Thwaites Glacier Discussion

[baking]

https://www.pnas.org/doi/10.1073/pnas.2211711120

Synchronous retreat of Thwaites and Pine Island glaciers in response to external forcings in the presatellite era

Rachel W. Clark et al., February 26, 2024

Abstract

Today, relatively warm Circumpolar Deep Water is melting Thwaites Glacier at the base of its ice shelf and at the grounding zone, contributing to significant ice retreat. Accelerating ice loss has been observed since the 1970s; however, it is unclear when this phase of significant melting initiated. We analyzed the marine sedimentary record to reconstruct Thwaites Glacier’s history from the early Holocene to present. Marine geophysical surveys were carried out along the floating ice-shelf margin to identify core locations from various geomorphic settings. We use sedimentological data and physical properties to define sedimentary facies at seven core sites. Glaciomarine sediment deposits reveal that the grounded ice in the Amundsen Sea Embayment had already retreated to within ~45 km of the modern grounding zone prior to ca. 9,400 y ago. Sediments deposited within the past 100+ y record abrupt changes in environmental conditions. On seafloor highs, these shifts document ice-shelf thinning initiating at least as early as the 1940s. Sediments recovered from deep basins reflect a transition from ice proximal to slightly more distal conditions, suggesting ongoing grounding-zone retreat since the 1950s. The timing of ice-shelf unpinning from the seafloor for Thwaites Glacier coincides with similar records from neighboring Pine Island Glacier. Our work provides robust new evidence that glacier retreat in the Amundsen Sea was initiated in the mid-twentieth century, likely associated with climate variability.

[Open Access]

[baking]

12-day high-res GIF of Thwaites Tongue.  You can see how the center is running aground which tends to spit the Tongue into two.

[baking]

I noticed these new cracks in the Tongue in the high-res GIF above.  Probably related to motion against the grounded icebergs at the front.

[vox_mundi]

Massive Damage at Thwaites Glacier
https://www.dailykos.com/stories/2024/2/24/2225146/-Massive-damage-at-Thwaites-Glacier

[interstitial]

Massive Damage at Thwaites Glacier
https://www.dailykos.com/stories/2024/2/24/2225146/-Massive-damage-at-Thwaites-Glacier

I Know this is freshly published but March 2021 was a very long time ago for Thwaites glacier.

[baking]

Massive Damage at Thwaites Glacier
https://www.dailykos.com/stories/2024/2/24/2225146/-Massive-damage-at-Thwaites-Glacier

I Know this is freshly published but March 2021 was a very long time ago for Thwaites glacier.

I think this is a lot of confusion between Thwaites Eastern Ice Shelf (TEIS), Thwaites Western Ice Tongue (TWIT), and Crosson Ice Shelf.

[interstitial]

Massive Damage at Thwaites Glacier
https://www.dailykos.com/stories/2024/2/24/2225146/-Massive-damage-at-Thwaites-Glacier

I Know this is freshly published but March 2021 was a very long time ago for Thwaites glacier.

I think this is a lot of confusion between Thwaites Eastern Ice Shelf (TEIS), Thwaites Western Ice Tongue (TWIT), and Crosson Ice Shelf.

Yes in my mind I tend to bunch them together as one.

[baking]

12-day GIF of the Tongue.

[baking]

Here is a 1-year GIF from Worldview.  Thwaites Eastern Ice Shelf (TEIS) is looking pretty vulnerable.

[baking]

6-day low-res GIF showing movement of icebergs in front of Thwaites Eastern Ice Shelf (TEIS.)

[Mr. Ä]

What are the black outlines in Worldview images?

[Linus]

Coastal outline overlay. You can turn it off on the filter layers tool on the left side of the screen.

[baking]

What are the black outlines in Worldview images?

They are the grounding line and the extent of the ice sheet at some point in the distant past—usually 2011.

Compare with Figure 1 in this paper: https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2014gl060140

Edit:  2011 was a good guess.  Here is Worldview from January 8, 2011.

[baking]

3-day low-res GIF showing more iceberg movement off the front of Thwaites Eastern Ice Shelf (TEIS) and the tip of Thwaites Western Ice Tongue (TWIT.)

[gerontocrat]

Sea ice in the BellinghamAmundsen sea is late in refreezing this year, with lots of open water along the Thwaites / PIG coastline. Maybe fast sea ice & berg losses can continue for some time yet?

Image from latest Univ Bremen sea ice concentration.

[baking]

Today's 12-day high-res GIFs with details of Thwaites Eastern Ice Shelf (TEIS) and Thwaites Western Ice Tongue (TWIT.)

[baking]

1-day GIF from Worldview showing loss from the Melange but not clear how many icebergs are involved.

[baking]

Today's 2-day low-res GIF updating recent changes to the TEIS, the Tongue, and the Melange.

[baking]

1-day GIF from Worldview showing a breakup of some of the fast ice West of Thwaites Tongue.

[baking]

2-day low-res GIF of a few small calvings at the front of Thwaites Tongue.

[baking]

The first high-res image from Thwaites Eastern Ice Shelf (TEIS) in 24 days shows a new potential shear margin forming in the center.

The middle orange line in this post: https://forum.arctic-sea-ice.net/index.php/topic,1760.msg394891.html#msg394891

It was always a possibility, but now it is looking like a strong favorite.

[Stephan]

...and it looks that at the SW edge (right down corner) five new icebergs will soon calve...

[IceConcerned]

THere is more to it when we look at the general picture, and in particular the rear portion of hte ice sheet
The whole IS has got loose, we have indeed the creation of a shear zone that baking is indicating, but the whole sheet is moving in a north-north-east direction. The crack at its back has lengthened and hugely widened since first reported a little more than 2 years ago, and is now (purple cross section) about 2.3km wide.
At the same time, it is bound to end up in the open water separating the IS from the tongue, along one of the 2 main cracks underlined in green. the are currently growing fast, each hi-res pictures brings some change
And on the western side,  the orange crack are multiplying, leading most likely to another shear zone.

Definitely the event to follow in the coming months, or maybe even weeks.

[baking]

5-day low-res GIF showing some icebergs breaking away from the melange and an iceberg moving away from in front of TEIS.

[baking]

2-day low-res GIF showing some icebergs breaking away from the Tongue and one from the Melange.

[baking]

Yesterday, the front of the melange West of Thwaites Tongue broke off.  24-day high-res GIF scaled down, but the low-res image from May 9 didn't show it.

[gerontocrat]

Yesterday, the front of the melange West of Thwaites Tongue broke off.  24-day high-res GIF scaled down, but the low-res image from May 9 didn't show it.

I thought things were supposed to go quiet during the Antarctic winter.

[baking]

Yesterday, the front of the melange West of Thwaites Tongue broke off.  24-day high-res GIF scaled down, but the low-res image from May 9 didn't show it.

I thought things were supposed to go quiet during the Antarctic winter.

It is beginning to ice up, but remember that because it was mostly free of ice in the Summer this is all new sea ice which is not very thick.  Also, there is still open water directly to the West of Pine Island Glacier (PIG) and Thwaites Eastern Ice Self (TEIS) because of the prevailing winds.  Finally, the number of icebergs has been greatly reduced from last year so the sea ice will have fewer grounded icebergs to hold it in place.

Last year, May and early June were quite busy for TEIS: https://forum.arctic-sea-ice.net/index.php/topic,1760.msg371147.html#msg371147

[vox_mundi]

Satellite Radar Data Uncover 'Vigorous Melting' at Antarctica's Thwaites Glacier
https://phys.org/news/2024-05-satellite-radar-uncover-vigorous-antarctica.html



A team of glaciologists led by researchers at the University of California, Irvine used high-resolution satellite radar data to find evidence of the intrusion of warm, high-pressure seawater many kilometers beneath the grounded ice of West Antarctica's Thwaites Glacier.

In a study published in Proceedings of the National Academy of Sciences, the UC Irvine-led team said that widespread contact between ocean water and the glacier—a process that is replicated throughout Antarctica and in Greenland—causes "vigorous melting" and may require a reassessment of global sea level rise projections.

... "Thwaites is the most unstable place in the Antarctic and contains the equivalent of 60 centimeters of sea level rise. The worry is that we are underestimating the speed that the glacier is changing, which would be devastating for coastal communities around the world."

Eric Rignot et al, Widespread seawater intrusions beneath the grounded ice of Thwaites Glacier, West Antarctica, Proceedings of the National Academy of Sciences (2024).
https://www.pnas.org/doi/10.1073/pnas.2404766121

[oren]

Good research, bad news.

[baking]

The breakup of the melange West of Thwaites Western Ice Tongue (TWIT) is spreading.  12-Day low-res GIF.

[Macalaga]

That looks like a big change, but I’m curious how normal / significant is it?

[baking]

Eric Rignot et al, Widespread seawater intrusions beneath the grounded ice of Thwaites Glacier, West Antarctica, Proceedings of the National Academy of Sciences (2024).
https://www.pnas.org/doi/10.1073/pnas.2404766121

2.7. Future Retreat.
At present, the GZ of Thwaites Glacier is retreating along a prograde slope, which is a configuration conducive to stabilization. Indeed, the grounding line retreat rate is twice slower than in the past when the grounding line was retreating on a flat bed (Fig. 2). Yet, the retreat is not halted by the prograde slope. Seawater intrusions extending 12 km may set up the glacier for further retreat (17). Once the glacier grounding zone retreats past Mouginot Ridge, which could happen in the next few years, it will migrate quickly to the South Ridge along retrograde slopes. South Ridge will be a smaller obstacle. It may only take 10 to 20 y before the glacier retreats past South Ridge, into the deeper basin, at which point a fast retreat will resume. In the nearby smaller-size basins of Smith and Pope Glaciers, retreat along retrograde slopes has proceeded at 2 to 3 km/y for multiple years (46). We conclude that the future of Thwaites—and other Antarctic glaciers—will hinge on how fast warm waters erode grounding zones over large distances, much faster than anticipated by current models.

[kiwichick16]

@  baking .....if i'm reading the paper correctly , are we looking at the start of the WAIS collapse within 20 years ?

[baking]

@  baking .....if i'm reading the paper correctly , are we looking at the start of the WAIS collapse within 20 years ?

The thing about Thwaites that makes it the "Doomsday Glacier" is that it is really wide, about 100 km across.  This study focuses on the "main trunk" of Thwaites which is the fastest moving part, but it is only 6 km wide.  There are other ridges to the East and the West that will slow down a complete collapse of Thwaites for probably many decades, or at least that is what modeling says.

Of course, it is all interconnected and one part moving faster thins out the ice and allows more seawater in under neighboring ice and the current models don't include all those effects.

[kiwichick16]

@  baking ....the study states that the process ...of sea water contact with the ice ......is widespread both across Antarctica and Greenland

that would seem to be obvious ....given that tides are present globally

[baking]

@  baking ....the study states that the process ...of sea water contact with the ice ......is widespread both across Antarctica and Greenland

that would seem to be obvious ....given that tides are present globally

Yes, but also the slope of the underlying seafloor plays a role.  Prograde slopes (going up as you move upstream) are more stable than retrograde slopes because the deeper you go the more buoyant the ice is.

[Capt Kiwi]

@  baking .....if i'm reading the paper correctly , are we looking at the start of the WAIS collapse within 20 years ?

There are other ridges to the East and the West that will slow down a complete collapse of Thwaites for probably many decades,

That still sounds a little scary if you have grandchildren!

[kiwichick16]

the slope of Thwaites is retrograde after the Mouginot Ridge

[Capt Kiwi]

the slope of Thwaites is retrograde after the Mouginot Ridge

Is that good or bad bro kiwi?

[Stephan]

retrograde beds are bad for the stability of a glacier because the further you go upstream the deeper the bedrock is which makes it easier for ocean water to flow beneath the glacier which then destabilizes it.

[baking]

The inherent nature of a ridge is that the slope is prograde before the ridge (as the grounding line recedes upstream) and retrograde after the ridge.

Thwaites has at least eight significant ridges or systems of ridges, three to the East, two in the center (main trunk), and one to the West, plus two deeper ridges that extend the full width.

I call them significant because they are identified through modeling as significant areas of stability for the receding grounding line.

I will try to provide sources and maps later today.

[kiwichick16]

@  baking  ....thanks   .....look forward to that 


just a bit worried by how the study on the sea water intrusion seemed to imply that the next ridge ....the South ridge .....might not provide as much stabilising effect as the Mouginot


sorry but i can't help thinking of the Maginot Line in France ......

[baking]

I will refer to three papers here.  There are other papers that are also worth looking at, but these are the ones that refer to the ridges I am talking about and can serve as a starting point for understanding the big picture of a possible retreat of Thwaites Glacier.

Yu 2018: https://tc.copernicus.org/articles/12/3861/2018/

Schwans 2023: https://www.cambridge.org/core/journals/journal-of-glaciology/article/model-insights-into-bed-control-on-retreat-of-thwaites-glacier-west-antarctica/4F3E4E4566CDAF1D143C08F058CDAE3F

Rignot 2024: https://www.pnas.org/doi/10.1073/pnas.2404766121

I show one figure from each paper and a detail that shows all ridges in one image.  The four ridges, three in the East and one in the West, are outlined with rectangles in Yu 2018.  Schwans 2023 shows the GHOST Ridge (named for a field project that is studying the ridge) and the Upper Thwaites Ridge.  Finally, the most recent paper, Rignot 2024, shows two ridges that are at the bottom of a sub-glacial trough so they are just points marked with stars.

The final image is my attempt to put all eight ridges on one image so you have a context to talk about them in relation to each other.  (Edit:  I used a different version of MSPaint to attempt to make this somewhat clearer.  The stars from Rignot 2024 are replaced with small black circles for clarity.)

[baking]

12-day high-res GIF showing a calving in the growing rifts at the rear of Thwaites Eastern Ice Shelf (TEIS) near the grounding line.

[RoxTheGeologist]

retrograde beds are bad for the stability of a glacier because the further you go upstream the deeper the bedrock is which makes it easier for ocean water to flow beneath the glacier which then destabilizes it.

As the base melts, the freshwater is less dense than seawater. So water melting deep on a retrograde slope has a large pressure difference and drives circulation, flowing back up against the glacier and maybe cutting a channel. It sucks the warm shelf water down all the way to the deepest part of the glacier. One hopes that the outgoing and incoming layers mix turbulently on the way down, but waters of different densities mix notoriously poorly, and if the freshwater flowing back up is in a channel, then the area for mixing is reduced.

Thinking about it - creating turbulence at the inlets of those channels with static mixers may slow down the melting, or perhaps a dense layer that insulates the base of the glacier may also help.

[Stephan]

Mini calving at TEIS.

A portion of ca. 3 km length has recently calved. It is located at the very eastern end of Thwaites Eastern Ice Shelf (TEIS, circled in orange). See attached picture, N is up.

[baking]

A couple of icebergs breakaway from the Tongue in this 12-day low-res GIF but growing sea ice probably locks them in for the winter.

[baking]

12-day high-res GIF of the same part of the Tongue as yesterday.

[gerontocrat]

12-day high-res GIF of the same part of the Tongue as yesterday.

a lot of widening gaps especially well into the centre-right