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solartim27

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Re: PIG has calved
« Reply #800 on: October 29, 2018, 03:56:18 AM »
That's a serious crack if you  can see it through clouds on worldview.  Dare we say it's calved again?  Aqua  band  Oct 28
https://go.nasa.gov/2JpJYfm
« Last Edit: October 29, 2018, 04:52:57 AM by solartim27 »
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Re: PIG has calved
« Reply #801 on: October 29, 2018, 04:40:29 AM »
Thanks for your update(s) solartim.
If, should we name it the Bolsonaro calving? Sorry, bad joke...
Omnia mirari, etiam tritissima.

solartim27

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Re: PIG has calved
« Reply #802 on: October 29, 2018, 05:50:47 AM »
We have met the enemy, and he is us
Oooops
Quote
it is possible for crevasses to initiate at depths of 10–30m. From December 2006 to January 2007, hot-water drilling on Pine Island Glacier, West Antarctica, was found to trigger crevasses.

https://mobile.twitter.com/AntarcticPIG/status/1056233402905444352

https://www.cambridge.org/core/journals/annals-of-glaciology/article/crevasses-triggered-on-pine-island-glacier-west-antarctica-by-drilling-through-an-exceptional-melt-layer/EB4D278110AAF79AEA2FDF622E7663CE
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Wipneus

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Re: PIG has calved
« Reply #803 on: October 29, 2018, 12:10:12 PM »
Yes it calved again. Sentinel 1 images, medium resolution (EW=40m/pix scaled to 80m/pix).

Sleepy

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Re: PIG has calved
« Reply #804 on: October 29, 2018, 12:52:55 PM »
Thanks Wipneus.
Omnia mirari, etiam tritissima.

Grygory

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Re: PIG has calved
« Reply #805 on: October 29, 2018, 01:30:02 PM »
Fast. Next crack will react to this calving in  this year?

AbruptSLR

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Re: PIG has calved
« Reply #806 on: October 29, 2018, 03:51:12 PM »
Yes it calved again. Sentinel 1 images, medium resolution (EW=40m/pix scaled to 80m/pix).

This image shows that for the time being, the PIIS no longer buttresses the SW Tributary Ice Shelf.
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Stephan

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Re: PIG has calved
« Reply #807 on: October 29, 2018, 07:52:50 PM »
Thanks Wipneus. Great job, good anmation.
I wonder about the structures left above "2018". Is that ice mélange or smaller areas of almost open water between the ice?
I also wonder about the SW tributary. Is there an acceleration detectable?
« Last Edit: October 29, 2018, 08:35:33 PM by Stephan »

Sleepy

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Re: PIG has calved
« Reply #808 on: October 30, 2018, 10:56:10 AM »
Breaking up further.
Omnia mirari, etiam tritissima.

AbruptSLR

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Re: PIG has calved
« Reply #809 on: October 30, 2018, 05:15:38 PM »
Thanks Wipneus. Great job, good anmation.
I wonder about the structures left above "2018". Is that ice mélange or smaller areas of almost open water between the ice?
I also wonder about the SW tributary. Is there an acceleration detectable?

Stephan,

While your questions are posed to Wipneus, I will offer my following opinions:

a. The 'structures left above "2018"' is ice fractured in shear where the PIIS slides past (& bears against) land.  This is not an ice mélange, but rather is fractured ice with small areas of 'open' water temporarily exposed to freezing.

b. One would not expect the ice flow velocity of the SW Tributary Glacier to accelerate to a point where it would be observable a few days after the loss of buttressing, but per the linked discussion of what happened after the abrupt loss of ice shelf buttressing in the Antarctic Peninsula, we should see measurable results in the coming months and years:

Title: "Antarctic Peninsula Ice Shelves"

http://www.antarcticglaciers.org/glaciers-and-climate/shrinking-ice-shelves/antarctic-peninsula-ice-shelves/

Best,
ASLR
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solartim27

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Re: PIG has calved
« Reply #810 on: October 30, 2018, 05:20:10 PM »
Nice Sentinel 1 gif of the rift progression
https://twitter.com/StefLhermitte/status/1057114507775037440
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oren

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Re: PIG has calved
« Reply #811 on: October 30, 2018, 05:57:42 PM »
The PIIS is surely in record retreat territory. I am hoping for a long-term animation or graphic showing the current calving front against the past few years of PIIS advance and calving activity.

Shared Humanity

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Re: PIG has calved
« Reply #812 on: October 30, 2018, 06:07:15 PM »
There appears to be a rise just south of the Southwest Tributary that the PIG slides past, noted by its circular gray appearance. Is there a name for this rise? Is there land beneath it? It appears to provide buttressing for the PIG and may prevent further retreat of the glacier.

crandles

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Re: PIG has calved
« Reply #813 on: October 30, 2018, 07:27:56 PM »
Are these the same features visible on last image and gif?
« Last Edit: October 30, 2018, 07:40:15 PM by crandles »

Stephan

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Re: PIG has calved
« Reply #814 on: October 30, 2018, 08:35:48 PM »

Stephan,

While your questions are posed to Wipneus, I will offer my following opinions:

...
Best,
ASLR

Thanks for your opinion and for the link to various smaller and larger ice shelves around the Peninsula.

AbruptSLR

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Re: PIG has calved
« Reply #815 on: October 30, 2018, 08:56:57 PM »
There are some nice video clips in the linked article:

Title: "Huge Antarctic iceberg breaks off Pine Island Glacier"

https://www.axios.com/giant-iceberg-breaks-off-pine-island-glacier-antarctica-bd762a27-69ef-4efc-91e5-0352fd180672.html

Extract: "An iceberg about five times the size of Manhattan has broken off the Pine Island Glacier in West Antarctica over the past 24 hours, an ominous sign of the continued retreat of this fast-flowing mass of ice. Like many other marine terminating glaciers in Antarctica, this glacier is retreating over time, and increasing the movement of ice into the sea."
« Last Edit: October 30, 2018, 09:11:36 PM by AbruptSLR »
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oren

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Re: PIG has calved
« Reply #816 on: October 30, 2018, 09:03:54 PM »
The PIIS is surely in record retreat territory. I am hoping for a long-term animation or graphic showing the current calving front against the past few years of PIIS advance and calving activity.
Turns out Stef Lhermitte has posted such an animation going back to 1973. The retreat is indeed into record territory, and especially so at the important junction of the SW tributary and the PIIS.

https://twitter.com/StefLhermitte/status/1057264449122373632

Edit: this is the same animation appearing in ASLR's link above.

Stephan

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Re: PIG has calved
« Reply #817 on: October 30, 2018, 09:25:07 PM »
Stef Lhermite also summarizes larger calving events in his blog. I paste them in here to get an overview of the accelerating rate of these calving events:
"In early 2000 large PIG calving events happened every ~5 yrs (2001, 2007, 2011), but since 2013 there were 4 of them (2013, 2015, 2017, 2018). Consequently, the glacier front retreated strongly from the 1972-2013 range and it is now ~5km further inland than in 2015-2017"
(Bad news, aren't it?)
I ask myself, whether there will be some new cracks developing in the ever faster flowing and stretching ice stream this austral summer which prepare another greater calving event next year...

AbruptSLR

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Re: PIG has calved
« Reply #818 on: October 30, 2018, 09:38:49 PM »
The PIIS is surely in record retreat territory. I am hoping for a long-term animation or graphic showing the current calving front against the past few years of PIIS advance and calving activity.
Turns out Stef Lhermitte has posted such an animation going back to 1973. The retreat is indeed into record territory, and especially so at the important junction of the SW tributary and the PIIS.

https://twitter.com/StefLhermitte/status/1057264449122373632

Edit: this is the same animation appearing in ASLR's link above.

Here is a screen grab from Stef Lhermittee's animation on his site:
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crandles

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Re: PIG has calved
« Reply #819 on: October 30, 2018, 11:11:18 PM »
from https://www.the-cryosphere.net/12/2039/2018/tc-12-2039-2018.pdf

Quote
Konrad et al. (2017) show how changes to the ice shelf
and grounding line region of PIG and other Amundsen Sea
embayment glaciers propagate upstream on a timescale of a
few years. Thus, the recent reduction of back stress can be
expected to propagate to the grounded trunk of PIG, causing
further acceleration of flow and thus further dynamic thinning.
Accordingly, a restabilisation of the ice shelf due to repinning
at a ridge, e.g. by a very rapid advance or thickening
of the ice shelf, cannot be expected in the foreseeable future,
at least for as long as rapid basal melting driven by CDW
incursion continues. Instead, the ice-shelf calving line seems
to have made an irreversible step to a new position and orientation
in 2015, which has been confirmed in 2017, following
progressive detachment from the pinning point over the
previous decade. We do not expect further significant rapid
calving line retreat in the next few years. The northern margin
is now stabilised by a pinning point near Evans Knoll,
which rises above sea level where the nearby ice-shelf thickness
is about 450 m, and the southern margin is stabilised by
thick tributary ice inflow (Fretwell et al., 2013). Nevertheless,
continued rapid ice-shelf thinning as observed in other
studies (Pritchard et al., 2012; Rignot et al., 2013) and as
confirmed by our observation of pinning point loss (Fig. 3)
will further destabilise the PIG ice shelf in the future and
at some stage is expected to lead to calving occurring even
further upstream.

The triangular feature is Evans Knoll.

Has calving now gone past Evans Knoll such that further calving can be expected? Or will the glaciers just accelerate so the calving front advances to stabilisation points of Evans Knoll and the SW tributary?

Perhaps also worth noting
Quote
rapid thinning of the ice shelf that has occurred over the past two decades,
exceeding 5 m yr−1 in recent years (Pritchard et al., 2012; Rignot et al., 2013)

sidd

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Re: PIG has calved
« Reply #820 on: October 30, 2018, 11:42:51 PM »
From the Arndt paper :

"We do not expect further significant rapid calving line retreat in the next few years."

 O dear. The paper was published this year. I suppose it depends on what they mean by "significant."

sidd
 

DrTskoul

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Re: PIG has calved
« Reply #821 on: October 31, 2018, 12:11:13 AM »
From the Arndt paper :

"We do not expect further significant rapid calving line retreat in the next few years."

 O dear. The paper was published this year. I suppose it depends on what they mean by "significant."

sidd

Great timing.... /sarc
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sidd

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Re: PIG has calved
« Reply #822 on: October 31, 2018, 04:51:56 AM »
In fairness, they did identify the rift R3 and state:

"The newly discovered rift R3 (inset of Fig. 5) will likely trigger the next calving event."

open access. it is a nice paper, my quibbles notwithstanding. do read all about it. bathymetry is revealing.

sidd

Jim Hunt

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Re: PIG has calved
« Reply #823 on: October 31, 2018, 10:02:24 AM »
There are some nice video clips in the linked article

It would have been nice if Andrew had credited Wipneus et al. for breaking the news:

https://twitter.com/ruth_mottram/status/1056891078933180416
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Sleepy

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Re: PIG has calved
« Reply #824 on: October 31, 2018, 10:29:25 AM »
Breaking up is not so hard to do.
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oren

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Re: PIG has calved
« Reply #825 on: November 01, 2018, 01:26:58 PM »
Just finished reading the Arndt paper. Very well written and explains quite a lot about the behavior of the calving front over the last few years, including that grounded rotating iceberg that spent more than a year in the bay. I strongly recommend reading to anyone interested in this thread.
The disturbing part is the realization that the current stabilization mechanism (besides Evans Knoll) is the point of contact with the SW tributary glacier, which has just been lost or seriously weakened. Bad times for the PIG and West Antarctica in general.

crandles

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Re: PIG has calved
« Reply #826 on: November 01, 2018, 02:34:53 PM »
I am not at all an expert but my reaction to

"the current stabilization mechanism (besides Evans Knoll) is the point of contact with the SW tributary glacier, which has just been lost or seriously weakened."

is to wonder what happens. I imagine that both PIG and SW tributary advance more rapidly until Evans Knoll and SW tributary again provide stabilisation pressures. This advancement further thins the glaciers so that might make PIG more prone to calving in response to pressure from SW tributary. OTOH the Arndt paper suggests the rift that recently calved was induced by (intermittent) back pressure from the grounding point that is no longer playing a part. It is not at all clear to me whether Evans Knoll will play that same role nor, if it does, whether more or less effectively.

That is no more than wild speculation by me. Anyway, any comments or further or different speculation welcome.


AbruptSLR

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Re: PIG has calved
« Reply #827 on: November 01, 2018, 04:12:03 PM »
That is no more than wild speculation by me. Anyway, any comments or further or different speculation welcome.

First, as the 2018-19 ENSO season is projected to produce a moderate El Nino event, I provide:
1. The first two images that show that such conditions tend to advect more warm circumpolar deep water, CDW, beneath the Pine Island Ice Shelf, PIIS.
2. The third image shows that such warm CDW beneath the PIIS tends to increase the rate of melting of the PIIS basal ice.
3. The fourth image panels A & C shows typical (ENSO neutral) water circulation (in 2009) beneath the PIIS and panels B & D show typical water circulation during La Nina conditions (with reduced CDW circulation).

See also
2010–12 La Niña event
https://en.wikipedia.org/wiki/2010%E2%80%9312_La_Ni%C3%B1a_event

Thus in the next year we should see enhanced basal ice melting, and enhance thinning, for the PIIS.
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AbruptSLR

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Re: PIG has calved
« Reply #828 on: November 01, 2018, 04:27:06 PM »
That is no more than wild speculation by me. Anyway, any comments or further or different speculation welcome.

Second, I note that:

1. As a minor point the first images shows that Evans Knoll sits on a peninsula and the PIIS actually contacts the peninsula rather than Evans Knoll itself. More importantly, the second image shows that shear rifting occurs (if the PIIS ever returns to this area) downstream of the peninsula, while local compress in the PIIS prevents shear rifting upstream of the peninsula.
2. The third image shows that as the PIIS thins (due both to ice volume conservation and basal ice melting) the grounding line retreats, thus allowing and subsequently calved icebergs to more easily float over potential pinning points.
3. The fourth image shows a typical computer simulations that shows stresses in the PIIS that are largely induced by flexure as the water elevation changes due to such factors as: tides, storm surge, and stagnation pressures due to advection of warm CDW.

All of these considerations can accelerate fracturing of the PIIS along zones of pre-existing weaknesses.
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AbruptSLR

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Re: PIG has calved
« Reply #829 on: November 01, 2018, 04:43:08 PM »
That is no more than wild speculation by me. Anyway, any comments or further or different speculation welcome.

Third, I note that:

1. The first image shows that currently the ice velocities PIIS are faster than those for the SW Tributary Glacier/Ice-Shelf, thus one might suspect that the buttressing action of the PIIS on the SW Tributary Glacier may restored in a few years; however, I note that on the left side of the PIIS there are extensive shear rifting (or marginal crevasses as shown in the second image) immediately upstream of the SW Tributary Glacier, and that such fractured ice many not buttress the SW Tributary Glacier as well as in previous years.
2. The third image shows the local bathymetry so that readers can better appreciate where the ice flow movement is occurring.
3. The fourth image from MacGregor et al shows a close-up of the old ice velocities in the SW Tributary Glacier; which now are likely accelerating due to the loss of buttressing from the PIIS.

This is largely background information to get readers oriented, and to reduce idle speculations.
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AbruptSLR

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Re: PIG has calved
« Reply #830 on: November 01, 2018, 05:01:03 PM »
That is no more than wild speculation by me. Anyway, any comments or further or different speculation welcome.

Finally, I note that:

1. The first image shows a cartoon of the conceptual transition of a marine glacier with an ice shelf to one with an ice cliff calving face.  Further, I note that DeConto & Pollard have estimated that before GMSTA reaches 2.7C that hydrofracturing will cause the PIIS to collapse leaving the PIG with an ice cliff calving face.
2. The second image shows a rendering of postulated paleo ice cliff failure calving of the PIG when it extending into the Pine Island Bay.  This shows how the calved icebergs can float over the top of potential subsea pinning points.
3.  The third image shows Durand et al's estimate of the profile of the PIG/PIIS in 2014, showing that the seafloor is relatively flat upstream of the current grounding line.  This means that if the Earth warms enough for hydrofracturing to occur for the PIIS then the PIG may calve icebergs associated with over a hundred kilometers of grounding line retreat before stabilizing.
4.  The fourth image shows a graph illustrating the relationship of ice cliff calving (in kilometers of retreat per year) versus both ice cliff freeboard and relative water depth.

Collectively, these images indicate that before GMSTA reaches 2.7C, the PIG ice face could retreat rapidly within a couple of decades.
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vox_mundi

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Re: PIG has calved
« Reply #831 on: November 01, 2018, 05:11:26 PM »
Cause of Long, Potentially Damaging Channels on Antarctic Ice Shelves Found



In a study published today in Nature Communications, researchers led by Imperial College London have connected a huge 130-km-long channel (the distance between London and Birmingham) on the surface of an Antarctic floating ice shelf to the landscape two kilometres below the ice sheet upstream.

The channel, and associated features on the ice surface, are thought to be a point of instability on the ice shelf. If the surface ice melts, water will preferentially run down these features, carving out a deeper channel and creating further weaknesses.

Ice-shelf surface channels are seen across Antarctica, so the process uncovered in the research is likely to be commonplace. Now the cause has been identified, researchers can investigate similar channels for signs of instability elsewhere in Antarctica, especially in regions known to be vulnerable to change.


As the ice, flowing from upper-left to lower-right, encounters a hill beneath the ice (light grey shape), a cavity is created under the ice shelf. Water (red and blue arrows) feeds into the cavity, melting a channel that is reflected on the ice surface (dark grey channel)

The Foundation Ice Stream is also the type of glacier that can have water at its base, flowing between the bottom of the glacier and the underlying rock. The team found that when the base of the glacier encountered a large solitary hill at the same point it starts to float,a gap emerged under the ice downstream of the hill.

This gap was filled by water from around the base of the glacier, which carved a gouge upwards into the ice. This gouge was 800 metres high in some places, and led to the extensive channel seen on the surface of the ice.
---------------------------------
Hafeez Jeofry et al. Hard rock landforms generate 130 km ice shelf channels through water focusing in basal corrugations, Nature Communications (2018)

Abstract
Satellite imagery reveals flowstripes on Foundation Ice Stream parallel to ice flow, and meandering features on the ice-shelf that cross-cut ice flow and are thought to be formed by water exiting a well-organised subglacial system. Here, ice-penetrating radar data show flow-parallel hard-bed landforms beneath the grounded ice, and channels incised upwards into the ice shelf beneath meandering surface channels. As the ice transitions to flotation, the ice shelf incorporates a corrugation resulting from the landforms. Radar reveals the presence of subglacial water alongside the landforms, indicating a well-organised drainage system in which water exits the ice sheet as a point source, mixes with cavity water and incises upwards into a corrugation peak, accentuating the corrugation downstream. Hard-bedded landforms influence both subglacial hydrology and ice-shelf structure and, as they are known to be widespread on formerly glaciated terrain, their influence on the ice-sheet-shelf transition could be more widespread than thought previously.


High-resolution multibeam echo-sounder swath bathymetry datasets for the Antarctic shelf, showing examples of relict hard-bedded landforms with dimensions directly comparable to those imaged with radar beneath the trunk of Foundation ice stream
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crandles

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Re: PIG has calved
« Reply #832 on: November 01, 2018, 05:29:55 PM »

This is largely background information to get readers oriented, and to reduce idle speculations.

Thank you.

AbruptSLR

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Re: PIG has calved
« Reply #833 on: November 01, 2018, 06:40:41 PM »
In the way of more background, the following 2013 reference makes it clear that both calving rates and basal ice melting rates are high for the PIIS (PI in the images); in part due to the frequent advection of warm CDW.

The linked reference better quantifies the ice mass loss from both calving and basal melting for the major Antarctic ice shelves.

The first attached image shows: Calving fluxes (green) and basal mass loss (−BMB; red). Pie chart shows numbers for surveyed ice shelves only. Errors, 1 s.d. b, Ratio between calving flux (green) and BMB (red), in per cent of total flux.

The second attached figure shows a significant correlation (R2 = 0.84 (coefficient of determination); P = 3.13 × 10−5; F-test) between surface lowering rates8 and our mean basal mass-loss rates (−SBMB) for thinning ice shelves.

M. A. Depoorter, J. L. Bamber, J. A. Griggs, J. T. M. Lenaerts, S. R. M. Ligtenberg, M. R. van den Broeke & G. Moholdt, (2013),"Calving fluxes and basal melt rates of Antarctic ice shelves," Nature, doi:10.1038/nature12567

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature12567.html?WT.ec_id=NATURE-20130919

Abstract: "Iceberg calving has been assumed to be the dominant cause of mass loss for the Antarctic ice sheet, with previous estimates of the calving flux exceeding 2,000 gigatonnes per year. More recently, the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front. So far, however, no study has reliably quantified the calving flux and the basal mass balance (the balance between accretion and ablation at the ice-shelf base) for the whole of Antarctica. The distribution of fresh water in the Southern Ocean and its partitioning between the liquid and solid phases is therefore poorly constrained. Here we estimate the mass balance components for all ice shelves in Antarctica, using satellite measurements of calving flux and grounding-line flux, modelled ice-shelf snow accumulation rates and a regional scaling that accounts for unsurveyed areas. We obtain a total calving flux of 1,321 ± 144 gigatonnes per year and a total basal mass balance of −1,454 ± 174 gigatonnes per year. This means that about half of the ice-sheet surface mass gain is lost through oceanic erosion before reaching the ice front, and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking. In addition, the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves. We find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering8 and enhanced discharge9. We suggest that basal mass loss is a valuable metric for predicting future ice-shelf vulnerability to oceanic forcing."
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Grygory

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Re: PIG has calved
« Reply #834 on: November 01, 2018, 07:15:33 PM »
I will draw attention to such factors that are not often mentioned:
The ice that flows slowly has time to warm up. When the shelf glacier accelerates the cold ice it comes in contact with hotter water and the cracking occurs faster
Colder ice is also less mechanically resistant and easier to crack
Estimation of glaciers retreating on the basis of paleo data may have one mistake - Glaciers that have already gone back have carved out the bottom and it is easier to retreat now (faster)




Stephan

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Re: PIG has calved
« Reply #835 on: November 01, 2018, 10:01:50 PM »
ASLR,
Thanks for the explanations, figures and information.
Stephan

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Re: PIG has calved
« Reply #836 on: November 01, 2018, 10:20:45 PM »
ASLR,
Thanks for the explanations, figures and information.
Stephan

They were all taken from earlier posts (that included the sources) in various threads, and there is a lot of other background discussions previously posted such as:

1. The first image shows the relationship between the SW Tributary Glacier and the Thwaites Glacier's eastern shear margin.
2. The second image shows the measured profiles of salinity and temperatures above freezing for the PIIS.
3. The fourth information shows a computer projection of representative CDW flow patterns in the ASE and beneath the PIIS.
4.  The fourth image shows Plastic Necking for Antarctica's four biggest ice shelves, which illustrates how warm CDW beneath an ice shelf can burn up through basal crevasses in the bottom of the ice shelf.
« Last Edit: November 01, 2018, 11:20:57 PM by AbruptSLR »
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Stephan

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Re: PIG has calved
« Reply #837 on: November 02, 2018, 05:21:39 PM »
The latest calving event made it into the scientific news in the show "Forschung aktuell" of "Deutschlandfunk", a nation-wide public information radio station.

AbruptSLR

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Re: PIG has calved
« Reply #838 on: November 06, 2018, 05:52:59 PM »
....
I imagine that both PIG and SW tributary advance more rapidly until Evans Knoll and SW tributary again provide stabilisation pressures.
...

In my opinion it is not a foregone conclusion that both the PIIS and the SW Tributary Ice Shelf, SWTIS will advance together until the SWTIS provides 'stabilization pressures' again, for reasons including:

1. As the PIIS ice flow velocity is faster than that for the SWTIS, the attached Sentinel image from Nov 5, 2018, indicates to me that it is likely that as the PIIS advances it will continuously peel-off the Northeast corner of the SWTIS, as I see a new crack (marginal crevasse/fissure/rift) there that I did not see a week ago.  If so, the PIIS may not provide buttressing action to the SWTIS anytime soon.
2. To me the pressure recently exerted by the SWTIS on the PIIS is the most significant factor that cause the splitting tension stress that caused the recent major calving event for the PIIS.  Thus I would not say the SWTIS provides 'stabilization pressure' on the PIIS.
« Last Edit: November 06, 2018, 07:39:28 PM by AbruptSLR »
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Re: PIG has calved
« Reply #839 on: November 07, 2018, 03:18:54 PM »
Landsat delivered a cloud-free image of the PIG and the recent calving, now officially named B-46 (as long as it does not disintegrates into small pieces ). The image is attached at 60m/pix.

The arrow points at a linear feature, that may be the next big crack. This is shown in detail, resized to 7.5m/pix and contrast enhanced.

A cloud-free Sentinel 2 image would be very nice now.

AbruptSLR

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Re: PIG has calved
« Reply #840 on: November 08, 2018, 06:13:15 PM »
The attached Nullschool weather image shows MSLP and surface wind patterns for Nov 8 2018.  This image shows that (likely due to the current El Nino condition) the Amundsen Sea Low, ASL, is positioned so as to direct surface winds directly into the Amundsen Sea Embayment, ASE; which tends to induce upwelling of relatively warm circumpolar deep water, CDW, into the ASE; which then accelerates basal ice melting of both the sea ice and floating ice shelves, therein.  If such conditions continue for several months this will promote ice loss from both the PIIS and the SWTIS (not to mention also the Thwaites Ice Shelf).
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ghoti

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Re: PIG has calved
« Reply #841 on: November 08, 2018, 10:40:23 PM »
New NASA Icebridge photos and video of the PIG.

Video is on Facebook so not sure if everyone can access it.

https://www.facebook.com/ICEatNASA/videos/448851502309932/

https://www.nasa.gov/feature/goddard/2018/massive-antarctic-iceberg-spotted-on-nasa-icebridge-flight

FredBear

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Re: PIG has calved
« Reply #842 on: November 09, 2018, 12:17:10 AM »
The NASA comparative image in the previous post (image Nov. 7, 2018) clearly shows a number of "cracks" appearing across PIG above the latest break?

Phil.

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Re: PIG has calved
« Reply #843 on: November 09, 2018, 01:13:15 AM »
Landsat delivered a cloud-free image of the PIG and the recent calving, now officially named B-46 (as long as it does not disintegrates into small pieces ). The image is attached at 60m/pix.

The arrow points at a linear feature, that may be the next big crack. This is shown in detail, resized to 7.5m/pix and contrast enhanced.

A cloud-free Sentinel 2 image would be very nice now.

Nat Geo website had an article with some NASA photos today.
https://www.nationalgeographic.com/environment/2018/11/exclusive-first-pictures-of-iceberg-three-times-the-size-of-manhattan/

Shared Humanity

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Re: PIG has calved
« Reply #844 on: November 09, 2018, 03:06:26 PM »
The NASA comparative image in the previous post (image Nov. 7, 2018) clearly shows a number of "cracks" appearing across PIG above the latest break?

Given the fractured, rubble like nature of the ice to the right of the glacier, I would not be surprised if there were another significant calving this melt season.  There appears to be very little pinning there and, if it does calve, I would expect this glacier to also rotate away from this side as the current glacier has done.

Shared Humanity

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Re: PIG has calved
« Reply #845 on: November 09, 2018, 03:51:26 PM »

2. The third image shows the local bathymetry so that readers can better appreciate where the ice flow movement is occurring.


On that 3rd image, what are the yellow and red lines? Is the red line the current grounding line?

AbruptSLR

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Re: PIG has calved
« Reply #846 on: November 09, 2018, 04:37:06 PM »

2. The third image shows the local bathymetry so that readers can better appreciate where the ice flow movement is occurring.


On that 3rd image, what are the yellow and red lines? Is the red line the current grounding line?

Shared Humanity,

That image is fig 2a (showing PIG) of the following paywalled reference, and the attached image is fig 2b for Thwaites.  As I am too cheap to purchase this paper, the images come from sidd, but these images make it clear that the red line shows the local grounding line and the yellow line shows some short of time averaged (from 2009 to 2014) position for the ice face of the associated ice shelves (note the dotted yellow line across the active calving front for the Pine Island Ice Shelf, PIIS, indicating that this ice face was actively shifting during the 2009 to 2014 period).

Also, I note that the attached image shows that Thwaites Eastern Ice Shelf, TEIS, is currently pinned by a subsea pinnacle, and that as the TEIS continues to thin (most significantly due to basal ice melting from warm CDW) at some point in the future (maybe years) the TEIS will become unpinned which will reduce the buttressing action of the TEIS on the Thwaites Glacier.  When this buttressing is eventually reduced, both this and the recent loss of buttressing on the SW Tributary Glacier, will both contribute to increasing the stress on the Eastern Shear Margin of the Thwaites Glacier (which is not a good thing):

Romain Millan et al. (09 January 2017), "Bathymetry of the Amundsen Sea Embayment sector of West Antarctica from Operation IceBridge gravity and other data", Geophysical Research Letters,
https://doi.org/10.1002/2016GL072071

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2016GL072071

Abstract: "We employ airborne gravity data from NASA's Operation IceBridge collected in 2009–2014 to infer the bathymetry of sub–ice shelf cavities in front of Pine Island, Thwaites, Smith, and Kohler glaciers, West Antarctica. We use a three‐dimensional inversion constrained by multibeam echo sounding data offshore and bed topography from a mass conservation reconstruction on land. The seamless bed elevation data refine details of the Pine Island sub–ice shelf cavity, a slightly thinner cavity beneath Thwaites, and previously unknown deep (>1200 m) channels beneath the Crosson and Dotson ice shelves that shallow (500 m and 750 m, respectively) near the ice shelf fronts. These sub–ice shelf channels define the natural pathways for warm, circumpolar deep water to reach the glacier grounding lines, melt the ice shelves from below, and constrain the pattern of past and future glacial retreat."

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

crandles

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Re: PIG has calved
« Reply #847 on: November 09, 2018, 04:45:20 PM »
That image is fig 2a (showing PIG) of the following paywalled reference, and the attached image is fig 2b for Thwaites.  As I am too cheap to purchase this paper, the images come from sidd, but these images make it clear that the red line shows the local grounding line and the yellow line shows some short of time averaged (from 2009 to 2014) position for the ice face of the associated ice shelves (note the dotted yellow line across the active calving front for the Pine Island Ice Shelf, PIIS, indicating that this ice face was actively shifting during the 2009 to 2014 period).

Just enter paper name into
https://sci-hub.tw

and you get

https://sci-hub.tw/10.1002/2016gl072071

Quote
New bathymetry of the Amundsen Sea Embayment (ASE) of West Antarctica with
the a) Pine Island, b) Thwaites/Haynes and c) Smith/Kohler glaciers. Grounding line positions
are red (year 1996), ice front positions (year 2008) are yellow, AUV tracks are green, and seismic
data are black crosses. Bed elevation is color coded from brown/yellow and green (above sea
level) to light blue and dark blue (-1,400 m), with light contours every 100 m and thick contours
every 400 m. Profiles A-A’ to F-F’ in orange with dots every 10 km are shown in Figure 3.

Stephan

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Re: PIG has calved
« Reply #848 on: November 09, 2018, 04:54:25 PM »
Landsat delivered a cloud-free image of the PIG and the recent calving, now officially named B-46 (as long as it does not disintegrates into small pieces ). The image is attached at 60m/pix.

The arrow points at a linear feature, that may be the next big crack. This is shown in detail, resized to 7.5m/pix and contrast enhanced.

A cloud-free Sentinel 2 image would be very nice now.
Would you mind to combine this photograph with the one you posted on Reply #767 on: September 21, 2018, 09:11:33 AM? Is this the same crack or a new one?

Thanks a lot!

AbruptSLR

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Re: PIG has calved
« Reply #849 on: November 09, 2018, 04:56:59 PM »
That image is fig 2a (showing PIG) of the following paywalled reference, and the attached image is fig 2b for Thwaites.  As I am too cheap to purchase this paper, the images come from sidd, but these images make it clear that the red line shows the local grounding line and the yellow line shows some short of time averaged (from 2009 to 2014) position for the ice face of the associated ice shelves (note the dotted yellow line across the active calving front for the Pine Island Ice Shelf, PIIS, indicating that this ice face was actively shifting during the 2009 to 2014 period).

Just enter paper name into
https://sci-hub.tw

and you get

https://sci-hub.tw/10.1002/2016gl072071

Quote
New bathymetry of the Amundsen Sea Embayment (ASE) of West Antarctica with
the a) Pine Island, b) Thwaites/Haynes and c) Smith/Kohler glaciers. Grounding line positions
are red (year 1996), ice front positions (year 2008) are yellow, AUV tracks are green, and seismic
data are black crosses. Bed elevation is color coded from brown/yellow and green (above sea
level) to light blue and dark blue (-1,400 m), with light contours every 100 m and thick contours
every 400 m. Profiles A-A’ to F-F’ in orange with dots every 10 km are shown in Figure 3.

Thank you.

Also, for those not familiar with the recent history of if the ice shelves in the ASE, I provide the attached image from MacGregor et al. (2012).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson