Arctic Sea Ice : Forum

Cryosphere => Antarctica => Topic started by: prokaryotes on October 21, 2016, 06:20:25 AM

Title: Thwaites Glacier Discussion
Post by: prokaryotes on October 21, 2016, 06:20:25 AM
Since there is no dedicated topic yet, here it is now.

For starters

This Antarctic glacier is the biggest threat for rising sea levels. The race is on to understand it https://www.washingtonpost.com/news/energy-environment/wp/2016/10/20/u-s-and-u-k-announce-major-research-mission-to-enormous-melting-antarctic-glacier/ (https://www.washingtonpost.com/news/energy-environment/wp/2016/10/20/u-s-and-u-k-announce-major-research-mission-to-enormous-melting-antarctic-glacier/)

(https://img.washingtonpost.com/wp-apps/imrs.php?src=https://img.washingtonpost.com/rf/image_960w/2010-2019/WashingtonPost/2015/09/22/Interactivity/Images/thwaits_icebrige_2012_lrg.jpg&w=1484)

Wikipedia https://en.wikipedia.org/wiki/Thwaites_Glacier (https://en.wikipedia.org/wiki/Thwaites_Glacier)

Some recent images, and link to the Worldview region

Link https://worldview.earthdata.nasa.gov/?p=antarctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2016-10-16&v=-1729024,-485504,-1483264,-355968 (https://worldview.earthdata.nasa.gov/?p=antarctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Coastlines&t=2016-10-16&v=-1729024,-485504,-1483264,-355968)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FSMPUol0.jpg&hash=b5c99630598756bb0e7be7f0e2fa7854)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2Faa6keCU.jpg&hash=da07a9e9212af35f259f983bdc6fa357)
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FRnAMmxi.jpg&hash=2e257e41fd016f67a5ee94ba1bc91147)
Title: Re: Thwaites Glacier Discussion
Post by: solartim27 on October 21, 2016, 08:40:48 AM
Since there is no dedicated topic yet, here it is now.
Try the 5 pages of discussions here
http://forum.arctic-sea-ice.net/index.php/topic,72.0.html (http://forum.arctic-sea-ice.net/index.php/topic,72.0.html)
Title: Re: Thwaites Glacier Discussion
Post by: prokaryotes on October 21, 2016, 10:02:23 AM
Since there is no dedicated topic yet, here it is now.
Try the 5 pages of discussions here
http://forum.arctic-sea-ice.net/index.php/topic,72.0.html (http://forum.arctic-sea-ice.net/index.php/topic,72.0.html)
Oh well, but do we want a dedicated discussion (without PIG), and here in this forum? Mods, go ahead delete/move as you see fit.
Title: Re: Thwaites Glacier Discussion
Post by: oren on October 21, 2016, 12:21:22 PM
That discussion is mostly about Thwaites, including following its movements and calvings. Just the thread name is misleading.
Title: Re: Thwaites Glacier Discussion
Post by: AbruptSLR on October 21, 2016, 05:08:01 PM
That discussion is mostly about Thwaites, including following its movements and calvings. Just the thread name is misleading.

When looking at the bigger picture (when considering cliff failures and hydrofracturing as GMSTA approaches 2.7C), the collapse mode for Thwaites is closely linked to the behavior of PIG.
Title: Re: Thwaites Glacier Discussion
Post by: DrTskoul on February 16, 2017, 03:21:29 AM
Quote
"There is currently large uncertainty about how much sea level will rise and much of this uncertainty is related to whether models incorporate the fact that ice sheets break," Bassis said. "What we are showing is that the models we have of this process seem to work for Greenland, as well as in the past so we should be able to more confidently predict sea level rise."

He added that portions of Antarctica have similar geography to Laurentide: Pine Island, Thwaites glacier, for example.

"We're seeing ocean warming in those region and we're seeing these regions start to change. In that area, they're seeing ocean temperature changes of about 2.7 degrees Fahrenheit," Bassis said. "That's pretty similar magnitude as we believe occurred in the Laurentide events, and what we saw in our simulations is that just a small amount of ocean warming can destabilize a region if it's in the right configuration, and even in the absence of atmospheric warming."

The study is called "Heinrich events triggered by ocean forcing and modulated by isostatic adjustment."

How an Ice Age paradox could inform sea level rise predictions (http://www.nature.com/nature/journal/v542/n7641/full/nature21069.html)

https://m.phys.org/news/2017-02-ice-age-paradox-sea.html (https://m.phys.org/news/2017-02-ice-age-paradox-sea.html)
Title: Re: Thwaites Glacier Discussion
Post by: FredBear on February 16, 2017, 11:47:37 AM
Heinrich events triggered by ocean forcing and modulated by isostatic adjustment.
They are saying that isostatic rebound reduced the contact of warm water with the ice sheet - but surely that reaction is much too slow? The relatively rapid rise in sea level would also increase water contact - although loss of mass could contribute by reducing local gravity? Recent calvings of ice shelves have led to the glaciers behind them speeding up and thinning, creating concerns about runaway reactions   .    .    .
Title: Re: Thwaites Glacier Discussion
Post by: RoxTheGeologist on February 16, 2017, 06:39:56 PM
Heinrich events triggered by ocean forcing and modulated by isostatic adjustment.
They are saying that isostatic rebound reduced the contact of warm water with the ice sheet - but surely that reaction is much too slow? The relatively rapid rise in sea level would also increase water contact - although loss of mass could contribute by reducing local gravity? Recent calvings of ice shelves have led to the glaciers behind them speeding up and thinning, creating concerns about runaway reactions   .    .    .

"On millennial timescales, isostatic adjustment causes the bed to uplift, isolating the terminus from subsurface warming and allowing the ice sheet to advance again"

It depends on the magnitude of the isostatic rebound and sea level rise. An ice sheet 1 km thick causes 1/2.6 *1000m of uplift. Basically you replace the ice mass with rock mass. However, I would tend to agree with you. I can't see how this can become a feedback cycle. The sea level change is on a decadal timescale, whereas the isostatic rebound takes much longer. I'd expect ice sheets to continually adjust to the new physical regime as the rebound progresses. Sedimentologists with muddy thoughts?

Title: Re: Thwaites Glacier Discussion
Post by: AbruptSLR on February 16, 2017, 07:41:00 PM
Many people think that when scientist look at the paleo-record, that as the climate oscillates that the paleo-record can be used to directly answer what is going to happen in the Anthropocene in the new few decades.  Such thinking is ludicrous, as the purpose of looking at the paleo-record is to better calibrate state-of-the-art Earth System Models (with state-of-the-art modules for marine glaciers including isostatic adjustments) so that when Anthropogenic forcing is applied we can better estimate what is likely to happen in the near future.

Perhaps the most important issue to consider about isostatic rebound for Thwaites is that the satellite record of ice mass loss (GRACE etc.) need to be corrected for this rebound; which means that recent ice mass losses from Thwaites are likely higher than previously reported.
Title: Re: Thwaites Glacier Discussion
Post by: RoxTheGeologist on February 17, 2017, 01:59:04 AM
Perhaps the most important issue to consider about isostatic rebound for Thwaites is that the satellite record of ice mass loss (GRACE etc.) need to be corrected for this rebound; which means that recent ice mass losses from Thwaites are likely higher than previously reported.

It would be interesting if there were exposed sections of rock close to to glacier, and undergoing substantially the same rebound. Height changes of the exposed rock would allow calibration of any rebound and perhaps allow for an isostatic adjustment to the mass loss.
Title: Re: Thwaites Glacier Discussion
Post by: sidd on February 17, 2017, 04:37:53 AM
Very pretty paper from a few years ago on seasonal uplift signal in Greenland.

www.pnas.org/cgi/doi/10.1073/pnas.1204664109 (http://www.pnas.org/cgi/doi/10.1073/pnas.1204664109)

but thwaites is much harder logistically and otherwise

Title: Re: Thwaites Glacier Discussion
Post by: AbruptSLR on February 17, 2017, 03:56:47 PM
It would be interesting if there were exposed sections of rock close to to glacier, and undergoing substantially the same rebound. Height changes of the exposed rock would allow calibration of any rebound and perhaps allow for an isostatic adjustment to the mass loss.

I am re-posting the following from the "Antarctic Tectonics" thread.  The first paper indicates that the GRACE satellite SLR contributions previously reported by NASA are probably 40% too low for at least the ASE area and probably for all of the WAIS due to treating the GIA correction for the WAIS like any other part of the earth when, as I have indicated in my prior posts in this thread, West Antarctica has a relatively unique tectonic history and current condition:


An investigation of Glacial Isostatic Adjustment over the Amundsen Sea sector, West Antarctica
by: A. Groh; H. Ewert, M. Scheinert, M. Fritsche, A. Rülke, A. Richter, R. Rosenau, R. Dietrich
http://dx.doi.org/10.1016/j.gloplacha.2012.08.001 (http://dx.doi.org/10.1016/j.gloplacha.2012.08.001)

"Abstract
The present study focuses on the Amundsen Sea sector which is the most dynamical region of the Antarctic Ice Sheet (AIS). Based on basin estimates of mass changes observed by the Gravity Recovery and Climate Experiment (GRACE) and volume changes observed by the Ice, Cloud and Land Elevation Satellite (ICESat), the mean mass change induced by Glacial Isostatic Adjustment (GIA) is derived. This mean GIA-induced mass change is found to be 34.1 ± 11.9 Gt/yr, which is significantly larger than the predictions of current GIA models. We show that the corresponding mean elevation change of 23.3 ± 7.7 mm/yr in the Amundsen Sea sector is in good agreement with the uplift rates obtained from observations at three GPS sites. Utilising ICESat observations, the observed uplift rates were corrected for elastic deformations due to present-day ice-mass changes. Based on the GRACE-derived mass change estimate and the inferred GIA correction, we inferred a present-day ice-mass loss of − 98.9 ± 13.7 Gt/yr for the Amundsen Sea sector. This is equivalent to a global eustatic sea-level rise of 0.27 ± 0.04 mm/yr. Compared to the results relying on GIA model predictions, this corresponds to an increase of the ice-mass loss or sea-level rise, respectively, of about 40%."

The first accompanying figure shows an overview of the Amundsen Sea sector, West Antarctica. The red line defines the generalised drainage basins of Pine Island Glacier, Thwaites Glacier and Smith Glacier (PITS). Locations of three GPS campaign sites are marked by red triangles.

The second figures shows the GRACE data from 2003 to 2009 which the papers says needs to be corrected to indicate about 40% more ice mass loss than previously reported

The second paper finds that ice mass loss estimates for GRACE observations for the Antarctic are highly dependent upon the GIA correction used (which the authors state to be uncertain).  That said the latest GIA data makes me believe the −147 ± 80 Gt/yr average ice mass loss for AIS from 2003 thru 2012, cited below:

Time-variable gravity observations of ice sheet mass balance: Precision and limitations of the GRACE satellite data
by: I. Velicogna, and J. Wahr; Article first published online: 27 JUN 2013; Geophysical Research Letters, DOI: 10.1002/grl.50527

Abstract:
"Time-variable gravity data from the Gravity Recovery and Climate Experiment (GRACE) mission have been available since 2002 to estimate the mass balance of the Greenland and Antarctic Ice Sheets. We analyze current progress and uncertainties in GRACE estimates of ice sheet mass balance. We discuss the impacts of errors associated with spherical harmonic truncation, spatial averaging, temporal sampling, and leakage from other time-dependent signals (e.g., glacial isostatic adjustment (GIA)). The largest sources of error for Antarctica are the GIA correction, the omission of l=1 terms, nontidal changes in ocean mass, and measurement errors. For Greenland, the errors come mostly from the uncertainty in the scaling factor. Using Release 5.0 (RL05) GRACE fields for January 2003 through November 2012, we find a mass change of −258 ± 41 Gt/yr for Greenland, with an acceleration of −31 ± 6 Gt/yr2, and a loss that migrated clockwise around the ice sheet margin to progressively affect the entire periphery. For Antarctica, we report changes of −83 ± 49 and −147 ± 80 Gt/yr for two GIA models, with an acceleration of −12 ± 9 Gt/yr2and a dominance from the southeast pacific sector of West Antarctica and the Antarctic Peninsula."

The third paper indicates up to 4.5 meters of bed uplift due to GIA for the Pine Island Bay in the next 100-years.  However, I believe that it is likely too conservative scientifically, and that basal melting rates, and earthquakes, will increase ice mass loss faster than the negative feedbacks mentioned in the article:

S. Adhikari, E. Ivins, E. Larour, H. Seroussi, M. Morlighem, and S. Nowicki, (2014), "Future Antarctic bed topography and its implications for ice sheet dynamics", Solid Earth Discuss., 6, 191–228, 2014, www.solid-earth-discuss.net/6/191/2014/; (http://www.solid-earth-discuss.net/6/191/2014/;) doi:10.5194/sed-6-191-2014

http://www.solid-earth-discuss.net/6/191/2014/sed-6-191-2014-print.pdf (http://www.solid-earth-discuss.net/6/191/2014/sed-6-191-2014-print.pdf)

Abstract: "The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) is generally losing its mass since the last glacial maximum (LGM). In a sustained warming climate, the AIS is predicted to retreat at a greater pace primarily via melting beneath the ice shelves. We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS. We find that the past loading is relatively less important than future loading on the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years 2100 and 2500AD, respectively, and that the East Antarctic Ice Sheet (EAIS) is likely to remain unchanged or subside minimally except around the Amery Ice Shelf.  The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay approaches roughly 45mmyr−1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is associated with the flattening of reverse bed, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote the stability to marine portions of the ice sheet in future."
Title: Re: Thwaites Glacier Discussion
Post by: steve s on March 24, 2017, 08:22:52 PM
Looks like the Thwaites tongue is calving.

(https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?project=antarctica_regions&subset=Thwaites_Tongue.2017083.terra.250m.jpg)
Title: Re: Thwaites Glacier Discussion
Post by: AbruptSLR on March 24, 2017, 09:30:40 PM
Looks like the Thwaites tongue is calving.

steve s,

Great catch, & the first attached image is a Sentinel image from March 22 2017, showing the same event.  That said, I think that rather than calling it a calving event it might be more accurate to say that the iceberg that calved in 2012 (see the second image) has finally become ungrounded (see the third image of the grounding point #2). 
Title: Re: Thwaites Glacier Discussion
Post by: maga on March 25, 2017, 11:00:03 AM
I would call it a calving event. The berg that calved in 2012 which is labeled as new iceberg in the picture has moved away long ago and is currently floating in the Ross sea, roughly along a line from the Sulzberger Ice Shelf to Cape Adare. What is breaking off now is a part of the remaining Thwaites Ice Tongue. It may have been grounded or possibly still is, but it's breaking apart rapidly.  The sea is getting deeper towards the land and we have to expect a rapid breakup of the complete remaining ice tongue. The Eastern Thwaites Ice Shelf will follow soon. It is still grounded at the tip but cracks are developing all over the place. Probably less than three more years to go...
Title: Re: Thwaites Glacier Discussion
Post by: AbruptSLR on March 26, 2017, 04:06:46 AM
The first image shows the Thwaites Ice Tongue in December 2012, and the second shows the Ice Tongue in March 2015.  It looks to me like the large grounded at the seaward end of the degraded Ice Tongue is the same feature but somewhat degraded with time.
Title: Re: Thwaites Glacier Discussion
Post by: maga on March 29, 2017, 09:10:55 PM
Yes, the tongue is the same. And it lost a few icebergs since 2012. But the big one marked as new iceberg in your September 2012 picture was already gone by December (it might actually still be visible in the top left corner under the cloud). The detailed pictures can be found at:
http://nsidc.org/data/iceshelves_images/cgi-bin/modis_iceshelf_archive.pl (http://nsidc.org/data/iceshelves_images/cgi-bin/modis_iceshelf_archive.pl)
Title: Re: Thwaites Glacier Discussion
Post by: steve s on April 06, 2017, 04:22:26 AM
Although this is awfully late in the year and new ice is forming, the calving activity on the Thwaites' tongue is continuing -- April 5th.

https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?project=antarctica_regions&subset=Thwaites_Tongue.2017095.terra.250m (https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?project=antarctica_regions&subset=Thwaites_Tongue.2017095.terra.250m)

(Link provided because the image is not appearing inline in my browser window.)
Title: Re: Thwaites Glacier Discussion
Post by: solartim27 on April 07, 2017, 08:14:37 AM
Who could have imagined?

Quote
The Amundsen Sea sector is experiencing the largest mass loss, glacier acceleration, and grounding line retreat in Antarctica. Enhanced intrusion of Circumpolar Deep Water onto the continental shelf has been proposed as the primary forcing mechanism for the retreat.
(Paywalled)
http://onlinelibrary.wiley.com/doi/10.1002/2017GL072910/abstract?utm_content=buffercf32a&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer (http://onlinelibrary.wiley.com/doi/10.1002/2017GL072910/abstract?utm_content=buffercf32a&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer)
Title: Re: Thwaites Glacier Discussion
Post by: sidd on April 07, 2017, 10:04:27 PM
That Seroussi paper on Thwaites is more hopeful that others. No collapse in 60 year. Some weaknesses in the model  are an essentially static ocean and atmosphere  (they repeat the 1992 ocean year every year of the simulation and 1979-2010 SMB and temperature), constant heat and salt transfer coefficients and lack of rifting. The advance in the paper is a realistic coupling underice cavities to the ocean.

I fear they are too optimistic, need more sophisticated model. I see Rignot is an author, and I wonder if he is backing away from some of his previous work showing faster retreat.

I think Mercer's intuition from 1968 is correct. The collapse will come when the midsummer 0C isotherm reaches the shelf.

sidd
Title: Re: Thwaites Glacier Discussion
Post by: Lennart van der Linde on April 08, 2017, 08:39:27 AM
In his talk in New Zealand that Jai Mitchell posted in the sea level thread Rignot indeed pointed to potential negative feedback at the cavities. Overall he stressed the MISI and didn't back away from his earlier work.
Title: Re: Thwaites Glacier Discussion
Post by: Tealight on April 10, 2017, 10:04:11 PM
The calved iceberg(1) is now visually detached on MODIS. The slightly smaller iceberg(2) right next to it moved a lot further out.
https://go.nasa.gov/2orQycz (https://go.nasa.gov/2orQycz)

The US National Ice Center tracks both icebergs as Iceberg B42 and Iceberg B43. The positions can also be seen on Polarview (select icebergs at the bottom)
http://www.polarview.aq//antarctic (http://www.polarview.aq//antarctic)
Title: Re: Thwaites Glacier Discussion
Post by: AbruptSLR on April 11, 2017, 07:10:28 PM
Just to keep track of the consequences of the recent calving of Icebergs B42 & B43 from the Thwaites Ice Tongue, I provide the attached overview image captured by Sentinel-1 on April 10 2017:
Title: Re: Thwaites Glacier Discussion
Post by: solartim27 on April 11, 2017, 07:36:29 PM
To go along with the bergs drifting off, there were several huge calvings along the glacier.  I've been watching these cracks growing for ages, but the developments were small, not worth posting.  They all went this week.  Kept the image full size, so you can zoom in any area you want to see.  Click to animate, 2.2 MB.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170411T041934_E729_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170411T041934_E729_S_1.final.jpg)   (73 Mb)

S1A_EW_GRDM_1SSH_20170225T044349_76BD_S_1.final.jpg    (62 MB)

(I cropped the original into a smaller file.  371 Kb)
Title: Re: Thwaites Glacier Discussion
Post by: solartim27 on April 11, 2017, 09:44:14 PM
Calving is easily seen on Worldview between the 9th and 10th, even with a cruddy image.  Over 10 miles of glacier can be seen moving.
Title: Re: Thwaites Glacier Discussion
Post by: AbruptSLR on April 13, 2017, 04:54:55 PM
To go along with the bergs drifting off, there were several huge calvings along the glacier.  I've been watching these cracks growing for ages, but the developments were small, not worth posting.  They all went this week.  Kept the image full size, so you can zoom in any area you want to see. 

solartim27,
Can you add the linked Sentinel-1 image from April 12 2017 to your animation sequence?

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170413T040314_FD28_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170413T040314_FD28_S_1.final.jpg)

Best,
ASLR
Title: Re: Thwaites Glacier Discussion
Post by: solartim27 on April 13, 2017, 10:55:09 PM
The matchup is not perfect, but it's close enough.  Doesn't seem to be a lot of change between the 11th to 13th.  Dates are 7, 11, 13 Apr.  3.2 MB, click to animate didn't work for me, had to right click and open in new window.

http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170413T040314_FD28_S_1.final.jpg (http://www.polarview.aq/images/105_S1jpgfull/S1A_EW_GRDM_1SSH_20170413T040314_FD28_S_1.final.jpg)

S1A_EW_GRDM_1SSH_20170411T041934_E729_S_1.final.jpg

S1A_EW_GRDM_1SSH_20170407T045217_E036_S_1.final.jpg
Title: Re: Thwaites Glacier Discussion
Post by: AbruptSLR on April 14, 2017, 12:06:17 AM
The matchup is not perfect, but it's close enough.  Doesn't seem to be a lot of change between the 11th to 13th.  Dates are 7, 11, 13 Apr.  3.2 MB, click to animate didn't work for me, had to right click and open in new window.


Thanks (I think I was looking at shadows between the 11th & the 12th)
Title: Re: Thwaites Glacier Discussion
Post by: Rick Aster on May 11, 2017, 05:49:01 PM
Rolling Stone has a feature story on Thwaites Glacier with background and context: http://www.rollingstone.com//politics/features/the-doomsday-glacier-w481260 (http://www.rollingstone.com//politics/features/the-doomsday-glacier-w481260)

Quote
"We like to think that change happens slowly, especially in a landscape like Antarctica," [Knut] Christianson tells me. "But we now know that is wrong."
Title: Re: Thwaites Glacier Discussion
Post by: Tealight on August 02, 2017, 12:07:51 AM
A close-up of Iceberg B42 & B43 which calved in March and traveled almost 100km north past the old iceberg tongue (north is on the left). It seems they won't get stuck and can travel freely into the open ocean to melt out over the coming years.
Title: Re: Thwaites Glacier Discussion
Post by: crandles on April 06, 2018, 12:17:00 AM
Antarctica 'gives ground to the ocean'
http://www.bbc.co.uk/news/science-environment-43627673

Re grounding line retreat

Quote
The new data-set confirms other observations that show the mighty Pine Island Glacier, one of the biggest and fast-flowing glaciers on Earth, and whose grounding line had been in major retreat since the 1940s, appears now to have stabilised somewhat.

The line is currently going backwards by only 40m/yr compared with the roughly 1,000m/yr seen in previous studies. This could suggest that ocean melting at the PIG's base is pausing.

Its next-door neighbour, Thwaites Glacier, on the other hand, is seeing an acceleration in the reversal of its grounding line - from 340m/yr to 420m/yr.
Title: Re: Thwaites Glacier Discussion
Post by: SteveMDFP on April 30, 2018, 08:50:50 PM
Article on research mission to Thwaites:

Boaty McBoatface leads £20m mission to melting Antarctic glacier
https://www.theguardian.com/environment/2018/apr/30/20m-study-to-investigate-collapse-risk-of-major-antarctic-glacier (https://www.theguardian.com/environment/2018/apr/30/20m-study-to-investigate-collapse-risk-of-major-antarctic-glacier)

"Any firm indication that the glacier could be responding to a warmer climate with faster icemelt could presage disaster for coastal areas of the globe, with the potential for sea-level rises some scientists put as high as 1.5m by the century’s end.

"One of the principal research vessels will be the RSS Sir David Attenborough, the £200m research ship originally voted to be christened Boaty McBoatface in an online poll two years ago. The joke name lives on in the ship’s remotely operated submarine...

The £20m will be used by the UK’s Natural Environment Research Council and the US National Science Foundation, involving about 100 scientists, in the biggest joint project by the two countries in Antarctica since the end of a mapping project in the late 1940s. Researchers from other countries, including South Korea, Germany, Sweden, New Zealand and Finland, will also contribute and the resulting science made available globally."

LiveScience has a similar article based on the above, with depressing comments from readers:
https://www.livescience.com/62435-thwaites-glacier-sea-level-study.html (https://www.livescience.com/62435-thwaites-glacier-sea-level-study.html)
Title: Re: Thwaites Glacier Discussion
Post by: AbruptSLR on April 30, 2018, 09:10:27 PM
There is a reason why Thwaites Glacier has been nicknamed the 'doomsday' glacier, and why research institutions keep spending more and more research dollars to study this important marine glacier.

Title: "Penn State researchers join international effort to study Antarctic ‘doomsday’ glacier"

https://stateimpact.npr.org/pennsylvania/2018/04/30/penn-state-researchers-join-international-effort-to-study-antarctic-doomsday-glacier/

Extract: "Researchers from Penn State University will be part of a major, international effort to better understand an Antarctic glacier, dubbed the “doomsday glacier” for its potential to contribute significantly to global sea level rise.

The Thwaites Glacier on the West Antarctic Ice Sheet is about the size of Pennsylvania. The threat of it collapsing is so significant that the National Science Foundation and the United Kingdom’s National Environmental Research Council today announced $25 million in funding for eight research efforts."
Title: Re: Thwaites Glacier Discussion
Post by: FredBear on January 18, 2019, 12:44:17 AM
British Antarctic Survey have been delivering supplies for research projects:-

https://www.bas.ac.uk/media-post/essential-cargo-delivered-for-science-on-thwaites-glacier
Title: Re: Thwaites Glacier Discussion
Post by: charles_oil on January 21, 2019, 12:40:55 AM
Thanks Fred for this - interesting articles - I assume / hope they will have some sort of live reporting (blog / diary) about activities which we can follow.  Scheduled to arrive late January and get started this season.


https://thwaitesglacier.org/news/mission-begins
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on January 25, 2019, 06:24:03 PM
A new crack runs through the Thwaites Ice tongue (it can't be fast sea ice as it moves every day) and a big portion is about to break off (direction indicated by arrows).
From EOSDIS worldview Jan 25, 2019
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on January 25, 2019, 08:07:02 PM
I have been watching this too for a while, it will be interesting to see how much of this area will become mobile this year.
It is worth scrolling back to 2002 on worldview to see how this looked before the Thwaites ice tongue broke off. Images are available back to March 2000 when this was clearly sea ice with a few icebergs frozen in. The grounding of the ice tongue in front of it then made it immobile. In 2013 much of the iceberg "rubble" cleared out in the eastern part of the area marked by Stephan. But now it is opening further to the west
Title: Re: Thwaites Glacier Discussion
Post by: FredBear on January 25, 2019, 08:56:05 PM
re:- Reply 33: British Antarctic Survey delivery of 600t of materials:-

Just looked up the delivery point since things are moving so fast at PIG/Thwaites - the Stange Ice Shelf at the base of the Antarctic Peninsular! Not exactly local  .   .   .
Title: Re: Thwaites Glacier Discussion
Post by: Adam Ash on January 26, 2019, 03:01:16 AM
So is it...

Chef “Bert! Can you get me another can of beans from the depot, please, old chap?”
Bert, glumly “I’m going outside. I may be some time.”
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft on January 26, 2019, 01:28:22 PM
Gif from EOSDIS Worldview (Aqua/Modis)

From 01.01. to today.
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on January 26, 2019, 02:45:32 PM
for a more detailed view I have been waiting for a clear image on Sentinel but now I just used the one from 10.1.
This isn't as up to date as the images posted above but I think it shows the stresses of faster glacier movement in the centre and slower movement on both sides.
comparison is between 25.1.2017 and 10.1.2019
orientation is different from worldview!
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on January 26, 2019, 03:14:00 PM
Thank you for this animation. Is it possible to estimate the velocity from that movement and compare it with values from, say 5-10 years, ago?
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on January 26, 2019, 03:26:00 PM
good point, I should have included a scale!
https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=-75.01204475258349&lng=-108.380126953125&zoom=8&preset=1-NATURAL-COLOR&layers=B01,B02,B03&maxcc=52&gain=0.3&gamma=1.3&time=2018-07-01%7C2019-01-10&atmFilter=&showDates=false (https://apps.sentinel-hub.com/sentinel-playground/?source=S2&lat=-75.01204475258349&lng=-108.380126953125&zoom=8&preset=1-NATURAL-COLOR&layers=B01,B02,B03&maxcc=52&gain=0.3&gamma=1.3&time=2018-07-01%7C2019-01-10&atmFilter=&showDates=false)
shows a 10km bar in the right hand bottom corner which is about as long as the longest red lines
doing this more acurately is a bit pointless because the Sentinel-2 images don't go any further back.
If wipneus could dig out some Landsats....
There are charts with colour coded glacier speed in the PIG thread I think
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft on January 26, 2019, 03:36:07 PM
Great work Andreas T! Thanks.
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on January 26, 2019, 03:51:16 PM
Instead of trawling through ASLR's posts over many many pages of the PIG thread which has loads of relevant information I just googled Pelto Thwaites glaicier and hey presto:
https://blogs.agu.org/fromaglaciersperspective/files/2012/10/thwaites-bedrock-2.jpg (https://blogs.agu.org/fromaglaciersperspective/files/2012/10/thwaites-bedrock-2.jpg)
which show 3000m /a speeds published in 2001
Title: Re: Thwaites Glacier Discussion
Post by: oren on January 26, 2019, 05:51:06 PM
Thanks for the animations. Thwaites is such a huge mess of sea ice, separated tongue, multitude of calved but lingering bergs, and the main glacier itself. Much more complicated than the PIG, and very difficult to make visual heads or tails of it. Every graphic helps, especially those showing animated movement.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on January 27, 2019, 09:14:32 PM
There is a new big crack going through the fast ice of the Thwaites Ice Tongue that separates Thwaites glacier (to the south) and thicker ice originated from Thwaites Glacier (to the north). I checked Sentinel images from earlier January and late December and the crack was only very partially visible at that time. The crack goes through the thinner sea ice, not through any of the bergs.
I wonder whether the whole thong can separate due to currents and winds in the next days or weeks or whether the northern part will stay where it is because it is grounded in shallow waters. Any idea?
See attached figure, crack again indicated by yellowish green line (the thicker parts of it south of the crack so you can directly see it). The thicker the line, the wider the crack.
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on January 27, 2019, 09:32:40 PM
I thought the broken off glacier tongue was grounded on an underwater ridge (moraine of the glacier during ice age?)
but the animated comparison with 2017 I posted above shows movement of the entire huge iceberg northward. I doubt that the sea ice could hold the glacier in place over so many summers if it was otherwise free to move. The "fetch" of something this size when driven by wind or water must be huge.
Maybe we will find out soon if this area between the berg and land disintegrates this austral summer.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on January 28, 2019, 05:59:41 PM
New big movement in the Thwaites fast ice / ice tongue / ice mélange (call it what you like). This time it goes further than any time this austral summer (orange line) and comes close to the calving front of Thwaites glacier (approx. 20-30 km). I also marked with a thin dotted yellowish green the position of the crack I posted yesterday (please note that Sentinel and EOSDIS use different orientations).
See attached image.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on January 28, 2019, 06:37:41 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.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan 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.
Title: Re: Thwaites Glacier Discussion
Post by: sidd 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
Title: Re: Thwaites Glacier Discussion
Post by: solartim27 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
Title: Re: Thwaites Glacier Discussion
Post by: vox_mundi on January 31, 2019, 12:50:38 PM
From the jpl article

(https://www.sciencealert.com/images/2019-01/031-thwaites-glacier-cavity-antarctica.gif)
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft 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
Title: Re: Thwaites Glacier Discussion
Post by: Stephan 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.
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T 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.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan 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...
Title: Re: Thwaites Glacier Discussion
Post by: Tealight 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.



Title: Re: Thwaites Glacier Discussion
Post by: Andreas T 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?
Title: Re: Thwaites Glacier Discussion
Post by: dingojoe 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. 
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft on February 02, 2019, 07:16:20 PM
Hey dingojoe,

you linked well. Good find! :)

Title: Re: Thwaites Glacier Discussion
Post by: Tealight 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.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan 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
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on February 03, 2019, 09:38:28 PM
(https://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=72.0;attach=96106;image)
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 (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 (https://go.nasa.gov/2HOnreJ) as seen on worldview
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T 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
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft on February 06, 2019, 06:50:56 PM
B22A moved a bit!
Title: Re: Thwaites Glacier Discussion
Post by: Gray-Wolf 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?
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft on February 09, 2019, 09:37:47 AM
The ice tongue behind B22A is breaking up now.
Title: Re: Thwaites Glacier Discussion
Post by: Bernard 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?
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft 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
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft on February 09, 2019, 12:30:11 PM
Bernard,

here you can find the position of iceberg B22A >> https://worldview.earthdata.nasa.gov/?p=antarctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,MODIS_Terra_Sea_Ice(hidden),MODIS_Aqua_Sea_Ice(hidden),MODIS_Aqua_Brightness_Temp_Band31_Night(hidden),MODIS_Aqua_Brightness_Temp_Band31_Day(hidden),MODIS_Terra_Brightness_Temp_Band31_Night(hidden),MODIS_Terra_Brightness_Temp_Band31_Day(hidden),VIIRS_SNPP_DayNightBand_ENCC(hidden),Coastlines&t=2011-08-30-T00%3A00%3A00Z&z=3&v=-2023193.48151667,-770746.8934159877,-1252121.48151667,-326842.8934159877&e=EONET_2736,2011-08-30
Title: Re: Thwaites Glacier Discussion
Post by: Bernard 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?
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft 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. :)
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft 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.
Title: Re: Thwaites Glacier Discussion
Post by: Bernard 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. ;)
Title: Re: Thwaites Glacier Discussion
Post by: Stephan 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...
Title: Re: Thwaites Glacier Discussion
Post by: Stephan 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.
Title: Re: Thwaites Glacier Discussion
Post by: Bernard on February 09, 2019, 11:35:42 PM
Thanks Stephan for the annotations on the images! Added value, much appreciated  ;)
Title: Re: Thwaites Glacier Discussion
Post by: oren on February 10, 2019, 12:03:46 AM
Thanks Stephan for the annotations on the images! Added value, much appreciated  ;)
+1
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T 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 (https://www.natice.noaa.gov/pub/icebergs/Iceberg_Tabular.pdf)

Title: Re: Thwaites Glacier Discussion
Post by: Stephan on February 10, 2019, 08:53:22 AM
OK, I will keep that in mind. Sorry for not having it thoroughly checked.
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft 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
Title: Re: Thwaites Glacier Discussion
Post by: Often Distant on February 12, 2019, 01:14:39 PM
One day. Strong wind. A significant breaking apart of a large floe.(https://s2.gifyu.com/images/nasa-worldview-2019-02-10T00_00_00Z-to-2019-02-11T00_00_00Z.gif)
Title: Re: Thwaites Glacier Discussion
Post by: Tor Bejnar 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)
Title: Re: Thwaites Glacier Discussion
Post by: Stephan 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!
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on February 28, 2019, 04:00:18 PM
This (marked by X) is where the Nathaniel B Palmer is today according to sailwx, S 74°54' W 107°18'. It probably be a while before we hear details of the research there, but the blog posts have a lot of information.
North marked for orientation.
https://thwaitesglacier.org/blog (https://thwaitesglacier.org/blog)
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on February 28, 2019, 05:44:04 PM
Thank you very much for the link to the "Snow on Ice" expedition.
Title: Re: Thwaites Glacier Discussion
Post by: b_lumenkraft on March 02, 2019, 05:08:14 PM
4 years of @ThwaitesGlacier ice tongue from @CopernicusEU #sentinel1 satellite imagery showing how this chaotic ice tongue has become a collection of icebergs glued together by sea ice.

Link >> https://twitter.com/StefLhermitte/status/1101870380623511552
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on March 03, 2019, 09:10:25 AM
Thank you very much for this linked video.
It is intersting to see that the ice in the upper left corner is so slowly moving compared to the Thwaites iteself.
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on March 03, 2019, 08:05:27 PM
this observation is confirmed by the ice velocities for the thwaites ice tongue posted further upthread
The reason lies in the shallower depth below the ice surface both upstream and downstream of the grounding line shown in the bathymetry posted by tealight

...

...

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.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on March 03, 2019, 09:14:46 PM
As for the Pine Island Bay (see my posting in that thread) also the Thwaites area was completely clear today which offered an analysis of the EOSDIS picture.
The limit between ice shelf and ice mélange is roughly indicated by the orange line. The distance to the calving front is now < 10 km. Its continuation to NNW (in blue) shows the same "crack" I reported about two weeks ago. It also seems to be the boundary between ice shelf/fast ice and the more moblie ice mélange NE of it.
Iceberg B-22-A has moved very slowly west-/northwestward (compared to its position on Feb. 04). And it has lost small pieces off its western shore (not on the picture). Many of the icebergs lost there stay in that area and seem to be grounded.
Another bigger grounded iceberg N of the tip of Thwaites Ice Tongue is circled in pale magenta. Imo these grounded bergs can cause floating sea ice to be stopped and help the formation of new sea ice/fast ice in the next freezing season around them.
The "outer ice field" has completely disintegrated, but the melting season is probably over, so that a melt-out of the sea ice between the icebergs will not take place anymore.
The green line differs between very slowly (or not moving at all) moving ice of the Thwaites Ice Tongue E of it and the area of faster movement of the many icebergs that Thwaites glacier endlessly produces (W of this line).
Comparing Thwaites and Pope the latter is much slower moving (a month difference almost does not show a change of position of individual features).

See attached picture
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on March 15, 2019, 08:37:05 PM
This is from the Thor cruise blog https://thwaitesglacieroffshoreresearch.org/news/2019/3/12/thwaites-glacier-there-and-gone (https://thwaitesglacieroffshoreresearch.org/news/2019/3/12/thwaites-glacier-there-and-gone) and shows some detailed bathymetry off the Twaites ice tongue and some pretty impressive sea floor coring sites (https://static1.squarespace.com/static/5ba299727c93278b5b0e72f5/t/5c885acd41920263418d9d6c/1552440018778/16+TG+9thMar2019_GIS_map.jpg?format=750w)
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on March 15, 2019, 11:20:09 PM
Thank you for that useful information!
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on March 16, 2019, 06:32:59 PM
from the same report come this photo which shows some pretty thick icefloes. That freeboard looks like 2m in places. I guess it is some of the ice which has been sitting between the icebergs of the Thwaites ice cube maker for years. a large part of that freeboard will of course be snow (multiyear firn I guess) of lower density so not a guide to below waterline thickness
(https://static1.squarespace.com/static/5ba299727c93278b5b0e72f5/t/5c885843eb39313d5ad9edf1/1552439374251/14+TG+seal+tag+with+emperors.JPG?format=750w)
Title: Re: Thwaites Glacier Discussion
Post by: solartim27 on March 19, 2019, 06:03:23 PM
I wonder if the expeditions got a close up of this good sized calving and breakup.  Shots from Polarview Mar 3 to 18th, though the breakup happened a bit earlier.
Title: Re: Thwaites Glacier Discussion
Post by: Sleepy on March 19, 2019, 08:50:28 PM
solartim, I haven't seen any pictures but according to Anna Wåhlin at the University of Gothenburg who took part with HUGIN on N.B. Palmer, they had a bit of drama just after retrieving the AUV when the ice suddenly pushed out a couple of kilometres in just a couple of hours. From an interview on Swedish radio last thursday.

She also stated that they wasn't sure about what this meant and that it could be a natural cycle, they only had data twenty years back.

I fail to understand that last part of her comment.
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on March 20, 2019, 07:57:50 AM
This is from the Thor cruise blog https://thwaitesglacieroffshoreresearch.org/news/2019/3/12/thwaites-glacier-there-and-gone (https://thwaitesglacieroffshoreresearch.org/news/2019/3/12/thwaites-glacier-there-and-gone) and shows some detailed bathymetry off the Twaites ice tongue and some pretty impressive sea floor coring sites (https://static1.squarespace.com/static/5ba299727c93278b5b0e72f5/t/5c885acd41920263418d9d6c/1552440018778/16+TG+9thMar2019_GIS_map.jpg?format=750w)
The ice position in this  looks like the last clear world view image on Feb 17. The ice edge probably stayed in that position enabling the NBP to reach all the places shown in the track. On the Mar 2. icebergs started to come off the mix of begs and sea ice and 3rd  and 4th this loosening spread further towards the actual calving front of the glacier. The icebergs set loose by this spread into the water crisscrossed by the NBP in the trackmap posted above (without dates which is a bit disappointing) I dont think any ship would want to be among this stuff when they would have to dodge multiple icebergs and thick sea ice shifting rapidly.
A clear out of the bergs has happened fairly recently so her comment was probably a general statement for an audience with isn't expected to know much about this topic.
Title: Re: Thwaites Glacier Discussion
Post by: Sleepy on March 20, 2019, 08:09:39 AM
She also said that they were very careful about where the ice edge was but was still surprised by the surge.

Edit; the recovery of HUGIN took place on March 1st.

Edit2: ASLR just posted an article from the RollingStone that included an image with N.B. Palmers locations around that event:
https://forum.arctic-sea-ice.net/index.php/topic,2205.msg192455.html#msg192455 (https://forum.arctic-sea-ice.net/index.php/topic,2205.msg192455.html#msg192455)
The "drama" was obviously not that dramatic aboard.
I like Alley's analogy: “if Thwaites were a car, you could say that it has lost part of its bumper. And, while that’s not hugely important, it is part of a pattern that is pointing toward larger changes to come.”
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on March 21, 2019, 10:27:22 PM
One consequence of this breakout is visible on the latest EOSDIS picture.
After nearly half a month of mostly complete cloud coverage, a glimpse between the clouds reveals that open water has almost reached the calving front of the Thwaites glacier (it is approx. parallel to the grey line ("2010 grounding line")) and marked in pale magenta.
I wonder whether the next days will allow a deeper look onto what happened there and whether the calving front is really affected.
See attached picture.
Title: Re: Thwaites Glacier Discussion
Post by: steve s on March 22, 2019, 05:08:55 AM
For a comparison with the previous post with respect to the retreat of the Thwaites Glacier's ice front, see the ice front on March 4, 2013 in the attached image. The variation in the pattern sea ice loss from year to year is a mystery to me.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on April 07, 2019, 10:21:08 PM
Weeks of cloudiness in Thwaites area. With Sentinel and EOSDIS - no chance of evaluation what is going on there.
Today the western edge of iceberg B-22-A is visible and I calculated its WNW movement between Feb 4 and Apr 7. It has moved around 3-4 km since then which is in my opinion a sign that it has melted a little bit from below and has lost some of its pinning points.
Title: Re: Thwaites Glacier Discussion
Post by: pietkuip on June 22, 2019, 03:22:50 PM
https://interactive.pri.org/2019/05/antarctica/submarine-glacier-tour.html

An AUV (autonomous underwater vehicle) was underneath the Thwaites ice shelf.
Title: Re: Thwaites Glacier Discussion
Post by: kassy on July 10, 2019, 08:41:05 PM
This Is The Most Important Antarctic Glacier The World Needs to Watch Right Now

in western Antarctica, a glacier the size of Florida is losing ice faster than ever before. Sections of the Thwaites Glacier are retreating by up to 2,625 feet (800 metres) per year, contributing to 4 percent of sea-level rise worldwide.

That ice loss is part of a broader trend: The entire Antarctic ice sheet is melting nearly six times as fast as it did 40 years ago.

In the 1980s, Antarctica lost 40 billion tons of ice annually. In the last decade, that number jumped to an average of 252 billion tons per year.

Now, authors of a new study report that over the last six years, the rate at which five Antarctic glaciers slough off ice has doubled. That makes the Thwaites Glacier a melting time bomb.


https://www.sciencealert.com/antarctic-glacier-on-track-to-irreversibly-melt-which-could-trigger-a-chain-reaction
Title: Re: Thwaites Glacier Discussion
Post by: vox_mundi on September 02, 2019, 11:31:36 PM
Vintage Film Shows Thwaites Glacier Ice Shelf Melting Faster Than Previously Observed
https://phys.org/news/2019-09-vintage-thwaites-glacier-ice-shelf.html

Newly digitized vintage film has doubled how far back scientists can peer into the history of underground ice in Antarctica, and revealed that an ice shelf on Thwaites Glacier in West Antarctica is being thawed by a warming ocean more quickly than previously thought. This finding contributes to predictions for sea-level rise that would impact coastal communities around the world.

... The researchers made their findings by comparing ice-penetrating radar records of Thwaites Glacier with modern data. The research appeared in Proceedings of the National Academy of Sciences Sept. 2.

"By having this record, we can now see these areas where the ice shelf is getting thinnest and could break through," ... "This is a pretty hard-to-get-to area and we're really lucky that they happened to fly across this ice shelf."

The researchers identified several features beneath the ice sheet that had previously only been observed in modern data, including ash layers from past volcanic eruptions captured inside the ice and channels where water from beneath the ice sheet is eroding the bottom of ice shelves. They also found that one of these channels had a stable geometry for over 40 years, information that contrasts their findings about the Thwaites Glacier ice shelf, which has thinned from 10 to 33 percent between 1978 and 2009.

Dustin M. Schroeder el al., "Multidecadal observations of the Antarctic ice sheet from restored analog radar records, (http://)" PNAS (2019)
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on September 03, 2019, 10:39:51 PM
Thank you for posting this  :)
Title: Re: Thwaites Glacier Discussion
Post by: sidd on September 04, 2019, 08:22:11 AM
The Schroeder paper on Thwaites is interesting.

doi: 10.1073/pnas.1821646116

"In contrast to the stability of the FRIS basal channel, a similar comparison between a 1978 SPRI profile from the Amundsen Sea Embayment (ASE) of West Antarctica with 2 2009 Operation Ice Bridge (OIB) radar-sounding profiles (27) reveals dramatic changes in the subsurface geometry of the remnant eastern ice shelf of Thwaites Glacier, West Antarctica (Fig. 10), which we refer to hereafter as the Thwaites Eastern Ice Shelf (TEIS). In general, the TEIS begins to float seaward of a potentially stabilizing inland ridge and regrounds on an offshore ridge (28)(Fig. 10). The TEIS currently buttresses a portion of the ASE grounding zone along the Walgreen Coast, which is the boundary between Thwaites Glacier and Pine Island Glacier, 2 of the most rapidly changing and potentially unstable glaciers in Antarctica(2, 29). This ice shelf was previously dynamically coupled to the faster-flowing tongue of Thwaites Glacier. However, after 2006, the section connecting the ice shelves collapsed, leading to divergent flow histories (29, 30). This dynamic event caused TEIS to become the only portion of the ASE with decelerating ice flow, in part due to the portion grounded on an offshore ridge(28). "

"By comparing the thickness of the floating and the regrounded portions of the iceshelf interpreted in the radargrams (Fig. 10), we estimate that TEIS lost∼115±62 m of ice thickness (∼10–33%) from 1978 to 2009 (Fig. 10E)(Methods). This contrasts with the regrounded portion of the shelf, which appears stable within our uncertainty estimate (∼19±43 m) (Fig. 10F) over the same period (Methods), suggesting that basal melting rather than dynamic thinning may be the primary cause of the observed thickness change in the floating portion of TEIS. "

"These results suggest that the reduced ice velocities of TEIS during the past decade will not serve to stabilize the Walgreen Coast (29), but instead the TEIS will undergo further thinning and unpinning (28) that could act to destabilize the rest of the ice shelf in the coming decades."

sidd
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on September 04, 2019, 10:24:12 PM
Thank you for that information.  :)
So we should all have an eye on TEIS in the coming years.
Title: Re: Thwaites Glacier Discussion
Post by: sidd on September 05, 2019, 08:40:55 PM
Add fig 10 from Schroeder.

sidd
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on September 12, 2019, 10:31:41 PM
Iceberg B-22 also has moved in this Austral winter. I checked at three different places, and its WNW movement is in the range of slightly above 2 km in the time between Feb 03 and Sep 10, 2019. Compared to last year this movement has become faster. I guess it must have lost some more pinning points. I have no detailed knowledge of the bathymetry of the sea, therefore I do not know whether a further movement into that direction will end up in a dead end street ?!?
Title: Re: Thwaites Glacier Discussion
Post by: gerontocrat on September 17, 2019, 09:33:47 PM
The data on Thwaites comes from a Jan 2019 Paper - https://www.pnas.org/content/116/4/1095
Four decades of Antarctic Ice Sheet mass balance from 1979–2017

They have extracted from a mass of previous studies, and they are confident enough on discharge data to produce analyses by years for data on nearly 200 sub-regions of Antarctica. But the SMB (mainly snowfall) data is not analysed by year, there are only 39 year totals.

But I am not a scientist worried about peer review. So on the attached graphs I have allocated SMB over years by the yearly average. I did this to show how a relatively small percentage annual increase in discharge leads to a high percentage increase in net mass loss.

In the 39 years of the analysis, discharge is estimated at just over 3,800 GT, but with just over  3,200 GT of SMB gain, net mass loss is only just over 600 GT. Half of that may well have happened in the first 30 years, half in the last 9 years.

The current annual net mass loss guesstimate is 37 GT a year. A pure guess at the future gives that increasing to around 60 GT per year in 10 years.
Title: Re: Thwaites Glacier Discussion
Post by: baking on September 26, 2019, 04:27:59 PM
Iceberg B22-A has shifted between September 22 and 26.  It is 44 by 24 nautical miles in size and broke off from Thwaites Ice Tongue in 2002 and drifted about 50 km to where it is grounded today.

What's interesting is that is seems to have caused the end of Thwaites Ice Tongue, about one quarter of its length, to separate slightly from the rest.

B22-A shifted in July 2018 and caused the calving of Iceberg B-45 from the nearby Crosson Ice Shelf. https://www.natice.noaa.gov/doc/PR%20-%2020180730%20-%20B-45%20Discovery.pdf

What's puzzling is the mechanism that could cause an effect on the Tongue 50 km away.  The sea between the Tongue and B22-A is covered with sea ice at this time of year so it is possible that the shifting sea ice eased pressure that was holding back the Tongue.  Although it doesn't seem likely, the appearance is that the Tongue was pulled by the sea ice because the remaining 75% of the Tongue did not move as much as the 25% at the end did.  In other words, it looks as if it was pulled away.

Below are links to full resolution images, six days apart.  A small part of B22-A is seen at the bottom edge of the frame.  Please Note that PolarView only hosts these images for 30 days.

https://www.polarview.aq/images/105_S1jpgfull/S1A_IW_GRDH_1SSH_20190926T043625_648C_S_1.final.jpg

https://www.polarview.aq/images/105_S1jpgfull/S1B_IW_GRDH_1SSH_20190920T043542_1AC1_S_1.final.jpg
Title: Re: Thwaites Glacier Discussion
Post by: baking on September 27, 2019, 04:47:52 AM
Here is a high resolution detail of the separation of the end of the Thwaites Ice Tongue between Sept. 20 and 26.  Motion on the right is the normal 5km/year.  Motion on the left represents a separation of about 200 meters over the course of six days across the breadth of the tongue.
Title: Re: Thwaites Glacier Discussion
Post by: baking on September 27, 2019, 05:31:00 AM
Here the image is scaled down 50% so the movement of the surrounding sea ice can be seen.
Title: Re: Thwaites Glacier Discussion
Post by: baking on September 27, 2019, 06:10:19 AM
Here's a final image scaled down by a factor of 8.  A tiny portion of B22-A can be seen at the bottom edge of the image.  The movement of sea ice over a vast region, along with isolated icebergs, iceberg formations, and a huge iceberg almost the size of Rhode Island cannot be a mere coincidence.

Ocean currents and/or wind had to have been the moving force, but the shifting position of B22-A must have allowed the sea ice behind it to follow along bringing smaller icebergs and formations with it.

It also raises the question of whether the fate of Thwaites Ice Tongue can be tied to Iceberg B22-A.  If B22-A were to ever unground and drift off, would the ice tongue become even more vulnerable?
Title: Re: Thwaites Glacier Discussion
Post by: blumenkraft on September 27, 2019, 08:31:25 AM
This is going to be an exciting Antarctic summer...
Title: Re: Thwaites Glacier Discussion
Post by: oren on September 27, 2019, 11:37:37 AM
Thanks for these updates, baking, especially for the multiple scales - making it much clearer. Seems like a serious shift in Thwaites, I hope it calms down again.
Title: Re: Thwaites Glacier Discussion
Post by: baking on September 27, 2019, 11:51:29 AM
A note on scales.  As far as I can figure, the PolarView high resolution images from Sentinel-1 are 20 meters per pixel.  (The Sentinel-1 specs are 10m/pixel, but I think PolarView reduces file sizes by producing a lower resolution.)  That makes the sizes for the above three pictures 14km, 28km, and 112km on a side.

The distance from Iceberg B-22A to Thwaites Ice Tongue is about 100km at their closest points.
Title: Re: Thwaites Glacier Discussion
Post by: Susan Anderson on September 27, 2019, 04:17:02 PM
Goodness gracious. I know it's a visual artifact, but I can't help being reminded of a shaking puddinglike entity. Since this is the beginning of the warming season, I would guess hope for inaction is sadly unlikely.
Title: Re: Thwaites Glacier Discussion
Post by: nanning on September 27, 2019, 04:40:18 PM
Nice one Susan. Thanks for all the images that your post invoked  ;D
Action it will be then. Or is there no hope? (whatever 'hope' means)
Title: Re: Thwaites Glacier Discussion
Post by: steve s on September 27, 2019, 05:09:52 PM
Another possibility is that we are seeing an artifact of instrument calibration or image alignment associated with stitching together pixels captured from different angles by a moving instrument. Perhaps the next image will offer a useful comparison.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on September 27, 2019, 05:23:12 PM
Thank you baking for this information. I'll keep an eye on B-22A, Thwaites Ice Tongue, Eastern Thwaites Ice Shelf and the fast ice surrounding them in the next months.
Title: Re: Thwaites Glacier Discussion
Post by: baking on September 27, 2019, 06:53:15 PM
Another possibility is that we are seeing an artifact of instrument calibration or image alignment associated with stitching together pixels captured from different angles by a moving instrument. Perhaps the next image will offer a useful comparison.

I know my immediate thought was that it was an artifact, but on closer look there is no evidence for it.  As for waiting for another image, here is a comparison of two images, different from the previous two, taken on 9/22 and today, 9/27.  They are from wider view images and are therefore at a lower resolution than the previous images, but they show they same separation.
Title: Re: Thwaites Glacier Discussion
Post by: blumenkraft on September 27, 2019, 06:59:38 PM
Another possibility is that we are seeing an artifact of instrument calibration or image alignment associated with stitching together pixels captured from different angles by a moving instrument. Perhaps the next image will offer a useful comparison.

I don't think so either. You clearly see some icebergs not moving (likely grounded). A killer argument for this not being optical issues IMHO.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on September 27, 2019, 09:24:32 PM
And, in addition, if this were an optical artifact or due to processing problems, there would be at least some icebergs that partly move and partly don't. But this animation clearly shows that the moving and the non-moving parts are all divided by cracks between the icebergs (scission line). So this is some sense "digital". Either they move fast (left from the scission line) or very slow (right from the scission line), apart for some "not moving at all" grounded icebergs.
Title: Re: Thwaites Glacier Discussion
Post by: oren on September 27, 2019, 11:31:18 PM
This must have been an extremely strong pull, with the thick sea ice of September (SH) acting as the rope.
On the positive side, I keep thinking (naively) if B-22 calved in 2002 and its sub-berg is still stuck around due to being grounded, perhaps Thwaites will have a hard time collapsing quickly with an iceberg armada, as one huge iceberg could delay the whole process by a decade or two
Title: Re: Thwaites Glacier Discussion
Post by: baking on September 28, 2019, 01:00:36 AM
On the positive side, I keep thinking (naively) if B-22 calved in 2002 and its sub-berg is still stuck around due to being grounded, perhaps Thwaites will have a hard time collapsing quickly with an iceberg armada, as one huge iceberg could delay the whole process by a decade or two

The way I look at it, B-22 broke loose in 2002, but it was fully formed and floating while still attached to grounded ice in 1992.  However it took 10-20 years to form, which means that ice has been floating for 40-50 years.  The old "Thwaites Tongue Iceberg" floated for at least 75 years before breaking up around 1990.  Meanwhile the newer ice in the Tongue floats for about 6 years before breaking up.  This is evidence to me that the Tongue ice is getting thinner.

Couple that with the recent analysis that the Thwaites Eastern Ice Shelf has thinned 23% since the 1970's and I'm not holding out much hope that the process will be delayed by much.

https://www.pnas.org/content/116/38/18867
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on September 28, 2019, 09:39:16 PM
I compared the Sentinel pictures from Sep 14 with Sep 27, 2019.
On the SE edge of the Thwaites Eastern Ice Shelf new cracks (green lines) grew in the last two weeks, generating two new icebergs, each around 1 km² in size.
To the east four icebergs float in the sea ice (circled in orange), turned around by 90°. So you can easily see their internal structure with a darker strip, probably weaker ice, which appears darker because these strips are shaded.
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on September 28, 2019, 09:47:11 PM


......

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.
Oren, it is worth looking through the thread for information on this.
The reason the broken off ice tongue has been stuck for so many years is the relatively shallow dept there. This does not stop more recently calved bergs from leaving the area and meting out further north. B22 does not melt in situ because the upper 300m of water are cold, warmer more salty water is found beneath that layer. Therefore this water reaches the grounding line of Thwaites via a deeper channel east of the stranded tongue. For calved ice to obstruct this water it would have to pile up much higher than the glacier surface. I can't see how it would do that.
Title: Re: Thwaites Glacier Discussion
Post by: oren on September 29, 2019, 06:41:17 AM
Thanks for these responses, Tealight and Andreas.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on October 05, 2019, 09:48:08 PM
The disintegration of the tip of Thwaites Ice Tongue continues. I analysed two pictures from Sentinel on Feb 09, 2019 and Oct 04, 2019 (see attached photographs). I marked the movements on the latter picture, together with scission lines (in red and blue) and zones of fragmentation (yellow circled). Longer/stronger arrows mean faster movement. All movements are "fixed" to the intrinsic movement of the whole ice tongue.
For orientation: N is up, to the right follows the Thwaites Eastern Ice Shelf. The picture has a size of approx. 36x19 km
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 06, 2019, 12:25:40 AM
All movements are "fixed" to the intrinsic movement of the whole ice tongue.

The important fact about the Tongue to understand is that it is not entirely free floating.  There is an underwater ridge under the end of the tongue and there are peaks at various points that slow down or ground the movement of icebergs passing over them.  The only way to understand the movements of the Tongue is to view its motion on a fixed reference to see the effects of these peaks.

For example, view this GIF in full-screen and try to place your cursor on the spot that you think is causing the icebergs to drag and cause other icebergs to backup behind them and to split off from the rest of the Tongue: https://twitter.com/StefLhermitte/status/1101870380623511552

I don't want to influence your observation, so I will leave you to find it and then we can talk about the consequences for the Tongue going forward.
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 06, 2019, 01:47:58 AM
Spoiler Alert!

Do the exercise in the above post first to see if you come to the same or a different conclusion than I do.  I have identified the approximate locations of four potential peaks in the picture below.  They are in order of importance.  Only the first two can be identified from the 4-year GIF, but the second one may be hard to pick out without knowing where it is.  The other two, lesser peaks, can be detected from a close viewing of the last eight months of Sentinel images.

1.  The iceberg currently at this location has been grounded for over a year, going back to September 2018.  With all the movement and chaos going on around it, that berg has not budged one bit.  The only possible explanation is a fairly high peak under it, which it is currently grounded on.  Before that time, the peak was probably responsible for causing two separate rows of icebergs to break away from the Western side of the Tongue in 2017 resulting in a substantial narrowing of the Tongue.

2.  A peak at this location is beginning to have a larger effect.  When Iceberg B-22A shifted during Sept. 22-26, the sea ice between it and the Tongue moved with it, along with the tip of the Tongue causing the rift Stephen has labeled in blue.  The most likely explanation is that this was built up compression from the Tongue during the Southern Hemisphere winter pushing against the thicker sea ice that was released when B-22A shifted.  The Eastern side of the Tongue expanded more naturally and pushed the rest of the tip to the North while the Western side of the Tongue was held by by Peak 2 causing the rift just to the North of it.

Peak 2 is also probably responsible for Stephen's red rift to the South that may cause a further narrowing of the Tongue in the near future.  There is a second parallel rift forming next to it which may also come into play.  The actual motion of the Tongue is shown roughly with the white arrow.

Peaks 3 and 4 are shown for completeness.  I don't expect either one to have a substantial effect on the Tongue going forward.

3.  The thicker of the two icebergs off the Northwestern corner of the Tongue has apparently been grounded ever since it broke off from the Tongue, but it is most likely about to float free since it has almost passed over it's original grounding point.  Its narrower companion berg does not seem to be grounded, but only sheltered by the other one.

4.  A peak can be detected here from the splitting of icebergs as they pass over it.  There is no sign that they are grounded enough to affect the movement of nearby icebergs.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on October 06, 2019, 08:17:09 AM
Thank you baking for this additional information. And a "Like" earned.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on October 06, 2019, 08:25:44 AM
I don't want to influence your observation, so I will leave you to find it and then we can talk about the consequences for the Tongue going forward.
Thank you for the Stef Lhermite twitter link with the wonderful video.

I have a general question:
With further warming of the planet Thwaites Glacier will probably further enhance its speed. Will that cause icebergs that are thicker as they are now, which will create further grounded icebergs or will the calving further upstream give the calved and glued-together icebergs enough time to melt from below which will make them thinner in the end which will cause less icebergs thick enough to get grounded in the shallow waters?
Title: Re: Thwaites Glacier Discussion
Post by: blumenkraft on October 06, 2019, 09:06:37 AM
BTW there was a minor calving also.
Title: Re: Thwaites Glacier Discussion
Post by: blumenkraft on October 06, 2019, 09:14:39 AM
I have a general question:
With further warming of the planet Thwaites Glacier will probably further enhance its speed. Will that cause icebergs that are thicker as they are now,

I don't think so. Keep in mind the grounding line is also retreating meaning upwelling warm waters would thin out the tongue further land inwards giving the ice more time to thin before they reach the shallow sea.

Hope that makes sense.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on October 06, 2019, 09:17:40 AM
blumenkraft, your answer does make sense to me.
And thank you for the calving information. I didn't have the time to study Thwaites calving front in detail so far.
Title: Re: Thwaites Glacier Discussion
Post by: FredBear on October 06, 2019, 03:31:47 PM
The thing about Thwaites is that it produces a raft of bergs that often don't topple over but move as one mass. The glacier seems to preferentially crack the ice vertically but in wide enough segments that they don't roll over as they run aground in relatively shallow water.
In comparison, Pine Island Glacier produces a more uniform berg that drifts away as a unit but sometimes shatters or breaks up later, not being impeded by shallow seas.
I notice that this year the break-up is starting earlier near the glacier fronts and the ice drifting north is filling the areas that have been more open in the last couple of years. Also that the nearby outer edge of the drifting Antarctic ice is closer to the continent this year, I wonder if the summer melt will hit harder?
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 06, 2019, 03:51:32 PM
I have a general question:
With further warming of the planet Thwaites Glacier will probably further enhance its speed. Will that cause icebergs that are thicker as they are now,

I don't think so. Keep in mind the grounding line is also retreating meaning upwelling warm waters would thin out the tongue further land inwards giving the ice more time to thin before they reach the shallow sea.

Hope that makes sense.

The way I think of it is that there is this massive pile of ice and snow that is the West Antarctic Ice Sheet.  The weight of all that ice and snow is causing a slow and steady flow at the edges.  As a first approximation, assume that the flow of ice into the glacier is constant.  The first result of faster flow would be thinner ice.  For example, the maximum speed of Thwaites Tongue used to be about 3km/year and now it is about 5km/year.  As a first approximation, I would expect the ice to be about 40% thinner.

As Eric Rignot has explained numerous times, thinner ice causes the grounding line to recede which causes more seawater contact from underneath and increases melting making the ice even thinner.  Thinner ice moves faster because there is less grounding.  It is a viscous circle.

Eventually the mass loss increases, but I would never expect the ice to get thicker as long as it continues to move quickly.

Of course at some point the calving line will recede deep into the glacier and Marine Ice Cliff Instability could kick in and we will see really massive (and rapid) calving events, but hopefully not in our lifetimes.
Title: Re: Thwaites Glacier Discussion
Post by: blumenkraft on October 06, 2019, 06:26:09 PM
A vicious circle indeed. :-/
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 06, 2019, 07:30:32 PM
I thought of another way to look at the ice velocity vs. ice thickness vs. ice mass loss equation.

You can think of the mass of ice as it calves and floats off, but then you have to account for the melting that takes place below the ice shelf between the time the ice first floats (at the grounding line) and when it finally calves.

A possibly simpler way to look at it is the mass of ice as it passes the grounding line.  With a fixed grounding line (at an underwater ridge) the mass loss is simply a a function of the thickness of the ice at the grounding line times the velocity of the ice at the grounding line.  We can assume the density of the ice and the width of the glacier do not change substantially.

What I am saying is that if something happens downstream to slow the flow of ice and the velocity at the grounding line drops X%, the ice at the grounding line will thicken, but by something less than X%, so the new mass loss will be lower.  Likewise, if you speed up the velocity by X%, the ice will get thinner but by less than X% and the mass loss will rise.

One thing I really like about this model is that it makes it relatively easy to incorporate a moving grounding line.  If the ice is moving forward at A km/year and the grounding line is receding at B km/year, you can add A plus B and multiply it by the thickness to get the mass loss.

Marine Ice Sheet Instability (MISI) is basically an unstable grounding line caused by a reverse-sloping sea bed, thinner ice, and warmer ocean water.  As ice gets thinner, it becomes easier to float.  As the grounding line recedes over a reverse-sloping sea bed, the water becomes deeper and it can support an even thicker layer of floating ice.  In this case, the ice sheet will be thicker at the grounding line, increasing the amount of mass loss significantly.  This might happen at Pine Island Glacier before it happens at Thwaites.

Marine Ice Cliff Instability (MICI) might happen after a MISI event that exposes ice cliffs over about 90 meters in height which are likely to collapse under their own weight and could lead to high speed runaway ice sheet retreat.  In this case the ice velocity might be an insignificant factor to the ice mass loss since the retreat of the grounding line should be significantly faster.
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 13, 2019, 06:25:03 PM
Below is a GIF of the last 8 months of movement of a 10km long "cork" that has been holding back the "melange" of ice between the Thwaites Eastern Ice Shelf and the Thwaites Tongue.  For at least 7 months it has been slowly turning and around the end of August and Early September it started sliding out towards the sea, being pushed by the ice behind it.  There is a strong possibility that it may be "caught" at its right front corner in the next few weeks by a couple smaller icebergs that are pinned against the eastern ice shelf.  Otherwise, it might be moving out to sea.  Something to watch anyway.

The "cork" broke off from the Eastern Ice Shelf during 2013-2014 and has turned almost 180 degrees clockwise as it tumbled in the melange.  It has been relatively stationary for the better part of a year, causing the melange behind it to build up.  Some of the larger pieces of ice behind it have been broken up in that time as the got caught between the rapidly moving Tongue and the stationary cork.

Also see the top of this GIF: https://twitter.com/StefLhermitte/status/1101870380623511552
Title: Re: Thwaites Glacier Discussion
Post by: Tom_Mazanec on October 13, 2019, 06:59:05 PM
Is there any order of magnitude how long a Thweites collapse would take?
A month, a year, a decade, a century?
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on October 13, 2019, 07:44:59 PM
It will, it must take a while.
AbrubtSLR has posted a lot about a possible Thwaites Glacier collapse including MICI type degradation in the Ice Apocalypse thread today.
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 13, 2019, 08:03:37 PM
Respectable scientists try not to be alarmists.  I got interested in Thwaites when I heard Richard Alley say it was something like "50 years give or take 50 years."  Maybe it was somewhere in this talk: https://www.youtube.com/watch?v=o4oMsfa_30Q but he has moderated his language somewhat since then to say that there is a risk that it could happen in decades but it may never happen.  More of a risk analysis rather than a prediction.

On the other hand, a paper published last December tried to model the collapse of Thwaites and it didn't see anything major for 30 years and the 100 year predictions were for something like a contribution of only 8 inches of sea level. https://www.the-cryosphere.net/12/3861/2018/

But if you read the paper, under section 4.6 "Limitations of the model study" you find "Another limitation is that the ice shelf front migration is not included in our simulations. We assume that the ice shelf front position of TG remains fixed" and later "The eastern ice shelf has been thinning and retreating, which means that the ice shelf could disintegrate in the coming decades."

It is hard to understand exactly what they are saying here.  They are making 100 year predictions assuming that the Eastern Ice Shelf remains fixed, yet they freely admit that the Eastern Ice Shelf could disintegrate in the coming decades.

Anyone who looks closely, knows that the Thwaites Eastern Ice Shelf (TEIS) is doomed to collapse in the next ten years.  The ice is visibly sliding eastward off the forward buttress which is at an angle to the current ice movement and not in a position to stop the forward progress.  (See GIF below.)  Meanwhile, the ice on the Western side of the TEIS has broken away (including the "cork" above) leaving no new ice to form a replacement TEIS.  It's impossible to say if the ice further inland might reform TEIS a few years after the collapse, but in my mind it is hard to find solace in these 100 year models based on the "stability" of the TEIS.

The models say that the Eastern half of Thwaites is the one most likely to collapse first, but the Eastern half is currently buttressed by the TEIS.  If the TEIS collapses and the Eastern half starts moving as fast as the Western half is currently, about 5km/year, I don't see how these 100 year predictions are worth anything.

The academic push has been to say "let's really study Thwaites" and they've done one season of observations so far.  Over the next 5 years expect to see a lot more papers published, but in the mean time, all we can do is watch the ice.

Title: Re: Thwaites Glacier Discussion
Post by: baking on October 13, 2019, 10:53:10 PM
Is there any order of magnitude how long a Thweites collapse would take?
A month, a year, a decade, a century?

Let me try to rephrase my answer.  Once the collapse "starts" it could take decades to wipe out most of the West Antarctic Ice Sheet.  But best guesses for WHEN it starts, is on the order of centuries and maybe millenia.

But on the other hand, things are happening at Thwaites.  The Tongue is much shorter and narrower than it was.  It is moving much faster and the ice is thinner.  Frankly, the Tongue could be gone after this Antarctic Summer.  Once the Tongue goes, the melange will probably float off also, exposing the Western side of the TEIS to open water during the summers.  We will see calving on both the western and eastern sides of the TEIS narrowing the ice shelf until it becomes unstable.  Collapse of the TEIS will speed up the ice on the Eastern half of Thwaites, pushing back the grounding line.  Then it will be just a matter of time.

Of course, the events above could be delayed for years or even decades.  Or the Tongue and TEIS may reform after collapsing.  The point is that there is plenty to watch for on the remote sensing front, and plenty of academic papers in the pipeline.  Things may happen slowly, but it won't be boring.
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 14, 2019, 04:34:02 PM
Today's Sentinel-1 images show a possible new crack on the Eastern calving front of the Thwaites Eastern Ice Shelf (TEIS) near the pinning point.  It's just a few pixels of shading so it may be an artifact, but it lines up with the crack opposite so is worth following up on in later images.
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 14, 2019, 08:45:51 PM
I think it's time for an overview of the whole ice front of Thwaites Glacier so the discussion of various areas can be put in context.  The image below is from October 4 and I discuss the major sections from top to bottom (East to West.)  The image size is 112 km on a side and the width of the front as a whole is about 120 km.

Eastern Calving Front:  This is my designation.  It is usually considered to be part of the Eastern Ice Shelf, but this section does not seem to be directly pinned to the offshore ridge.  However it is slow moving because the ice behind it is probably affected by the pinned ice shelf.

Eastern Ice Shelf:  Ice that is caught directly between the glacier behind it and the undersea ridge in front of it.  This shelf was found to have thinned from 10 to 33 percent between 1978 and 2009 after early films of ice penetrating radar were recently digitized.

Melange:  Irregularly shaped ice that has calved from a transition zone between the slow moving Eastern Shelf and the fast moving Tongue.  It tends to stay trapped between the shelf and the tongue before reaching open water after 5-10 years.

Tongue:  Ice that calves from the fasting moving part of Thwaites Glacier, often called the Main Trunk, and tends to stay in formation until it passes over the submerged offshore ridge.  The trunk and the tongue move at about 5 km/year.  The ice tends to calve in long transverse pieces about 10 km long and 1 km wide, which then breakup into roughly 1km squares and get glued to each other with sea ice over many winters before finally breaking up.

Western Calving Front:  This used to be a slower moving part of the Tongue, but now the calving ice tends to float free although it doesn't always move away quickly.  There is usually a lot of ice just offshore combined with ice from the neighboring Haynes Glacier and the Crosson Ice Shelf fed by the Pope and Smith Glaciers.  The Western Calving Front is very close to the Thwaites grounding line in this sector, about a km at points.  The worst case scenario for Thwaites would be if the entire front were to degrade into a calving front like this sector, just dumping icebergs out near the grounding line and providing no buttressing to the glacier.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on October 14, 2019, 09:11:22 PM
baking,
thank you for that comprehensive description and the differentiation of the various parts of this huge and vulnerable glacier :). I also keep an eye on it, but I have to wait for clear pictures from Sentinel to do an evaluation of the things that are going on.
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 14, 2019, 09:49:23 PM
baking,
I have to wait for clear pictures from Sentinel to do an evaluation of the things that are going on.

I get all of my images from polarview.org.  I have not had much success with other sources and I find Polar View to be "good enough" for what I'm doing.
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 19, 2019, 05:12:04 AM
This will be the first in a short series of posts which will attempt to overlay published bathymetry and grounding line data on recent Sentinel-1 satellite images.

I will start with the bathymetry map found in Millan 2017 "Bathymetry of the Amundsen Sea Embayment sector of West Antarctica from Operation IceBridge gravity and other data"
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL072071

The first image below is box (b) "Thwaites/Haynes" from figure 2.

The second is the matching Sentinel-1 "Extra Wide Mode" image from October 16, as processed by Polar View.

The third is the bathymetry overlaid over the satellite image at 50% opacity.  Grounding line positions are red (year 1996), ice front positions (year 2008) are yellow. Bed elevation is color coded from light blue to dark blue (−1400 m), with light contours every 100 m and thick contours every 400 m (300, 700, 1100 m) although the light contour lines are very faint in the overlay.

The next step will be to update the grounding lines from Milillo 2019 "Heterogeneous retreat and ice melt of Thwaites Glacier, West Antarctica"
https://advances.sciencemag.org/content/5/1/eaau3433

For those that are interested, here is the process that I used to generate these images.  Anyone with minor proficiency in GIMP or any similar image processing software (Photoshop, etc.) should be able to duplicate this and verify my results.

Start by downloading this Sentinel-1 image from Polar View (available for 30 days): https://www.polarview.aq/images/105_S1jpgfull/S1B_EW_GRDM_1SSH_20191016T041914_9DC8_S_1.final.jpg

If you wish to use another image, make sure that the full rectangle, 100 to 110 degrees West and 74 to 75 degrees South is visible.  Your scaling numbers may vary slightly from the ones below.

Download Figure 2 from Millan 2017 (link above) using the "Open in Figure Viewer" link then "Save Image as..."

I opened the satellite image in GIMP first and then "Open as Layers..." Figure 2.  (It only works in that order because the satellite image is larger.)

I measured the 100 to 110 degrees West and 74 to 75 degrees South rectangle in both images and estimated that I needed to scale the satellite image down by a factor of 4.46.  (I confess that this calculation was non-trivial, but the results were surprisingly good.)  I scaled the image from 14060x14406 to 3152x3230.

Then I just reduced the opacity of the top layer to 50% and lined up the corners of the rectangle.  It was not off by more than a pixel so I was happy.  Finally I cropped to image to the edges of the black box (b) and saved it.

Let me know if you have any problems duplicating this.
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 19, 2019, 08:09:34 AM
A quick update.  I was able to fairly easily (details below) add the grounding lines through late November 2017 (2017.91 in decimal years) as a very faint (30% opacity) overlay.  It's a very busy diagram, but I hope at some point to be able to mask out the extraneous details and increase the opacity.

In general, I was quite surprised at the size of the ground line retreat.  Seeing it laid on top of the satellite images I have grown quite familiar with was a bit of a shock.  Also, at first glance, it would appear that there has been some additional grounding line retreat in the last two years.  In particular, the West side of the "Butterfly" looks like it is no longer grounded, although it should probably be compared to older satellite images to see if it is a new feature or not.

Edit: Added an annotated version.

This is Figure 1(B) from Milillo 2019 "Heterogeneous retreat and ice melt of Thwaites Glacier, West Antarctica"
https://advances.sciencemag.org/content/5/1/eaau3433

The only way I found to obtain a high resolution image of the figure was to click on the "View this article with LENS" button, then click on "Figures" and click on Figure 1.  I cropped and masked the figure to just get the bathymetry, then rotated it clockwise 70 degrees and scaled it down 4% (0.96 scaling.)  The 1996 grounding lines then lined up quite nicely, yellow in Milillo and Red in Millan.
Title: Re: Thwaites Glacier Discussion
Post by: baking on October 29, 2019, 09:21:04 PM
This is a follow up to Reply #132 about the underwater peaks under Thwaites Tongue and the effects they have had over the past two weeks.  The concern is that the peaks will cause shearing of the Western side of the Tongue.  Already we can see increased rifting from what had occurred before.

The first image is a radar image from Sentinel-1 taken on October 26, 2019.  It shows the approximate location of the highest two peaks identified previously, and cracks and rifts that have widened significantly since October 14.

The second is a 3 image GIF from October 14, 20, and 26.  The motion is relative to the rest of the Tongue, not absolute, to better see the effect of the rifting.
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 02, 2019, 04:52:49 AM
Here is an updated GIF through November 1, showing the rifting in the Tongue described in the post above which is showing no sign of slowing down.
Title: Re: Thwaites Glacier Discussion
Post by: Tor Bejnar on November 02, 2019, 02:23:06 PM
Baking's 2nd image (the GIF) shows the latitude or longitude line moving about.  It appears the one iceberg that moves the most in the GIF moves in sync with with red line, suggesting everything else is 'actually moving' and that one berg is (relatively) standing still.  An alternate interpretation would be the red line is approximate (and therefore is not stationary): if so why include it in the first place?  (I know this is not Baking's doing.)

Other that that, I really appreciate Baking's close look at the relative movements of the mostly glued-together icebergs.
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 02, 2019, 04:03:29 PM
Baking's 2nd image (the GIF) shows the latitude or longitude line moving about.  It appears the one iceberg that moves the most in the GIF moves in sync with with red line, suggesting everything else is 'actually moving' and that one berg is (relatively) standing still.  An alternate interpretation would be the red line is approximate (and therefore is not stationary): if so why include it in the first place?  (I know this is not Baking's doing.)

Other that that, I really appreciate Baking's close look at the relative movements of the mostly glued-together icebergs.

Great questions, Tor.  I tried to explain in the post before that these GIFs are relative to the regular movement of the Tongue.  The red line is the 75 South line of latitude, so its movement in the GIF reflects the absolute motion of the Tongue.  The lone iceberg that is moving with the line is in fact grounded and has been for over a year.  It rests on a underwater peak and there is another peak directly above it in the GIF, just below the midline where you can see cracks widening.  This second peak is also responsible for the expansion of the rifts to the right (South or upstream.)

Most of my GIFs show absolute motion, but this is one case where the relative motion is more subtle and easier to see with movement of the main flow removed.  Make sure you follow the discussion at Reply #132 and above and don't hesitate to ask any questions.  I'd be happy to clarify.

The significance of this is best highlighted in this GIF https://twitter.com/StefLhermitte/status/1101870380623511552 which shows how the underwater peaks shear lines of icebergs off the Western side of the Tongue making it ever thinner.

All of my pictures are from PolarView.aq who are responsible for the lines of latitude and longitude for which I am forever grateful.
Title: Re: Thwaites Glacier Discussion
Post by: Tor Bejnar on November 02, 2019, 05:13:16 PM
Thanks!
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 09, 2019, 12:46:55 AM
Here is a quick update on the Western side of Thwaite's Tongue.  I'm only showing two images in this GIF, November 1 and 7, to emphasize that the rifting is still continuing to expand at a rapid rate.  All motion here is relative.

If the underwater peak continues to push against the Tongue, you can see where a row of icebergs, 3-4 across, will be stripped off reducing the Tongue's width by about a third.
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 13, 2019, 09:49:40 PM
Another 6-day Sentinal-1 radar update on the rift in the Western side of Thwaites Tongue.  This GIF shows the last 3 months.  Motion is relative to the Tongue.  This rifting is being caused by an underwater peak just to the left of the red latitude line
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 18, 2019, 05:15:53 PM
For those that like the Sentinel-2 MultiSpectral Instrument (MSI) images, here is the Tongue rift between 11/12 and 11/17.  Rendering is Normalized Difference Water Index (NDWI) which I find gives me the best results.  We should have another Sentinel-1 radar image tomorrow for comparison.
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 20, 2019, 06:45:30 AM
New Sentinal-1 radar image from November 19 shows the Western Tongue Rift continues to widen over the past 6 days.  A new fracture perpendicular to the main rift at it widest point is now evident, highlighted in the second picture, giving further evidence of breakup.
Title: Re: Thwaites Glacier Discussion
Post by: kassy on November 22, 2019, 02:03:42 PM
Pathways of ocean heat towards Pine Island and Thwaites grounding lines

...

In this study, we use an unprecedentedly high-resolution (200 m horizontal and 10 m vertical grid spacing) ocean model that resolves shelf-sea and sub-ice-shelf environments in qualitative agreement with existing observations during austral summer conditions. We demonstrate that the waters reaching the Pine Island and Thwaites grounding lines follow specific, topographically-constrained routes, all passing through a relatively small area located around 104°W and 74.3°S. The temporal and spatial variabilities of ice shelf melt rates are dominantly controlled by the sub-ice shelf ocean current. Our findings highlight the importance of accurate and high-resolution ocean bathymetry and subglacial topography for determining mCDW pathways and ice shelf melt rates.

...

https://www.nature.com/articles/s41598-019-53190-6
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 23, 2019, 03:45:18 PM
For those that like natural color images, here is a 10-day movement of the Western Tongue Rift between November 12 and 22.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on November 23, 2019, 07:38:54 PM
Thank you for that animation.
I wonder once those bergs will be drifting away whether the rest of the ice tongue will remain stable or if the next row of bergs will start to move.
Title: Re: Thwaites Glacier Discussion
Post by: Tor Bejnar on November 23, 2019, 09:09:17 PM
Stephan,
Those frozen-together floes that 'don't move' in Baking's posts are actually moving already - he just adjusts the images to emphasize the difference between the accelerating lead floes and the others.  Look up thread at his November 20 GIF that includes a latitude or parallel line.  The line actually isn't moving across the Earth, all the ice is.

This is frequently done to show relative changes in rifts on glaciers.  Glaciers move every day, but most of the ice moves in tandem with its neighboring ice.   By moving a 2nd image so that certain features exactly cover each other, other features are obvious.
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 23, 2019, 09:15:35 PM
I wonder once those bergs will be drifting away whether the rest of the ice tongue will remain stable or if the next row of bergs will start to move.

This row is being forced out by an underwater peak near the top crack in the GIF.  It is possible that in time the next row will be forced out by that same peak.  Another possibility is that this narrowing of the Tongue will create so much instability that the entire Tongue will float off in pieces or that the Tongue will lose it's leading end and it won't be long enough to maintain contact with the ridge that has helped to hold it in place.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on November 23, 2019, 09:49:50 PM
Stephan,
Those frozen-together floes that 'don't move' in Baking's posts are actually moving already - he just adjusts the images to emphasize the difference between the accelerating lead floes and the others.  Look up thread at his November 20 GIF that includes a latitude or parallel line.  The line actually isn't moving across the Earth, all the ice is.

This is frequently done to show relative changes in rifts on glaciers.  Glaciers move every day, but most of the ice moves in tandem with its neighboring ice.   By moving a 2nd image so that certain features exactly cover each other, other features are obvious.
I of course know that and by adjusting the pictures in such a way as baking did it the "extra" movement (in this case westward) is obvious. This "extra" movement of further bergs in the ice tongue I was asking for - baking has already answered this question (see posting above).
Title: Re: Thwaites Glacier Discussion
Post by: Tor Bejnar on November 23, 2019, 11:32:07 PM
I'm glad you knew, Stephan.  I've been sick and didn't have the energy to point to Baking's reply to my earlier surmise clarifying all that.
Cheers (even if subdued!),
Tor
Title: Re: Thwaites Glacier Discussion
Post by: blumenkraft on November 24, 2019, 05:29:58 AM
Oh man! Get well soon, Tor.
Title: Re: Thwaites Glacier Discussion
Post by: Andreas T on November 24, 2019, 10:08:31 PM
B22A has been moving more than it has in the last few years I think. This has of course not much significance since it is just a stranded iceberg but as a start to the season it makes one wonder what effect it may have on the fast ice between it and the coast.
https://go.nasa.gov/2DeQwLr (https://go.nasa.gov/2DeQwLr)
Title: Re: Thwaites Glacier Discussion
Post by: blumenkraft on November 25, 2019, 05:34:05 PM
Great find, Andreas.

I took every cloud-free(ish) Sentinel shots since September.
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 25, 2019, 06:26:57 PM
Here is the latest 3-month GIF of Sentinel-1 radar images of the Western Tongue Rift as of today.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on November 25, 2019, 06:32:00 PM
How would you evaluate the influence of the sea ice? In other words, would the "peeling off" of the icebergs happen faster if there were no sea ice W of Thwaites Ice Tongue?
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 25, 2019, 06:36:56 PM
B22A has been moving more than it has in the last few years I think. This has of course not much significance since it is just a stranded iceberg but as a start to the season it makes one wonder what effect it may have on the fast ice between it and the coast.

B22Ahas shifted significantly to the NW in the last week.  As mentioned previously in this thread, moves to the West or Northwest are not very concerning because it is just further grounding.  Moves to the East or Northeast are cause for concern because that would be towards deeper water.  The previous shift to the NW was followed by a smaller move to the East I think.  Probably worth a longer-term analysis to see what has been happening so far this season.
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 25, 2019, 06:52:57 PM
How would you evaluate the influence of the sea ice? In other words, would the "peeling off" of the icebergs happen faster if there were no sea ice W of Thwaites Ice Tongue?

My Reply #111 from September 26 kind of ties this discussion with the iceberg B22-A thread.

Basically, my conclusion there was that the sea ice was holding back parts of the Tongue from breaking off.  Once we see the sea ice clear as we get into January and February "loose" pieces of the Tongue may just float off.

This rift is being driven by a irresistible force (Thwaites Glaicer) hitting an immovable object (an undersea ridge) so this rift is probably going to continue to widen no matter the condition of the sea ice.  But these pieces that are getting knocked loose will be much more vulnerable when the sea ice goes away.  And the remaining parts of the Tongue might also be less stable.

If you look at the recent history in the link below, large rafts of icebergs of icebergs tend to drift off together, so the Tongue will most likely be much smaller in six months.

https://twitter.com/StefLhermitte/status/1101870380623511552
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 26, 2019, 01:16:44 AM
I have overlaid a recent bathymetric chart over a Sentinel-1 radar image of B22-A from November 21, that shows the iceberg is probably grounded in two locations.  In the West and a large shallows area and in the East on a smaller peak.  Both are higher than 300 meters below the surface.

When looking at movements of B22-A it should be useful to have these reference points in mind.  I will make another post detailing the recent movements of B22-A, but as a first pass the iceberg seems to be pivoting on the Western shallows and the Eastern end is rotating counter-clockwise to the North.  This means that it is moving over the Eastern Peak, but it far from moving off the peak.

I note that the trough under the middle of B22-A means that is the most likely place for basal melting and the possibility of the iceberg splitting into two pieces has to be considered.

Millan 2017: "Bathymetry of the Amundsen Sea Embayment sector of West Antarctica from Operation IceBridge gravity and other data"
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL072071
Title: Re: Thwaites Glacier Discussion
Post by: baking on November 26, 2019, 08:42:12 AM
Here is one series of Sentinel-1 radar images of Iceberg B22-A.  This one has huge gaps, and I can probably find a longer series, but I think it makes a good representation.

There is a lot of back-and-forth motion from East to West.  It's almost like the iceberg is caught between the two shallow areas and is just drifting back and forth between them, with currents or the tide.  That movement is minor, roughly a kilometer, but it does seem to imply that B22-A is no longer firmly grounded.

Over time there is also a gradual counter-clockwise rotation to the North.  One could imagine that as B22-A bounces back and forth in a tight space it is also slowly working its way lose, although I still think it was a long way to go if it is going to work free without breaking up.

If it does break in two, the smaller halves might be less constrained and will have more freedom of motion to drift off.

This GIF has one image from March 8, 5 images from September 16 through October 10, and 5 more images from October 28 to November 21.  There is a pause before each gap and at the end.  The things to note are the gradual movement to the North (right to left) and small back-and-forth motions East and West (up and down.)  Also, it tends to pivot counter-clockwise around the Western (bottom) end.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on November 26, 2019, 08:24:19 PM
Thanks a lot, baking for the bathymetry map and the gif.
If I understand correctly B-22A must turn clockwise by about 110° to be in line with the trough which would allow it to be exported into deeper seas northward. But this will probably not happen with dominant SE winds and currents.
In the end it will sit there for a longer while moving back and forth a little bit until it melts sufficiently and gets unpinned or until it breaks into smaller more mobile parts.
Title: Re: Thwaites Glacier Discussion
Post by: blumenkraft on December 05, 2019, 09:26:56 AM
New study models impact of calving on retreat of Thwaites Glacier

Link >> https://blogs.agu.org/geospace/2019/12/04/new-study-models-impact-of-calving-on-retreat-of-thwaites-glacier/
Title: Re: Thwaites Glacier Discussion
Post by: sidd on December 06, 2019, 08:08:08 AM
There is a nice paper from the same gang in 2018 that illuminates this paper.

doi:10.5194/tc-12-3861-2018

open access, chekitout.

sidd
Title: Re: Thwaites Glacier Discussion
Post by: baking on December 06, 2019, 03:39:03 PM
There is a nice paper from the same gang in 2018 that illuminates this paper.
The newer paper isn't on sci-hub yet, but the older paper notes this limitation of their model:

"Another limitation is that the ice shelf front migration is not included in our simulations. We assume that the ice shelf front position of TG remains fixed; i.e., all ice passing the ice shelf front calves immediately. Densely distributed crevasses along the ice shelf of TG, however, make the ice shelf conducive to rapid calving (Yu et al., 2017). Once the ice shelf is removed, the grounding line will retreat into deeper regions, and the probability of calving increases according to the marine ice-cliff instability theory (Pollard et al., 2015; Wise et al., 2017). Crevassing and calving will therefore reduce ice shelf buttressing and accelerate ice speed; i.e., our simulations underestimate the potential mass loss of TG (MacGregor et al., 2012). On PIG, calving has increased in frequency and its ice front is now 35 km farther inland on the eastern side than in the 1940s (Jeong et al., 2016; MacGregor et al., 2012). On TG, the floating ice tongue in the center trunk retreated by 26 km from 1973 to 2009 (MacGregor et al., 2012). The eastern ice shelf has been thinning and retreating, which means that the ice shelf could disintegrate in the coming decades."

Presumably, the newer paper addresses this issue and is "the other shoe" that we've been waiting to drop.
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on December 07, 2019, 09:14:57 PM
The actual EOSDIS picture shows a further "peeling-off" of the row of icebergs from the Thwaites Ice Tongue (see postings in this thread above). The change of flow direction (green arrows) is marked by a dotted red line. This line has further widened and open water is visible.
Further east, there is a change in flow speed at the western edge of Thwaites Eastern Ice Tongue (TEIS), marked with a dotted green line.

See attached picture, looking forward to an actual Sentinel picture of that area in the next days...
Title: Re: Thwaites Glacier Discussion
Post by: baking on December 07, 2019, 11:18:32 PM
. . . looking forward to an actual Sentinel picture of that area in the next days...

Here is today's Sentinel-1 radar image compared with 12 days ago.  Fairly substantial movement, but nothing "surprising" to anyone who has been following along.
Title: Re: Thwaites Glacier Discussion
Post by: Darvince on December 08, 2019, 09:44:15 AM
Is that a slight rotation of the main body of the tongue I see?
Title: Re: Thwaites Glacier Discussion
Post by: Stephan on December 08, 2019, 12:13:13 PM
I would be careful with such an interpretation. Baking has adjusted the pictures in that gif to the movement of the ice tongue (visible in the shift of the red latitude line). Depending on which floe he chose to make that adjustment it may be that others' flows slightly differs - therefore a kind of rotation appears, although it objectively doesn't happen.
Title: Re: Thwaites Glacier Discussion
Post by: Darvince on December 08, 2019, 01:17:57 PM
Taking a closer look at their previous posts makes me think that you are correct and that it is indeed nothing; baking's previous GIFs seem to show a similar amount of noise.

Actually, after a second and even closer look, the main body of the tongue does appear to have begun rotating in the last month or so of their last GIF, after the relative motion of the soon-to-break-away armada picks up again. Could this also be from the same underwater feature as what's causing the breakaway?
Title: Re: Thwaites Glacier Discussion
Post by: baking on December 08, 2019, 03:59:20 PM
Nice catch, Darvince.  Yes, these images are overlaid to show relative motion, but I only do an X-Y move, I don't correct for any rotation.  So any rotation you are seeing is real, or at least the result of a curved trajectory.

The main explanation seems to be that the "Melange" caught between the Thwaites Eastern Ice Shelf (TEIS) and the Tongue is pushing against the Tounge from the East (top) and causing the Tongue to turn slightly to the West.

Specifically, the Tongue is driving a wedge into a large mass of ice caught behind a 10 km long "cork" and part of that ice is being forced against the Eastern side of the Tongue.  See the image below.

This has been going on for at least a year, but a few months ago the cork started moving and the rotation was lessened.  However in the last two weeks the cork has become hung up again on some different pieces of ice and the rotation has returned.  One caveat is that there seems to some visual effect (artifact) in the radar images of the "shadows" between the icebergs in the latest image that may be misleading about small motions.

But yes, there is a rotation and it has been there for a while.  It may continue if the cork becomes stuck again.  It doesn't seem to have anything to do with the underwater peaks, except that the rotation may be forcing the Tongue on to the peaks and causing the premature break-up.  The Tongue is fragile enough that it will break before it bends.
Title: Re: Thwaites Glacier Discussion
Post by: baking on December 08, 2019, 04:34:11 PM
I should add that I have been very concerned about a potential weakness in the Tongue in the area circled in the detailed image below.  I do note that it is between the peak and the point where the melange is forcing against the Tongue (arrow.)  Basically, the fear is that it could cause major East-West rifting in the Tongue and effectively cut its length in half.

So, if the "cork" gets stuck again this might be a major risk.  Of course if the cork doesn't get caught and floats off free the melange might also float off and then who knows what will happen to the stability of the Tongue and the Eastern Ice Shelf.
Title: Re: Thwaites Glacier Discussion
Post by: baking on December 08, 2019, 05:06:45 PM
I thought I would show a long-term GIF to demonstrate what I've been talking about.  It shows the "wedge" being driven into the ice mass and the pressure point is causes on the Tongue.  All motion is relative to the Tongue, so things you see moving left to right are moving slower than the Tongue.

There are three phases to the GIF: 1) February-August The wedge is being driven into the ice mass, 2) September The ice mass pushes "down" on the Tongue, and 3) October-November The "cork" comes free (not shown) and everything moves along with the Tongue so there is little relative motion.

It may not be a coincidence that the "cork" pops free just as the melange starts to push hard against the Tongue.  It could be that the Tongue pushing back put enough pressure on the cork.

EDIT: See my Reply #142 from October 13 for a GIF of the "cork" coming loose.
Title: Re: Thwaites Glacier Discussion
Post by: blumenkraft on December 08, 2019, 05:53:20 PM
Amazing!

Thank you, Baking!
Title: Re: Thwaites Glacier Discussion
Post by: baking on December 11, 2019, 05:23:40 PM
We finally have boots on the ice for the 2019/2020 research season!

https://twitter.com/Alpinesciences/status/1204548226466156546

Follow this Twitter Stream for all updates:

https://twitter.com/GlacierThwaites