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