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Author Topic: Petermann Gletscher / Petermann Fjord / North West Greenland  (Read 159055 times)

sidd

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #400 on: April 16, 2016, 05:10:05 AM »
Thanx for the detailed explanation on Petermann and Nares fluxes, that helped me.

Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #401 on: April 18, 2016, 08:11:29 PM »
We might now see a picture of what will be giving birth to a new giant ice berg from Petermann Gletscher, the Starboard crack seems to be resting for a while, but the Port crack is developing a bit (see the animation), the 2 cracks will probably meet sometimes in the near future and result in another "Breaking News" calving :
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A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #402 on: April 18, 2016, 11:41:13 PM »
Worth keeping an eye starting in mid-June? It's too cold there for water to melt or cracks to propagate. There have been clear Landsats almost daily ... nothing is happening that I can see except that the ice tongue is slowly marching seaward.

The calculation in the 4th image shows the 'sverdrups' of new ice flowing into ice tongue, more conveniently thought of as cubic meters per second crossing the grounding zone flux gate. The bottom 400 m of this 600 m thick ice will have melted by the time it reaches the front line in ~30 years. Under the old rules.

Petermann did speed up slightly after the last massive calvings (from 1.1 km/yr to 1.2), attributed to loss of buttressing back-pressure. However resistance at the sides is fairly minimal and even if the whole floating ice shelf is lost, Petermann won't speed up dramatically, even with warmish water swirling around the vertical ice front at the grounding zone. According to published theory.

Andreas Muenchow

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #403 on: April 19, 2016, 04:41:30 PM »
@ A-Team:

The 450 m^3/s is the volume of ice moving across the grounding zone. About 2/3 of this melts as the 600 m ice at the grounding line appears 30 years later at the terminus with a ice thickness ~200 m. This gives 450*2/3=300 m^3/s. Density of ice is about 90% of water, so if all the melt goes into the ocean as freshwater, we expect 300*0.9=270 m^3/s of glacier meltwater to enter Petermann Fjord as freshwater. This is about half a Delaware River or a Thames River.

We get almost the same number (280 and 340 m^3/s) via a very different method from ocean-only measurements of salinity and temperature with depth and across a Petermann Fjord section along with a arguments on the physics of ocean circulation and mixing. We get two values because we got two sections.
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A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #404 on: April 20, 2016, 12:08:01 AM »
we expect 300*0.9=270 m^3/s of glacier meltwater to enter Petermann Fjord as freshwater. This is about half a Delaware River or a Thames River.

That is absolutely amazing to have a river of this magnitude flowing out from under a frozen glacier whose surface features have stable for decades, giving no indication of the melt turmoil underneath. And where is all this fresh water going (to the south) and to what effect?

I would guess there is only minor seasonality to the flow since circulating ocean water deep below has vast thermal inertia and lacks effective contact with the freezing winter or warmer summer air above.

However within ocean circulation per se, in addition to tides, there could be both seasonal effects associated with Nares Strait as well as longer term trends attributable to climate change induced rearrangements in large scale circulation. It is great to have some actual data to put bounds on speculation and put model theory to the experimental test.

Down the road, after total disappearance of the ice shelf, the melt would come from the newly exposed vertical face as the bottom sits on bedrock and is not exposed to sea water. This presents far less surface area (12 km2 than the horizontal under-shelf (~800 km2). It's not clear to me how much of the current oceanic circulatory pattern would carry over to the shelf-free situation, perhaps quite a bit.

Petermann might retreat fairly slowly under oceanic facial melt up its prograde slope until a broad sill is reached several dozen km upglacier so is not a proxy in this sense for the more worrisome retrograde West Antarctic ice shelves.

In terms of temperature-with-depth of ice within the floating ice shelf, this situation presents interesting but manageable boundary conditions for Fourier's heat equation which would have an exact solution here (after certain idealizations) on a trapezoidal slab. Still, it's good to have the thermister strings.

It might be feasible to get at the temperature profile a ways upglacier from the grounding line, though it is problematic that this would shed light on the basal upheaval anomalies which barely extend to Schoubye. Logistically, it would make far more sense to drill basal features at Eqip than here.

sidd

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #405 on: April 29, 2016, 10:52:15 PM »
nice ice folding around petermann

 DOI: 10.1038/ncomms11427

open access

A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #406 on: May 01, 2016, 10:26:55 PM »
sidd, nice spotting.

We got an earlier taste of this article from the 3nd author's dissertation, F Mundel. It is a very interesting approach -- forget that it's ice, just model it along the lines of any geological formation distorted by flow.

The graphics are nicely done and provided at a very generous scale (as extracted from the pdf version of the article with ImageJ).

It will be interesting to see the response from the glaciologists who previously put out rather different explanations for it. What sort of additional experimental data could distinguish between them? I am offline traveling the rest of this month and hope to pursue this farther in June.

http://forum.arctic-sea-ice.net/index.php/board,12.0.html
http://forum.arctic-sea-ice.net/index.php/topic,154.msg65364.html#msg65364

Converging flow and anisotropy cause large-scale folding in Greenland's ice sheet
PD Bons et al
http://forum.arctic-sea-ice.net/index.php/topic,154.msg65364.html#msg65364

http://www.nature.com/ncomms/2016/160429/ncomms11427/extref/ncomms11427-s1.pdf supplementa

http://www.nature.com/ncomms/2016/160429/ncomms11427/extref/ncomms11427-s2.mov fly-thru of sheath fold
« Last Edit: May 02, 2016, 08:39:37 PM by A-Team »

Wipneus

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #407 on: May 18, 2016, 07:04:51 PM »
I am quite sure this shows that the upper (and shorter) of the two cracks is widening.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #408 on: June 19, 2016, 04:13:01 PM »
Also on the Petermann Gletscher melt ponds are forming. Here is a reasonable cloud free image scaled to 30m/pix.

Click for the big picture.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #409 on: June 19, 2016, 04:18:50 PM »
And a detailed animation in 10m/pix of the discussed cracks.

CraigsIsland

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #410 on: June 19, 2016, 06:23:05 PM »
Wipneus- I really like that orange contextual information overlaid on your images/animations. Really helpful!

A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #411 on: June 19, 2016, 10:02:27 PM »
The re-processed image below 'triangulates' the three east side cracks of Petermann. Unless one of the cracks lengthens or widens, we expect the triangle to move downstream with fixed geometry (in R028 S2A images) as the central Petermann ice sheet moves as a rigid block.

The longest crack has extended its tip about 560 (or it least its visibility has improved) from what I recall from following it last fall into November. However this extension is upstream, nearly perpendicular to the direction it 'needs' to go if the ice shelf is to fracture across its entire width.

Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #412 on: June 27, 2016, 03:33:07 AM »
Adam Ash posted a GIF of Nares Strait that included The Petermann Glacier fjord (reposted below).  I find it interesting how much the Petermann Glacier has advanced since 'they' last set the calving front mask in the Worldview images Adam posted.  As Perermann G. is about 20 km wide, the glacier has advanced about 5 km since when(?), last autumn?

(Edit: per Andreas Muenchow's following post, the mask must have been drawn a few years ago.)
« Last Edit: June 27, 2016, 06:42:03 PM by Tor Bejnar »
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Andreas Muenchow

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #413 on: June 27, 2016, 04:57:28 PM »
Petermann Gletscher speeds vary both in space and time. The advance of the terminus is about 1.25 km per year. This figure summarizes glacier speeds from both remote sensing and GPS tracking. It is part of a manuscript currently under review, but a pre-print is at

http://muenchow.cms.udel.edu/papers/Muenchow2016-TOS.pdf
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oren

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #414 on: June 27, 2016, 10:31:35 PM »
Petermann Gletscher speeds vary both in space and time. The advance of the terminus is about 1.25 km per year. This figure summarizes glacier speeds from both remote sensing and GPS tracking. It is part of a manuscript currently under review.

Very interesting and well written (only had time to read a quarter for the time being).

TerryM

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #415 on: June 27, 2016, 11:34:35 PM »
Wonderful!!


Questions and comments.


Line 62 - I was aware of the "surface undulations" on the former large ice shelves off Ellesmere & Greenland but was not aware of their presence on the Peterman shelf. Are they still present? Do they run with the flow or at right angles to it? Do we know their cause?


Line 192 - I had no idea that the sill would be so far out in the Lincoln Sea. Are most sills so far removed from the straits or fjords they guard?


Line 228 - Any idea why these warm, salty waters would have entered the fjord between 2012 to 2015? Will this drive more rapid melting, or does it indicate less melt water mixing in 2015?


Line 261 - Should "but" be replaced with "and" for clarity?


Line 276 - Any speculation on how, when, or why this very warm, salty core could have been forced over the sill? Am I correct in assuming that this will cause unprecedented melting when it starts rubbing against our glacier, or is it 0nly a small incursion that won't noticeably change things?


Line 322 - I don't understand bothand. Possible typo? Sentence is still difficult for me.


Line 354 - Has this "heat flux" increased since the destruction of almost all of Ellesmere Island's formerly extensive ice shelves?


Line 381 - That's a LOT OF ICE. How does it compare to PII2010 & PII2012?


Line 393 - Are these 10 day eddies only present when ice is flowing, or are they present but hidden through the year?


Fig. 1 - Did PII2012 follow roughly the same path as PII2010?
What do the yellow areas indicate?


Fig. 2 - Koch's map seems to me to be indicating a greater thickness, particularly near Sigurd & Porsild. Is this my imagination, their mistake, or a thinning of the shelf over time.


Fig. 3 - The speed graph seems to indicate highest speed near the grounding line, then a slow down further along. How is that possible? Does the glacier thicken or widen enough to absorb this?


Fig. 4 - Will ice temperature affect how much flex the ice can take before fracturing, or is this too small an amount to be concerned with?


Fig. 5 - For lack of a better place for my question. Is it the Hall Basin Gyre that is driving AW into Petermann Fjord? I had assumed that the coriolis effect would have kept the currents to the right and that the northerly current would have been feeding in.


Please don't feel any obligation to reply. These were just questions and observations that came to me as I read your paper.


Another wonderful example of publishing in a timely manner.


I don't know if you are aware of it, but your dust-up with our former government got a fair amount of publicity on this side of the border, and had some effect on our last election where we "threw the bums out". Canada owes you a huge debt of gratitude.


As Do I
Terry


Andreas Muenchow

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #416 on: June 28, 2016, 04:11:59 AM »
Whow ... this is a full-blown, most constructive review, Terry. I will not address your questions and comments here, but will do so in the revised version of the manuscript. Thank you so much for the detailed feed-back.

I will try to clarify one questions you raised:

The largest glacier speed is indeed at the grounding line with much smaller speeds landward and somewhat smaller speeds seaward. The conservation of mass states that this must be balanced by both melting and/or a change over time in the thickness h of the glacier. More specifically, the time rate of change of ice thickness [d(h)/d(t)] equals the convergence/divergence of the ice thickness [u*d(h)/d(x)] plus the melting. Traditionally people assume a steady state [d(h)/d(t)=0] in which case mass is conserved by a balance between melting=u*d(h)/dx, however, there are two ways that the convergence/divergence term can balance melting: First, the glacier speed u varies along the glacier, that is u=u(x) and second, the rate of change of ice thickness along the glacier can change with distance as well, as it indeed does as the cavity is curved.

For the last 10 years or so, however, Petermann Gletscher is NOT in steady-state because the climate is changing and so does Petermann. This adds another term, d(h)/d(t) to the mass balance which makes matters a tad more complex. This last non-steady term accounts for about half the melting and thinning (5 m per yer) of Petermann. More details on all of this you find in the (peer-reviewed and published) open access Muenchow et al. (2014) at

http://muenchow.cms.udel.edu/papers/Muenchow2014-JGlac.pdf

Have fun ... and thank you again for your wonderful questions and comments ... to be addressed in the revised manuscript ;-)
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oren

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #417 on: June 28, 2016, 11:44:26 PM »
After reading the full article, I must say it is very interesting and highly informative. Andreas - thank you for sharing the preview.

A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #418 on: June 29, 2016, 02:28:45 AM »
very interesting and highly informative. Andreas - thank you for sharing the preview.
Indeed this sets the gold standard for timely public dissemination of ongoing research results!

I am wondering though if the situation is not somewhat more heterogenous in horizontal cross-section than a GPS flowline can reveal, especially at the grounding zone and nearer to the walls.

 A German group has been posting interferometric pairs of consecutive S1A IW-grade Petermann imagery (see earlier on this forum). We also have a high resolution fluke of a 2015 Radarsat pair run in S1A emulation.

Additionally, between them, S2A and Landsat-8 cover Petermann almost daily. At 10m resolution over a year, a surface feature would be displaced ~125 pixels, so even a month would do for differential optical interferometry (ie mask the rock, bump the later date back ~12 pixels so the feature is motionless at say the grounding zone, make an RGB using neutral shade for B).

This imagery sees only a plan view of the surface so it knows very little about tidal or buoyant vertical displacements and nothing per se about melt cavities. There may be be swath-reprocessed lidar available though for a very few recent dates.

With a mass conservation law in force, it seems like it should be possible to produce synthetic interferograms of both types from the data. The extent to which these differed from observation is then a measure of this putative horizontal cross-section heterogeneity, or put another way, see what it takes to bring the rest of the flowlines into compliance.
« Last Edit: June 29, 2016, 02:45:39 AM by A-Team »

magnamentis

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #419 on: June 30, 2016, 06:53:34 PM »
@Bill Fothergill

thank you for the detailed and comprehensive elaboration in the  IJIS thread :-)

always good to get the greater picture as to at least main and/or all factors that contribute to events or non-events :-)

i thought i post this here to put an end to further OT over there as per your suggestion.
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A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #420 on: July 11, 2016, 12:34:04 PM »
Looking now at matched pairs of Sentinel 2A ie 10n days apart, for 'starboard' (northeast wall) crack widening just using band 4 at 8-bit of a 20XNQ of 09 Jul 16, nothing dramatic seems to be happening on the floating ice shelf.

This is a fabulously clear image however so it would make an excellent baseline for developments 10, 20, 30 days out. The slow animation below is a gallery of scenes at resolution along the ice shelf and lower glacier, not a time series.

Melt ponds are numerous right now just below the grounding zone but are not unusually abundant. The twin lakes near the longest starboard crack do not have water in them at this point; nor does the central kayakable channel. There is an unusual feature, possibly sastrugi. south and east of the grounding zone. The melange by the calving front area is complex and would benefit from a color image.

http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/20/X/NQ/2016/7/9/1/
« Last Edit: July 11, 2016, 01:21:36 PM by A-Team »

Cate

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #421 on: July 18, 2016, 11:39:28 PM »
Permalink: http://www.arctic.io/explorer/4Xa5A/2016-07-18/9-N81.3175-W60.81283

Crack opens up in Petermann fjord.

Toggle from 17 July to 18 July 2016 to see the big crack appear---looks like a fairly wide stretch of open water right across the channel of Petermann, about midway between the calving front and the mouth of the fjord.
« Last Edit: July 19, 2016, 11:17:46 AM by Cate »

Tor Bejnar

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #422 on: July 19, 2016, 12:12:52 AM »
Screen shot from today's LANCE MODIS
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A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #423 on: July 31, 2016, 05:58:50 PM »
We mustn't get distracted by Ryder Glacier and miss the big event here at Petermann. The last 4 years have seen some slow development on the starboard cracks but nothing dramatic (1st animation, pinned to twin lake blue dot).

The pattern here has been for new cracks to develop to the south as the glacier moves past some fixed point on shore. There has been a substantial extension of a new crack in 2016 and this may be "the one to watch".  Indeed Sentinel of July 25th does not show the middle of this new crack as well as the later Landsat despite being of higher resolution (5m shown).

The dates on these match fairly well but the Landsat-8 path, row geometries differ because of unavailability of sufficient clear days.
« Last Edit: July 31, 2016, 06:13:55 PM by A-Team »

TerryM

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #424 on: July 31, 2016, 09:41:28 PM »
A-Team
If Petermann should calve either late this season or early in 2017, PII-2016 or PII-2017 might plug up Nares Strait for few years, putting a wrench into any plans for a huge melt-out in that time frame. That said, none of the cracks seem to be racing towards the center channel which Dr. Muenchow seems to regard as a precursor to a calving event.
Relieving Lincoln Sea's buildup of MYI by advection through Nares Strait, and opening the pack in this critical area seems necessary if we are to best 2012's record ice loss.
If Petermann should calf, the resulting ice island might be so deep that it gets stranded within Petermann Fjord and therefor presents no problems to Nares ice advection.
Exciting times.
Terry

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #425 on: July 31, 2016, 10:44:15 PM »
What A-Team is mentioning is very important when predicting a future calving, but to become a "Good barn party" you will need a partner (most of the times, and luckily she is from the other side of the valley ).
We have 2 important shear  points at this time in the lifespan of Petermann Gletscher they are Belgrave Gletcher (marked 1.) and Faith Gletscher (marked 2.), and as you see in the animation below   she is getting closer (Port side):
« Last Edit: July 31, 2016, 10:52:51 PM by Espen »
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A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #426 on: July 31, 2016, 10:58:04 PM »
plug up Nares Strait for few years
Terry, very good point. That's probably the main effect.

Loss of another big piece of the ice shelf will not result in acceleration of Petermann Glacier per se because there is not much buttressing with the rock walls to begin with.

Thus even total loss would not result in sea level rise acceleration attributable to Petermann, even though its inland velocities are remarkable in the overall north-central Greenland context, following Jakobshavn and Zachariae.

The analogy to loss of floating ice shelves in Antarctica at first seems flawed (lack of confining rock walls), as does unstoppable retreat (Petermann has an upstream sill rather than retrograde slope). However the melt underneath by warming ocean waters is spot-on, given Petermann is some years ahead of the Antarctic curve.

Major ice shelf loss at Petermann will trigger another day-after-tomorrow manhatten-sized media circus. While we're best positioned here to provide them dramatic imagery, that should always be accompanied with the fine print about what it does and does not portend.

The new crack is circled below to make clear where the new cross-shelf break might occur. It is the most active feature so far in 2016 though it could end up a dud like the three above it.

And Espen's point is also valid -- port side initiation cannot not be ruled out just because the last two full breaks came from starboard. Actually looking at that history closely, the second event was just a continuation of the first. One event is really meagre statistically, almost as bad as the PDO.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #427 on: July 31, 2016, 11:09:01 PM »
I dont think the plug up is a real issue , the berg is too "small" for that to happen, it might have problems exiting but I believe the current is strong enough to be beat it out?
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #428 on: August 02, 2016, 05:18:11 PM »
If Petermann calves this year at the big crack than the calving front would be around 7km further inland than in 2012. Taking the 4.8km advance into account than the ice island would be 11-12km long or wide. Hard to say how the geometry will turn out.

I made the comparison to practice annotations with layers for gifs. The colours of the arrows should be bright red and bright orange, but for some reason GIMP makes them very dull. Does anyone know why? They look correct in the colour selection tool and appear correct in a new blank image.

Click image to animate

A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #429 on: August 02, 2016, 08:34:30 PM »
for some reason GIMP makes them very dull. Does anyone know why?
Yes. You have the transparency set too high in either the drawing layer, the mode, tool options, or the brush choice. I find sometimes just mousing over the mode sends it somewhere I never intended to go. Gimp comes defaulted to rather arty settings so it takes a while to get it into a scientific configuration.

While you are on a roll, can you pull the depth profile for the putative next ice island from A Muenchow's latest? It might need vertical exaggeration which you can do in gimp by scale change with height uncoupled from width.

This, along with km of width, would give an estimate of ice volume (neglecting all the bottom channelling erosion). I am recalling thickness ramping from 600 m at the grounding zone to 200 m at the front. This could be overlaid on Nares bathymetry (IBCAO) to see where the hangups are out in the channel. I'm thinking that because of the depth ramping, the island won't sit level (freeboard) once it is cut loose though the angle would be meagre. And how many events of this size would it take, allowing for glacial advance, to cut all the way back to the grounding zone?

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #430 on: August 02, 2016, 09:26:25 PM »
A-Team
Exactly!
It's the depth of a future ice island that could pose a problem. PII-2012 grounded in mid channel and spent a freezing season there. A thicker island might slow or halt advection of Lincoln Sea ice for much longer.
PII-2010 had problems exiting Petermann Fjord IIRC, but PI-2012 found a better channel. A new, thicker island might get hung up before entering Nares, or it might not calve until bottom melt has eaten away at the keel.
An island that calves within the next couple of years, while the ice is still very thick, could push back the date for new record melt. I wonder if ice of this depth could damage any sill features and allow more WAW to attack Petermann Glacier.
Terry

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #431 on: August 02, 2016, 11:51:00 PM »
wonder if ice of this depth could damage any sill features and allow more WAW
Interesting proposal. These sills are often just terminal moraines (glacial till left from previous highstands, as at Illulisat). So what's not to like about a strong outgoing tide, supporting katabatic wind off the ice sheet, and a broad keel reaming a gap in soft deposits? Drag marks from the Last Glacial Maximum are often seen in high resolution sonar, even on the Arctic Ocean floor itself.

It's too late for ice-penetrating radar once the shelf has become ungrounded. The major sill up-glacier from Kap Schoubye looks more like bedrock than saturated till, though there's meagre seismic data however.

The first August S2A image is in. The jp2 will open in gimp (eventually) but only as 8-bit. For people too busy to dink with Sverdrup and Ryder, a snippet from that is shown below at 10 m, click to see full size. Some possible crack extensions since the Landsat above but more likey just the better resolution. Still, this image makes a great baseline for monitoring developments this month.

http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/20/X/NQ/2016/8/1/0/

Tealight

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #432 on: August 04, 2016, 01:21:09 AM »
While you are on a roll, can you pull the depth profile for the putative next ice island from A Muenchow's latest? It might need vertical exaggeration which you can do in gimp by scale change with height uncoupled from width.
Did you mean from this paper?
http://muenchow.cms.udel.edu/papers/Muenchow2016-TOS.pdf

He mentions that the ice tongue is about 200m thick and his depth figures show at least 380m deep water at the end of Petermann fjord. If true the ice island shouldn't get stuck at the exit.

I also checked data from NSIDC Bedmachine, but there isn't any bedrock elevation available for most of Petermann Fjord. The surface and thickness values corresond to around year 2000 levels and are useless now.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #433 on: August 05, 2016, 01:15:28 PM »
The ice shelf is somewhat level at ~200 m below sea level as the above profile (from laser altimeter) shows, so I do not thin plugging up of Nares Strait will be an issue, however, I am concerned about this crack that A-Team documents so well as it is spreading and extending fast, albeit not in a linear fashion towards the central channel.

The cited paper is not yet published, but we got good peer reviews with lots of constructive criticism (as well as a review here by Terry, thank you again) that will make this paper much better than it currently is.

Perhaps related, it looks as if I will be able to get to Petermann via Greenland Air helicopter in 2-3 weeks in order to recover data and repair some of the stations we placed on the ice shelf in 2015 that stopped transmitting data via satellite phone in February. I am both excited and very nervous about the high stakes and price tag of such work ... helicopter rentals are >$70 per minute for 8-10 hours of flying over 2 days and this is AFTER we placed two fuel caches last year along the way from Qaanaaq so that one reach this remote location. Without those caches, the flying time would be 2-4 times as high burning fuel while placing fuel for the grand last leap to Petermann.
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #434 on: September 06, 2016, 08:56:42 PM »
Petermann's ocean weather station is back online after some repairs and replacement of faulty components. It was a very rough night working 33+ hours without sleep, but, amazingly, 800+ meter cables still connect ocean sensors just above the seabed through the 100-m thick ice to the surface and via Iridium (lets hope it works better now with a swapped unit and swapped dataloggers) back to us all.

« Last Edit: September 06, 2016, 09:36:57 PM by Andreas Muenchow »
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #435 on: September 06, 2016, 11:58:29 PM »
Petermann's ocean weather station is back online after some repairs and replacement of faulty components. It was a very rough night working 33+ hours without sleep, but, amazingly, 800+ meter cables still connect ocean sensors just above the seabed through the 100-m thick ice to the surface and via Iridium (lets hope it works better now with a swapped unit and swapped dataloggers) back to us all.
That's great. Thank you for the updates (and the project itself!)

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #436 on: November 30, 2016, 02:45:36 PM »
My 1st post here - I feel like the new kid on the block.  :-)

I've been looking at the Petermann glacier again after a break of some years.  I expect at least one major calving within 3 years.  I base this on what happens with a material which is pushed through a restriction: the sudden strain release can initiate discontinuities in flow - i.e. cracks.

My best guess - and it is a guess at this stage - is a calving about 6 km forward of the large crack shown in all the images above.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #437 on: November 30, 2016, 03:50:09 PM »
Welcome to the Forum, Patrick! I've released your account, so you should be able to post freely now.
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #438 on: December 01, 2016, 10:39:09 PM »
Hi Patrick

Petermann glacier is almost guranteed to calve within the next 3 years. In fact next year is very likely. Today  I looked at Sentinel 1 images and found that the big crack split near end. The new part moved directly towards the center. I believe in the vicinity another crack is developing directly from the center towards the other shore. If those two combine the calving is 60-70% complete.

Click on image for full resolution

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #439 on: December 02, 2016, 02:00:04 AM »
Petermann glacier is almost guranteed to calve within the next 3 years. In fact next year is very likely.

I think we are both talking about major, or even spectacular calving as agaisnt run-of-the-mill calving which a given.

During my absence from blogging due to other commitments I have looked at satellite images from time to time, but didn't copy any to my computer or keep notes of dates etc.  Relying entirely on memory - and I know I shouldn't - I recall hints of cracks which appear and disappear from time to time.  It is as if the glacier pressure/flow  is opening and closing some cracks.

With all eyes on the big one, these tiny ones pass by un-noticed.

It may happen that the big crack and others combine to make a 'loose tooth' which rotates slightly and acts as a kind of ratchet.  In that case, a large calving event forward of the big crack becomes more probable.

I reiterate that this is guesswork and memory- no substitute whatsoever for boots on the ground.

Image not showing in preview -  I'm learning the new-to-me interface here - I hope the image shows.
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #440 on: December 30, 2016, 08:25:50 PM »
A feature on Andreas Muenchow and Petermann in the Washington Post:

http://www.washingtonpost.com/sf/business/2016/12/30/with-enough-evidence-even-skepticism-will-thaw/
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #441 on: December 30, 2016, 08:59:35 PM »

I reiterate that this is guesswork and memory- no substitute whatsoever for boots on the ground.

100% agree. Over multiple disciplines/workplaces etc. - there is nothing like "raw" observations.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #442 on: December 30, 2016, 10:35:37 PM »
A feature on Andreas Muenchow and Petermann in the Washington Post:

http://www.washingtonpost.com/sf/business/2016/12/30/with-enough-evidence-even-skepticism-will-thaw/

Wow! Truely great science journalism. Spread the news, the U.S. MSM is not yet brain-dead.

A sensor in 3,000-foot-deep waters had found that in the warm, salty Atlantic layer, temperatures were even warmer than just a year earlier, in 2015. Those waters are likely flowing toward Petermann glacier’s grounding line and helping to melt the shelf from below.

“The temperatures at the bottom end of the array continue to increase,” said Muenchow. “It’s getting warmer.”
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #443 on: January 01, 2017, 12:36:00 AM »
Great article.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #444 on: February 15, 2017, 10:39:31 PM »
https://www.eurekalert.org/pub_releases/2017-02/uod-usr021517.php

UD scientists report ocean data from under Greenland's Petermann Glacier

Andreas Muenchow and colleagues---report includes video:

"The researchers recently reported in the journal Oceanography that sensor data from August 2015 to February 2016 confirms that that the floating ice shelf is strongly coupled, or tied, to the ocean below and to Nares Strait, and temperatures vary with the tides and seasons.

Specifically, the paper found that the same water that has been measured in the fjord is under the glacier, lending credence to the idea that the continuity of the glacier depends on the conditions outside the glacier in the fjord....


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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #445 on: March 14, 2017, 03:04:09 PM »
Looks like a calving is underway in the right-hand corner of the tongue!!  PolarView image from yesterday:  [edit: the 'hand' doesn't point to anything; it's just a relic.]
« Last Edit: March 14, 2017, 03:11:27 PM by Tor Bejnar »
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #446 on: March 14, 2017, 04:05:39 PM »
I can see most of this crack in Tealight's posting (above) on August 2, 2016 and in A-Team's July 11, 2016 posting.  Some calving happens more slowly than others, I guess.
« Last Edit: March 14, 2017, 04:12:40 PM by Tor Bejnar »
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #448 on: April 14, 2017, 03:42:22 PM »
Hydrofracturing???
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #449 on: April 14, 2017, 03:45:13 PM »
Hydrofracturing???

Eric Rignot, a NASA and University of California-Irvine scientist who has studied Petermann up close, commented:

The ice shelf is slowly but surely falling apart. It has been stable from 1901 till the 2000s, then started to break up, especially in 2010-2012. We have seen the glacier speed up for the first time around 2014-2015. Whether this new crack is significant or not is hard to tell as of now. It is unusual to see cracks forming from the center, they usually start from the sides. This could indicate that the ice shelf has gotten too thin in the middle.

Since a meltwater river runs in the middle, hydrofracturing might cause the thinning?