern is if B22-A were to drift away and no longer protect the sea ice that usually keeps Thwaites Tongue from breaking up any faster than it already is.

Previous discussions of B22-A can be found in the links below and in subsequent posts:
https://forum.arctic-sea-ice.net/index.php/topic,1760.msg230715.html#msg230715
https://forum.arctic-sea-ice.net/index.php/topic,1760.msg238401.html#msg238401

Also: https://forum.arctic-sea-ice.net/index.php/topic,2245.msg254666.html#msg254666
« Last Edit: April 11, 2020, 06:09:00 AM by baking »

Tor Bejnar

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Re: Thwaites Glacier Discussion
« Reply #253 on: April 11, 2020, 05:59:27 AM »
Baking,
your GIF is huge (24 mb) and took well over a minute to download on my computer, but very interesting once it got going!  I think GIFs like this are best when they have to be clicked to run.  (But I'm rather illiterate on these things.)
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baking

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Re: Thwaites Glacier Discussion
« Reply #254 on: April 11, 2020, 06:13:08 AM »
Baking,
your GIF is huge (24 mb) and took well over a minute to download on my computer, but very interesting once it got going!  I think GIFs like this are best when they have to be clicked to run.  (But I'm rather illiterate on these things.)
Oops!  Thanks for pointing that out.  I always make my GIFs 700x700 so they don't need to be clicked on to run, but I hadn't foreseen the consequences of that one being autorun.  I could maybe make it one pixel larger and replace it?  I don't know any other way to do it.

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Re: Thwaites Glacier Discussion
« Reply #255 on: April 11, 2020, 07:11:57 AM »
I could maybe make it one pixel larger and replace it?

That would be the best way, yes. :)

IceConcerned

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Re: Thwaites Glacier Discussion
« Reply #256 on: April 11, 2020, 10:41:39 AM »
Highly instructive, we can see many more things on animations like this
It appears that the small movement northwards of the western part has already opened an evacuation channel for the accumulated ice

Stephan

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Re: Thwaites Glacier Discussion
« Reply #257 on: April 11, 2020, 10:56:39 AM »
Highly instructive, we can see many more things on animations like this
It appears that the small movement northwards of the western part has already opened an evacuation channel for the accumulated ice
Yes that is right. Anyway, a smaller iceberg has been washed into this channel and got grounded. I have named it "Cork" in one of my postings about B-22 in the "iceberg" thread. But now a way has opened for sea ice between this cork and B-22, because some parts of B-22, embedded in "fast ice" [sea ice fastened to B-22] have disintegrated and flushed out into the sea. If now wasn't freezing season I'd expect an emptying of the sea ice between B-22 and the fast ice in front of Thwaites/Crosson.
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Re: Thwaites Glacier Discussion
« Reply #258 on: April 11, 2020, 11:33:18 AM »
I've included a one year GIF that shows a significant Northern movement.  It may not seem like much, but the iceberg has been grounded there since 2002 and that much movement in one year has to be a significant change.  The fracture has not yet floated away clear, but it has continued to separate gradually since throughout early April.

How are you making this gif? Manually or is there a tool to do it automatically?

IceConcerned

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Re: Thwaites Glacier Discussion
« Reply #259 on: April 20, 2020, 11:47:51 AM »
It has been already mentioned before that the ice tongue has crumbled little by little. I will not come back to that point, the slow-motion disintegration has just gone on.
But on top of that, the tongue is detaching itself from the main body ; one of the main zones of separation is underlined in yellowish purple.
The backpressure on the flow from the mainland is thus gone, and we can see quite worrysome (in my opinion) new cracks appear. The most significant is underlined in green, with dots to show its likely progress. But others parallel to it are also becoming more apparent.
Combined with the existence of the underice cavities mentioned in several publications, we may approaching a critical point for this portion of the glacier.


PS : I am slightly color blind, please accept my apologies if the color names are not fully adequate... :-[
« Last Edit: April 20, 2020, 01:05:36 PM by IceConcerned »

oren

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Re: Thwaites Glacier Discussion
« Reply #260 on: April 20, 2020, 12:05:48 PM »
I can see the green but it's barely perceptible. Best to make it thicker or darker. I am still searching for the yellow...

IceConcerned

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Re: Thwaites Glacier Discussion
« Reply #261 on: April 20, 2020, 01:07:15 PM »
It was apparently a compression issue, yellow being too pale and diffused through the compression. I corrected to purple, I hope it is clearer now.

Stephan

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Re: Thwaites Glacier Discussion
« Reply #262 on: April 20, 2020, 01:16:11 PM »
Thank you Ice Concerned for your posting. Colours don't matter, everything is clearly visible. :)
It would be fine to have that information supported by a gif, maybe with a difference of 2-3 months to be able to see what really happened. Thank you in advance.
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baking

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Re: Thwaites Glacier Discussion
« Reply #263 on: April 20, 2020, 10:30:46 PM »
The GIF below is 43MB.  I have made it large enough to prevent autoloading, so you must click on it to run it.  Movement is relative to the end of the Tongue.  This may not be optimal for this purpose, but it was handy and quick to produce.  Movement to the right in the GIF is ice that is slower than the fastest part of the Tongue.  Upwards movement in the GIF is simply due to the slight counter-clockwise rotation of the Tongue and can safely be ignored.

The important point is that formation of these transverse rift is normal, and at least one scientific paper has been written analyzing the periodicity in the spacing between these rifts.  What would be more clear in a GIF where movement was absolute, is that these rifts tend to form in the same location.

In particular, if you refer to the second image where I have numbered the rifts, numbers 1, 5, and 6 actually appeared "on-time" and pretty much as expected.  Rifts 2, 3, and 4 are the anomalies and were delayed in their formation.  (Assuming Rift 4 eventually forms from the connection of 4A to 4B.)

I was thinking/hoping that the ice between rifts 1 and 5 might form a large block that would resist breaking up for many years.  See the block at the center left of the GIF for an example.  This was sadly not to be.
« Last Edit: April 20, 2020, 10:41:48 PM by baking »

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Re: Thwaites Glacier Discussion
« Reply #264 on: April 23, 2020, 11:05:55 AM »
https://doi.org/10.5194/tc-2019-294
https://doi.org/10.5194/tc-2020-25
New bathymetry from 2020 related source articles if you want them.

baking

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Re: Thwaites Glacier Discussion
« Reply #265 on: April 29, 2020, 06:22:33 PM »
This is an update on Iceberg B22A.  (See reply #252 above for context.)  The large piece that broke off had continued to stay closely aligned through most of April, giving hope that it might refreeze and stay attached.  Today's high resolution image shows a significant widening of the gap and a greater risk of total separation.

The main significance is any decrease in the size of B22A might allow it to move more freely and possibly rotate in a way that might allow it to float off.  The loss of this corner might be significant.  The iceberg is not really grounded since it is constantly making small movements.

Below is a GIF since April 11.  Click to play due to the size.

Stephan

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Re: Thwaites Glacier Discussion
« Reply #266 on: April 29, 2020, 07:05:02 PM »
Thank you baking for this update. To my knowledge it is the biggest calving event this iceberg has experienced for many years. I wonder whether a larger separation will happen soon - the waters to the west of B-22 are quite shallow, documented by a lot of grounded smaller icebergs in that area.
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baking

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Re: Thwaites Glacier Discussion
« Reply #267 on: April 29, 2020, 09:18:21 PM »
Stephen,
   B22A is very old.  It calved 20 years ago, but as an ice shelf it has been floating for at least 30-40 years, depending on which part.  (The Western end is the oldest.)  So you have to wonder is basal melting has been balanced by snow accumulation.  That is why I am more worried about it floating off mostly intact.
   I think the biggest warning sign would be if the iceberg started drifting North relative to the recently calved piece, showing that the corner was grounded and the iceberg might then be floating free.

EDIT: A lot of the ice floating off the Western end has recently (in the last few years) broken off from B22A so it may reflect that the older section is in fact beginning to break up.
« Last Edit: April 29, 2020, 09:24:38 PM by baking »

Stephan

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Re: Thwaites Glacier Discussion
« Reply #268 on: April 29, 2020, 10:56:42 PM »
I do not think that the western corner (the one that broke off) had been grounded. I analysed the movement of B-22A (see my postings in the iceberg thread) some weeks and some months ago and the western part, generally moving northward, was the fastest part of B-22A (if some m/day is "fast").
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baking

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Re: Thwaites Glacier Discussion
« Reply #269 on: April 30, 2020, 12:55:44 AM »
I'm just basing it on the bathymetry and that the Southwestern corner would need to sweep through the shallows to the North if B22A were to pivot on the Northeastern corner in the clock-wise direction.  If the corner comes off, the area swept by the rotation would become significantly less.

baking

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Re: Thwaites Glacier Discussion
« Reply #270 on: May 12, 2020, 03:06:59 PM »
Today the Iceberg B22-A fully separated from its Southwest corner and rotated clockwise to the North.  Below is a 6-day GIF.  Yesterday's 6-day comparison showed no change.

As you can see, the pivot of the rotation is in the Northeast (top left) corner and the concern is that the Western end of the iceberg may eventually escape from the shallows which can be roughly defined as the group of grounded icebergs in the bottom left of the image.  The loss of the SW corner may make it easier to float off.

B22-A broke off from Thwaites Tongue in 2002 and has been grounded in its current location since then.  If seems to stabilize the sea ice off of Thwaites and the surrounding glaciers to the West and if it were to float off it could weaken the melange of ice currently trapped off of these glaciers.

Stephan

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Re: Thwaites Glacier Discussion
« Reply #271 on: May 12, 2020, 07:50:30 PM »
Thank you baking for that information. It is the same observation I made months ago, that there is a center of clockwise rotation close to the NE corner of B-22.
I wonder whether the new SW corner of B-22 may force the broken-off SW part into deeper seas further west of it. You can see the movement of the broken-off part. Otherwise it will stay there almost grounded for a longer period of time.
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oren

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Re: Thwaites Glacier Discussion
« Reply #272 on: May 12, 2020, 07:56:05 PM »
An ominous development.
It appears that the same force that pulled the sea ice away (I guess a strong wind combined with the underlying current) is what managed to move the giant iceberg.

baking

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Re: Thwaites Glacier Discussion
« Reply #273 on: May 12, 2020, 11:26:17 PM »
I wonder whether the new SW corner of B-22 may force the broken-off SW part into deeper seas further west of it. You can see the movement of the broken-off part. Otherwise it will stay there almost grounded for a longer period of time.
Good point.  The rotation of B22-A is pushing the bulk of the smaller iceberg away from the shallows.

Stephan

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Re: Thwaites Glacier Discussion
« Reply #274 on: May 13, 2020, 01:05:14 PM »
Thank you oren (??) for having sticked three of the most important threads about Antarctic Ice.
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baking

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Re: Thwaites Glacier Discussion
« Reply #275 on: May 17, 2020, 07:43:34 PM »
There was a large calving at the Eastern end of the what I'm going to start calling the Thwaites Eastern Calving Zone (TECZ) which I've traced back to May 3.  The TECZ is the area of the Thwaites Eastern Ice Shelf (TEIS) between the grounded calving front at the Eastern end of Thwaites and the "pinned" Western part of the TEIS.  It's the general area where research teams were on the ice recently, drilling holes and deploying sensors.

As discussed on this thread back in December 15, this zone is the most potentially interesting area of research because the Western end of Thwaites is already moving at a really fast pace and the central portion is pretty much fixed behind the pinned ice shelf.  This might be a good place to look for developing effects of climate change.

The second image is a larger view of the TECZ.  The color reflects the observed ice speed with a greener/lighter shade representing a faster speed.  Base image is from http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=4&image_date=200407_200413
« Last Edit: May 17, 2020, 07:48:58 PM by baking »

baking

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Re: Thwaites Glacier Discussion
« Reply #276 on: May 17, 2020, 09:54:49 PM »
Here is an additional image that puts everything from the last post in context.  Note the many fractures at the Western transition of the TECZ which are caused by ice moving faster than the neighboring pinned ice.

The grounding line from 2011 is in blue.

baking

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Re: Thwaites Glacier Discussion
« Reply #277 on: May 18, 2020, 02:35:21 PM »
The former Southwestern corner of iceberg B22-A is continuing to drift off and even breaking up.  Not terribly notable except for the fact that it apparently wasn't grounded.  Maybe it is the Northeastern and Northwestern corners of B22-A that are grounded.

oren

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Re: Thwaites Glacier Discussion
« Reply #278 on: May 18, 2020, 03:28:32 PM »
Interesting. There is also the possibility that the violence of the breakup caused it somehow to unground, if indeed it was grounded at all.

baking

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Re: Thwaites Glacier Discussion
« Reply #279 on: May 18, 2020, 05:05:23 PM »
Interesting. There is also the possibility that the violence of the breakup caused it somehow to unground, if indeed it was grounded at all.
Great point.  We know there is at least one nearby area of grounding because of the group of smaller stationary icebergs.  If you scroll up and look at my earlier postings, especially the first one from April 11, you can speculate that the piece broke off when it encountered the ocean floor at that point so it was never fully grounded.  Although, those small icebergs had been grounded to the South before being pushed into their current location by the movement of B22-A so that spot may not be shallower than any other nearby location.

Stephan

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Re: Thwaites Glacier Discussion
« Reply #280 on: May 18, 2020, 06:34:30 PM »
I want to remind you about my posting #256 in the Iceberg Thread where I analysed the movement of B-22A from Jan to March 2020. https://forum.arctic-sea-ice.net/index.php/topic,2245.250.html
In that analysis I measured the movement of the five corners of that iceberg, where its SW tip (the one that recently broke off) was the fastest moving part. This indicates that it was not grounded at that corner.
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baking

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Re: Thwaites Glacier Discussion
« Reply #281 on: June 01, 2020, 06:59:28 AM »
Today's 6-day GIF of Iceberg B22-A shows that the Southwestern corner that broke off has moved away and possibly not coincidentally the larger iceberg has shifted to the West.  The theory being that the corner was grounding in the shallows and thus limiting the motion of B22-A.

Without the corner the iceberg may now have more freedom to move and rotate out of its trapped position and eventually float off, exposing Thwaites and neighboring glaciers to more currents and threaten their protecting sea ice.

baking

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Re: Thwaites Glacier Discussion
« Reply #282 on: June 01, 2020, 09:28:10 PM »
On another note, I was looking at how the ice in the melange (between the and the Eastern ice shelf) was breaking up recently and I noticed how the red wedge near #8 in the image below has been developing over the past year.  To make a long story short, I began to see it as a part of a much larger multi-year pattern which I will try to sketch out.  There is a lot to unpack here so bear with me.

What I am calling the "Escalator" is a series of ice wedges that form in the "Fracture Zone" between the fast moving and slow moving areas of Thwaites ice shelf.  The wedges (or "steps" in the analogy) are formed from the faster moving shelf that breaks away from the slower moving shelf at the shear margin.

The rest of the faster ice does not display this behavior.  Most of the faster ice is in the calving zone where transverse (East-West) rifts form with separation of about a kilometer.  Those long trips of ice eventually break into more square shaped tabular icebergs that form the bulk of the Tongue.  Another portion of the faster ice calves at a front to the West.

The wedges are larger, 2-5 km in size, and they don't appear to fracture.  The mechanism of their formation is a bit of a mystery, but I assume that they undergo some amount of compression before they break away from the slower ice, giving them atypical strength and thickness that makes them more durable than the surrounding icebergs.

I have tentatively identified and numbered these wedges in the picture below.  The last two are still in formation so I am simply speculating on how they might emerge.  The choice of numbering is not arbitrary, since #1 is the first wedge that can be identified in the current Tongue.  Any previous wedges have since floated off (although the current tip of the Tongue may be the back end of an earlier wedge.)

This 5+ year GIF of the Tongue (https://twitter.com/kevpluck/status/1228472054430781440) can help give a better picture of what may have led to the current structure and it deserves more analysis.  The calving of the current Cork from the Eastern Ice Shelf in 2014 and a massive calving East of the Fracture Zone in 2016 which makes up most of the current Melange have resulted in the Tongue being pushed to the West.  Before 2011 the Tongue was still connected to the Eastern Ice Shelf and it calved from an angular front which can still be seen in the pattern of the icebergs at the end of the Tongue.

The Western push from about 2015 to 1019 created the stair-step shape of the Escalator.  It also exposed more of the Northern faces of the wedges which caused them to push on more of the melange.  Most of the wedges can be associated with rifts in the melange (shown in red) where the points of the wedges have pushed apart the ice and even broken larger icebergs that they came in contact with.  Two of the wedges (#3 and #5) have pushed icebergs in front of them which are indirectly pushing on the cork.  The Western movement of the Tongue also resulted in it colliding with the underwater peak that has stripped off many of its icebergs.

Since the Cork now appears to be loose, it is assumed that the melange will eventually move off behind it.  If the Tongue is no longer pushed as far Westward (no new hangups in the Melange) then the new wedges could continue in more of a straight line and the width of the Tongue could be restored to at least part of its former glory.  However, the Western calving front will probably never be a part of the Tongue again.  Of course, the Shear Zone could be causing permanent damage and that part of the Tongue may also join the calving front.

Another reason to track these wedges is that they are becoming proportionally a larger and larger part of the Tongue.  In particular, #4 and #5 may comprise the entire width of the Tongue at some point, as the ice to their West gets stripped off.  It is hard to so how such a reduced Tongue could hold together if the sea ice were to retreat.

I expect to keep studying this and hope to glean more details as I go along and I am willing to answer questions or make clarifications.
« Last Edit: June 01, 2020, 09:40:55 PM by baking »

baking

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Re: Thwaites Glacier Discussion
« Reply #283 on: June 19, 2020, 12:51:14 AM »
Fieldwork on Thwaites for the upcoming season has been cancelled due to COVID-19.

https://www.sciencemag.org/news/2020/06/coronavirus-forces-united-states-united-kingdom-cancel-antarctic-field-research

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Re: Thwaites Glacier Discussion
« Reply #284 on: June 19, 2020, 09:27:45 AM »
Welp... :(

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Re: Thwaites Glacier Discussion
« Reply #285 on: July 12, 2020, 12:42:45 PM »
Quote
Sequence of schematic figures illustrating some ideas on how ice shelf pinning points may develop during glacial retreat.
posted by R. Larter https://twitter.com/rdlarter/status/1272834862706237440

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Re: Thwaites Glacier Discussion
« Reply #286 on: July 14, 2020, 09:09:51 AM »
You get the feeling we are really in trouble when you see a newspaper like the Financial Times highlighting Twaites' concerns.

https://www.ft.com/content/4ff254ed-960d-4b35-a6c0-1e60a6e79d91?segmentID=09cf3415-e461-2c4a-a8cc-80acc4846679

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Re: Thwaites Glacier Discussion
« Reply #287 on: July 14, 2020, 07:32:57 PM »
You get the feeling we are really in trouble when you see a newspaper like the Financial Times highlighting Twaites' concerns.

https://www.ft.com/content/4ff254ed-960d-4b35-a6c0-1e60a6e79d91?segmentID=09cf3415-e461-2c4a-a8cc-80acc4846679
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Re: Thwaites Glacier Discussion
« Reply #288 on: July 14, 2020, 07:45:56 PM »
You get the feeling we are really in trouble when you see a newspaper like the Financial Times highlighting Twaites' concerns.

https://www.ft.com/content/4ff254ed-960d-4b35-a6c0-1e60a6e79d91?segmentID=09cf3415-e461-2c4a-a8cc-80acc4846679
paywalled

From the Ice Apocalypse thread:

The linked article indicates that the NSF is concerned about the stability of the Thwaites Glacier and that a collapse of Thwaites could then trigger a collapse of the WAIS:

Title: "‘Teetering at the edge’: Scientists warn of rapid melting of Antarctica’s ‘Doomsday glacier’"

https://www.independent.co.uk/environment/thwaites-glacier-antarctic-melting-doomsday-climate-a9616966.html

Extract: "The Thwaites glacier is 74,000 square miles, roughly the size of the UK. The ice melt draining from Thwaites into the Amundsen Sea already accounts for 4 per cent of global sea-level rise but scientists are concerned its continued existence is hanging in the balance as the world warms.

“The big question is how quickly it becomes unstable. It seems to be teetering at the edge,” Paul Cutler, programme director for Antarctic glaciology at America’s National Science Foundation told the Financial Times this week.

“It is a keystone for the other glaciers around it in West Antarctica,” he said. “If you remove it, other ice will potentially start draining into the ocean too.”"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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baking

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Re: Thwaites Glacier Discussion
« Reply #289 on: July 15, 2020, 12:37:21 PM »
Some minor Iceberg B22-A news to report.  I tend to post these here instead of the Iceberg thread because they effect the sea ice off of Thwaites and neighboring glaciers.  The flow of smaller icebergs to the south of B22-A has been blocked by a 7km iceberg that calved in two on July 10.  No sign that this will have any significant effect, but it may be something to watch especially if B22-A shifts to the North again.

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Re: Thwaites Glacier Discussion
« Reply #290 on: July 16, 2020, 12:04:10 AM »
While not major movements I have observed rotation in b22a  on every 6th day image for months. It may not be free floating exactly but it does not appear to be completely grounded either.

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Re: Thwaites Glacier Discussion
« Reply #291 on: July 16, 2020, 06:19:59 AM »
While not major movements I have observed rotation in b22a  on every 6th day image for months. It may not be free floating exactly but it does not appear to be completely grounded either.
". . . if when B22-A shifts to the North again."

Is that better?

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Re: Thwaites Glacier Discussion
« Reply #292 on: July 16, 2020, 06:55:23 AM »
It was meant less as a correction than it was an observation. Thanks

Stephan

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Re: Thwaites Glacier Discussion
« Reply #293 on: September 12, 2020, 07:28:27 AM »
Comparison of movements of different parts of the Thwaites glacier between Nov 15, 2019 and Sep 11, 2020 using the "measure distance tool" in EOSDIS.

The first picture shows the points I analysed, the second picture is the screenshot from EOSDIS. Please do not take the second digit too seriously; scalingis too large, and exactly placing the mouse into the correct position is not possible with that precision.

TEIS is slightly moving into NE direction; but the very northern/northwestern tip has not changed its position in the last 10 months because it is grounded.
The other places have moved roughly 3-5 km in 10 months, the "peeling" of parts of the Thwaites Ice Tongue has resulted in a slightly varying flow direction, see little black bars in the first picture.
This "peeling off" of parts of the toungue led to a widening of the tongue itself.

I also measured the movement of icebergs, frozen in sea ice - their movement is roughly identical to that of Thwaites Glacier behind it.

See attached pictures.
It is too late just to be concerned about Climate Change

baking

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Re: Thwaites Glacier Discussion
« Reply #294 on: September 15, 2020, 04:27:24 PM »
Two large icebergs that have been grounded in front of Thwaites have floated off in the past couple of days.  I fear this early sign does not portend well for the upcoming season.

The first iceberg (B-46) was part of the October 2018 PIG calving event and it grounded in front of Thwaites in October 2019.  The second iceberg was from the February 2020 PIG calving and it grounded in March.

The GIF below has images from July 10, 2019, Oct. 26, March 12 and 24, 2020, May 23, June 10, and Sept. 8 and 14.

Last Antarctic Summer, Thwaites Tongue was protected from breaking up by landfast sea ice that was in part protected by these two icebergs.

Of course PIG may be calving again shortly and could be sending more icebergs this way.  Also the old gigantic B22-A iceberg is still in place and helping to shelter Thwaites from the West but it is moving around quite a bit between its grounding points.

Note:  Thwaites Tongue is the fast moving collection of icebergs in the lower right.
« Last Edit: September 15, 2020, 05:19:17 PM by baking »

Juan C. García

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Re: Thwaites Glacier Discussion
« Reply #295 on: September 15, 2020, 06:42:36 PM »
Quote
Two major Antarctic glaciers are tearing loose from their restraints, scientists say
Pine Island and Thwaites glaciers already contribute 5 percent of sea-level rise.
By Chris Mooney
September 14, 2020 at 2:03 p.m. CDT

“The stresses that slow down the glacier, they are no longer in place, so the glacier is speeding up,” said Stef Lhermitte, a satellite expert at Delft University of Technology in the Netherlands who led the new research along with colleagues from NASA and other research institutions in France, Belgium, Austria and the Netherlands.
https://www.washingtonpost.com/climate-environment/2020/09/14/glaciers-breaking-antarctica-pine-island-thwaites/
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Juan C. García

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Re: Thwaites Glacier Discussion
« Reply #296 on: September 15, 2020, 06:50:56 PM »
Damage accelerates ice shelf instability and mass loss in Amundsen Sea Embayment
Stef Lhermitte, Sainan Sun, Christopher Shuman, Bert Wouters, Frank Pattyn, Jan Wuite, Etienne Berthier, and Thomas Nagler
https://doi.org/10.1073/pnas.1912890117

Abstract
Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are among the fastest changing outlet glaciers in West Antarctica with large consequences for global sea level. Yet, assessing how much and how fast both glaciers will weaken if these changes continue remains a major uncertainty as many of the processes that control their ice shelf weakening and grounding line retreat are not well understood. Here, we combine multisource satellite imagery with modeling to uncover the rapid development of damage areas in the shear zones of Pine Island and Thwaites ice shelves. These damage areas consist of highly crevassed areas and open fractures and are first signs that the shear zones of both ice shelves have structurally weakened over the past decade. Idealized model results reveal moreover that the damage initiates a feedback process where initial ice shelf weakening triggers the development of damage in their shear zones, which results in further speedup, shearing, and weakening, hence promoting additional damage development. This damage feedback potentially preconditions these ice shelves for disintegration and enhances grounding line retreat. The results of this study suggest that damage feedback processes are key to future ice shelf stability, grounding line retreat, and sea level contributions from Antarctica. Moreover, they underline the need for incorporating these feedback processes, which are currently not accounted for in most ice sheet models, to improve sea level rise projections.

https://www.pnas.org/content/early/2020/09/08/1912890117
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

Juan C. García

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Re: Thwaites Glacier Discussion
« Reply #297 on: September 15, 2020, 07:10:23 PM »
https://www.pnas.org/content/early/2020/09/08/1912890117

Quote
In the future, this mechanical weakening and increased velocity gradients due to loss of frictional gradients at the ice shelf margins are not expected to trigger negative feedbacks that counterbalance the damage as damage healing is expected only for negative maximum strain rates, which are limited for ice shelves (38). As such, it is different from other ice shelf weakening processes such as surface or subshelf melt as these can be counterbalanced by changes in atmospheric or oceanic processes, which are prone to climatic variability (3⇓–5). Therefore, the damage process and mechanical weakening in the shear zones have similar far-reaching consequences for ice shelf stability as localized ice shelf thinning in basal channels (27, 39). This sensitivity suggests that incorporating damage processes in future ice sheet models in combination with accurate knowledge of ocean forcing, bathymetry, bedrock topography, ice velocity, and surface melt is crucial to assess the future sea level contributions from major Antarctic glaciers.

What it means to me, with my very limited knowledge, is that we (humanity) cannot yet assess the sea level rise that we will face at the end of the 21st century, with this high-speed anthropogenic global warming.

But only one meter I consider it very unlikely. It is less than 1.8% of the possible total melt of 56-60 meters, with Greenland facing an ice-free Arctic on 2035 or earlier (65+ years receiving heat).
« Last Edit: September 15, 2020, 09:13:44 PM by Juan C. García »
Which is the best answer to Sep-2012 ASI lost (compared to 1979-2000)?
50% [NSIDC Extent] or
73% [PIOMAS Volume]

Volume is harder to measure than extent, but 3-dimensional space is real, 2D's hide ~50% thickness gone.
-> IPCC/NSIDC trends [based on extent] underestimate the real speed of ASI lost.

paolo

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Re: Thwaites Glacier Discussion
« Reply #298 on: September 15, 2020, 09:28:49 PM »
Thank you very much for the article, JCG

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Re: Thwaites Glacier Discussion
« Reply #299 on: September 17, 2020, 07:06:50 AM »
The sea ice surrounding Antarctica varies greatly from year to year, with most of the area melting out over the summer. This year has had higher sea ice extent than many others.

Looking at Worldview the sea ice in the Amundsen Sea Embayment has already been blown north this year leaving new ice forming close to the coast and between the broken-up sea ice. The surface flows north may be pulling more deep "warm" water south towards the glaciers in this area earlier in the melt season?

This is in contrast with the situation last year when the sea ice was relatively unbroken but extended only about half as far north - but broke up and dispersed north about a month later.