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Author Topic: Thwaites Glacier Discussion  (Read 15054 times)

Stephan

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Re: Thwaites Glacier Discussion
« Reply #50 on: January 30, 2019, 07:00:20 PM »
New melting and breaking off at Thwaites Glacier. Today I analysed the outer ice field which continues Thwaites Ice tongue to the northwest. I compared the EOSDIS data from Jan 12 and Jan 30, 2019. I marked lost fast sea ice positions in pale magenta and newly formed cracks in orange. I wonder whether this outer ice field, which now has almost completely lost its connection to the Thwaites Ice tongue, will survive this fading austral summer.
See attached picture.

sidd

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Re: Thwaites Glacier Discussion
« Reply #51 on: January 30, 2019, 11:12:30 PM »
Big hole under Thwaites: melt rate much higher than models find

Apparently CDW induced melt is much faster in cavities when bed slope is prograde than retrograde.

"The newly formed cavity at B is thin, however, which does not favor warm CDW intrusion from geostrophic flow and efficient vertical mixing (19, 24) and explains the low ice shelf melt rates. In contrast, the prograde bed at A favors an efficient opening of a new ice shelf cavity, stronger CDW intrusion, and efficient mixing, with melt rates 20 times higher than those at B. "


"Ice shelf melt at A exceeds values used in numerical ice sheet/ocean models by factors of 2 to 3"

open access, read the whole thing: DOI: 10.1126/sciadv.aau3433

sidd

solartim27

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Re: Thwaites Glacier Discussion
« Reply #52 on: January 31, 2019, 04:57:19 AM »
Good summary and pictures of above here:
https://www.jpl.nasa.gov/news/news.php?feature=7322
FNORD

vox_mundi

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Re: Thwaites Glacier Discussion
« Reply #53 on: January 31, 2019, 12:50:38 PM »
From the jpl article

“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

b_lumenkraft

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Re: Thwaites Glacier Discussion
« Reply #54 on: January 31, 2019, 01:00:50 PM »
Comparison Thwaites Glacier - Nighttime Imagery (Day/Night band, enhanced contrasts via Suomi NPP VIIRS)

Left hand 2019-01-30
Right hand 2019-01-06

Stephan

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Re: Thwaites Glacier Discussion
« Reply #55 on: February 01, 2019, 05:42:09 PM »
In addition to the posting I have just made and in addition to my post from yesterday I have to report that a further new crack in the fast ice / ice mélange of Thwaites has developed yesterday.
See attached image.
Colour code: orange is the crack I have just mentioned, yellowish green is the crack I reported of yesterday and the new crack which connects both cracks is painted in pale magenta.
It seems that the whole thing is about to collapse.
Update 31 Jan 2019: The crack in pale magenta has massively widened. The whole eastern part moves to the southeast. The crack in yellowish green has not changed significantly.

Andreas T

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Re: Thwaites Glacier Discussion
« Reply #56 on: February 01, 2019, 06:48:22 PM »
Looking through past years i noticed there has been a swathe of grounded icebergs in the past which seemed to follow the same line as some of the present sea ice.
To have a better comparison I have overlayed an image of 21 feb 2008 in a purple tint over 22 jan 2019
This shows that the stranded icebergs were mostly further west than the curved piece of sea ice. In the same location there are still icebergs which don't move when other bits of ice move around them.
We will probably see soon how much the mobility of the large chunk of sea ice is constrained by frozen in icebergs.

So, my hunch was a bit off, but I thought it might be worth sharing because it tells us something about water depth in that area.

Stephan

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Re: Thwaites Glacier Discussion
« Reply #57 on: February 01, 2019, 08:20:25 PM »
I have also noticed that many of the ice bergs west of the Thwaites Ice Tongue might be grounded. Comparing day-by-day or week-by-week some of them just turn around at their position, others seem to be completely immobile. The waters must be shallow there.
If I look at the outer ice field I mentioned some days ago, it contains only few ice bergs originated from Thwaites. Therefore I think that - if sea temperature and currents are "right" - it will further disappear or move, and some of the grounded bergs in it will just stay where they are at the moment...

Tealight

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Re: Thwaites Glacier Discussion
« Reply #58 on: February 01, 2019, 09:14:44 PM »
New melting and breaking off at Thwaites Glacier. Today I analysed the outer ice field which continues Thwaites Ice tongue to the northwest. I compared the EOSDIS data from Jan 12 and Jan 30, 2019. I marked lost fast sea ice positions in pale magenta and newly formed cracks in orange. I wonder whether this outer ice field, which now has almost completely lost its connection to the Thwaites Ice tongue, will survive this fading austral summer.
See attached picture.

What you have marked as "Thwaites Ice tongue" has been named iceberg B22A for several years., since it is not connected to the main glacier anymore.

Looking through past years i noticed there has been a swathe of grounded icebergs in the past which seemed to follow the same line as some of the present sea ice.
To have a better comparison I have overlayed an image of 21 feb 2008 in a purple tint over 22 jan 2019
This shows that the stranded icebergs were mostly further west than the curved piece of sea ice. In the same location there are still icebergs which don't move when other bits of ice move around them.
We will probably see soon how much the mobility of the large chunk of sea ice is constrained by frozen in icebergs.

So, my hunch was a bit off, but I thought it might be worth sharing because it tells us something about water depth in that area.

The water depth is known relatively well and available on the bedmap2 from the British Antarctic Survey.

https://www.bas.ac.uk/project/bedmap-2/#data

The whole ice field is over a roughly 300-400m deep part.This is about half the depth of the surrounding areas. I attached an image of the bedrock overlayed with a coastline mask. The mask is maybe from 2012 when the bedmap2 was created and doesn't have the newest glacier front positions.




Andreas T

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Re: Thwaites Glacier Discussion
« Reply #59 on: February 02, 2019, 02:37:04 PM »
thank you very much, Tealight.
This is really helpful, I guess that means B22A would need to move north or north east if it becomes mobile, westwards its path is blocked. The small amount of movement since it arrived in its present position is probably due to some bottom melting. I guess there is ice thickness data for B22A somewhere? I hope it isn't too cheeky to ask, instead of searching for it myself, but if somebody has done the work already, or can tell me where to look?

dingojoe

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Re: Thwaites Glacier Discussion
« Reply #60 on: February 02, 2019, 06:04:57 PM »
In addition to the posting I have just made and in addition to my post from yesterday I have to report that a further new crack in the fast ice / ice mélange of Thwaites has developed yesterday.
See attached image.
Colour code: orange is the crack I have just mentioned, yellowish green is the crack I reported of yesterday and the new crack which connects both cracks is painted in pale magenta.
It seems that the whole thing is about to collapse.

Hi, I rarely post and am not sure how skilled I am at linking, but the tongue did fracture along your yellow and pink line back in 2016

https://go.nasa.gov/2S6IUoa

However, the fractured ice really didn't have a means of exiting the area due to the large block/iceberg/grounded ice north of the yellow line.  It does seem like that block has slowly ground it's way westward which may be making it easier for fractured ice on the east side of the tongue to flow out of the area. 

b_lumenkraft

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Re: Thwaites Glacier Discussion
« Reply #61 on: February 02, 2019, 07:16:20 PM »
Hey dingojoe,

you linked well. Good find! :)


Tealight

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Re: Thwaites Glacier Discussion
« Reply #62 on: February 03, 2019, 02:01:16 AM »
I guess there is ice thickness data for B22A somewhere? I hope it isn't too cheeky to ask, instead of searching for it myself, but if somebody has done the work already, or can tell me where to look?

The only two instruments that could measure thickness is the not yet in science phase ICESat-2 and CryosSat, but CryosSat doesn't have a public thickness product for icebergs.

The offical CryosSat data ditribution only has Arctic Sea Ice and Greenland /Antarctic Ice sheets elevations.
http://www.cpom.ucl.ac.uk/csopr/index.html

If you are lucky there a published scientific papers about iceberg thickness, if not then you have to request the raw data yourself, find the icebergs in the data and calculate the thickness yourself.

Stephan

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Re: Thwaites Glacier Discussion
« Reply #63 on: February 03, 2019, 07:23:51 AM »
Further retreat of the ice mélange west of Thwaites ice tongue. The distance between open water and the calving front of Thwaites glacier is reduced to 15-18 km. You can also recognize that iceberg B22A is slightly moving westward - this was not visible the last months. May melting from below have thinned it so that it lost connection to some of the pinning points?
See the link (comparison of Jan 22 with Feb 02, 2019) to EOSDIS worldview
https://worldview.earthdata.nasa.gov/?ca=false&cm=swipe&cv=94&p=antarctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&l1=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2019-02-02-T00%3A00%3A00Z&z=3&t1=2019-01-22-T00%3A00%3A00Z&v=-1699945.223835678,-608838.4314290967,-1487465.223835678,-490822.43142909673
« Last Edit: February 03, 2019, 09:30:19 AM by Stephan »

Andreas T

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Re: Thwaites Glacier Discussion
« Reply #64 on: February 03, 2019, 09:38:28 PM »

from an earlier post by ASLR
I found the attached radar soundings which give an idea of the (initial) thickness of B22A. The line RS is along the ice tongue from which B22A broke off a few years before.
source https://www.the-cryosphere.net/11/1283/2017/tc-11-1283-2017.pdf

How much bottom melting has occurred since then is hard to know but we know that it is the deeper water which is melting the glacier and that melting rates become smaller as ice shelves thin towards the seaward end.

Stephan, I think there is slight pivoting of B22A but no westward (i.e. down in the worlview image) movement. But the key point is that it is now clear that it is not held in place by sea ice, since that has now cracked across its width on the landward side.
For comparison the movement since march 2012 when it arrived in its present vicinity https://go.nasa.gov/2HOnreJ as seen on worldview
« Last Edit: February 03, 2019, 10:21:06 PM by Andreas T »

Andreas T

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Re: Thwaites Glacier Discussion
« Reply #65 on: February 04, 2019, 01:22:54 PM »
I have found some more information on thickness of Thwaites ice tongue, although it does not tell me more because it again is the tongue after separation of B22A (I am guessing this from the shape, no date is given).
It is very low resolution because it comes from a small picture in a slide show type PDF
but it shows that data is around, I am guessing that this comes from the 1km elevation model

b_lumenkraft

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Re: Thwaites Glacier Discussion
« Reply #66 on: February 06, 2019, 06:50:56 PM »
B22A moved a bit!

Gray-Wolf

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Re: Thwaites Glacier Discussion
« Reply #67 on: February 07, 2019, 01:23:59 PM »
https://www.theguardian.com/environment/2019/feb/07/cavity-two-thirds-the-size-of-manhattan-discovered-under-antarctic-glacier

Looks like the recent flip flip in Antarctic sea ice behaviour coincides with this uptick in melt and the potential for rapid collapse as the ice thins further?
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b_lumenkraft

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Re: Thwaites Glacier Discussion
« Reply #68 on: February 09, 2019, 09:37:47 AM »
The ice tongue behind B22A is breaking up now.

Bernard

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Re: Thwaites Glacier Discussion
« Reply #69 on: February 09, 2019, 12:09:35 PM »
I've been following this thread for a while, but it's often very hard in this complex zone to figure out scale of things, and what is what, default explicit scale and orientation of pictures. Would it be difficult to have some reference map, with scale and orientation, on which background the different pictures posted here could be localized? Or are things so mobile there that the very notion of such a map is impossible?

b_lumenkraft

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Re: Thwaites Glacier Discussion
« Reply #70 on: February 09, 2019, 12:24:43 PM »
Sorry, Bernard,

you are right. Just a screenshot is confusing without context.

Picture was taken from >> https://www.polarview.aq/antarctic
Link to source (yellow box)>> http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201902/S1A_EW_GRDM_1SSH_20190207T041138_0C53_S_1.8bit.jp2


Bernard

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Re: Thwaites Glacier Discussion
« Reply #72 on: February 09, 2019, 12:54:49 PM »
Thanks a lot! Will try to make sense of all this.

Makes me wonder, BTW, how to make people aware that understanding what's going on behind those difficult-to-grasp images and data has a critical impact on their future?

b_lumenkraft

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Re: Thwaites Glacier Discussion
« Reply #73 on: February 09, 2019, 01:00:00 PM »
You are welcome. If you have any problems with the tools i linked, feel free to PM me Bernard. :)

b_lumenkraft

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Re: Thwaites Glacier Discussion
« Reply #74 on: February 09, 2019, 01:09:06 PM »
how to make people aware that understanding what's going on behind those difficult-to-grasp images and data has a critical impact on their future?

You don't. If people don't ask independently they will not listen most likely anyway. So spear your breath i say.

When people ask you, you have already won. In this case, encourage them to stay curious.

Bernard

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Re: Thwaites Glacier Discussion
« Reply #75 on: February 09, 2019, 05:09:40 PM »
how to make people aware that understanding what's going on behind those difficult-to-grasp images and data has a critical impact on their future?

You don't. If people don't ask independently they will not listen most likely anyway. So spear your breath i say.

When people ask you, you have already won. In this case, encourage them to stay curious.

Wisdom indeed. But now that Thwaites news are flowing in mainstream media, maybe time has come to be a bit more proactive. ;)

Stephan

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Re: Thwaites Glacier Discussion
« Reply #76 on: February 09, 2019, 09:40:59 PM »
I carefully compared Thwaites Glacier cracks Dec 15, 2018 with Feb 09, 2019. A new one, around 15 km long, has formed within the last 8 weeks.
See attached figure.
I indicated some of the features so you have a better orientation. Thanks Bernard for letting us know that we should give some additional information, where exactly all these things are going on...

Stephan

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Re: Thwaites Glacier Discussion
« Reply #77 on: February 09, 2019, 10:04:19 PM »
New development at the fast ice east of Bear Peninsula and South of Iceberg B-25 B-22-A.
In-between the coloured lines (I used the same colours as in Reply #49 earlier in this thread) there are hundreds of cracks. So one might expect a further degradation and dis-integration of the fast ice.
But summer is fading rapidly and some features already show a thin ice cover, for example parts of the pale magenta coloured crack, or the blue circled area close to the open ocean.
So the late austral summer may prevent the fast ice from a complete collapse.
See attached picture.
« Last Edit: February 10, 2019, 08:58:01 AM by Stephan »

Bernard

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Re: Thwaites Glacier Discussion
« Reply #78 on: February 09, 2019, 11:35:42 PM »
Thanks Stephan for the annotations on the images! Added value, much appreciated  ;)

oren

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Re: Thwaites Glacier Discussion
« Reply #79 on: February 10, 2019, 12:03:46 AM »
Thanks Stephan for the annotations on the images! Added value, much appreciated  ;)
+1

Andreas T

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Re: Thwaites Glacier Discussion
« Reply #80 on: February 10, 2019, 03:08:33 AM »
Sorry for being pedantic but to avoid confusion, the large iceberg is named B22A by the US National Ice Centre https://www.natice.noaa.gov/pub/icebergs/Iceberg_Tabular.pdf


Stephan

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Re: Thwaites Glacier Discussion
« Reply #81 on: February 10, 2019, 08:53:22 AM »
OK, I will keep that in mind. Sorry for not having it thoroughly checked.

b_lumenkraft

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Re: Thwaites Glacier Discussion
« Reply #82 on: February 10, 2019, 06:35:29 PM »
From 2017 but i think it belongs here.

Quote
CryoSat data have been processed in a new way and reveal that, in 2013, four interlinked lakes under Thwaites drained into the ocean. The image shows how the surface of the ice over one of the lakes sank by as much as six metres as a result of the drainage. The ice sank in a similar way over the other three lakes. Subglacial lakes have been found in many parts of Antarctica and are, indeed, commonly associated with fast-flowing glaciers. However, this is the first time that they have been found and observed draining into the Amundsen Sea. Also, this draining process is thought to happen only every 20–80 years.
Link >> https://www.esa.int/spaceinimages/Images/2017/02/One_of_four_lakes_under_the_glacier

Often Distant

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Re: Thwaites Glacier Discussion
« Reply #83 on: February 12, 2019, 01:14:39 PM »
One day. Strong wind. A significant breaking apart of a large floe.

Tor Bejnar

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Re: Thwaites Glacier Discussion
« Reply #84 on: February 12, 2019, 05:59:33 PM »
The break apart of two large floes/bergs (triangular one just left of center of image, and slightly-crooked-finger-shaped one just below center of image)
Arctic ice is healthy for children and other living things.

Stephan

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Re: Thwaites Glacier Discussion
« Reply #85 on: February 16, 2019, 09:39:19 PM »
In addition to my post #50 in this thread I state that most of the "outer ice field" has dis-integrated into many pieces of smaller sea ice.
I tried to cover the original area of this ice field in orange. It seems to have "grown" in the last days, but this extra sea ice derives from the massive clean up at Pine Island Bay and Thwaites (circled in light blue) I wrote about the last days in the "PIG has calved" thread.
Below (in magenta) you see the iceberg B-22-A which moves slightly westward, on some days more in a counterclockwise manner than in a direct flow. Unfortunately this Sentinel picture is partly cloudy - but there is no better view available. The latest picture before this is from Jan 30. It shows a more or less intact outer ice field with a lot of cracks, that indicated the future collapse which has now occurred.
In the NE part of the picture is Burke Island for a better orientation.
The picture covers an area of ~ 320x175 km, so it is huge!
« Last Edit: February 16, 2019, 10:09:52 PM by Stephan »