Support the Arctic Sea Ice Forum and Blog

Author Topic: Pine Island Glacier (PIG) Calving and Discussion  (Read 489318 times)

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2650 on: January 13, 2021, 05:30:54 PM »
From uniquorn post
>
"For analysis, best to download it and view frame by frame. (or better, download the original .png files, the ani is half size, cropped)"
I completely agree and moreover it is necessary to juggle between the images because of the gray zones (uncalculated velocity). That's why I hadn't published any animations, but only an example (choosing a date that showed the SIS velocity in their entirety). 

In general you should have an idea to show and choose the images to support it !

>
"x,y coordinate scaling may not be quite right"
I too have just started with panoply (a year ago I even had to ask how to make an animated gif 😊)
For me they are good, in fact for what I understood it is necessary that the intervals of the coordinates X and Y are in the ratio 2 : 1.

>
The second image shows the "standard deviation (STD) of the velocity" and not the velocity.
« Last Edit: January 13, 2021, 05:37:28 PM by paolo »

uniquorn

  • Young ice
  • Posts: 3028
    • View Profile
  • Liked: 1347
  • Likes Given: 282
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2651 on: January 13, 2021, 08:54:09 PM »
Thanks Paolo. I found 4 scales with the same palette a bit confusing so I tried 3 different ones. The first is 0m-500m to show the outline shape, then 450m-2000m and 1950m-4500m. The overlap is to cut down on white space between the different palettes.
Possible transparency issue with the second palette

Ill add one more image to the collection which might add some reasoning behind the standard deviation image. This one features more contour lines. The gradient along the glacier edge being so steep would probably raise the STD. Contours said more to me than colours in the end.

And a close up. Now I will leave you in peace :)
« Last Edit: January 14, 2021, 08:28:41 PM by uniquorn »

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2652 on: January 17, 2021, 06:21:17 AM »
The Sentinel2 image of the 16/01 is of poor quality, but allows to focus on the SIS on the SWT side.

Click to enlarge

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2653 on: January 17, 2021, 07:41:51 PM »
Calculation of the PIG speeds from the data on the site: http://www.cpom.ucl.ac.uk/csopr/iv/index.php?glacier_number=3 for the months of June and December, from December 2014 to December 2020.

Averages used:
To avoid problems related to doubtful variations in the measurements provided between close points along the transect for the same period and between close intervals for the same position along the transect I calculated the average of the existing measurements for :
> the same interval of points along the transect: 20-30 km, 30-40 km, ..., 120-130 km (I considered that the measurements of the other intervals:  > 130, did not provide sufficiently reliable measurements)
> 5 periods for each month of June and December. For the month of December 2016 and for all months starting in December 2017 we have files that calculate the speeds from intervals of 6 days that follow each other regularly (which makes a global interval of 36 days).This is no longer true for the months prior to December 2016 and for the month of June 2017; in these cases I took the 5 periods closer to the month of calculation, with, as a result, an overall interval between 42 and 108 days and with overlaps between the periods used for the velocity calculations. Moreover for the months of June 2015 and 2016, for one of the chosen intervals I find no valuation of the speed and for these two months I calculate the speed using in reality only 4 intervals.  For the month of December 2015 I find no valuation for the points between 20 and 30 km.

Sources of speed valuations along the transect:
> for the period 2014-2019 I based myself on the text files containing the valuations per point and per period, files contained in the global zip that I downloaded. 
> For the month of June 2020 I am based on the individually downloaded text files.
> for the month of December 2020 no text files are available and I based on the image of the downloaded diagram to value the speeds by interval: 20-30 km up to 60-70 km and I dropped the other intervals for which a reliable valuation was not possible (in the first image I give an example of the images used for my valuations)

Results :
> The measures found are presented in the second image and it can be seen that they are consistent with each other.
> There is indeed a more or less constant acceleration from June 2018. To bring it out more clearly I calculated the averages for the 20-70 km interval that I show in the third image.

Click to enlarge

ADD : In the third image it is the average over the interval 20-70, the values for the interval 20-30 are higher, e.g. for December 2020 there are 4.816!
« Last Edit: January 17, 2021, 07:48:54 PM by paolo »

interstitial

  • Grease ice
  • Posts: 899
    • View Profile
  • Liked: 270
  • Likes Given: 78
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2654 on: January 17, 2021, 08:45:43 PM »
Thanks Paolo. I know sorting through that data was more work than it appears.
Did some major obstruction clear around Dec 2017 - Jun 2018?

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2655 on: January 17, 2021, 09:46:47 PM »
There was mainly the calving on 23/09/2017, after which the pinning point provided by the SWT lost its strength and it gradually eroded to disappear with the calving of 29/10/2018, after which it remained only an indirect and further upstream pinning point: the Cork, which in turn calved on 09/02/2020.
Since no more action of the SWT on the PIG
To these elements can be added a progressive instability of the ice sheet: MISI (see Rosier et al. 2020).

And it's not going to get any better  :(

baking

  • Frazil ice
  • Posts: 429
    • View Profile
  • Liked: 165
  • Likes Given: 18
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2656 on: January 18, 2021, 03:28:54 AM »
There was mainly the calving on 23/09/2017, after which the pinning point provided by the SWT lost its strength and it gradually eroded to disappear with the calving of 29/10/2018, after which it remained only an indirect and further upstream pinning point: the Cork, which in turn calved on 09/02/2020.
Since no more action of the SWT on the PIG
Thank you Paolo for doing this.  I've been putting off doing it myself for a week now.

I agree that the calvings of September 2017 and October 2018 along with the disconnect from the SWT are significant factors.  One important point however is that the constantly increasing velocity in the last three years implies an ongoing and worsening positive feedback effect, such as the worsening situation in the Southern Shear Margin.

Take a look at this 6-year movie of PIG:
https://movie-usa.glencoesoftware.com/video/10.1073/pnas.1912890117/video-1

You can clearly see the relative stability before September 2017 and the rapid collapse after October 2018, so the interesting time to me is the period between those two calvings when the velocity started really accelerating.

What I think is the turning point is in April 2018 when the SWT suffered a major collapse and it no longer supported the Southern Shear Margin.  Also, the calvings in the South have been almost constant since then.

Of course, the collapse of the SWT came about because of the September 2017 PIG calving, but the velocity of PIG did not really pick up until after the SWT collapse.

oren

  • Moderator
  • First-year ice
  • Posts: 6683
    • View Profile
  • Liked: 2458
  • Likes Given: 2173
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2657 on: January 18, 2021, 03:49:19 AM »
Big thanks paolo for the velocity over time charts. Very useful and extremely disconcerting.

Indeed, from the video it appears the SWT calving was the immediate trigger for acceleration - and it makes perfect sense that such loss of buttressing would result in exactly this outcome. And the SWT calving was triggered by the main PIG calving, which got too near to where it mattered.

sidd

  • First-year ice
  • Posts: 5816
    • View Profile
  • Liked: 815
  • Likes Given: 0
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2658 on: January 18, 2021, 05:53:47 AM »
Re: Rosier et al. 2020

may i please have a doi for that reference ?

sidd

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2659 on: January 18, 2021, 08:24:12 AM »
"The tipping points and early-warning indicators for Pine Island Glacier, West Antarctica"
Sebastian H. R. Rosier, Ronja Reese, Jonathan F. Donges, Jan De RydtG. Hilmar Gudmundsson, and Ricarda Winkelmann
doi.org/10.5194/tc-2020-186
Preprint. Discussion started: 4 August 2020
Review status: this preprint is currently under review for the journal TC

baking

  • Frazil ice
  • Posts: 429
    • View Profile
  • Liked: 165
  • Likes Given: 18
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2660 on: January 18, 2021, 04:37:30 PM »
"The tipping points and early-warning indicators for Pine Island Glacier, West Antarctica"
Sebastian H. R. Rosier, Ronja Reese, Jonathan F. Donges, Jan De RydtG. Hilmar Gudmundsson, and Ricarda Winkelmann
doi.org/10.5194/tc-2020-186
Preprint. Discussion started: 4 August 2020
Review status: this preprint is currently under review for the journal TC
"Critical slowing is measurable as an increase in the state variable auto-correlation. We measure this here using the lag-1  auto-correlation  function  (Dakos  et  al.,  2008;  Scheffer  et  al.,  2009;  Held  and  Kleinen,  2004)  applied  to  the  grounding line flux over a 300 year moving window preceding each tipping point (hereafter referred to as the ACF indicator)."

This might come in handy after we have 300 years of data.

On a more serious note, another way to look at it is that as long as the velocity is increasing, PIG is in an unstable state.  Only when the velocity levels out can we say that it has at least temporarily stabilized.

sidd

  • First-year ice
  • Posts: 5816
    • View Profile
  • Liked: 815
  • Likes Given: 0
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2661 on: January 19, 2021, 02:48:16 AM »
Thanks for the Rosier reference.

sidd

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2662 on: January 20, 2021, 10:25:49 PM »
My apologies, I discovered yesterday that an error was slipped in the Excel formulas, a ";" instead of a ":" when taking into account, for each month (June or December) and for each sector, the data relating to the fifth and last file.This meant that when calculating the average I only took into account the valuations of the first and last position of the fifth file, if they were valued, instead of taking into account all the existing valuations (when displaying the formula on the screen, this error was not  very visible  >:().

The corrections clearly don't change the data significantly, but I prefer to repost the corrected diagrams (first and second image)

General remark and not related to the correction: regarding the speed for the period December 2019 sector 20-30 km: the high value in this case is explained by the progressive opening of the rifts that will lead to February calving.

I also post :
> the table of corrected valuations
> a table of differences between the corrected version and the previous version. The differences are minimal except for the measures for June 2015 and 2016. These are the old periods corresponding to the southern winter and these old measures were very little valued, as will be seen in the following tables
> a table containing for each month (June or December) and for each sector the number of existing valuations
> a table containing for each month (June or December) and for each sector the number of existing valuations and the number of files containing at least one valuation.
> a table with the differences between the valuations with those of December 2014.

Many images => two posts

Click to enlarge.

« Last Edit: January 20, 2021, 10:32:17 PM by paolo »

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2663 on: January 20, 2021, 10:28:16 PM »
Suite

interstitial

  • Grease ice
  • Posts: 899
    • View Profile
  • Liked: 270
  • Likes Given: 78
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2664 on: January 21, 2021, 02:10:06 AM »
Thank you for the corrections even if it does not change things much. 

grixm

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 218
  • Likes Given: 77
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2665 on: January 21, 2021, 12:56:34 PM »
New small perpendicular crack in the SWT is growing, and if it reaches the first parallel crack, a large piece will calve.

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2666 on: January 21, 2021, 04:56:15 PM »
Some remarks and observations from the Sentinel2 image of the 20/01/2021 :

> First image relative to the NdDZ (Northern downstream Damage Zone):
   * The NE-IS (NorthEast Ice Shelf) since the calving of February 2020 is no longer supported downstream by the NIS (the two are no longer connected), but it is supported only by the Ice Rise Evans Knoll. As a consequence it is accelerating, which causes its detachment from the Ice Rise Evans Knoll (several calvings on the north side of the NdDZ have already occurred and others will follow). Moreover this acceleration causes a decrease in the velocity gradient with the PIG and therefore a lower shear (it can be noticed that new marginal rifts are rare and do not develop inside).
   * A disconnection between the PIG and the NE-IS is occurring. This could slow down the acceleration of the NE-IS.
   * In conclusion: NdDZ will continue to develop upstream.


> Second image related to the future iceberg (northern front, calving 2020 residue):
   * Several longitudinal rifts have appeared and this part of the front could start calving soon.

> Third image related to the rifts cR1 (central Rift 1) and SmR2 (Southern marginal Rift 2) :
   * The cloud image does not allow to detect if these two rifts have extended, but we can observe at the base of SmR2 that now there are two completely detached icebergs (one of them had already been reported by Grixm, if I remember well)

> Fourth image related to the SdDZ (Southern downstream Damage Zone):
   * The progressive detachment of the SIS iceberg (future iceberg signaled by Baking) continues
   * The disconnection between PIG and SIS is expanding. This could slow down calving from the previous point.
   * In conclusion: SdDZ will continue to develop upstream.

Click to enlarge

baking

  • Frazil ice
  • Posts: 429
    • View Profile
  • Liked: 165
  • Likes Given: 18
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2667 on: January 21, 2021, 05:26:06 PM »
New small perpendicular crack in the SWT is growing, and if it reaches the first parallel crack, a large piece will calve.
nice catch, but just to be clear that is the Southern Ice Shelf (SIS) not the Southwest tributary (SWT) although it may be a moot point soon enough.  See the labels below.

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2668 on: January 21, 2021, 06:32:13 PM »
I would like to complete Grixm's post by giving a global vision of the progressive deterioration of the western part of the SIS (which practically coincides with T11).
Note the opening of new rifts on the SWT side corresponding to the rifts already open on the SIS side.

Successive calvings will not be long in coming.

Click to enlarge

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2669 on: January 21, 2021, 06:44:07 PM »
To finish an image on the deterioration, also in the west, of the SWT

Click to enlarge

Stephan

  • Nilas ice
  • Posts: 1514
    • View Profile
  • Liked: 539
  • Likes Given: 255
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2670 on: January 21, 2021, 07:10:26 PM »
Thank you paolo and all the others to keep us up to date.
Do you think that the calvings which will unavoidably occur in the (near) future may be delayed due to almost complete coverage of the sea with sea ice?
It is too late just to be concerned about Climate Change

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2671 on: January 23, 2021, 08:53:04 PM »
I have just completed the diagrams of the Along-Flow speeds with a more detailed view of the upstream speeds: between 60 and 110 km using 2 km sections. In this case to avoid abnormal data I have set minimum conditions to take into account the valuations.

 From this table I will give two presentations: in absolute values (first image) and as differences, in percentage, with the valuation of December 2014 (second image).

I will also take the opportunity to present the Along-Flow velocity diagram, already published in absolute values version, in this new version as differences, in percentage, with the valuation of December 2014 (third image).

I foresee an update in 6 months with the publication of the three diagrams: Along-Flow (20-130 km, 10 km sections), downstream (20-70 km, single section; the "thermometer") and detailed upstream (60-110 km, 2 km section) in both versions. If there are interested persons I could also publish the corresponding tables.

As soon as I have time I will complete with the Across-Flow speed diagram (in both presentations)

Click to enlarge.

interstitial

  • Grease ice
  • Posts: 899
    • View Profile
  • Liked: 270
  • Likes Given: 78
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2672 on: January 23, 2021, 09:59:12 PM »
Thanks Paolo

Stephan

  • Nilas ice
  • Posts: 1514
    • View Profile
  • Liked: 539
  • Likes Given: 255
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2673 on: January 24, 2021, 09:40:55 AM »
Yes, interstitial.
Absolutely appreciated, paolo. And another "Like" earned.
It is too late just to be concerned about Climate Change

RoxTheGeologist

  • Grease ice
  • Posts: 526
    • View Profile
  • Liked: 156
  • Likes Given: 127
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2674 on: January 24, 2021, 02:45:37 PM »
I have just completed the diagrams of the Along-Flow speeds with a more detailed view of the upstream speeds: between 60 and 110 km using 2 km sections. In this case to avoid abnormal data I have set minimum conditions to take into account the valuations.

 From this table I will give two presentations: in absolute values (first image) and as differences, in percentage, with the valuation of December 2014 (second image).

I will also take the opportunity to present the Along-Flow velocity diagram, already published in absolute values version, in this new version as differences, in percentage, with the valuation of December 2014 (third image).

I foresee an update in 6 months with the publication of the three diagrams: Along-Flow (20-130 km, 10 km sections), downstream (20-70 km, single section; the "thermometer") and detailed upstream (60-110 km, 2 km section) in both versions. If there are interested persons I could also publish the corresponding tables.

As soon as I have time I will complete with the Across-Flow speed diagram (in both presentations)

Click to enlarge.


Wow! Nice work.

grixm

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 218
  • Likes Given: 77
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2675 on: January 25, 2021, 03:53:39 PM »
Hmm, look at this updated look at the new rift from paolo's second image in https://forum.arctic-sea-ice.net/index.php/topic,429.msg298845.html#msg298845

It almost looks like it has already calved because the rift is complete.. But the iceberg has not moved, so maybe not.

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2676 on: January 25, 2021, 04:31:17 PM »
Probably yes, and in this case would enter the large family of icebergs which, when they reach the majority, always stay with their parents: currently both in the SWT, both in the SSM (PIG side), ...

It must be said that this winter there were almost no polynias and now the bay is still almost completely ice-covered: no strong outgoing current and therefore no strong CDW.  Decisively the weather had pity on him and tried to help him as much as she could...

But the final result is not great...

Seriously, it signals the senescent state of the big future iceberg which should decay into several pieces, including the one reported here.

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2677 on: January 26, 2021, 10:26:18 PM »
Tonight's Sentinel2 image is beautiful, too bad that there are no updates to the images already published on 20/01, so there is no real need to publish new images ...
 
The case of the piece of the future iceberg is apart, but even with Sentinel2 we cannot completely decide and validate the calving.

I also publish the image of the NdDZ for its beauty.

Click to enlarge


grixm

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 218
  • Likes Given: 77
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2678 on: January 27, 2021, 07:24:30 PM »
Now the rectangular piece has calved.

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2679 on: January 27, 2021, 08:06:44 PM »
Sorry, but checking the Worldview images from previous days and I don't see any difference.
It is attached and tenacious like a mold  ::) ;)

grixm

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 218
  • Likes Given: 77
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2680 on: January 27, 2021, 08:43:40 PM »
Sorry, but checking the Worldview images from previous days and I don't see any difference.
It is attached and tenacious like a mold  ::) ;)
Ah you're right, I could have sworn that was detached. It looks so different from the polarview radar shots.

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2681 on: February 05, 2021, 08:44:10 PM »
As expected, the north side of the NuDZ has collapsed.

Animation with the images of 04/02 and 05/02

Click to animate

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2682 on: February 05, 2021, 08:53:37 PM »
The block in the process of detaching, signalled by grixm, should soon do so, now the rift is also visible in the low-resolution Sentinel 1 image.

Click to enlarge

grixm

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 218
  • Likes Given: 77
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2683 on: February 12, 2021, 10:12:17 PM »
So do we think the fast ice in front of the glacier will clear out at all, this year? It's getting pretty late in the season but the ice still looks rather solid.

interstitial

  • Grease ice
  • Posts: 899
    • View Profile
  • Liked: 270
  • Likes Given: 78
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2684 on: February 13, 2021, 04:25:29 AM »
Grixm it makes me wonder what has changed. If the water has just rerouted like I suspect it could cause problems elsewhere.

baking

  • Frazil ice
  • Posts: 429
    • View Profile
  • Liked: 165
  • Likes Given: 18
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2685 on: February 13, 2021, 03:16:22 PM »
One reason might be the large number of icebergs from earlier calvings still in place where the polynya usually start to form.  Debris from the calvings gets frozen into the sea ice and probably results in a much thicker layer than usual.  We still have a couple more months to see what might happen this season.  Thwaites is in a really tricky spot where it might go either way.

Of course, the glacier keeps flowing no matter what.  In the big picture, seasonal sea ice probably doesn't have a huge effect.

FredBear

  • Frazil ice
  • Posts: 196
    • View Profile
  • Liked: 20
  • Likes Given: 34
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2686 on: February 13, 2021, 05:53:45 PM »
There certainly seems to have been a lack of polynya at the front of Pine Island Glacier this year (the break-up of the fast ice usually starts from the back?). The presence of old calvings may have reinforced the local fast ice there, as may the motion of the glacier compressing the ice in front.

Looking on the opposite side of the continent:-  The Amery ice shelf seems to have had a quiet melting season too in spite it of losing D28 from the front last year. Much less "blue" melting on/around the area and no pools of water on the shelf this year. Maybe there has also been less flow of fresher water to flush ice away north from the front of the glacier too?

(On another aside - the Larsen B embayment was largely cleared of fast ice, often as late as March, until 2013, since then it has not lost all of the covering in spite of blue signs of melt in the "warm" season.)

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2687 on: February 13, 2021, 07:08:19 PM »
Small historical analysis based on the southern summers from 2002/2003 (19 summers in total) using images from the Modis archive (until summer 2018-2019):
In 12 summers the sea ice in the Pine Island bay in front of the PIG has completely melted (in 7 cases already in October and in 4 cases in November).
In two summers the 3 polynyas, corresponding to the NSM, the centre and the SSM, merged to form a long polynya along the entire front, but no melting of the sea ice in Pine Island Bay.
In 5 summers there was no melting of the sea ice in front of the PIG.
It is remarkable that in the summers from 2003-2004 to 2007-2008 (five summers therefore) there was no melting of the sea ice in front of the PIG and these years correspond to years of powerful CDW and accelerated retreat of the grounding line.
It is thus necessary to be careful, there is a link, more or less strong, between CDW and polynyas, but not between CDW and sea ice melting!
For sea ice, one should rather look for atmospheric conditions and sea surface currents.
For this summer we can say :
That it has snowed a lot and that there hasn't been, in general, a big melting (see attached pictures).
Based on the Sentinel2 images, which are very often very cloudy, one can imagine that in general the weather was often cloudy or very cloudy.
This is unfortunate, but there is no global information on winds and sea currents at the surface.
As far as the polynyas are concerned, the one in front of the NSM was well visible, when it was not filled with the rubbish from a calving, and sporadically the one in the centre when it was not filled with rubbish of NSM origin (there were nevertheless movements of the sea ice, even if very slow), but the one corresponding to the SSM is missing.  This can be explained by the presence in the SSM of a dense ice mélange which is much more difficult to melt. Concerning the small polynya in front of the SM between the SWT and the SIS, its origin is due to the fact that the outgoing current corresponding to this SM, because of the retreat of the front line, no longer merges with that corresponding to the SSM and has become independent.
So even from the presence or not of the polynyas is not obvious under these conditions to make diagnostics on the power of the CDW.
In any case the fact that the dense mixture remains close to the SSM is not a valid defense for the PIG, it only slows down the emptying and deepening of the SdDZ. The state of health of the PIG is and remains very bad. 

click to enlarge

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2688 on: February 16, 2021, 12:33:19 AM »
New Sentinel2 images, many of the clouds, but also some beautiful lightning.
The deterioration of the SIS and SWT, especially on the east side, continues and calving should not be long in coming.

Click to enlarge

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2689 on: February 16, 2021, 12:38:35 AM »
North side much more clouds but we can notice that the situation of the "future iceberg" is always more degraded and that upstream of the NdDZ there are several new rifts and that therefore the DZ is going to advance upstream.

Click to enlarge

grixm

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 218
  • Likes Given: 77
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2690 on: February 19, 2021, 07:07:49 PM »
Looks like refreezing in the bay. Temperature is around -10C

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2691 on: February 20, 2021, 10:26:35 PM »
I am posting a SIS animation based on Sentinel2 images with intervals between images of about one month: 12/10, 11/11, 11/12, 16/01 and 15/02, covering a period of 4 months.
One can notice the rapid deterioration, already documented in this forum, but also that the maximum deformation of the SIS is not on the SWT side, but more in the centre. This can be seen by taking into account the global opening of the rifts, but it can be highlighted by comparing the front at 12/10 with that at 15/02, as shown in the last image of the animation. Moreover, the bending induced on the edges of the SIS explains very well the opening of the North/South rifts opening from the outer side, i.e. from North to South (both rifts are highlighted in the last image).
It seems that the action of the SWT on the SIS is therefore not only limited to shear, but that compression towards the east must also be taken into account.

Click to animate

baking

  • Frazil ice
  • Posts: 429
    • View Profile
  • Liked: 165
  • Likes Given: 18
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2692 on: February 21, 2021, 03:46:04 AM »
I see the SIS "bowing" out in the center due pressure from the SWT and downstream pressure from PIG.

baking

  • Frazil ice
  • Posts: 429
    • View Profile
  • Liked: 165
  • Likes Given: 18
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2693 on: February 22, 2021, 05:10:18 PM »
I've made a GIF of the central part Southern Ice Shelf (SIS) blown up 200% going back to January 11 including up to today's hi-res Sentinel 1 radar image.  What I noticed is that during January is that all three "slices" going back to R4 were moving together, but in February only the front two "slices" going back to R3 were moving.  This might be due to weakening of the ice between R3 and R4 at the Eastern end.

In any case, this is putting a lot of strain on R2 and R3 and the perpendicular cracks that have been developing.  It does seem like something is about to happen and soon.

Note: For those wondering, R1 is the current ice front, the point of an earlier rift and calving in May 2020.  (EDIT:  On second thought, I think we labelled the current front "R1.5" since it appeared between R1 and R2.)
« Last Edit: February 22, 2021, 05:56:59 PM by baking »

grixm

  • Frazil ice
  • Posts: 397
    • View Profile
  • Liked: 218
  • Likes Given: 77
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2694 on: February 25, 2021, 09:29:44 PM »
Absolutely pristine sentinel-2 image today.

Looks like this berg in the north is about to pop, or already has.

paolo

  • Grease ice
  • Posts: 687
    • View Profile
  • Liked: 286
  • Likes Given: 10
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2695 on: February 25, 2021, 10:15:12 PM »
Indeed very beautiful images

Enclosed are images of the SIS, SWT and the "future iceberg" in the north.

Click to enlarge

baking

  • Frazil ice
  • Posts: 429
    • View Profile
  • Liked: 165
  • Likes Given: 18
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2696 on: February 25, 2021, 10:28:46 PM »
Sentinelhub Playground is acting up for me, but here is a 30-day GIF of the Southern Ice Shelf made from screenshots.

interstitial

  • Grease ice
  • Posts: 899
    • View Profile
  • Liked: 270
  • Likes Given: 78
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2697 on: February 26, 2021, 01:59:33 AM »
As this Antarctic melting season has/is winding down I am surprised how little visible action took place in the PIG. I suspect severe damage will have been done this year when we figure out where the warm water went.

sidd

  • First-year ice
  • Posts: 5816
    • View Profile
  • Liked: 815
  • Likes Given: 0
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2698 on: February 26, 2021, 06:46:30 AM »
Re: where the warm water went

Worst case, it went underneath to the grounding line.

sidd


interstitial

  • Grease ice
  • Posts: 899
    • View Profile
  • Liked: 270
  • Likes Given: 78
Re: Pine Island Glacier (PIG) Calving and Discussion
« Reply #2699 on: February 26, 2021, 10:34:11 AM »
Re: where the warm water went

Worst case, it went underneath to the grounding line.

sidd


that is basically my fear that the water is realeasing all of its heat moving around under there and we will not know it untill something collapses. What if it found its way throygh one of the many ice filled gaps below sea level? this is pure speculation of course but it could do much damage before we even know what is happening.