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A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #300 on: August 07, 2015, 07:55:01 PM »
Odd situation.

Search works. The small 731 preview image works and enlarges.

The large 731 preview image gives this error message: Not Found The requested URL /browse/full/landsat_8/LC80342482015218LGN00 was not found on this server.

The big package download started but then stalled, now it is going again, now it is stalled again.

This is Friday noon in America, not to mention lunchtime at Chicago server center. Your expectations are too high? Check back with us mid-morning Monday. At least it is a clear enough day!

Hmm, now I am seeing everything works fine going back four images to 03 August. I recall them having announcing some service downtime on Wednesday or so. Probably messed things up rather than fixing. So they have one bad pointer to the big preview but why 3% or so of the big file downloads ok is harder to understand.

Ok ... now they are back from lunch and looking into it. New message: "Service Temporarily Unavailable. The server is temporarily unable to service your request due to maintenance downtime or capacity problems. Please try again later."

It is working again. Is this a great country or what!?! Not the 'Natural Color' though, just the big package (from which you can make your own 'Natural Color' by stacking bands 731 in ImageJ and going to Color -> RGB.
We should be able to see the Oden at 15 m resolution
« Last Edit: August 07, 2015, 08:39:43 PM by A-Team »

Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #301 on: August 07, 2015, 08:00:30 PM »
OK, I thought I was banned for bashing a certain middle east "allied" of the US ;)
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A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #302 on: August 07, 2015, 08:54:35 PM »
Allies? http://www.wrmea.org/2006-may-june/uss-liberty-and-the-nsa-one-deceit-too-many.html

Meanwhile, no sign of the ship along the calving front. Do we have lat,lon for them today? -- that Oden tracker is lame at higher resolution. The calved piece is in the upper left of the second image. Too bad they didn't arrive in time to put an AWS/GPS on it ... I am assuming its motion is more due to wind than to current.

Nothing happening at the Big Rift.
« Last Edit: August 07, 2015, 09:13:07 PM by A-Team »

Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #303 on: August 07, 2015, 09:01:56 PM »
And my grandfather was "prisoned" or rather "K-Zded" because of them, waist of life!
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Andreas T

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #304 on: August 07, 2015, 09:04:47 PM »
This http://polar.se/blogg/en-resa-historien-att-kunna-forutspa-framtiden/ has a  picture of a warmwaterdrilling site next to a meltwaterchannel on Petermann. Maybe a Swedish speaker can translate?

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #305 on: August 07, 2015, 09:18:04 PM »
This http://polar.se/blogg/en-resa-historien-att-kunna-forutspa-framtiden/ has a  picture of a warmwaterdrilling site next to a meltwaterchannel on Petermann. Maybe a Swedish speaker can translate?

Often I am proud to be 100% Scandinavian, and together we do pretty well, socially in the top (despite the high taxes)  but one of the reasons we are there, and because we have the trust in other people, that really makes the difference, and believe me I have to more visited mote than 70 countries.
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A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #306 on: August 07, 2015, 09:29:48 PM »
säker, inga problem min svenska är grov men

2015-08-07
Expedition: Petermann 2015
A trip in history to predict the future

Latitude: 81 ° 4'N
Longitude: 61 ° 28'W
Speed: 4 knots
Temperature: 5 ° C

It is now a week since we left Thule,  and after a polar bear visit, amazing views and more than 40 seals, we reached Petermann Glacier in northwestern Greenland on Tuesday.

In recent days, researchers from participating countries flew in. The first group to reach solid ground, the Swedish project, explored two Arctic areas near Petermann Glacier - Hall Land and Ellesmere Island both of which really belong to Denmark (just like Hans Island) which in turn we think of as a Swedish colony and so it's all Swedish property. ;)

On Monday they were flown in and pitched their first field camp in Hall Land where they will collect plants, insects and bones and drill permafrost cores to look for ancient DNA. By looking at these ancient DNA samples, researchers want to reconstruct how the ancient ecosystem structures looked and use that to predict how the Arctic ecosystem will be affected by future climate change.

The second field group packed two full helicopters on Tuesday and flew out to the Washington Land to investigate how the ice has retreated in history. They will be using a hammer and chisel to collect stones so that with Be10 and  Cl36 dating, they can determine when stones were last exposed to cosmic rays -- the stones thus can reveal how the ice and sea levels have changed over the last 15,000 years.

The last group consists of four scientists from the British Antarctic Survey (BAS) and the University of Delaware. They were flown in yesterday a couple of kilometers up on the glacier. Using a hot water drill, they will bore through the ice shelf, then use a CTD to find out how the circulation of water looks under the ice over time. By studying water circulation researchers get some clues about what links there are between the ocean and the large melt water channels running under the glacier.

[The lat,lon are not provided to much precision; they should really be given as kml files in Google Earth. I am not seeing the big orange tent on Landsat. The northernmost location provided a few posts back in Andreas M's lab sketch is more than a few km in from the calving front.]
« Last Edit: August 07, 2015, 10:10:21 PM by A-Team »

Andreas T

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #307 on: August 07, 2015, 09:43:18 PM »
Thank you for the (not too literal ;)) translation

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #308 on: August 08, 2015, 06:13:27 AM »
A-team, översättningen var väl ok, förutom ett stycke. Är även du från våra kolonier?

Here's a bit more about cosmogenic exposure dating from the 2004 expedition.
http://polarforskningsportalen.se/en/arktis/forskarrapport/cosmogenic-approach-glacial-history-greenland/

ghoti

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #309 on: August 08, 2015, 04:27:05 PM »
More photos and description of activities by the Oden expedition on twitter...

https://twitter.com/Petermann_Ice

and Instagram

https://instagram.com/petermann_ice/

Jim Hunt

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #310 on: August 08, 2015, 04:31:12 PM »
Not to mention on YouTube:



via https://twitter.com/polarforskning
Reality is merely an illusion, albeit a very persistent one - Albert Einstein

A-Team

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #311 on: August 09, 2015, 07:25:40 AM »
Real-time information quite a difference from the old explorer days where they would go off the radar for years at a time, frozen into the ice.

It appears that a really small additional piece has calved off. I traced it back to its origin...

Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #312 on: August 09, 2015, 02:37:50 PM »
It looks like the 2 cracks below Belgrave and Hubert Glacier are expanding:
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #313 on: August 09, 2015, 07:49:50 PM »
Melt and sun angle can affect images at different dates (which do not have the same path,rows and so cannot be accurately aligned). Note especially the lower right hand corner where the drainage is changing markedly in appearance. It may be better to just watch for rift tip growth on the B8 15 m band -- the main rift cannot really pivot about a fixed tip because it is too weak to resist such a torquing (and so propagates instead). That has indeed happened this year but not recently.

That would be cool if the Petermann expedition could hang a grad student out the helicopter window to take a high resolution picture of the rift tip.

* To what extent do secondary (and here, tertiary) parallel up-glacier rifting distribute shear forces away from the initial rift and so delay eventual calving?

* Will one of these become the eventual rift assuming the primary freezes in to stagnancy?

* Is this process influenced by absolute position relative to the fixed rock wall frame, ie as the ice shelf moves towards the sea, the shearing point may stay fixed favoring lower rifts?

The second image takes 3 different dates (days 140, 188, 220) with the same Landsat path,row to see if an 80-day interval resolved the widening issue of the second rift. These Landsats annoyingly had different pixel sizes meaning they could not be precisely co-registered within ImageJ for cropping to the ice sheet.

It may be that the tributary ice streams from Porsild and Sigurd Berg are falling back unevenly due to friction at their interface with the moving ice shelf and the immovable rigid walls. This does not apply a torque to the portion of ice sheet that has already passed by but does enlarge the lower edge of the rift (but does not lengthen its tip). Thus this secondary feature may now have taken up the response to rifting forces. Between days 140-220 the upper rift tip has noticeably lengthened by a few hundred meters (shown in earlier posts).

I added 2013 and 2014 Landsats almost exactly a year earlier ... very instructive. Tearing of the ice shelf makes global alignment infeasible in addition to the path,row geometric mismatch problems. However large patches in the central shelf are rigid enough to align. This ice shelf is changing much faster than 'glacial speed' but still over a moderate annual scale (until it abruptly fractures without warning).
« Last Edit: August 09, 2015, 09:33:57 PM by A-Team »

nukefix

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #314 on: August 10, 2015, 10:03:48 AM »
Oden nicely visible just outside the calving front (S-1 IW 7.8.2015)

Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #315 on: August 10, 2015, 07:24:15 PM »
Just received some images from our friend Andreas in the far north:
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #316 on: August 10, 2015, 08:30:23 PM »
Ship has moved over to other side. I'm thinking that metal decks make it a very strong radar reflector. Chopper a big improvement over schlepping gear across rough ice like in the olden days. Does Andreas M have enough web to see the forum or is he just attaching photos to email?

Hmm, is that a crack and incipient rifting (arrow)? Logical place for it. Landsat is cloudy today.,
« Last Edit: August 10, 2015, 08:37:42 PM by A-Team »

Espen

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #317 on: August 10, 2015, 08:33:51 PM »
Espen:

I have not forgotten about you and the wonderful Arctic Sea Ice community with regard to news and reports from Oden, but I get barely by on 3 hours of sleep per night. Nevertheless, there are a few pictures that you wanted and I sent you. This one is of the Petermann terminus with a view towards the southwest. Faith Gletscher is hidden by the perspective, but you see the indentation in the coastline of Washington Land where it should.

Please feel free to share this with anyone in any form on the Sea Ice Forum, including any snipes from e-mails that you think may be of interest.

Andreas

P.S.: Please recall that I do NOT have any access to the internet, only e-mail with attachments <100 kBytes.
________________________________________
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #318 on: August 10, 2015, 11:08:04 PM »
Just received some images from our friend Andreas in the far north:

Beautiful!

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #319 on: August 10, 2015, 11:24:37 PM »
Those images are wonderful and nice to hear from Andreas, especially since he is obviously super busy.
While poking around the Petermann expedition site, I came across this set of updates (https://petermannsglacialhistory.wordpress.com/updates-from-co-chief-scientist-alan-mix/ ) from the Co-Chief scientist and found them very interesting.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #320 on: August 10, 2015, 11:59:09 PM »
Thanks, Espen! And Andreas!
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #321 on: August 11, 2015, 07:32:30 AM »
Those images are wonderful and nice to hear from Andreas, especially since he is obviously super busy.
While poking around the Petermann expedition site, I came across this set of updates (https://petermannsglacialhistory.wordpress.com/updates-from-co-chief-scientist-alan-mix/ ) from the Co-Chief scientist and found them very interesting.

Very interesting, he explains the scientific missions in quite a lot of detail.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #322 on: August 11, 2015, 04:55:04 PM »
Decent enough Landsat today. It seems like a lot of ice has blown in. The calved piece is still holding together and can be seen at the top. The lower image shows the imaginary band 8 rift I also imagined seeing in Sentinel the other day, qite plausibly just meltwater drainage features. The large piece that calved had a typical piecewise linear fracture coming in from the east that was met by a curvaceous rift coming down from the north so not all fractures are straight lines.

The third image is taken from a zoom provided by Digiglobe to Google Earth. Since this is much higher resolution that Landsat 15m, it is suitable for accurate measurement of rift width, using relocatable points spanning the rifts (rather than rift widths themselves because their boundaries are not reproducibly measured).

The idea is to measure the same distance in 2015 Landsat images to get an idea both of absolute rift width and the average rate of widening. I suspect the team out on the ice, using two of their high precision GPS units straddling the rifts, could actually measure the widening velocity over a 24 hr period even if that were just a cm or two. Not a scientific priority obviously compared to drilling, nor a safety issue (compared to low elevation helicoptering over open water) given they are well up-glacier from these rifts.
« Last Edit: August 11, 2015, 05:31:43 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #323 on: August 12, 2015, 04:57:45 PM »
From Sentinel 1A, there appears to be something going on in the NW corner of the calving front, possibly a prelude to a few sq km of calving. The brightening in radar does not correspond to anything yet in Aqua/Terra; indeed nothing dramatic in yesterday's higher resolution Sentinel. Image shows 11, 10, 09 of August. The Landsat 731 is deeply shadowed in the ROI.

The 30-day widening is shown in the 3rd image, perhaps one 15 m pixel farther across. The tips have not extended at all. That means the torque is growing that could lead to sudden brittle fracture, predictably a SW extension of affected tip (more likely the 3rd than 2nd or 1st.)

Today's Landsat is not showing any calving action in the NW corner, though the ice margin has melted out to the rock wall. The remaining ice is properly called an ice tongue, a specialized part of an ice shelf.
« Last Edit: August 12, 2015, 09:42:36 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #324 on: August 12, 2015, 06:41:47 PM »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #325 on: August 12, 2015, 09:59:15 PM »
Here's the year to year comparison of the NW corner. Changes, but not dramatic for a whole year.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #326 on: August 13, 2015, 08:22:45 PM »
Andreas reporting from Petermann:

Hi all:

I am ecstatic to report that our weather station on Petermann Gletscher is alive collecting and reporting data. The earlier shut-down 8-hours after deployment on Aug.-10 was caused by Iridium satellite transmissions, not the set-up of hard- or software of the weather station itself. I attach a plot of the data collected so far that is being used by  the ship's operators to prepare and plan for flight operations over the glacier. There will be a massive increase in helicopter flying, because on saturday the CBS 60-Minute team will arrive via helicopter from Qaanaaq, Greenland about 250 miles to the south.

The five ocean sensors are NOT yet plugged into the UDel observing system, because ice drilling operations at that site will not start until monday or tuesday. Our graduate student Peter Washam is on the glacier right now. The so-called Ice-Shelf team just completed a second drill hole near the grounding line of Petermann Gletscher where the ice is about 365 m deep with another 300 m of water below the ice. The picture shows Peter at that (second) drill site shortly after the camp there was established there monday. The weather station was set-up about 13 km seaward  at what will become the third drill site. Hopefully he did not forget to re-program the ocean sensors to move bits and bytes along the 600 m long serial cable (4800 baud) at a slower rate than we used them in an calibration test lowering them from the ship to the 600 m deep bottom of the ocean near Petermann Fjord.

The 2 1/2 day long time series shows air temperature about 0.5 and 2.0 m above the ice as well as wind speed and direction as well as atmospheric pressure. A GPS unit shows that the station is drifting about 3 m per day towards the ocean as is expected for this fast moving glacier moving about 1.2 km per year.

My spirits are high after several days of anxious anticipation and waiting for a call from the weather station. Wish us luck.

Andreas (aboard I/B Oden at 81 32.28' N 062 04.0' W on 09:49 UTC)
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #327 on: August 13, 2015, 10:11:16 PM »
Good luck, Andreas!
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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #328 on: August 13, 2015, 10:59:42 PM »
Wow, this is a dicey business -- one mistake or one equipment going south and years of preparation go down the drain.

Did he include any location information on the second drill hole? I will guess that it is sitting right on one of the 2014 radar flight lines. Since it is drifting along each day, it would probably be more useful to locate it on a Landsat relative to identifiable stable features, rather than having one-time lat,lon. That is, lagrangian coordinate work better here (until a widening rift is encountered.

I'm thinking  that they may have drilled deliberately into one of the underside channels (or crevasses) past the grounding line. The 350 m depth of the ice is an important clue as to where they are relative to underside features. I'm recalling the ice actually getting thicker down icesheet for a ways.

Alternatively, they may have drilled through the center of a longitudinal flowline; some reports envision these as hydrostatic equilibrium adjustments of the surface to freshwater melt channels carved in the underside. I am not aware of any previous quantitation of Petermann meltwater, much less buoyant plumes entraining ocean water.

No sonar studies have looked at emergent meltwater cavities at the grounding line -- here the drill hole is too small in diameter and refreezes too fast to lower a sonar device down.

On the PI's blog, he notes they "deployed a seismic profiler and air gun to investigate the sediments and deeper geology of the seafloor. This equipment uses compressed air to produce waves that penetrate deep into the layers of sediment and underlying rock that make up the seabed; this allows us to understand how this important region of Greenland was formed. We’re currently mapping these deeper layers throughout Petermann Fjord and into Nares Strait."

You can see what type of data this type of study produces at the open source article:
Late quaternary ice flow in a West Greenland fjord and cross-shelf trough system: submarine landforms from Rink Isbræ
JA Dowdeswell et al 2014
Quat. Sci. Rev., 92, 292–309.

They were able to get three sediment cores from beneath the ice shelf -- the first ever taken through an ice shelf in Greenland. This was at the first camp, not the grounding line one. I was fascinated by the first step in core logging, which is gamma density scanning with the core still in its tube which is usually done with a heavily shielded Cs137 source. How in the world do they get this thing through natl and internatl airport security and how much does it weigh?

The link below explains the first steps in finding out (non-destructively) what's in the core. Obviously most of this technology was developed for commercial logging, with the climate change research community a side benefit.

http://www.geotek.co.uk/products/sensors
« Last Edit: August 14, 2015, 04:10:03 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #329 on: August 14, 2015, 04:50:36 PM »
The 2015 Petermann expedition posted high resolution images of the 28 July 2010 and 06 Aug 2012 mega-calving events and links to the NASA hourly time series. There are a couple of interesting things in those images that have not been commented on before which are relevant to the next big event (which I don't foresee happening in 2015).

First, the 2010 event came very close to calving off not only its 251 km2 but also the 119 km2 of the event that only happened 24 months later. That is, the rift tip of the 2012 event was already well across the central flowline in 2012 and a massive shear zone cutting across the tributary glacier ice had already developed. This would have been 379 km2, a very substantial proportion of the whole ice shelf.

The second thing to notice is that tributary ice, along with its glacial till covering, remained frozen on to the main Petermann ice shelf piece for some days. I don't believe this would be possible today because the relative motion observable over short time scales shows tributary ice is not moving as a block with the ice sheet itself and could not remain attached after calving, as indeed we've seen this year in miniature. This suggests the ice at the interface is warmer than before.

The additional cut-outs below illustrate these points but it is really best to look at the original imagery (which is too large for the forum at 4896 x 3672 pixels). The third image shows a minor rift that is still stagnant today (blue arrow) and on that has become a major development by 2015 (magenta)

The expedition had a meeting on the future of Petermann, with the PI saying "idle speculation" on the ice shelf future should be avoided (until they finish collecting and processing data?).

https://petermannsglacialhistory.wordpress.com/background/
https://petermannsglacialhistory.files.wordpress.com/2015/06/petermann_ali_2010228_lrg.jpg
« Last Edit: August 15, 2015, 03:11:37 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #330 on: August 15, 2015, 03:46:57 PM »
Here is the first round of data, 2.5 hours worth, from the AWS from http://icyseas.org/. With the sub-centimeter precision of the GPS units they got at the last minute, lurches in glacier movement should be clearly resolved. However issues with variable ionospheric delay and inaccuracy in satellite orbital and
clock information can degrade precision.

There is definitely some noise over short intervals, ie the glacier in reality is only moving forward, not retreating as some successive data points would suggest. The 1200 m/yr is in line with expectations but does not look like a least squares fit yet. This would make more sense with after a week or month of data is at hand.

From blowing up the graph to recover the underlying cvs, it looks like the AWS is sampling displacement 12 times per half hour (576 times per day). The successive readings I looked at below had a 4 m difference, suggesting the noise level is ±2 m. If the ice sheet moves 3.3 meters per day, that would be 0.0057 m (5.7 mm) between sample points.

Convolution smoothing (rolling weighted average) might make some sense here though optimal processing could depend on understanding sources of systematic error (if any). Conceivably, fourier transform would reveal a tidal effect, motion being faster at high tide if the grounding zone is lifted somewhat instead of the ice shelf merely hinging.

Temperatures are well above freezing. The channel shown drains into the small lake that they are using for the steam drill (tower shown). It would be a challenge to locate the drill site on Landsat from the data provided so far.
« Last Edit: August 15, 2015, 08:41:31 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #331 on: August 15, 2015, 05:27:34 PM »
Very nice Landsat today, suitable for locating drill sites, GPS, and weather station. LC80420012015226LGN00 at EarthExplorer taken at 2015:226:18:20:01. These have to be located relative to ice sheet features as their lat,lon coordinates drift. I looked for the yellow tent, helicopter, stream drill near the grounding site on the 731 preview -- rather small and hard to say when the Landsat was taken relative to their short time on site. There are a fair number of drainages and melt lakes in the region and they may have adjusted the site location relative to the earlier sketch Andreas M posted.

I've repeated below GPS velocities from 2011-12 that we considered in #203 on June 19, 2015.
http://forum.arctic-sea-ice.net/index.php/topic,53.msg54449.html#msg54449
http://www.earth-syst-sci-data.net/5/277/2013/essd-5-277-2013.pdf
« Last Edit: August 15, 2015, 08:29:52 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #332 on: August 15, 2015, 09:37:53 PM »
We're seeing some changes in the NW corner of the calving front; the animation below shows the progression of various rifts from 2013 and 2014 to today. As usual, a progression of rifts develops further upglacier over time and come to adsorb most of the shearing stress. The wall shadows cannot fully be removed and of course vary according to day of year; note too moving lagrangian coordinates providing the alignment give an apparent motion Faith Glacier and fixed rocks as an artifact. With interesting exceptions, many features are remarkably stable over time. If I had to pick a characteristic time scale for time series developments on this ice sheet, it would be a few weeks rather than daily or decadal.
« Last Edit: August 15, 2015, 09:46:16 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #333 on: August 15, 2015, 09:51:28 PM »
A-Team an interesting observation, nice work! ;)
Have a ice day!

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #334 on: August 17, 2015, 06:07:24 PM »
Looking at a long Landsat series of this northwest corner of Petermann, the slow-moving story of the aftermath of the the he slow-moving 2010/2012 collapse comes down to gradual ocean penetration of the region between the ice sheet and its vertical wall, with the loss of ropy ice there not so far from Faith Glacier.

Some glaciologists differentiate between ice sheets and ice tongues. The former are buttressed on their sides by fjord ice or other glaciers with only the calving front facing the ocean; the latter are peninsulas surrounded by ocean water on three sides. Here we have something in between.

The effect here on Petermann is first an insignificant loss of buttressing retarding ice sheet advance, there being no longer resistance on the upper NW side. Second, as the ocean works its way further south (a process measured in years, not decades or seasons), the ice sheet becomes more susceptible to rifting from CCW torques (which would otherwise force the ice sheet against rock). This would favor rift development on the northeast junction of the ice sheet with its tributary glaciers.

The land boundary is not so easy to see because it is almost always in shadows. Below in the 2015-13 comparison, it is tinted green.

It is possible but unproven that the recent calving event was thus facilitated. However forcing from Belgrade glacier may having been a more significant contributor.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #335 on: August 19, 2015, 08:28:22 PM »
A new development on the NE corner of the calving front. Looks more like a melt surge than a calving, most pronounced in hv polarization. No Landsat at this time. The enlargement, using both polarizations, does not immediately clarify the interpretation.
« Last Edit: August 19, 2015, 08:35:19 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #336 on: August 21, 2015, 03:26:58 PM »
We've sort of lost track of the Petermann 2015 expedition, what with all the excitement down at Jakobshavn. However some very interesting material is being posted from the Oden which we should capture and consolidate here.

The image below shows a very suggestive bathymetry of the upper fjord (no depth scale provide but maybe 500 meters max), key sills, old lateral moraines, and data collection sites. Some of the tributary glaciers are currently contributing a fair amount of sediment in plumes.

The map also provides a useful history of the calving front right up the minor loss this August. Note some of the sediment cores are at sites that have been covered by the ice sheet, probably for 4,000 years or more. Petermann is already freezing up so further fracturing is unlikely this season.

http://www.geo.su.se/index.php/expedition-logs/1276-petermann-glacier-2015

The Delaware researches discovered warm water (0.323ºC) some 800 meters down a hole drilled 100 m through Petermann Gletscher ice. This warm water did not originate in the fjord but arose in the Atlantic and entered the Arctic Ocean near Spitsbergen. Prior to northern Greenland, the water had circulated along Siberia, Alaska and the coast of northern Canada. This data was obtained from the first of five holes drilled through the ice shelf by the British Antarctic Survey crew.

The water temperature is high enough at all depths to melt the underbelly of the ice shelf all the way up to the grounding zone. However the rate will depend strongly on circulation of the contacting water. Tides, up-glacier meltwater exiting at the grounding zone and incoming tributary meltwater would all contribute to this mixing.

There are five ocean sensors packages deployed down each cable. A weather station designed by David Huntley of the University of Delaware provides the command and control between ocean sensors, battery and solar panels. The system calls home every three hours with stored data through the flaky Iridium satellite phone. The battery system is quite challenging to keep alive during the long dark cold winter, but automated data collection represents a huge step forward over systems requiring someone on site or periodically revisiting a very remote area to retrieve data.

http://icyseas.org/2015/08/20/ocean-observing-station-reporting-from-below-petermann-gletscher-greenland/
« Last Edit: August 21, 2015, 04:11:01 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #337 on: August 22, 2015, 12:34:37 AM »
Don't recall if we've seen this very large scale map before ... maybe a few new place names and elevations on it.
http://maps.pgc.umn.edu/arctic/nga/03/preview/Petermanns%20Gletscher.jpg

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #338 on: August 24, 2015, 10:01:40 AM »
Repost from : http://icyseas.org/2015/08/23/taking-the-pulse-of-petermann-gletscher/
Posted by Pat Ryan for Andreas Muenchow

23-August-2015 at 80:57.3 N 061:27.1 W

(note correction below)

I just may have made a discovery that I cannot share with anyone on the ship right now. The giant mass of ice that is Petermann Gletscher just slowed down moving only 1 meter per day for the last 3 days rather than the 3 meters per day that it usually does and that has been reported in the scientific literature. This measurement comes from the newly deployed University of Delaware weather station that also contains a not-so-fancy $300 Garmin GPS as well as 5 ocean sensors that measure temperature and salinity about 95-m, 115-m, 300-m, 400-m, and 810-m below the surface of the floating and moving ice.

Time Series of Glacier Drift

Time Series of Glacier Drift (correction appears below)
As the glacier puts on the breaks, I also see a rather dramatic increase in ocean temperature from -0.6 to -0.35 degrees Celsius within about 10-m of the ice-ocean interface. The saltiness of the ocean also increased from below 34.1 to above 34.2 practical salinity units that you can think of as grams of salt per kilogram of water, roughly. Only 20 m below in the water column, the opposite is happening: The water there cools a little bit and becomes fresher. This suggests some mixing as the salinity differences become smaller and heat from the lower layer moves up towards the ice. Some force must be applied to the fluid to do this. Recall that a force is mass times acceleration. The force of a mosquito splashing on the wind shield of your car is small, because the mass of the mosquito is small even though its acceleration (from zero to the speed of your car) is large. Now imaging this glacier: Its mass is enormous, so you only need to change its velocity a tiny amount, from 3 to 1 meter per day, say, to generate a massive amount of force.


As I look outside my cabin window right now, I see the terminus of Petermann sitting there innocently not appearing to do much, but it is literally changing the face of the earth as it moves fast, slows down, moves some more, and over 1000s of years cut a very deep fjord and perhaps canyon deep into the mountains and even deeper into the sea floor. The helicopters are whizzing overhead right now returning all the gear that was needed to drill through 100s of meters of hard glacier ice to provide access holes to both ocean and sediments that has been in total darkness for many 100s of years.


Still, there is life down there, lots of it Anne Jennings, who closely looks at the sediment cores, tells me. We speculate that the life is supported by vigorous ocean flow that connects the open fjord with the glacier covered deep ocean. Food stuff like plankton may move some distance under the floating glacier to support a population of other critters that I know nothing about. No narwhals this year so far, though.

So why I am writing this up here rather than share it with people on the ship? Well, this is Sunday morning and there was much to celebrate last night when the ice drilling team returned after 2 weeks camping on the ice and collecting data from their three drill holes. Furthermore, the the ocean weather station reported for the first time in over 2 days uploading all the data I show above. This happened well past midnight and several of us discussed the data and future plans in the cafeteria until 1:30 am. So the people not working right now are all sleeping (10:30 am here) as we probably will work through the night to map the Atlantic waters flowing into the fjord at its sill towards Nares Strait …  which we have not yet done over the 3 weeks we have been in the area. I probably also should help with unloading the helicopters or getting the Chief Scientist Alan the data files he needs to catalogue the water samples we collected last night. Work on Oden never stops … as there is so much to do as we are barely scratching the surface or bottom of the ocean here. [Incoming helicopter, 4th one since I wrote these lines too fast, perhaps.]


Correction:

Petermann Gletscher did slow down the last few days by about 10% as measured by the GPS at the UDel ocean-weather station. The suggested slow-down to 300 meters per year, however, is false, because I did not properly take into account how the station was moved by 30 meters to the south-west. The correct and updated estimate is the figure below. Please discard the the above figure erroneous.

Sorry for the confusion … more data coming from this station will place the short term change in glacier speeds into a larger context. Furthermore, the present “cheap” GPS system will need to be verified by a set of three “fancy” differential UNAVCO GPS that were recovered today, but we have not yet decoded the data contained on those units.

Back to CTD profiling the water properties across the sill at the entrance to Petermann Fjord that we will have to complete by 3 am or in about 6 hours.

Open other end.

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #339 on: October 05, 2015, 04:54:52 PM »
Quick Petermann update from this morning :)


"Petermann Glacier's remnant floating ice shelf, from an altitude of 34,000'. This photograph was shot at roughly 0845 Thule local time. Note the very low illumination angle of the sun on the terrain. These low sun angles create challenges for DMS photography, especially for our sea flights, which lie far to the north, and thus farthest from the sun in early autumn in the high Arctic. Note also the thick haze on the horizon, an indication of high atmospheric moisture content and increased likelihood of cloudiness (NASA/Operation ICEBridge/John Sonntag)."

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #340 on: October 05, 2015, 05:37:25 PM »
Beautiful photo ... oblique images are very helpful in visualizing terrain and steepness of tributary glaciers. Note how the NE corner -- the region that broke off this summer, seems to be filling up with ice again (dotted line on Sentinel). The ice shelf only gains a km from a year of forward motion so never really catches up on the larger calving events (as these amount to decades of glacier motion).

Andreas Muenchow has a couple of very informative posts about the research they did on Petermann this August from the Oden. The differential GPS units needed to measure tidal heaving of the ice sheet were in place for 12 days. It is quite a job to unravel the information in this kind of data. The graphic below shows where instrumentation was moored through drill holes below the ice sheet. They have CTD sensors strung at five different depths (to 800 m).

Quote
The 25 Sep 15 Iridium call was the first in two weeks, but it provided a complete data download without ANY gaps in the hourly time series of weather in the atmosphere (wind, temperature, humidity) and weather in the ocean (temperature, salinity, pressure). The ocean data show that about every 2 weeks with the spring-neap cycles, we see very large excursions of colder and fresher water appear at 2 sensors within about 30 meters of the underside of the ice shelf...
http://icyseas.org/
« Last Edit: October 05, 2015, 06:11:53 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #341 on: October 08, 2015, 03:05:55 PM »
Petermann is situated at a far more favorable location than Jakobshavn in terms of both Landsat and Sentinel coverage frequency. For example some 32 high resolution 'IW' class images are available from Sentinel between February and October of this year. This enable time series with a given instrument.

While we shouldn't expect too much rifting drama during the winter months, Sentinel will be our only observational tool as Landsat has already gone dark.

Note it is not currently possible to define a polygon covering Petermann (unlike at EarthExplorer) and the ridiculous Sentinel search tool provides a 'match' even if only a tiny corner of the search rectangle is hit.

The horrible user interface at ESA is currently undergoing a long-overdue overhaul -- desperately needed with Sentinel-2 already launched in June (but so far not producing any West Greenland images). There are so many things broken with the site now that there hardly space to list them all. Common web features such as pull-down menu options would greatly help in restricting searches but these seem unknown to the inept interface contractor.

The search tool currently seems to return only Sentinel-1A images unless the user has learned from an unlinked page to type in one of four restricting terms (were we supposed to guess S2MSI1C?):

•   collection:S2samples
•   S2A*
•   platformname:Sentinel-2
•   S2MSI1C
•   producttype:S2MSI1C

The most amusing bug is the long-running typo in the page title: 'Sentinels Scientific Data Hub'. I don't expect this to be fixed -- there is no reporting mechanism for users.

Here is the incoherent update posted today.  Some performance degradation? The interface has been in a state of near-total collapse for months, unable even to put up error messages!

Quote
In view of Sentinel-2 In-Orbit Commissioning Review (IOCR) that is planned for next week we are currently configuring the system in preparation for the routine operations of Sentinel-2. At the same time we are experiencing some performance degradation that will be resolved by the new installation of the Data Hub Software that is currently being deployed.The new software will also introduce a new and improved User Web Interface that will be announced in the coming days. We apologise for any inconvenience caused. 08 Oct 2015 - 10:53
S1A_IW_GRDH   2.10.2015
S1A_IW_GRDH   2.10.2015
S1A_IW_GRDH   20.9.2015
S1A_IW_GRDH   08.9.2015
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S1A_IW_GRDH   08.9.2015
S1A_IW_GRDH   20.9.2015
S1A_IW_GRDH   12.9.2015
S1A_IW_GRDH   15.8.2015
S1A_IW_GRDH   07.8.2015
S1A_IW_GRDH   15.8.2015
S1A_IW_GRDH   27.8.2015
S1A_IW_GRDH   27.8.2015
S1A_IW_GRDH   31.8.2015
S1A_IW_GRDH   19.8.2015
S1A_IW_GRDH   10.7.2015
   S1A_IW_GRDH   10.7.2015
S1A_IW_GRDH   26.7.2015
S1A_IW_GRDH   16.6.2015
S1A_IW_GRDH   28.6.2015
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S1A_IW_GRDH   23.5.2015
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S1A_IW_GRDH   27.5.2015
S1A_IW_GRDH   17.2.2015
S1A_IW_GRDH   04.2.2015
S1A_IW_GRDH   05.2.2015
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« Last Edit: November 11, 2015, 01:39:59 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #342 on: November 11, 2015, 02:47:27 PM »
Petermann Glacier ... 2015 the year in review

This year saw some interesting developments on the floating ice shelf, precious experimental data being collected beneath it, and new explanations proposed for upstream upheavals so characteristic of north-central Greenland and a few regions in Antarctica.

The event getting the most attention was cleavage of a minor tabular ice in the northeast corner. Events in this region are driven by intrusion of Belgrave glacier almost orthogonally into the advancing ice shelf. Partial pinning then causes rifting as the adjacent region of ice shelf is held back. We can expect a similar repeat event from the same mechanism in 2016.

The northwestern corner above Faith Glacier is undergoing a curious melt-out along the rock wall that, though paused for the winter, may resume this spring. Here the ice shelf is ~100 m thick but winter saltwater ice will only reform to ~2 m and not bond well to older ice. This melt-out may propagate further upglacier in 2016, reducing friction between the ice shelf and the confining fjord walls, resulting in a very slight increase in discharge velocity. However recent papers make a case for the totality of Petermann buttressing being inconsequential (for future sea level rise).

The fractures midway up the ice shelf on the eastern side above Kap Agnes lengthened and widened during early and mid-summer but paused in August. These fractures form in succession as the ice shelf bends around a curve in its fjord and responds to pinning from side glaciers, whose ice continues to slowly revolve as a band of ball bearings mediating transverse differences in flow velocities.

In 2016, the upper fractures will take up the strain as the first rift passes by the source and approaches dormancy, possibly extending to mid-channel or even cleaving off a major berg. Much of the real action is taken place underneath where circulating warm ocean water is eating away the bottom of the ice sheet, predisposing it to rifting that otherwise might not have happened.

The fourth area of interest, extensional crack induced by the west side bend in the fjord walls near Kap Bremerton, showed limited change. Again the glacier moves on during the winter but the crack mechanism does not, so we can expect the action in 2016 to either expand one of the more recent cracks or initiate a new one to the south. This region historically has not been the source of full width rifting (calving).

Petermann Glacier ... new observational data in 2015

Due to its extreme northern latitude and the nature of near-polar satellite orbits, Petermann receives almost daily coverage by Landsat-8 and Sentinel. However due to darkness, Landsat wrapped up its season almost six weeks earlier than at west-central Greenland glaciers like Jakobshavn. However Sentinel embarked on five months of high resolution IW coverage that will allow, in conjunction with differential GPS measurements in August, very high resolution determination of seasonal velocity slowing.

We discussed 18 months ago a very fine interferometric image taken by Radarsat-2 operating in Sentinel mode (#86 to #97). I've since located a much higher resolution version of that image that will reactivate this discussion. However the associated metadata still leaves a lot to be desired (such as the coordinate projection used).

It's imperative to get this image co-located with Landsat and Sentinel in mercator UTM21 as well as IceBridge Cresis radar grids (which come with kml track files). However it is not easy to warp an unknown projection onto the upper ice sheet because Kap Schoubye and Kap Egedesminde across the fjord entrance are the last available ground control points. We'd like to know how the islands of slower motion shown in the SAR correlate with radar upheavals co-locating along flow lines.

Petermann Glacier ... new academic publications in 2014-15

These are somewhat tricky to locate comprehensively as dissertations are not indexed at Google Scholar, papers solely about Petermann don't always indicate that in title or abstract, articles of broader scope may have important sections dedicated to Petermann, and quite a few are indeterminate being buried behind expensive firewalls.

An investigation into the feasibility of applying 3D geological modeling techniques to polar ice sheets
F Mundel
https://epic.awi.de/38445/1/BachelorThesis_FelicitasMundel.pdf

Radiostratigraphy and age structure of the Greenland Ice Sheet
JA MacGregor
http://tinyurl.com/owjb4al

Warming and deformation of the Greenland Ice Sheet by refreezing meltwater
RE Bell 2014
http://tinyurl.com/os5lzru

Traveling slippery patches produce thickness-scale folds in ice sheets
M Wolovick
http://tinyurl.com/nt35lfp

Widespread Persistent Thickening of the East Antarctic Ice Sheet by Freezing from the Base
RE Bell
http://www.sciencemag.org/content/331/6024/1592

Ice Shelf Melt Rates and 3D Imaging
C Lewis
https://tornado.rsl.ku.edu/sites/default/files/biblio/TechRpt162.pdf

Airborne fine-resolution UHF radar: englacial reflections, firn compaction and ice attenuation rates
C Lewis, S Gogineni, F Rodriguez-Morales
http://www.igsoc.org:8080/journal/61/225/j14j089.pdf

Ocean observations from below Petermann Gletscher
A Muenchow
https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/62148
http://ows.udel.edu/
http://icyseas.org/
https://petermannsglacialhistory.wordpress.com

Interannual changes of the floating ice shelf of Petermann Gletscher, North Greenland from 2000 to 2012. J. Glac., 60, doi:10.3189/2014JoG13J135, 2014. .pdf
A Münchow, L Padman, and HA Fricker
http://muenchow.cms.udel.edu/papers/Muenchow2014-JGlac.pdf

Bathymetry in Petermann fjord from Operation IceBridge aerogravity
KJ Tinto, RE Bell, JR Cochran, A Münchow
http://muenchow.cms.udel.edu/papers/Tinto20

Resolving bathymetry from airborne gravity along Greenland Fjords
A Boghosian
http://onlinelibrary.wiley.com/doi/10.1002/2015JB012129/abstract

Unprecedented retreat in a 50-year observational record for Petermann Glacier
OM Johannessen
http://159.226.119.58/aosl/CN/article/downloadArticleFile.do?attachType=PDF&id=383

C51B-0712: Over-wintering of Supraglacial Lakes on the Greenland Ice Sheet from Sentinel-1 and Landsat-8 Data
https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/85347
C Benedek

The response of Petermann Glacier, Greenland, to large calving events, and its future stability in the context of atmospheric and oceanic warming
FM Nick
http://tinyurl.com/qdo6s8g

Basal topographic controls on rapid retreat of Humboldt Glacier, northern Greenland
JR Carr, A Vieli, CR Stokes, SSR Jamieson
http://www.igsoc.org:8080/journal/61/225/j14j128.pdf

A comprehensive interpretation of the NEEM basal ice build-up using a multi parametric approach
T Goossens
www.the-cryosphere-discuss.net/9/5555/2015/

Small-scale disturbances in the stratigraphy of the NEEM ice core: observations and numerical model simulations
D Jansen
www.the-cryosphere-discuss.net/9/5817/2015/

Petermann place names located on Google Earth
https://www.google.com/maps/d/viewer?mid=zbdKKg4fRHYo.kjkUmepfXc9A
« Last Edit: November 12, 2015, 01:07:38 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #343 on: November 20, 2015, 03:11:32 PM »
Attached is the new Sentinel velocity map for Petermann and Hammond glaciers. The coastal regions have better coverage than the interior (which so far does not represent an improvement). They badly damaged the data with a clumsy jpg overlay of a lat,lon grid. The original all-Greenland map is at the link below. It appears to be in polar stereographic projection though this is not stated.

Quote
This map of Greenland ice sheet velocity was created using data from Sentinel-1A in January–March 2015 and complemented by the routine 12-day repeat acquisitions of the margins since June 2015. About 1200 radar scenes from the satellite’s wide-swath mode were used to produce the map, which clearly shows dynamic glacier outlets around the Greenland coast. In particular, the Zachariae Isstrom glacier in the northeast is changing rapidly, and recently reported as having become unmoored from a stabilising sill and now crumbling into the North Atlantic Ocean. (Colour scale in metres per day). http://www.esa.int/spaceinimages/Images/2015/11/Ice_sheet_in_motion

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Have a ice day!

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #345 on: December 16, 2015, 02:24:48 PM »
Quote
Andreas Muenchow: The First 100 Days
First rate job in providing open source, real time accessibility to work in progress.

It's worth noting that the much awaited high precision GPS data (1-2 cm) needed to determine tidal flexure of the ice shelf has not been analyzed yet. Processing that dual-frequency UNAVCO GPS is a whole subspecialty ... the temptation is just to post the raw data online with the hope that a collaborator surfaces (it costs nothing to add another name to a paper).

The comment section notes that K Nicholls of the British Antarctic Service installed radars at two of the three sites that will measure ice thickness directly to give daily melt rates (next season or just Aug 2015?) but that data has not been processed or released (which would make no sense without lots of accompanying experimental context).

The data itself is being updated over at http://ows.udel.edu/ rather than on the blog section. The Iridium communication satellite, in my view, is very flaky:

2015-12-14: No Iridium Connectivity for 14 days (14 failed calls)
2015-11-19: Air temperature/humidity sensor #1 gives wrong values
2015-11-05: Conductivity sensor at 810-m reporting low, clogged?
2015-10-17: Software upload to reduce data transmissions to 1/day during polar night
2015-10-13: Wind-Sensor reporting 0 until Oct.-15
2015-09-13: No Iridium Connectivity for 12 days (36 failed calls)

The forward velocity of the ice sheet is running just below 1.2 km per year with no indication of a winter slowdown or year-on-year acceleration in the manner of Jakobshavn. The graph of "ocean properties under Petermann ice shelf" is providing the real highlights from the expedition though it takes a background in physical oceanography to draw any conclusions about any warm water circulating under the ice shelf.

The graph is unusual in that the data is displayed over an alpha transparency channel. This makes it convenient to change the background color or drop in a picture. Below, the CTD data at the five different depths along the sensor string are overlaid on a light blue gradient suggesting the increasing depth top to bottom.

It is also easy to lay in grid lines for the temperature, salinity and date that lie underneath (do not interfere with) the data display. As shown, the salinity over-rides temperature. Slightly better practice here would be to use a non-animated gif (or multi-layer tif) so that visitors can download the file and tease apart the data layers.

Tinting grayscales could also embed the data into an arithmetically interactive graphic. Ultimately though, to do any analysis, it's more convenient to just have numerical data in a spreadsheet or statistical package for say, interpolating between the depths sampled to search for stratification.

This data -- which was expensive, risky to acquire, and not experimentally reproducible (time has moved on)  -- should be archived somewhere at the time of publication so that analyses can be checked (or done under alternative assumptions or with additional data years); however that's hardly ever done in glaciology. The notion of emailing authors to get data was seriously undercut by two deaths last year in the same small research group.

Note that the units are 'potential temperature' rather than nominal. The reason for that is explained at:
http://oceanworld.tamu.edu/resources/ocng_textbook/chapter06/chapter06_05.htm
« Last Edit: December 16, 2015, 03:14:43 PM by A-Team »

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #346 on: December 16, 2015, 05:31:31 PM »
In view of yet another conflicting interpretation of basal ice upheavals in northern Greenland (see first ref in #342), especially in the Petermann and Zachariae areas, I'm looking to revisit the whole issue during the slack season. A separate forum for this and related phenomenon would require moving many dozens of earlier posts and graphics.

While fascinating and unexpected, these basal structures tell us something important about melt conditions at the end Eemian. The response of the ice sheet at that time to warming is our most important paleo clue to Greenland's response to present-day anthropogenic warming and the contribution of melting ice to global sea level rise and Atlantic meridional current disruption.

The merits of explanatory proposals can be compared using the checklist below:

What's the theory predict?
If competing theories can't be distinguished by experimental outcomes, then the relative validity of proposed mechanisms can't be assessed. Conversely if proponents cannot agree to observational outcomes that would invalidate their hypotheses, they have departed planet science for la-la land.

Here we don't get to nuances -- none of the competing upheaval papers explicitly commit to concrete predictions. It's not clear what these theories expect from drilling down to bedrock even through an extreme upheaval. Some will modify their proposal after the fact to fit whatever temperature, ice fabric, impurity, meltwater, conductivity, meteoric vs accreted ice, isotopic profiles emerge. A theory that flexible isn't in the science realm, it's merely curve-fitting.

Experimental ice core data from an upheaval is not in view. The only ongoing drilling to bedrock is at NEGIS. While site coordinates have only been disclosed in vague terms, we can be sure that extensive sled and air radar have shown regular stratification to bedrock -- there won't be tilted layers much less an upheaval at the drill site. That was certainly the choice made at the Renland ice cap.

Steam cores are quite feasible at accessible locations at the relevant depths. While these don't preserve the full ice archive, wire logging devices can capture many properties of the ice. Logged boreholes of Luethi at Swiss Camp and Hubbard at Store Glacier illustrate modern opportunities. It is really on these measurables that theories need to take a stand.

Sled or drone radar surveys are easier still. Radar to date has prioritized bedrock elevation and ice thickness; grid cells appropriate to that are too coarse relative to the intrinsic scale of upheavals and coherent systems of them. It is very difficult to reconstruct a 3D object from a couple of intersecting transects randomly oriented relative to key structural attributes and skew to the local ice velocity field. What's needed are radial grids in polar coordinates centered on individual features and grids of flowlines and isotachs.

Only one paper to date has attempted to reconstruct the overall regional 3D structure of an integrated upheaval system and that only for Petermann. Some papers envision recumbent and overturned folds where others see sheath folds; better radar grids can distinguish these (as can held-back or post-paper radar transects not used in model building).

Eqip is the most convenient site logistically, though it is not clear whether it (or any other upheaval) is 'representative' of all. The extensive upheaval there is 94 km from the Illulisat airport with a ship dock at the calving front hotel. Swiss Camp and Store research sites are close by. Crevasse and snow bridge risk is minimal inland within the nearly flat and slow moving Eqip ablation zone. Sled radars have used nearby, as have steam drills.

Occam's Razor: does it still cut it?
This 14th century principle asserts a simplest most boring explanation is most often right. This translates here to every upheaval in all of Greenland and Antarctica having the same underlying physical mechanism. Such parsimony is perhaps unattractive given very different bedrock, geothermal gradient, basal stress, temperature, viscosity, ice thickness, ice sheet histories, and surface velocity fields where upheavals are observed. So perhaps two physical mechanisms are operative but certainly no more than three. If so, a classification scheme is needed and predictions subordinated to it. Multiple contributing mechanisms at individual features is incompatible with Occam's principle and should be considered only as a last resort.

Absence of upheavals is just as informative as presence.
What accounts for the distribution of upheavals on the Greenland ice sheet? They are overwhelmingly concentrated today north of Eqip with many but not all in regions of moderate thickness and higher surface velocity. Yet for every upheaval, the same radar flight line can show many 'unoccupied' but seemingly indistinguishable sites. Any mechanistic explanation must give equal weight to predicting absence.

Are upheaval radar reflectors distorted isochrons?
In Greenland, upheavals are always bounded from above by the ubiquitous 'three sister" isochrons, accurately dated at NEEM to the middle of the last ice age. The nearly as ubiquitous 'older brothers' dating to 91 kyr sometimes bound the upheaval but more often are caught up in its contortions. Below that there are few consistent markers. Numerous mechanisms attenuating radar returns arise from something other than these presumptive massive volcanic depositions.

Upheaval areas in radargrams can be delimited from above by dark lines but these are often blurrier than any isochron ever observed in calmer regions, There may also be large dark blocks that have no counterpart in isochrons. These dark areas can have elaborate substructure that also require explanation. In these regions, processing radargrams at native resolution to optimally enhanced contrast is imperative, lest important clues be discarded. It's very poor practice to theorize without considering experimentally revealed complexity. The first image below compares a figure from a peer-reviewed geophysics at author-submitted resolution to actual upheaval data.

In their comprehensive mapping study of Greenland stratifications, MacGregor 2015 take a cautious perspective:

Quote
In numerous locations within Greenland’s interior, the deepest radiostratigraphy does not drape smoothly over the observed along-track bed topography. Instead, it is deflected upward across horizontal scales of several kilometers or more, distorting the depth-age relationship of the ice column by up to several hundred meters. These features are most prominent in the onset region of Petermann Glacier in northwestern Greenland (Animation S2).

Bell 2014 mapped the larger instances of these features. The precise cause of this disruption/deflection is unknown, but it is unlikely to be due to flow over undetected highs in the bed topography as previously hypothesized in Legarsky 1998, because extensive radar surveying of the GrIS fails to reveal these postulated highs.

This disruption may be due to buckling associated with spatially or temporally varying basal friction [Hindmarsh 2006 Wolovick 2014], basal freeze-on as inferred for East Antarctica [Bell 2011], or rheological variability within the basal shear layer [NEEM 2013].

Given the variability in magnitude of these radiostratigraphic disruptions, a combination of the above phenomena is also possible, or another as-of-yet unknown process. At least for Petermann Glacier, a plausible scenario is that recently described by Bell 2014 and modeled by Wolovick 2014: basal freeze-on uplifts and overturns the overlying strata, generating complex units that include both accreted and distorted meteoric ice.

These features can contain unusually bright, indistinct, or overturned reflections that do not resemble the monotonous radiostratigraphy of the overlying ice sheet. Unusually bright reflections may be due to a large fabric contrast between meteoric and accreted ice, as hypothesized to occur over Lake Vostok in MacGregor 2009a.

It is possible that some of these coherent reflections and diffuse reflectivity are not isochronal, although they likely remain useful indicators of past flow [NEEM 2013].

Are upheavals oriented along flow lines?
That's not so easily determined because flight lines rarely followed surface flow lines. The few orthogonal grids take a skew angle with respect to flow and, at Petermann, the rare flight lines that did follow flow were unfortunately from years with unsatisfactory radars. The grids are not tight enough to pick up intervening upheavals; at best 2-3 cross sections are available for a body of unknown shape and dimensions, eg there's no reason to suppose the peak height happened to be transected.

Many of those most dramatic upheavals occur in regions of deep and essentially stagnant ice. It simply isn't credible to draw a causal association with flow (or associated frictional basal heat) at meter-per-year sites as there's hardly been any movement since the Eemian, not to mention that a few km over with slightly faster flow there are no upheavals. This leads to the equally unpalatable choices of either disregarding Occam's Razor or the extended upheavals that seem coherently oriented with flow for hundreds of km.

Is the inventory of upheavals comprehensive?
No thresholding criteria were provided in the original mapping article [Bell 2014], no database of relevant Cresis accessions was begun, no kml path file exists. It appears that only the larger dramatic features were mapped based on subjective criteria. And not all of these were found because radar tracks are fairly sparse.

All the work on the Cresis image portfolio thus has to be repeated from scratch. This means the actual distribution of upheavals, perhaps stratified by upward magnitude and horizontal extent, has not been determined. This seriously undermines all manner of correlations with other basic attributes of the Greenland ice sheet.

Most troubling is the NEEM drill hole itself: overturned stratigraphy was carefully documented in the core but nothing resembling an upheaval can be seen in radar despite very intense surveys over the borehole and vicinity. This suggests the ability of radar to detect upheavals at depth is not adequate to locate them, not just at NEEM but by implication over much of north-central Greenland.

Is this an exercise in structural geology?
Yes and no. Stress-strain physics of stratigraphic deformation and flow of sedimentary deposits have been studied for centuries and have clear counterparts in ice sheets. Salt beds and lava flows have temperature/viscosity relationships reminiscent of ice. There are counterparts as well to till hydration state, melt phase change, and crystallization in plate tectonics but with diminishing relevance to glaciers, melt lakes, moulins and basal drainage channels.

Quote
“When I use a word,” Humpty Dumpty said in rather a scornful tone, “it means just what I choose it to mean — neither more nor less.”
“The question is,” said Alice, “whether you can make words mean so many different things.” (Through the Looking Glass, Chapter 6)
Anticline and syncline are terms for compressional folds borrowed from structural geology often inappropriately applied to Greenland ice upheavals. It's impossible to recognize these from a single radar flight lines because the requirement for a longitudinal fold axial plane is inherently two dimensional. If this axis has not been observed, the fold type cannot be distinguished from a dome or basin (technical terms for folds with non-axial symmetries).

An upward deformation of stratigraphic isochrons might be an anticline but such an inference is premature without supporting evidence from multiple flight lines -- these are so sparse that it can't be determined when one feature stops and another has started. It's really a stretch to apply these terms to basal freeze-up deformations: mechanistically more related to salt diapirs, this concept is only dimly related to compressional waves of alternating synclines and anticlines.

In structural geology, overturned and recumbent folds are distinguished from sheath folds. That can sometimes be done from a single transect should it happen to pass through the signature concentric 'eye' of a sheath fold. The second image shows that the folds labelled 'overturns' in the figure above are part of a sheath fold. The subject of folds is very complex overall and highly developed within structural geology.

Are these fossil features or still active processes?
In one scenario, upheaval processes began shortly after the Eemian ended, continued for a few tens of thousands of years, then ceased as an active process, no longer initiating new features nor building out older ones, which however persisted to the present day.

An alternative scenario posits that forces responsible for upheavals are fundamental basal processes not specifically tied to one-off historic ice warming during the Eemian that continue to the present. Processes mentioned here include freeze-on of meltwater at the ice/bedrock interface, slip-stick motion of the glacier and associated heat from friction, hotspots in the geothermal gradient, basal strain from ice sheet motion, temperate ice at the pressure melting point and associated lower viscosities, and so on.

North-central Greenland did not fully melt out during the Eemian (as mapped by MacGregor 2015 via a stratigraphic  age-depth function) but what didn't melt came close. In particular, the upheaval areas of Petermann and Zachariae are not underlain with Eemian ice today even a hundred km and more inland from the grounding line.

In the first scenario, this created a persistent body of temperate ice, perhaps with pockets of meltwater or hydrated till underneath, that was subsequently buried under thousands of meters of subsequent ice age snowfall. Slow equilibration with cold from above meant the temperature and buoyancy anomalies played out slowly, perhaps along the lines of 'thermal-viscous collapse' considered in Colgan 2015 (http://onlinelibrary.wiley.com/doi/10.1002/2015EF000301/full).

The second scenario predicts ongoing development of upheaval features and perhaps observable effects from the Holocene, its Thermal Optimum, or even contemporary anthropogenic warming. However the time scale needed for an observable effect isn't clear:

Even if the earliest radar flight line of 1993 had been fortuitously re-flown in the latest 2015, it isn't plausible than any upheaval change could be seen over 12 years, first because glacier processes generally precede at glacial paces, second the radars would be of very different design and third because a 100 m mismatch in flight lines would invalidate the comparison.

Eqip has favorable repeat radar coverage in different years but the east-west flight lines are displaced to 61 m and north-south to 29 m (3rd image). Note the bedrock drainage map resolution is delusional because kriging guesswork has filled in the blanks left by sparse radar coverage in active topography -- there is no other data other than what is seen along radar tracks (airGrav has been deployed in fjords, ice shelves and ice streams).

Is ice predictably deformed over an upheaval?
It's fair to say that stratigraphic layers above basal upheavals are conformally uplifted with that effect tapering off in Holocene ice, sometimes to the point of imperceptibility. This requires reconciliation with the near-incompressibility of ice, its viscosity, depth and status of firn, and conservation of mass because the ice surface is not notably deformed.

There is no known method by which the presence of upheavals can be systemically detected by any combination of measurable surface properties (such as ultra high resolution DEMs, surface velocity, and surface slope). We only wish there were because then the upheavals could be comprehensively mapped from continuous 2D data, with sparse radar tracks only employed as a cross-check and for details.

At Petermann, the case can be made that the upheavals themselves are anisotropically distributed with respect to surface velocity flowlines (though it's not so clear how to make that point objectively). This has implications for anisotropy of younger layer deformation which so far have not been pursued.

At the Eqip upheaval on a south-to-north track of 2008, isochrons do not notably conform with either bedrock profile nor the upheaval (4th image). This suggests (if not a unique situation) a basis for upheaval categorization.
« Last Edit: January 16, 2016, 09:25:19 AM by A-Team »

Andreas Muenchow

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #347 on: December 17, 2015, 02:27:55 AM »
@ A-Team:

1. The "lightly" processed, calibrated, and unpublished data are from 5 ocean sensors are posted as ASCII files at

http://ows.udel.edu/data/sbe.all

Edit: Formats of (all) data file(s) are explained at

http://ows.udel.edu/data/read.me

2. Iridium dial-up via a 9522B modem is indeed frustratingly intermittent. It may relate to a design flaw that expects the modem to initiate calls in order to stay "registered." I do not know what this means precisely, but neither does the generally respectable company that sells these products. Since I call the Greenland modem from my home (rather than the modem in Greenland calling me at home), the Greenland modem apparently disconnects itself from the network. This makes zero sense to me, this is not documented, actually, the manufacturer discovered this itself. The fix is simple, two lines of code at most, but without a connection there is not way to send this new code to the station. I connected with other people at the Fall AGU who have exactly the same type of problem with the same product in British Columbia and Ellesmere Island. The best case scenario that I am hoping for is that military operations in the area take away bandwidth for a limited time. Data are recorded and stored locally even when Iridium does not connect, but this project was supposed to be real-time with a 2400 baud dial-up serial connection (1980ies style modems).

3. The survey-grade GPS data are about 1 GB per day per station as we accidentally collected data at 1 second intervals rather than the more standard 10 s or 30 s. Furthermore, I currently have zero funds to do this work, but a proposal to do so (as well as maintain the site beyond Aug.-2016) is pending with NSF.

4. The radar data at two sites are collected right now, but data volume is too high for the low-bandwidth we got; so the data will have to wait until we get there next year to pick it up

In summary, this is tiny project done on a shoe-string at multiple institutions in multiple countries by people who genuinely like each other and do what they think is both fun and, we feel, important. Communication with platforms, sensors, and ships north of 78 N latitude is still very much a non-trivial challenge ... at least for me, but Sen. McCain got also rudely disconnected by Iridium when he called the ship in Petermann Fjord last summer.
« Last Edit: December 17, 2015, 06:38:38 AM by Andreas Muenchow »
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mati

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #348 on: December 18, 2015, 01:44:18 AM »
i did some work on the original Iridium system, and the trouble arises when switching between satellites.  I wonder as well if the northern lattitudes and solar activity contribute to the problem.

oh, and here is a neat thing:
https://en.wikipedia.org/wiki/Satellite_flare#Iridium_flares
http://spaceweather.com/submissions/large_image_popup.php?image_name=J.-Dana-Hrubes-iridium-4-28-08-3-b2-slo_1209376592.jpg
and so it goes

sidd

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Re: Petermann Gletscher / Petermann Fjord / North West Greenland
« Reply #349 on: December 18, 2015, 05:41:07 AM »
Great data, thanx a million Prof. Muenchow. Actually seeing meltwater pulses at 10-30 day periods in depthwise temp and salinity puts mass and heat flux mechanisms in a new light for me.

I am sorry for your bad experience with communications. It has paid me in the past to always have the site with flaky comm (in your case, Iridium) initiate connection attempts. On the other end i need to have two static sites (with large UPS and guarded by ferocious leopards) always listening for connect attempts.

Why two ? Therein lies a tale or five ...

sidd