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Stephan

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Re: Thwaites Glacier Discussion
« Reply #200 on: December 24, 2019, 03:14:07 PM »
Evaluation of the latest Sentinel-1 photo of TEIS.

The latest photo shows some new and widened cracks (marked in red). I added the movement direction with yellowish green arrows. The northern part seems almost immobile (= grounded). I see a shear zone (pale dotted line), SE of it a small movement in NE direction is apparent.
The "Thwaites Ice Tongue Cork" has been very mobile (compared with Nov 3, 2019), heading into NNW direction. All icebergs behind it follow in roughly the same speed.
Compared to PIIS everything here is much slower, but changes are obvious.

See attached picture.
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Stephan

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Re: Thwaites Glacier Discussion
« Reply #201 on: December 24, 2019, 07:12:18 PM »
Analysis of Thwaites Ice Tongue as of 2019-12-22.

I compared the images between Nov 03 and Dec 22. The rift in the center of the Thwaites Ice Tongue has widened massively. Open water is visible in it. Yellowish green arrows show the flow direction. A new row of icebergs prepares for being peeled-off in the next weeks (red line). The grounded iceberg in the NW is still grounded (pale blue circle). I have no idea why there is open water in the SW of this picture. Looks like one of the small icebergs has sunk  ;) and has left open water behind (pale magenta circle).

See attached picture.
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baking

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Re: Thwaites Glacier Discussion
« Reply #202 on: December 24, 2019, 08:08:40 PM »
Icebergs don't sink. ;)  The pink circle is a polynya caused by warmer currents coming up from under the ice shelf and melting the sea ice when they hit the surface.  They are used by scientists to estimate the locations of basal rifts under the shelves and to model the under-shelf currents.  There are quite a few of them around Thwaites right now since the seasonal melting has started.

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Re: Thwaites Glacier Discussion
« Reply #203 on: December 27, 2019, 11:33:51 AM »
Minor calving between 23th and 26th.

baking

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Re: Thwaites Glacier Discussion
« Reply #204 on: January 23, 2020, 08:10:58 PM »
"We show that Thwaites Glacier has now begun generating glacial earthquakes similar to those observed in Greenland."

Winberry 2020 "Glacial Earthquakes and Precursory Seismicity Associated with Thwaites‐Glacier Calving"

https://doi.org/10.1029/2019GL086178

Stephan

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Re: Thwaites Glacier Discussion
« Reply #205 on: January 23, 2020, 10:47:12 PM »
The latest Sentinel picture gave insight into the further development on the "peeling-off" of the Thwaites Ice Tongue.
The flow direction remains the same as it has been on Dec 24 (see my posting above) and is indcated by blue arrows. Therefore the gap has widened massively (large pale green circle) and lengthened in S direction (small pale green circle). A newly developed crack SE of it (red lines) seems to indicate that the "peeling off line" will march further southeast and probably include all the ice west of that N-S crack.
The NW directed movement also makes the gap between the Thwaites Ice Tongue and the icebergs west of it smaller, because they move in NNE direction.

In addition I still see the mini polynya which I had "explained" by the sunk iceberg (pale magenta circle)  ;)

See attached picture
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philopek

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Re: Thwaites Glacier Discussion
« Reply #206 on: January 23, 2020, 11:48:26 PM »


In addition I still see the mini polynya which I had "explained" by the sunk iceberg (pale magenta circle)  ;)

See attached picture

can you explain how an iceberg can sink, until now i would have bet a lot that it's not possible but always ready to crosscheck my views,hence you tell me ;) ;)

FredBear

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Re: Thwaites Glacier Discussion
« Reply #207 on: January 24, 2020, 04:50:34 AM »
The polynya marked by the pale magenta circle in replies 201 & 205 has a darker streak running northwards - implying that there is some source of warmth coming to the surface in that area?

AbruptSLR

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Re: Thwaites Glacier Discussion
« Reply #208 on: January 24, 2020, 06:10:53 PM »
The polynya marked by the pale magenta circle in replies 201 & 205 has a darker streak running northwards - implying that there is some source of warmth coming to the surface in that area?

It seems probable to me that the 'darker streak running northwards' in the sea ice from the pale magenta circle might be caused by relatively warm water existing the southwestern subglacial cavity shown in the attached image, associated with the relatively warm water entering into that cavity indicated by the western yellow arrow on this image (i.e. water entering into the subglacial cavity from the eastern side of the cavity likely exists from the western side of the cavity).
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Jim Hunt

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Re: Thwaites Glacier Discussion
« Reply #209 on: January 28, 2020, 10:54:13 PM »
The BBC have just published a long article about Thwaites Glacier:

https://www.bbc.co.uk/news/science-environment-51097309

Here's the associated video:

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Re: Thwaites Glacier Discussion
« Reply #210 on: January 29, 2020, 09:46:44 AM »
More news/video from the Thwaites grounding zone:

https://schmidt.eas.gatech.edu/2019-field/firstlookunderthwaitesglacier/

« Last Edit: January 30, 2020, 05:41:16 AM by Jim Hunt »
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blumenkraft

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Re: Thwaites Glacier Discussion
« Reply #211 on: January 29, 2020, 10:10:57 AM »
Wow, amazing!

So what is that mirroring effect we see there? Two layers of different water (fresh/salty)?

FredBear

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Re: Thwaites Glacier Discussion
« Reply #212 on: January 29, 2020, 10:56:50 AM »
Scientists have just "hot-water drilled" through 600 metres of floating ice - looks like the fresh/salt water interface locally now is just a small layer below the main iceberg!
And some of the local beasties float at the surface of the salty layer/bottom of the ice so that they don't just get swallowed up into the depths (but they are already hundreds of metres down!).
(I could not understand what was happening when I saw it appear on the news!)
« Last Edit: January 29, 2020, 03:26:56 PM by FredBear »

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Re: Thwaites Glacier Discussion
« Reply #213 on: January 30, 2020, 01:28:00 AM »
Scientists Find Record Warm Water in Antarctica, Pointing To Cause Behind Thwaites Glacier Melt
https://phys.org/news/2020-01-scientists-antarctica-glacier.html

A team of scientists has observed, for the first time, the presence of warm water at a vital point underneath a glacier in Antarctica—an alarming discovery that points to the cause behind the gradual melting of this ice shelf while also raising concerns about sea-level rise around the globe

... The recorded warm waters—more than two degrees above freezing—flow beneath the Thwaites Glacier, which is part of the Western Antarctic Ice Sheet. The discovery was made at the glacier's grounding zone—the place at which the ice transitions between resting fully on bedrock and floating on the ocean as an ice shelf and which is key to the overall rate of retreat of a glacier.

... "The fact that such warm water was just now recorded by our team along a section of Thwaites grounding zone where we have known the glacier is melting suggests that it may be undergoing an unstoppable retreat that has huge implications for global sea level rise," notes Holland, a professor at NYU's Courant Institute of Mathematical Sciences.

... Aurora Basinski, an NYU graduate student who made the turbulence measurement, said, "From our observations into the ocean cavity at the grounding zone we observed not only the presence of warm water, but also its turbulence level and thus its efficiency to melt the ice shelf base." ... "This is an important result as this is the first time turbulent dissipation measurements have been made in the critical grounding zone of the West Antarctic Ice Sheet."

https://thwaitesglacier.org/projects/melt
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RoxTheGeologist

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Re: Thwaites Glacier Discussion
« Reply #214 on: January 30, 2020, 07:47:55 PM »
Scientists Find Record Warm Water in Antarctica, Pointing To Cause Behind Thwaites Glacier Melt
https://phys.org/news/2020-01-scientists-antarctica-glacier.html

A team of scientists has observed, for the first time, the presence of warm water at a vital point underneath a glacier in Antarctica—an alarming discovery that points to the cause behind the gradual melting of this ice shelf while also raising concerns about sea-level rise around the globe

... The recorded warm waters—more than two degrees above freezing—flow beneath the Thwaites Glacier, which is part of the Western Antarctic Ice Sheet. The discovery was made at the glacier's grounding zone—the place at which the ice transitions between resting fully on bedrock and floating on the ocean as an ice shelf and which is key to the overall rate of retreat of a glacier.

... "The fact that such warm water was just now recorded by our team along a section of Thwaites grounding zone where we have known the glacier is melting suggests that it may be undergoing an unstoppable retreat that has huge implications for global sea level rise," notes Holland, a professor at NYU's Courant Institute of Mathematical Sciences.

... Aurora Basinski, an NYU graduate student who made the turbulence measurement, said, "From our observations into the ocean cavity at the grounding zone we observed not only the presence of warm water, but also its turbulence level and thus its efficiency to melt the ice shelf base." ... "This is an important result as this is the first time turbulent dissipation measurements have been made in the critical grounding zone of the West Antarctic Ice Sheet."

https://thwaitesglacier.org/projects/melt

2°C above freezing, so that would be....? Is that 0.2°C (assuming saltwater at -1.8°C) or 2°C? The latter is scary, the former, that's not much above the melt point of the freshwater glacier. Basically an order of magnitude less energy to melt the glacier. that 10x difference may become important....
« Last Edit: January 30, 2020, 08:24:50 PM by RoxTheGeologist »

blumenkraft

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Re: Thwaites Glacier Discussion
« Reply #215 on: January 30, 2020, 07:54:34 PM »
I read that as 2˚C.

But now that you mention it, Rox.

That's stupid phrasing.  :-\

baking

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Re: Thwaites Glacier Discussion
« Reply #216 on: January 30, 2020, 08:06:15 PM »
That's stupid phrasing.  :-\

It might be 34 degrees F.  :D

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Re: Thwaites Glacier Discussion
« Reply #217 on: January 30, 2020, 08:07:48 PM »
LOL  ;D

AbruptSLR

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Re: Thwaites Glacier Discussion
« Reply #218 on: January 30, 2020, 08:43:46 PM »
Scientists Find Record Warm Water in Antarctica, Pointing To Cause Behind Thwaites Glacier Melt
https://phys.org/news/2020-01-scientists-antarctica-glacier.html

A team of scientists has observed, for the first time, the presence of warm water at a vital point underneath a glacier in Antarctica—an alarming discovery that points to the cause behind the gradual melting of this ice shelf while also raising concerns about sea-level rise around the globe

... The recorded warm waters—more than two degrees above freezing—flow beneath the Thwaites Glacier, which is part of the Western Antarctic Ice Sheet. The discovery was made at the glacier's grounding zone—the place at which the ice transitions between resting fully on bedrock and floating on the ocean as an ice shelf and which is key to the overall rate of retreat of a glacier.

... "The fact that such warm water was just now recorded by our team along a section of Thwaites grounding zone where we have known the glacier is melting suggests that it may be undergoing an unstoppable retreat that has huge implications for global sea level rise," notes Holland, a professor at NYU's Courant Institute of Mathematical Sciences.

... Aurora Basinski, an NYU graduate student who made the turbulence measurement, said, "From our observations into the ocean cavity at the grounding zone we observed not only the presence of warm water, but also its turbulence level and thus its efficiency to melt the ice shelf base." ... "This is an important result as this is the first time turbulent dissipation measurements have been made in the critical grounding zone of the West Antarctic Ice Sheet."

https://thwaitesglacier.org/projects/melt

2°C above freezing, so that would be....? Is that 0.2°C (assuming saltwater at -1.8°C) or 2°C? The latter is scary, the former, that's not much above the melt point of the freshwater glacier. Basically an order of magnitude less energy to melt the glacier. that 10x difference may become important....

The attached image shows comparable measurements taken beneath the Pine Island Ice Shelf several years ago; and to me it is clear that the 2oC is above the freezing temperature of seawater under pressure.  No other interpretation makes any sense.
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Stephan

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Re: Thwaites Glacier Discussion
« Reply #219 on: January 30, 2020, 09:58:12 PM »
Anyway, an accurate information of the real temperature (°C) would be helpful for a better understanding of the possible threat to the glacier and its grounding line ("more than two degrees (°C?) (°F?) above freezing") allows too much speculation.
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AbruptSLR

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Re: Thwaites Glacier Discussion
« Reply #220 on: January 30, 2020, 10:15:39 PM »
...
2°C above freezing, so that would be....? Is that 0.2°C (assuming saltwater at -1.8°C) or 2°C? The latter is scary, the former, that's not much above the melt point of the freshwater glacier. Basically an order of magnitude less energy to melt the glacier. that 10x difference may become important....



Sea water density changes with temperature, salinity and pressure and the freezing point is also a function of pressure & salinity; therefore, it is best to talk specifically about the water under the specific location (the linked reference gives the conditions under the PIIS shortly before 2011).

Stanley S. Jacobs, Adrian Jenkins, Claudia F. Giulivi & Pierre Dutrieux (2011), "Stronger ocean circulation and increased melting under Pine Island Glacier ice shelf", Nature Geoscience, Volume: 4, Pages: 519–523, doi:10.1038/ngeo1188

http://www.nature.com/ngeo/journal/v4/n8/abs/ngeo1188.html

Abstract: "In 1994, ocean measurements near Antarctica’s Pine Island Glacier showed that the ice shelf buttressing the glacier was melting rapidly. This melting was attributed to the presence of relatively warm, deep water on the Amundsen Sea continental shelf. Heat, salt and ice budgets along with ocean modelling provided steady-state calving and melting rates. Subsequent satellite observations and modelling have indicated large system imbalances, including ice-shelf thinning and more intense melting, glacier acceleration and drainage basin drawdown. Here we combine our earlier data with measurements taken in 2009 to show that the temperature and volume of deep water in Pine Island Bay have increased. Ocean transport and tracer calculations near the ice shelf reveal a rise in meltwater production by about 50% since 1994. The faster melting seems to result mainly from stronger sub-ice-shelf circulation, as thinning ice has increased the gap above an underlying submarine bank on which the glacier was formerly grounded. We conclude that the basal melting has exceeded the increase in ice inflow, leading to the formation and enlargement of an inner cavity under the ice shelf within which sea water nearly 4 °C above freezing can now more readily access the grounding zone."

&

According to: https://nsidc.org/cryosphere/seaice/index.html as salinity increases the maximum density approaches the freezing point and in sea water with salinity above 24 psu density is highest at freezing temperature (see the first image).

&

The density of sea water has the same pressure and temperature relationships as fresh water but, with the addition of "salt", its mass is increased (see the second image).
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RoxTheGeologist

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Re: Thwaites Glacier Discussion
« Reply #221 on: January 30, 2020, 10:26:27 PM »

Thanks ASLR, that makes a lot more sense now. I didn't consider the pressure changes on melting temperature.

baking

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Re: Thwaites Glacier Discussion
« Reply #222 on: February 01, 2020, 07:10:13 PM »
Thwaites is in the news a lot right now as scientists have begun returning home from the glacier, but this article is particularly comprehensive: https://eos.org/features/diagnosing-thwaites

The second half of this seasons work will be performed on a couple of ice-breaking research vessels, the RV Araon and the RV Nathaniel B. Palmer.  Their current locations can be tracked on the sailwx.info website:

https://www.sailwx.info/shiptrack/shipposition.phtml?call=DSQL7
https://www.sailwx.info/shiptrack/shipposition.phtml?call=WBP3210

The RV Araon has been off of Thwaites for a few days already on some pictures of the landfast sea ice (and some cute penguins and seals) can be seen here:

https://twitter.com/a_wahlin/status/1223166518546042880

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Re: Thwaites Glacier Discussion
« Reply #223 on: February 03, 2020, 06:38:06 PM »

...

2°C above freezing, so that would be....? Is that 0.2°C (assuming saltwater at -1.8°C) or 2°C? The latter is scary, the former, that's not much above the melt point of the freshwater glacier. Basically an order of magnitude less energy to melt the glacier. that 10x difference may become important....

The attached image shows comparable measurements taken beneath the Pine Island Ice Shelf several years ago; and to me it is clear that the 2oC is above the freezing temperature of seawater under pressure.  No other interpretation makes any sense.
This interpretation is supported by an article from the Washington Post where the temperature measurement is reported in a less-ambiguous fashion.

Quote
At a region known as the “grounding line,” where the ice transitions between resting on bedrock and floating on the ocean, scientists measured water temperatures of about 0 degrees Celsius (32 degrees Fahrenheit). That is more than 2 degrees warmer than the freezing point in that location, said David Holland, a New York University glaciologist. He performed the research with Keith Nicholls of the British Antarctic Survey.
Source: https://www.washingtonpost.com/climate-environment/2020/01/30/unprecedented-data-confirm-that-antarcticas-most-dangerous-glacier-is-melting-below/

blumenkraft

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Re: Thwaites Glacier Discussion
« Reply #224 on: February 03, 2020, 06:42:20 PM »
Case closed!

I'm glad this came up as a topic. :)

baking

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Re: Thwaites Glacier Discussion
« Reply #225 on: February 03, 2020, 08:43:54 PM »
The first paper submitted based on last year's field work has just been made available for review.

Hogan 2020 "Revealing the former bed of Thwaites Glacier using sea-floor bathymetry"
https://www.the-cryosphere-discuss.net/tc-2020-25/

"To date, few vessels have been able to access this area due to persistent sea-ice and iceberg cover. This critical data gap was addressed in 2019 during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project, with more than 2000 km2 of new multibeam echo-sounder data (MBES) were acquired offshore TG."

"At TG, the bathymetry is dominated by a > 1200 m deep, structurally-controlled trough and discontinuous ridge, on which the Eastern Ice Shelf is pinned. The geometry and composition of the ridge varies spatially with some parts having distinctive flat-topped morphologies produced as their tops were planed-off by erosion at the base of the seaward-moving Thwaites Ice Shelf, suggesting a positive feedback mechanism for ice-shelf ungrounding. Knowing that this offshore area is a former bed for TG, we applied a novel spectral approach to investigate bed roughness and find that derived power spectra can be approximated using an inverse-square law, a result that is consistent with spectra for bed profiles from the modern TG."

EDIT:  I found an error in the legend for the color of the bathymetry.  The legend for figure 2a is incorrect (the colors are reversed) and the legend for figure 3s is correct.  Since the color in the maps is the same, just use the legend for 3a for both.
« Last Edit: February 03, 2020, 08:59:53 PM by baking »

baking

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Re: Thwaites Glacier Discussion
« Reply #226 on: February 06, 2020, 04:40:56 PM »
I haven't been posting many GIFs of Thwaites Tongue lately for a couple of reasons.  One having to do with the quality of the images I've been getting.  The other is that the landfast sea ice surrounding Thwaites is still firmly in place.  Sea ice in the Antarctic usually hits its minimum in March so we only have a little over a month left this season to see if anything really interesting is going to happen.  Last year the sea ice was mostly gone in February which caused a lot of icebergs to move off.

Anyhow, I saw this GIF posted on twitter this morning so I thought I would link it and give my own commentary on the happenings so far this season.

https://twitter.com/peter_neff/status/1225421674092388352

If you click on the link you will see a few things happening, that I reference in the picture below.

1.  The "cork" is apparently "recorking."  It had begun to move free, rotating clockwise, moving past an obstacle and on out to sea, but it is now hanging up again on a new iceberg pinned to the Eastern Ice Shelf and rotating counter-clockwise.  The forward motion is almost directly lined up with the resistance and it is possible that there will be no sliding past it.  One possible problem is that as the melange backs up behind the cork it could resume putting sideways (westward) pressure on the Tongue destabilizing it.

2.  In the GIF you can see the Eastern side of the Tongue is now moving faster than the Western side which means that the West continues to be blocked by the underwater peak.

3.  A new part of the rift between the Eastern and Western sides of the Tongue has widened significantly recently.  The less attached the Western side is, the more likely it will be to drift off in pieces once the sea ice gone, whether it is in this season or a subsequent one.

steve s

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Re: Thwaites Glacier Discussion
« Reply #227 on: February 06, 2020, 07:52:28 PM »
The GIF showed more apparent northward motion in the EIS than I expected, with a slight eastward component visible at the north end. Is this movement new or is merely faster or in a different pattern?

baking

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Re: Thwaites Glacier Discussion
« Reply #228 on: February 07, 2020, 12:44:44 AM »
The GIF showed more apparent northward motion in the EIS than I expected
This is definitely just an artifact or an alignment issue.  You won't see any significant movement over 30 days at this scale.

Here is a high resolution comparison over the same time period.  You can see a little flexing around the margins, but that's about it.   The only new feature is the flexing on the Western side (bottom of picture) where the "cork" is apparently pushing against TEIS.

[Click below to play.]

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Re: Thwaites Glacier Discussion
« Reply #229 on: February 07, 2020, 02:52:44 AM »
I don't agree. The visible direction of movement varies spatially over the interval throughout the images. Look at the upper right corner of the GIF. This area shows the eastward component of the mostly northerly motion.

(When you reply with images, please provide the dates of those images.)

baking

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Re: Thwaites Glacier Discussion
« Reply #230 on: February 07, 2020, 03:39:51 AM »
Look at the upper right corner of the GIF.
Which GIF are you talking about?
(When you reply with images, please provide the dates of those images.)
My GIFs always have the dates in the title.  In this case it is 2020/01/06 to 2020/02/05 the same as the other GIF, but I only have the first and last images so you can see any actual motion.  I also have the highest resolution available in SAR and it is aligned to within a pixel, or 20 meters.

steve s

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Re: Thwaites Glacier Discussion
« Reply #231 on: February 07, 2020, 10:26:40 AM »
I was referring to the Peter Neff GIF, but I believe the same small motion is visible in your GIF also. In a few places lighting changes can be ruled out in your GIF, with feature relative positions changing, gaps closing between crevasses, etc. The Neff sequence shows a smooth transition of motions -- both directions and speeds -- throughout the tongue and shelf. I thought the shelf to be less mobile before seeing his sequence.

Thanks for the heads up on your naming convention.

baking

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Re: Thwaites Glacier Discussion
« Reply #232 on: February 07, 2020, 07:05:16 PM »
In a few places lighting changes can be ruled out in your GIF

There are no "lighting changes" with radar images.  What appear to be shadows is the presence of liquid water which responds differently to radar.  There may also be contrast issues with the image processing or attempts to adjust the contrast to highlight the amount of melt but I have no control over that.  The best you can do is look at specific points and try to find movement.

And yes there is movement, but there has always been movement.  The very end of the TEIS moves about 300 meters per year or about 1/2 pixel per month at the highest resolution.  The rest of TEIS moves about 600 meters per year or about 1 pixel per month.  See this source for more details: http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=4&image_date=200120_200126

The only thing that I see which is new is the very western edge of the end of the TEIS has flexed recently from being pushed by the "cork" which I've circled in the detail below.

If you are still seeing something in my GIF which you don't think I see, just point it out specifically and I would be glad to look at it further.  The SentinelHub GIF in Peter Neff's tweet has too many obvious alignment issues for me to take seriously regarding the TEIS.  You need a lot more resolution and a lot more careful alignment to see anything happening there.

EDIT: Just to clarify, the arrow in the image below is showing how the "cork" is pushing against the TIES at the circled area.
« Last Edit: February 07, 2020, 07:19:35 PM by baking »

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Re: Thwaites Glacier Discussion
« Reply #233 on: February 13, 2020, 07:11:04 AM »
I wonder if the difference in the way PIG calves into large icebergs and the way Thwaites into "small" melange is due to Pine Island glacial exit being fairly well confined with presumably large side support while Thwaites is this ice plain (ten times or more wider than Pine Island, depending on where you draw the lines) flowing into the ocean.

https://earthobservatory.nasa.gov/images/146247/thwaites-glacier-transformed

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Re: Thwaites Glacier Discussion
« Reply #234 on: February 13, 2020, 03:01:21 PM »
I wonder if the difference in the way PIG calves into large icebergs and the way Thwaites into "small" melange is due to Pine Island glacial exit being fairly well confined with presumably large side support while Thwaites is this ice plain (ten times or more wider than Pine Island, depending on where you draw the lines) flowing into the ocean.
I would agree, or at least that is part of it.  The fast moving part of Thwaites calves almost right at the grounding line, which I think results in frequent calving and smaller icebergs.  The grounding line at Pine Island is set way back from the front.  The sides of Pine Island help support the large ice shelf which keeps the front together until the ice thins from melting underneath.

Another factor may be the thickness of the ice as it crosses the grounding line and I don't really have enough data or expertise to talk about that.

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Re: Thwaites Glacier Discussion
« Reply #235 on: February 16, 2020, 05:51:16 AM »
This tweet has a very nice 5+ year GIF of Thwaites showing quite a bit of detail.  Much better than anything I've seen for that timeframe.

https://twitter.com/kevpluck/status/1228472054430781440

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Re: Thwaites Glacier Discussion
« Reply #236 on: February 16, 2020, 07:01:13 AM »
Great animation.

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Re: Thwaites Glacier Discussion
« Reply #237 on: February 21, 2020, 04:22:08 AM »
Just to have it here (Good video):
The linked article/video provides some nice color commentary about this season's ITGC field mission:

Title: "A risky expedition to study the ‘doomsday glacier’"

https://www.pbs.org/newshour/show/visiting-the-most-vulnerable-place-on-earth-the-doomsday-glacier
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.

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Re: Thwaites Glacier Discussion
« Reply #238 on: February 23, 2020, 06:25:50 PM »
A few things happened on Thwaites this week.  All GIFs are Sentinel-1 radar images over the past six days.

1.  The iceberg that was pinning the "Cork" to the Thwaites Eastern Ice Shelf (TEIS) has broken off it's tip and is now moving free.  The cork and the melange behind should be more free to move.  This might take some pressure off the Tongue that was behind pushed from the side by the backed up melange.

2.  Routine calving on the Western calving front.

3.  Update on the Western edge of the Tongue that is being stripped away as it is caught behind an underwater peak.  Nice image showing the rest of the Tongue marching Northward and the Icebergs to the West being shoved to the North by the force of the Calving, while the Western Edge is stuck in place and being forced away from the rest of the Tongue as the irregular edges collide at points.  (Larger image.  Click to play.)

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Re: Thwaites Glacier Discussion
« Reply #239 on: March 03, 2020, 09:30:42 PM »
The eastern edge of the Thwaites Eastern Ice Shelf is about to calve.
The latest Sentinel image shows an almost complete separation of a new, long iceberg at its SE-most point (circled in yellow). The gap between it and the TEIS has widened.
At its NW-most end it is still connected with the TEIS. In that area there has not been much of a change since Feb 01, 2020.

See attached picture.
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Re: Thwaites Glacier Discussion
« Reply #240 on: March 03, 2020, 09:52:34 PM »
The eastern edge of the Thwaites Eastern Ice Shelf is about to calve.
It's been 90+% calved for years.  Don't hold your breath.

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Re: Thwaites Glacier Discussion
« Reply #241 on: March 03, 2020, 09:55:12 PM »
Yes, I know and I have watched it for a while now. But I wanted to point out that - at least at the surface - the SE tip now lost its connection to TEIS.
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Re: Thwaites Glacier Discussion
« Reply #242 on: March 03, 2020, 10:08:01 PM »
It is still slightly connected, but now there isn't any compression on it so the other end may stay connected until the fast ice goes away which may be another year or two.

I've basically decided that it is "mostly calved" and decided to focus my attention elsewhere.  I don't really see how it effects anything else.  I posted about it maybe six months ago, so now I am "burned" and you may be too in six months.  ;)

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Re: Thwaites Glacier Discussion
« Reply #243 on: March 03, 2020, 10:20:01 PM »
You are probably right. Compared to the action happening around PIIS/SWT and its surroundings everything at TEIS moves in "snail speed". Just imagine you have to wait until it fully calves and you must not do anything else before this happens. So you stare at it and wait and wait and wait...
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Re: Thwaites Glacier Discussion
« Reply #244 on: March 03, 2020, 10:28:13 PM »
It is still slightly connected, but now there isn't any compression on it so the other end may stay connected until the fast ice goes away which may be another year or two.

I've basically decided that it is "mostly calved" and decided to focus my attention elsewhere.  I don't really see how it effects anything else.  I posted about it maybe six months ago, so now I am "burned" and you may be too in six months.  ;)

Since we are taking trips down memory lane, attached are images of both TEIS and the Thwaites Ice Tongue, posted earlier in this thread, from March 6, 2015 and April 10, 2017, respectively.  They both show that the TEIS and the Thwaites Ice Tongue have both degrades in the ensuing years.  All that is needed to activate these features is a sufficiently large oceanic perturbation of warm modified CDW and we could see action comparable to that at the PIIS in five years or so  ;).
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Re: Thwaites Glacier Discussion
« Reply #245 on: March 15, 2020, 05:17:29 PM »
An interesting and well-made video of the series "JustHaveAThink" about the Doomsday Glacier (Thwaites). Nothing new for experts, but a good start for newbies in this forum. Unfortunately the speeding-up-calving video is not from Thwaites, but from neighbouring Pine Island Glacier, which hasn't been mentioned at all in this video.

Just Have A Look:
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Re: Thwaites Glacier Discussion
« Reply #246 on: March 25, 2020, 11:39:32 PM »
The fast sea ice off of Thwaites Tongue shifted today.  The Tongue has been weakening this past season, but has been held in place this annual ice that is usually held "fast" to grounded icebergs.
 
Typically every 3 or 4 years, the fast ice is substantially reduced which allows the melange of loose icebergs to float off, substantially changing the shape of the Thwaites Tongue.  This often happens in March or April near the sea ice minimum.  The last time this happened was last year in 2019.  Up until yesterday, it would have seemed that it was unlikely to happen in 2020.

The GIF below show the last three days.  The mass of ice floes on the left (North) moves around quite a bit with the current and winds while the fast ice to the right (South) is firmly attached to a number of grounded icebergs and protected by the smaller bay around it.

Why the fast ice moved today is unclear.  Did it freeze to the ice floes and get pulled along?  Were they both pushed by the same wind and/or current and today was just they day that it broke free (after thawing all Summer.)

Will this continue tomorrow, maybe into April?  It is certainly hard to say.  What is clear is that the Tongue is extremely vulnerable and at high risk if more fast ice continues to break up.  The icebergs that are normally locked frozen together to form the Tongue have had a rough Summer.  The Northern end has seen a general spreading and separation since last Winter.  The Western side has sheared off after encountering an underwater peak.  To the East, the melange between the Tongue and the Thwaites Eastern Ice Shelf has been blocked behind a 10km long "cork" that may have finally broken free.  Details of all of these can be found above in this thread.  I will continue to keep a close eye on the fast ice and have my fingers crossed.

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Re: Thwaites Glacier Discussion
« Reply #247 on: March 26, 2020, 07:52:34 PM »
I noticed the crack in the fast ice on EOSDIS a few days ago, but I didn't post it. So thank you very much, baking, for the gif.
What worries me is that on the second last image there is even a new crack in the fast ice in the SW close to Bear Peninsula (lower right corner). I wouldn't have expected that to happen so late in the melting season (which has turned into a freezing season already).
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Re: Thwaites Glacier Discussion
« Reply #248 on: March 26, 2020, 08:54:06 PM »
there is even a new crack in the fast ice in the SW close to Bear Peninsula
I hadn't even noticed that one.

I've been trying to see if it has had an effect on the Tongue yet.  There was a new high-resolution image today and the 6-day GIF was looking a little strange to me, so I made a large scale GIF to compare 12 days ago, 6 days ago, and today.  It almost seems that the Toungue has changed direction slightly since the changes in the fast ice, moving a little bit more to the West than usual.

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Re: Thwaites Glacier Discussion
« Reply #249 on: March 26, 2020, 09:32:37 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?
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