Thwaites Glacier Discussion

[paolo]

I don't see anything new compared to the animation provided by baking on 14/06 (post 636, last image).

[gerontocrat]

Thank you for that finding.
This means that roughly 25% of the NW flank of the slowly moving part of TEIS which has been protected by icebergs is now open to oceanic waters.

& now without resistance to movement? There was a recent paper saying it all might fall apart this decade?

[Stephan]

I don't see anything new compared to the animation provided by baking on 14/06 (post 636, last image).

You're completely right, paolo. Should have checked all gifs before writing a new post... 

[grixm]

Sunlight has started to hit Pine Island and Thwaites glacier. Less than a month left until we start seeing the first Sentinel-2 satellite imagery. But before that, we still have thermal imaging, so we can get an overview of the state of the glaciers and ice around them going into the season.

I have attached two images, the first one is from August 23rd, and the second one is from August 19th.

There are a few notable things:

There is still no strong fast ice in front of the Pine Island glacier. In fact there is a big polynya with almost no ice at all. The ice further out looks fast-ish in the most recent image, but that's why I included the second image too, to show that as recently as 8 days ago that ice was actually completely shattered. Does anyone know whether this is normal or rare? In any case it doesn't bode well for the PIG this season, although there are still no big cracks in it that would signal a calving soon.

You can see the B-22 iceberg in the bottom of the first image. It hasn't moved a lot over the freezing season, but it's well out of the way for the Thwaites shelf. Nevertheless, there is strong fast ice stretching out to where B-22 used to sit. I guess this is because of the same shoals that caused B-22 to get stuck in the first place. It remains to be seen how the absence of B-22 affects the ice dynamics of the surrounding area this season.

[baking]

2-Day low-res GIF shows new calving on the Western flank of the stationary portion of Thwaites Eastern Ice Shelf (TEIS).

[baking]

High-resolution 12-day GIF of the calving above showing many more details.

[IceConcerned]

I would note BET on the triangle North of thé last calving holding for long

[christinetoth]

I came across this article that pinning point 5 is no longer there. https://www.dailykos.com/stories/2023/9/29/2195755/-Pinning-point-five-collapsed-the-sea-ice-barrier-buttressing-Thwaites-and-Pine-Island-Glacie

I was wondering if anyone could verify if this information is correct?  And is it significant?

[oren]

Welcome!
I can't answer the question myself as it's based on a Twitter thread which I cannot read.

[interstitial]

I am no expert but it looks to me like point 5 is gone. The problem is that most of the physical landmarks near point 5 do not look anything like what they used to. 1,2 and 4 are probably still there though again it is hard to say without overlaying the original image. 3,5,6,7,8 and 9 are gone. 11, 12 and 13 have cleared the original icebergs but are shallow enough that new burgs have gotten stuck there at least temporarily.


The overlay of images seems like the sort of thing that Paolo seems to like to do but I do not think he has posted recently. 

[baking]

I came across this article that pinning point 5 is no longer there. https://www.dailykos.com/stories/2023/9/29/2195755/-Pinning-point-five-collapsed-the-sea-ice-barrier-buttressing-Thwaites-and-Pine-Island-Glacie

I was wondering if anyone could verify if this information is correct?  And is it significant?

I saw that too, and I don't think it is very significant for a number of reasons.

The basic idea seems to be that there are a number of shallow spots where icebergs become grounded.  Sea ice becomes anchored to those grounded icebergs and becomes "fast" or fastened to those points.  During the melting season, sea ice begins to breakup and those points and the icebergs grounded there play a big role in retaining the sea ice through the season.

The role that sea ice plays in protecting the ice shelf and glaciers is another more complicated matter that I won't go into here.  Suffice it to say that the loss of sea ice might be bad, but it doesn't mean the inevitable failure of the ice shelf.

As for "pinning point 5" I cannot see what they are seeing from Worldview.  In the radar images from Polarview the same icebergs are still there from 6 months ago.  There may be some cracks in the sea ice, but if the grounded icebergs are still grounded, I'm not sure of the significance of cracks in the sea ice.

Even if the icebergs become ungrounded and float off to sea, other icebergs are likely to be grounded there and the cycle will repeat.  It is a fairly stable process.  There are currently many ungrounded icebergs locked in the sea ice.  If the grounded icebergs melt enough to float off and release the sea ice, some of the many newer icebergs will probably ground on the same spot.

[baking]

I am no expert but it looks to me like point 5 is gone.

I can do an overlay if you tell me what area and time period to look at.

[christinetoth]

@baking     

Thanks for the explanation... 

[interstitial]

a recent polarview image and this image overlayed. At least I think this is the image referred to with point 5. The only landmarks I can still see are the mountain structures below and to the right of point 10.

[baking]

a recent polarview image and this image overlayed. At least I think this is the image referred to with point 5. The only landmarks I can still see are the mountain structures below and to the right of point 10.

That image is from Worldview on January 18.  You can do a simple A/B slider comparison with a clear image from October 1.

Here is one you can play with and zoom: https://worldview.earthdata.nasa.gov/?v=-2084985.7939357073,-763160.5399041437,-1252366.2384907715,-377748.753497015&p=antarctic&l=Reference_Labels_15m(hidden),Coastlines_15m,MODIS_Terra_CorrectedReflectance_TrueColor&lg=false&l1=Reference_Labels_15m(hidden),Coastlines_15m,MODIS_Terra_CorrectedReflectance_TrueColor&lg1=false&ca=false&cv=64&t=2023-01-18-T20%3A00%3A00Z&t1=2023-10-01-T07%3A42%3A33Z

A high-resolution Polarview GIF at that scale would break the site.  I could give you a detail around the area of point 5 and include multiple images throughout the year, but I don't think it would show anything, or at least anything in the past few months.

Take a look at the large GIF on this post for the January-June time period on the Western flank: https://forum.arctic-sea-ice.net/index.php/topic,1760.msg371147.html#msg371147

[interstitial]

A little snow and it is hard to see anything useful on worldview.


If I knew precisely where the points were especially point 5 it would be easier to answer the question if point 5 is still anchored. A closeup polarview image with point 5 identified would work to confirm that. It does not matter that much to me I was just trying to offer christinetoth something of an answer.   

[baking]

I think I've figures out what they are talking about.  The only thing that has happened in the past month is that a largish iceberg off of TEIS has shifted position.  I include a GIF of the icebergs off of TEIS over the last year, 5 images about 3 months apart, to show how old icebergs move off the grounding points and new ones move in.  As long as there are some icebergs to anchor the sea ice over the Summer, I think that is the important thing.

[christinetoth]

Thanks for the info @Baking..

[baking]

Thanks for the info @Baking..

I'm glad I could help.  I'm not an expert but I've been observing Thwaites daily for over four years now and it has given me some perspective.

[FredBear]

My comment would be that it is surprising that so many of the icebergs in baking's image in reply 666 are floating at the point of grounding! Gradually over time anything that has grounded moves on, often to the next grounding    .     .    only for other icebergs to appear and similarly get stuck!
The main high points that "fix" the Eastern Ice Shelf are under the blue area of the image.

For more history it may be worth looking back at paolo's animations in replies 629 and 630 in this thread.

[Sublime_Rime]

The question in my mind is how much can these scattered small icebergs amidst sea ice exert back pressure against the glacier? Doesn't that require more of a continuous stream of bergs with the outermost in contact with the grounding points?

[interstitial]

The question in my mind is how much can these scattered small icebergs amidst sea ice exert back pressure against the glacier? Doesn't that require more of a continuous stream of bergs with the outermost in contact with the grounding points?

That would be my interpretation and even that would not be as resistant as solid ice.

[baking]

The question in my mind is how much can these scattered small icebergs amidst sea ice exert back pressure against the glacier? Doesn't that require more of a continuous stream of bergs with the outermost in contact with the grounding points?

That would be my interpretation and even that would not be as resistant as solid ice.

Sea ice does not hold back the glaciers.  What happens is the sea ice buckles upwards.

As I understand it, the sea ice protects the ice shelf by holding in icebergs closer to the shelf which in turn prevent open water from weakening the outer edge of the shelf.  You see this with the increase in calving when the sea ice is swept away.

So grounded icebergs anchor the sea ice which traps many more icebergs near the ice shelf, protecting it from exposure to open water and inhibiting calving.

[baking]

A couple of additional thoughts:

1)  To some extent the process is self-correcting.  Calvings mean new icebergs that can be grounded where the older icebergs were, so the loss of one iceberg is not necessarily a problem, however...

2) The loss of Iceberg B22-A last Summer had a direct effect on the breakup of the Western flank of the TEIS and given the current state of Thwaites Tongue, the likelihood of another B22-A sized iceberg coming along seems very slim.

Smaller or even medium-sized icebergs I wouldn't worry about.  Those happen quite frequently.

[Stephan]

Just a thought or maybe a "wrong" memory...
Do I remember correctly that there were more grounded icebergs in the main stream of Thwaites Ice Tongue years ago? So their number decreases over time (interpreting that the ice tongue gets thinner with time, leading to less and less thick enough icebergs to get grounded?)

[baking]

Just a thought or maybe a "wrong" memory...
Do I remember correctly that there were more grounded icebergs in the main stream of Thwaites Ice Tongue years ago? So their number decreases over time (interpreting that the ice tongue gets thinner with time, leading to less and less thick enough icebergs to get grounded?)

There is a grounding point near the end of the current Tongue.  You can see icebergs either being grounded or interacting with it all the time.  There may have been a time, ten years of more ago, when the grounding point helped to stabilize the Tongue.  The Tongue was twice as long and twice as wide as it is now and you could see as the ice passed over the grounding point that it left a "rumple" in the ice.  Did it slow the ice and cause it to be thicker (fast ice is thinner because the volume is about the same) or did it compress the icebergs together and allow them to refreeze making them stronger?  I can't say, but in  the past ten years there are numerous cases where the Tongue was disrupted as it encountered the grounding point so it clearly no longer stabilizes the Tongue and hasn't for a while.  At least in that area, the Tongue is more stabilizing than the grounding point.

[grixm]

First Sentinel-2 images of the cracks near the pinning point that have been of interest in the last few months. The northernmost crack has actually not grown much in length at all, despite continuously being wedged open by the moving glacier.

Attachment is a comparison gif between now and February this year.

[FredBear]

grixm, in your last reply I think north is approximately top left in the image (with the ice shelf expanding eastward and icebergs breaking away from the west).
The old ice which is grounded at the tip of the Thwaites Eastern Ice Shelf and provided back pressure to the glacier is now being bypassed by the ice moving eastwards. The fracture zone down the centre of the image is taking most of the distortion, so there is less resistance against the flow of the glacier?

[baking]

grixm, in your last reply I think north is approximately top left in the image (with the ice shelf expanding eastward and icebergs breaking away from the west).
The old ice which is grounded at the tip of the Thwaites Eastern Ice Shelf and provided back pressure to the glacier is now being bypassed by the ice moving eastwards. The fracture zone down the centre of the image is taking most of the distortion, so there is less resistance against the flow of the glacier?

In this projection, North is straight up.  I think grixm is talking about the two vertical cracks in the center, in particular the one to the right (East) which is longer and extends further North.

While the diagonal (to the Northeast) shear margin is the prime mover, its main impediment seems to be the interlocking wedges (spurs?) that are driving that Easternmost vertical crack.

You can see the growth in that crack over the past year in my most recently posted GIF above.

[baking]

The sea ice across the entire width of Thwaites has broken up in the past 12 days.  This GIF is huge even though it has been scaled down.  It might also be huge in other ways considering how early it is in the season.

[oren]

Very bad, and quite surprising.

[christinetoth]

Does the sea ice across  across the width of Thwaites usually break up later in the year like around December or so?    Or is it the first time that sea is is breaking up?     Thanks

--Christine

[grixm]

Does the sea ice across  across the width of Thwaites usually break up later in the year like around December or so?    Or is it the first time that sea is is breaking up?     Thanks

--Christine

It is normal for the fast ice to break up later in the season.

[baking]

Does the sea ice across  across the width of Thwaites usually break up later in the year like around December or so?    Or is it the first time that sea is is breaking up?     Thanks

--Christine

It is normal for the fast ice to break up later in the season.

Last year it happened at the end of July: https://forum.arctic-sea-ice.net/index.php/topic,1760.msg343516.html#msg343516

In 2020 it was September: https://forum.arctic-sea-ice.net/index.php/topic,1760.msg286496.html#msg286496

and

https://forum.arctic-sea-ice.net/index.php/topic,1760.msg287441.html#msg287441

2021 seems to have been later, but there was some open water in December.

Every year is different, but this is the first year without B22-A holding the Western end in place.

[gerontocrat]

The sea ice across the entire width of Thwaites has broken up in the past 12 days.  This GIF is huge even though it has been scaled down.  It might also be huge in other ways considering how early it is in the season.

Sea ice in the BellinghausenAmundsen Sea quickly refroze to average area after its very low minimum in early 2023. So there is no reason to believe that sea ice and ice in general in the Thwaites region was exceptionally weak and fragile at this year's maximum freeze.

BUT Grixm's post on September surface air temperature anomalies ( https://forum.arctic-sea-ice.net/index.php/topic,445.msg385026.html#msg385026 ) might give a clue.

What's going on?

[oren]

Actually the sharp growth in Bel-Am sea ice extent/area throughout the season could be related to winds blowing mostly from the south, this might cause coastal sea ice to actually be thinner (more export outwards, less compaction). But this belongs in the Antarctic sea ice threads.

[gerontocrat]

Actually the sharp growth in Bel-Am sea ice extent/area throughout the season could be related to winds blowing mostly from the south, this might cause coastal sea ice to actually be thinner (more export outwards, less compaction). But this belongs in the Antarctic sea ice threads.

Connections, connections.
Sometimes I think the ASIF has the climate science disease of only considering the narrow data at hand and not its connections to other climate variables.

https://forum.arctic-sea-ice.net/index.php/topic,520.msg385081.html#msg385081

[baking]

Let me create a new tangent, or at least refer back to an old one.  I decided to overlay yesterday's image onto the best bathymetry we currently have from Millan 2017.  While the data is not very precise, and it is hard to tell how accurate it is, icebergs are about 300 meters deep and should not ground in water 400 meters deep or deeper.

(Note for future me:  The scaling used was 2128:9520)

[Often Distant]

A quick zoomed out animation of changes in the region spanning 9 years in 9 red October images. The alignment moves a bit so it's quite rough, though still quite interesting.

[grixm]

Came across this nice animation on Twitter: https://twitter.com/kosmi64833127/status/1715105144574967831

[grixm]

An iceberg just recently calved near the tongue has neatly flipped over, allowing us to observe exactly how thick the glacier ice is at this location. The answer is just about 700 meter, at least to my eyes.

[kiwichick16]

@  grixm   .....wow !   ......well spotted

[sidd]

Thanks, grixm. I was wondering myself about thickness of calving there.

sidd

[baking]

The sea ice in the melange between Thwaites Eastern Ice Shelf (TEIS) and Thwaites Western Ice Tongue (TWIT) is beginning to break up.

[Stephan]

Calving at Thwaites Glacier.

This calving happened at a place I wouldn't expect. It occurred east of the Thwaites Eastern Ice Shelf, a third way towards Pine Island / SWT.
At two places, marked in orange boxes, the glacier calved, the calvings had a length of ca. 5 km (western) or ca. 2 km (eastern calving). The newly formed icebergs float N of the calving zone. I thouught at that place there the glacier was almost grounded.

See attached picture. N is up. TEIS is to the NW of the picture, the SWT is a little bit further east.
One click to enlarge it.

[Stephan]

Observations at TEIS.

EOSDIS data from Dec 25 in comparison to Nov 29 reveal that the connection between the slowly moving SE part of TEIS to the grounded NW part of TEIS became weaker again. There only a few kilometers of solid connection left (brown lines). It won't take too long until the grounded part of TEIS will be isolated and become dead ice.
Furthermore two cracks have markedly widened (blue lines).
The red arrows indicate flow direction and speed.

See attached picture. N is up.

[Ajpope85]

Do we know anything of the effects of erosion on the anchor points? I would imagine if the icebergs themselves are getting thinner, then that means that tidal forces and collisions with other icebergs would make those anchored icebergs grind the bedrock more and more.

[John_the_Younger]

[grounded] icebergs grind the bedrock

Ice is much weaker than most rock types, so moving pinned icebergs will have minimal affects on the bedrock.  I expect changing sea level (tidal or global changes) and thinning of ice (melt) will affect the movement of icebergs much much more.

What turns V-shaped mountain valleys into U-shaped valleys is the grinding of rock debris at the base of a thick (heavy) glacier with the bedrock beneath it (turning both bedrock and debris into smaller debris - the 'bolder-clay' till that may become lateral or end moraines).  Much of the rock debris is from landslides and from plucking frozen rock at the top end of a glacier.  Some rock is plucked off the bedrock at the bottom of a glacier, too.  (Ice can freeze to the rock, and when the ice next flows, the rock sometimes breaks along joints or other weaknesses, rather than separating from the ice.  What breaks off ranges from sand-sized to room-sized slabs of rock.)

[Ajpope85]

[grounded] icebergs grind the bedrock

Ice is much weaker than most rock types, so moving pinned icebergs will have minimal affects on the bedrock.  I expect changing sea level (tidal or global changes) and thinning of ice (melt) will affect the movement of icebergs much much more.

What turns V-shaped mountain valleys into U-shaped valleys is the grinding of rock debris at the base of a thick (heavy) glacier with the bedrock beneath it (turning both bedrock and debris into smaller debris - the 'bolder-clay' till that may become lateral or end moraines).  Much of the rock debris is from landslides and from plucking frozen rock at the top end of a glacier.  Some rock is plucked off the bedrock at the bottom of a glacier, too.  (Ice can freeze to the rock, and when the ice next flows, the rock sometimes breaks along joints or other weaknesses, rather than separating from the ice.  What breaks off ranges from sand-sized to room-sized slabs of rock.)

How is the ground beneath the icebergs around the anchor points? Is there a lot of silt and small rocks or mostly bare bedrock?

[John_the_Younger]

Ice will tend to push any debris off what it rubs against; true, though, some rock debris is stuck to some icebergs. If I was between an iceberg and some bedrock, I wouldn’t bet on my survival, but the forces a mostly floating iceberg exerts on a pinning point must be much less then what the glacier exerts on the valley floor.