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Author Topic: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland  (Read 329051 times)

Shared Humanity

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #300 on: September 11, 2014, 02:51:03 AM »
Espen..

Looking at the animation, there is the appearance of a very odd dark area that is well back of the calving face. It runs parallel to the calving face, is quite long and is just southeast of where you placed your name. It seems to be showing up where there appears to be significant thinning of the glacier. Is this snow melt? Could this be a fracturing or calving of such a large part of  the glacier?

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #301 on: September 11, 2014, 05:19:54 PM »
Shared Humanity, I think it is a "watermark" of the bedrock, showing up at the surface?
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A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #302 on: September 11, 2014, 05:29:05 PM »
Here are the areas of the various calving front changes assuming 30 m Landsat pixels. Now showing orange and yellow swapped per comment below. Pixel count is divided by 30x30 = 900 m^2 to arrive at areas. Volumes (not shown) require using ice depth from recent radar imagery.
« Last Edit: September 11, 2014, 07:33:32 PM by A-Team »

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #303 on: September 11, 2014, 06:06:41 PM »
A-Team nice work, I think you should swap yellow (aug22) with orange (sep9)?

It is correct, I did not change the resolution (30M)
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Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #304 on: September 11, 2014, 09:05:55 PM »
A-Team but is still impressing how much glacier ice was lost in just 5 years, and that is more than 3 times the area of Manhattan (A figure Americans will understand)?
« Last Edit: September 11, 2014, 09:17:10 PM by Espen »
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A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #305 on: September 12, 2014, 03:56:19 PM »
I put together the vertical grids for the area described above west of 79N. These intersect with the horizontal grid and so give some idea of the areal extent of bottom freezeup features. The table below shows the separate horizontal and vertical rescaling necessary to join pairs of Cresis radar tracks, even those on the same flight path.

Each round of rescaling degrades the image -- this was a terrible way to store primary experimental data. It would have been far better to have left each flight as a continuous image with visitors provided a  'rectangle select' portal.

It is a complete nuisance to locate and retain intersections of horizontal and vertical grid flight segments because flight segments are oblique with respect to lat, lon lines and no correspondence exists between frame breaks. It is almost easier to align the images after the fact, as indicated in the image below.

While this example shows that it is feasible to get orthogonal sections to a given feature of interest (eg the small coastal cones), the several km scale intrinsic to features is not adequately sampled by the ~ 6 km scale that separates flight grid segments here.

Bottom freezeups are an important new mechanism for heat transfer into the deep interior of the ice sheet (from surface melt lake moulins and geothermal/pressure melt) -- ice deformation is exceedingly sensitive to temperature. Future ice flow would be seriously mis-modeled (on the slow side) by assuming temperature profiles from summit cores like NGRIP that did not happen to pass through a freezeup. However it may prove necessary to drill through one to experimentally determine both temperature and origin of these deformations.

HorVerFrame
100.0100.020100330_07_18
99.3099.4320100330_07_17
96.56100.020100330_07_14
102.8100.020100330_07_13
99.5299.7120100330_07_9
101.0100.020100330_07_10
100.3100.020100330_07_5
103.0100.020100330_07_6
103.7100.620100330_07_1
109.099.4320100330_07_2
107.6100.020100330_06_1
77.0499.1420100330_06_2

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #306 on: September 14, 2014, 03:17:11 PM »
The first image shows a favorable horizontal radar flight path segment for 3D reconstruction (20110502_01-033) -- it has an interesting bottom freezeup feature and is sliced by four vertical flight path segments that provide cross-sectional information.

The process begins by drawing flight paths in Google Earth, linking Cresis images to the segments, and then assembling thumbnails onto to a screen shot. This assures that the final product will be informative.

Next, equations for each of the five lines are determined in slope-intercept form (neglecting earth curvature, WGS84, ice surface elevation and so forth) along with intersection lat,lon coordinates. This is a mild nuisance to set up in a spreadsheet but once done it provides pseudo code for marking up all flight path intersections (and angles if oblique) for all flights for all years, something Cresis could have done. An extra decimal point is also needed because of subtractions of numbers with little variation.

Transforming the grid pieces into perspective view allows the 3D structure of the freezeup to be visualized, noting that the sections here are ~9 km apart. This quickly gets complicated as one layer blocks the next, so it is necessary to have on-off and transparency controls. That's a bit much so I simply made an animation that steps through the layers.

This is the very first reconstruction of a freezeup as far as I know. The icesheet here is flowing slowly from lower left to upper right.

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #307 on: September 14, 2014, 03:55:14 PM »
A-Team it is fantastic what you can retrieve from those data, and on top of that you show it in a way not experts can understand it.
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A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #308 on: September 14, 2014, 04:32:49 PM »
Thx, Espen!

I have a hidden agenda though, explain things once by example, get people to realize they could be doing this themselves, then just kick back and just enjoy their results. (So far this hasn't worked real well.)

Some places have a much higher density of flight path grid lines than 79N/Zachariae, such as Eqip/Jakobshavn, Petermann and Camp Century. They can be seriously katywumpus in terms of orientation. I shall leave these as an exercise for our esteemed blog visitors.

Down the road, I expect freezeups will be flown in tight orderly grid by the radar drone (which is capable of 5m turns). However Petermann especially is worth doing at this time since its longer feeder canyon is providing it with water for what may be one gigantic connected freezeup feature.

While freezeups are primarily a northern Greenland story, that is precisely the area that is waking up. Overall i think the Greenland story will be one of more heat working its way into and underneath the icesheet, warming it, and so softening the rheology. This will result in unblocking the margins faster than IPCC envisions, which in turn will remove the main resistive force holding the central ice sheet in place, and so the restraint on sea level rise.
« Last Edit: January 16, 2016, 09:29:11 AM by A-Team »

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #309 on: September 14, 2014, 05:09:57 PM »
A-Team, why all the activities at Camp Century, must have been a sub contract to the Military, wonder if they ever cleared the site for nuclear debris?
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A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #310 on: September 15, 2014, 12:09:49 AM »
I suppose they have to start from Thule when flying northern Greenland, that being the only full airport. Not sure they do that much straight instrument flying in bad weather (have to stay very low for radar to minimize side-scatter) so might head up to Camp Century for visual orientation, then head out on the mission from there if conditions are still go.

Seems like they pass over NEEM and NGRIP quite a bit too. Since nothing happens on the summit ridge, if the radar configuration changes in some fashion every year, they have year-on-year interpretive controls as well as the borehole characteristics.

In the 1968 Broken Arrow incident -- a pilot of an always-in-the air B52 stuffed foam cushions over a hot air vent catching the plane on fire -- the crew mostly ejected but the plane flew on with four hydrogen bombs (and their conventional explosive fuses) until it crashed on sea ice in North Star Bay and exploded.

Some of the nuclear contamination was taken back to the US  -- 500,000,000 gallons worth -- but they never could find the 4th secondary.

This should not be confused with separate Camp Century nuclear contamination. During its brief operational life, that reactor (loaded with 20 kg of enriched uranium-235) discharged 47,078 gallons of radioactive liquid waste into an  icecap well. No attempt was ever made to recover it; the site is slumping badly and the waste would have moved with it.

Eventually the US resolved the Thule situation by declaring there never was a fourth bomb with serial number 78252, or maybe 78252's components had been removed with the others, in any case not to worry just because one itty bitty 1.1 megaton hydrogen bomb named 78252 could not be located, see, because there was, like, maybe a typo in the cargo manifest or sumpin and it didn't never exist.

One US document BBC obtained in July 1968 said the futile Star III submarine "search for a missing weapon is confidential NOFORN.” NOFORN means no foreigners can see, especially not Danes or Five Eyes partners, so familiar today from Snowden documents.

However a blackened section of ice was found which had refrozen with shroud lines from a weapon parachute, with a US  document reading: "Speculate something melted through ice such as burning primary or secondary."

The US was concerned back then, but not now, that the Russians would find the missing bomb and learn secrets of  nuclear warhead design. WH Chambers, a former nuclear weapons designer at the Los Alamos nuclear laboratory, told  BBC "there was disappointment in what you might call a failure to return all of the components."

Years later, a definitive 279-page report of the Danish Institute of International Studies (DIIS) resolved the matter once and for all claiming: "There is no bomb, there was no bomb and they were not looking for a bomb [with the risky submarine search].”

Period photos and datasheets for the B28 bomb show a 4.2 m long, 0.5 m diameter object weighing 984 kg containing plutonium, lithium-6 deuteride and tritium, plus fission and high explosive components.

The very same Fogh Rasmussen in charge today of fomenting NATO aggression in countries like Georgia and the Ukraine, blew off Thule workers exposed to plutonium, saying elevated thyroid cancer could surely be attributed to heavy drinking at the remote airbase. Workers were to accept a small one-time payment in exchange for future silence.

A nuclear scientist recently told reporters "we really don’t know what has happened to this bomb. It’s not going to explode but the possibility remains of very large contamination with all of the dangers that involves."

Nobody got around to measuring land contamination until 2007:

"The results show levels of plutonium in soil at Narsaarsuk ranging from background values around 39 Bq m-2 up to levels of 1.7 MBq m^2. Local sub-areas of sizes ranging from a few hundred to a few thousands of square metres show elevated levels above 10 kBq m^2 of plutonium. Based on geostatistical analysis, the total amount of plutonium in soil at Narsaarsuk is estimated at 270 GBq (100 g)."

"Investigations were carried out at  to determine the occurrence of radioactive particles in air. This involved collection of airborne particles with an air sampler, collection of airborne particles on sticky foils, collection of rain samples and collection of particles that could be resuspended by wind from the soil surface to the air. Small amounts of plutonium were found in air and rain samples..."

http://orbit.dtu.dk/en/publications/id%28c3b7244a-5c9d-49a1-84aa-4397903103ec%29.html

There's a comprehensive account of the contamination at wikipedia:

https://en.wikipedia.org/wiki/1968_Thule_Air_Base_B-52_crash

The local people avoided direct exposure because the US had previously relocated them to a canvas tent concentration camp at Qaanaaq:

"The town of Qaanaaq was established in the winter of 1953 when the United States expanded their airbase at Thule and forcibly relocated the population of Pituffik, Dundas, and Uummannaq 31 km to the north within four days during the height of the Cold War. The settlement was subsequently moved another 100 kilometers to the north."
 

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #311 on: September 15, 2014, 03:45:35 AM »
Zachariae Isstrøm update: Massive calving activity ( in just 5 days) along the whole glacier front.

This season seems to be one of the largest retreats at Zachariae in recent times, only the 2011 retreat was larger (until now).
« Last Edit: September 15, 2014, 04:23:40 AM by Espen »
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A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #312 on: September 15, 2014, 04:20:18 PM »
Interesting how Zach continues to calve this late in the season. Jakobshavn has been so cloudy lately, no Landsats for weeks and weeks. Just like last Sept-Oct.

This is my last post of the season. I will be traveling offline for the next 5-6 weeks as I move operations down to Tucson for the winter.

Here are a few things I didn't have time to finish. Hopefully someone else will have a chance to work them up:

-1- Develop a surface map of Greenland colored by a classification scheme indicated what is below: layer cake, freeze-up, bedrock deflection, icestream, shear margin and so forth. Tint to show age of oldest identifiable stratum, deploy saturation to show residual thickness of undateable ice, reserve grayscale for surface elevation.

-2- Explain common second rank tensors of continuum mechanics used in Greenland icesheet modeling with pictures and examples, with special attention to invariants and a self-evident proposition called Glen's Flow Law. The idea here is not to do numerical modeling ourselves but get visitors to the point where they can better evaluate model icesheet predictions being published.

-3- Ramifications of the new N15 temperature dates for Greenland ice cores: if Greenland didn't melt during the Eemian as claimed, why aren't there thousands of meters of additional ice below the summit ridge (where little movement towards the coast occurs)? If the Eemian was warmer earlier and longer than O18 indicates, what becomes of model calculations? NEEM drilled through a double fold of recumbent ice -- was this down-ridge slumpage as stated or a small bottom freezeup feature associated with local geothermal warm spot meltwater?

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #313 on: September 15, 2014, 08:53:55 PM »
A-Team I will be missing you and your great posts.
« Last Edit: September 15, 2014, 09:24:20 PM by Espen »
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A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #314 on: September 16, 2014, 03:24:38 PM »
Seems like we should write up a review of the season highlights for Greenland ... something that Neven might run on the sea ice blog during a slack period. And you would be the perfect person to pull it all together.

I'm not sure what these gentlemen are discussing below, something seismic no doubt. But look at the stratigraphy in the background -- an uncanny resemblance to ice-penetrating radar sections of Greenland. You just know that petroleum geologists have fantastic display and analytic software ... if only we could get them to take an interest in Greenland!

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #315 on: September 16, 2014, 05:13:24 PM »
Seems like we should write up a review of the season highlights for Greenland ... something that Neven might run on the sea ice blog during a slack period. And you would be the perfect person to pull it all together.

I'm not sure what these gentlemen are discussing below, something seismic no doubt. But look at the stratigraphy in the background -- an uncanny resemblance to ice-penetrating radar sections of Greenland. You just know that petroleum geologists have fantastic display and analytic software ... if only we could get them to take an interest in Greenland!

A-Team yes I will try to sum up, the glacier situation around Greenland, maybe sometimes in October, I am glad my key interest nowadays is the glaciers in Greenland, far more interesting than the sea ice ;)
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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #316 on: September 16, 2014, 05:27:13 PM »
Thank you sirs -I'm assuming of course. It's been eye-opening to watch the posts on Greenland. I'll try to out forth some time dedicated to analysis if I get around to it. Have a nice break A-Team!

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #317 on: September 16, 2014, 11:36:50 PM »
Seems like we should write up a review of the season highlights for Greenland ... something that Neven might run on the sea ice blog during a slack period. And you would be the perfect person to pull it all together.

A lot of thanks from me too, Espen and A-Team. You have really been doing a great job over here!

I had actually promised Espen to do a blog post on all those animations he did of various glaciers showing changes over time, but never came round to it (sorry, Espen!). I'll very gratefully post any summary you guys come up with, but I'll leave that up to you to decide.
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Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #318 on: September 30, 2014, 10:19:39 PM »
And here is my favorite, Zach always impress me, because this is not a "Mickey Mouse" glacier like so many others, and here she come:
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Sonia

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #319 on: October 01, 2014, 03:57:43 PM »
The calves appear to be moving more freely now.  Compare to animations posted over the summer where many of them appeared grounded.

Looking at some of those prior animations now, it looks like maybe the calves weren't exactly stationary but were staying in formation as they moved with the glacier advance.  So maybe they were being pushed over the ground.  Yet something keeps them separated from each other.  I wonder if it is regolith scoured upstream that becomes a moraine now at the end of glacier.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #320 on: October 02, 2014, 08:34:48 AM »
My hexagonal feature - handy to track the movement of the glacier over the years - has now calved.

(click for hi-res image)

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #321 on: October 02, 2014, 04:12:05 PM »
Wipneus,

Nothing last forever! ;)
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Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #322 on: October 22, 2014, 11:36:19 AM »
My first shot at the Sentinel data are  Zachariae and  Nioghalvfjerdsfjorden. This is just half the usual resolution (to keep the image size manageable).

Click the picture for a 3MB image.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #323 on: October 22, 2014, 12:32:14 PM »
That last image has a resolution of 80m/pix (from the original 40m). There are also images available with 25m resolution such as one on October 20.

With some scaling and rotating I assembled a quick animation of Zachariae. It shows that the calving continues while optical information is missing.

(pic needs a click to animate)

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #324 on: October 22, 2014, 04:49:46 PM »
This really shows there is something serious going on at Zachariae, we are in an unplugged mode?
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Sonia

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #325 on: October 22, 2014, 04:54:33 PM »
Oh these are nice.  I've been enjoying the Sentinal images on the DMI site recently but the higher resolution here is impressive.

oren

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #326 on: October 23, 2014, 12:03:32 AM »
This really shows there is something serious going on at Zachariae, we are in an unplugged mode?

I was thinking the same thing.

A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #327 on: November 02, 2014, 12:48:31 PM »
Wipneus,

Your animation of Zachariae showing calving continuing late into October makes me wonder how far upstream Sentinel could still measure icestream movement. The two dates you provided are a good start on the three needed for false color RGB interferometric fringe counting (as done so nicely on Petermann).

It would be interesting to compare velocities today to older data in the standard Greenland-wide map (below). That ESA search interface (https://scihub.esa.int/dhus/) is a mediocrity compared to EarthExplorer -- if they can't do it better,  just borrow the code. At this file size, some preview imagery would be helpful.

I attached the best available overall velocity map for NEGIS along with (after struggling with the inept interface) a map showing Sentinel coverage of upper Zachariae. There is better recent data midway in 3  papers from 2014.

The head of Zachariae (about 75ºN -40ºW) is quite remarkable: it seems to sit over an anomaly of the geothermal field. The icestream was not even discovered until 2000 -- the initial paper proposed (most improbably) that melting starts over a caldera.

Fahnestock, M., W. Abdalati, I Joughin, Brozena and P. Gogineni. 2001.
High geothermal heat flow, basal melt, and the origin of rapid ice flow in central Greenland.
Science, 294 (5550), 2338-2342. doi:10.1126/science.1065370.

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #328 on: November 08, 2014, 11:23:47 AM »
More action is seen at Zachariae Isstrøm:

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A-Team

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #329 on: November 10, 2014, 08:45:54 PM »
Hopefully some ppts from Session 4806 of the Dec 2014 AGU meeting will become available soon. This sounds like a warming ocean story propagating up-glacier in a delayed reaction, rather than change emanating from more basal lubrication (more melt lakes or increasing geothermal hotspot at the head of the icestream).

Quote
J Mouginot et al:  We study the 79north (Nioghalvfjerdsbræ) and Zachariæ Isstrøm sector of the Greenland Ice Sheet using a combination of satellite and Operation IceBridge (OIB) remote sensing data and numerical ocean modeling.

Around 2004, the southern portion of the floating ice tongue of Zachariæ Isstrøm began to break up, presumably due to changes in sea-ice/ocean conditions in the northeast.  Although the floating portion of the glacier started to speed up in response to the reduction in ice shelf buttressing, it was not until 2012 that the velocity of the grounded portion increased significantly.

In 2014, Zachariæ is calving at its grounding line, which retreated 5 km in 1996-2011. The southern ice tongue is gone, and the northern ice tongue is detached from the glacier. We use satellite-derived ice velocity and refined ice thickness based on mass conservation to estimate discharge of these glaciers.

We compare the results with RACMO2.3 surface mass balance and reconstruct the mass balance of this sector for the period 1992-2014 to show that most mass loss picked up after 2012, not in the earlier 2000's as stated in a recent study.

We reconstruct the sea floor bathymetry beneath the former ice shelves for the first time using OIB gravity data. The results reveal the natural passages of subsurface warm waters and help constrain the simulation of ice shelf melt rates.

The grounding line of 79north also retreated in 1996-2011, but its flow speed has remained constant. We attribute this contrasting evolution of the two glaciers to a difference in sea floor bathymetry, which allows an intrusion of larger amounts of warm subsurface waters for Zachariæ since the early 2000s, but limits access of such currents for 79north.

Nioghalvfjerdsbræ will likely undergo a fast recession [# years?] until its grounding reaches a topographic barrier [sill] about 30 km upstream, where ice retreat will temporarily slow down.

We conclude that since about 2012, major change in glacier dynamics have started to hit north Greenland.

Espen

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #330 on: November 10, 2014, 09:29:39 PM »
Hopefully some ppts from Session 4806 of the Dec 2014 AGU meeting will become available soon. This sounds like a warming ocean story propagating up-glacier in a delayed reaction, rather than change emanating from more basal lubrication (more melt lakes or increasing geothermal hotspot at the head of the icestream).

Quote
J Mouginot et al:  We study the 79north (Nioghalvfjerdsbræ) and Zachariæ Isstrøm sector of the Greenland Ice Sheet using a combination of satellite and Operation IceBridge (OIB) remote sensing data and numerical ocean modeling.

Around 2004, the southern portion of the floating ice tongue of Zachariæ Isstrøm began to break up, presumably due to changes in sea-ice/ocean conditions in the northeast.  Although the floating portion of the glacier started to speed up in response to the reduction in ice shelf buttressing, it was not until 2012 that the velocity of the grounded portion increased significantly.

In 2014, Zachariæ is calving at its grounding line, which retreated 5 km in 1996-2011. The southern ice tongue is gone, and the northern ice tongue is detached from the glacier. We use satellite-derived ice velocity and refined ice thickness based on mass conservation to estimate discharge of these glaciers.

We compare the results with RACMO2.3 surface mass balance and reconstruct the mass balance of this sector for the period 1992-2014 to show that most mass loss picked up after 2012, not in the earlier 2000's as stated in a recent study.

We reconstruct the sea floor bathymetry beneath the former ice shelves for the first time using OIB gravity data. The results reveal the natural passages of subsurface warm waters and help constrain the simulation of ice shelf melt rates.

The grounding line of 79north also retreated in 1996-2011, but its flow speed has remained constant. We attribute this contrasting evolution of the two glaciers to a difference in sea floor bathymetry, which allows an intrusion of larger amounts of warm subsurface waters for Zachariæ since the early 2000s, but limits access of such currents for 79north.

Nioghalvfjerdsbræ will likely undergo a fast recession [# years?] until its grounding reaches a topographic barrier [sill] about 30 km upstream, where ice retreat will temporarily slow down.

We conclude that since about 2012, major change in glacier dynamics have started to hit north Greenland.

"We conclude that since about 2012, major change in glacier dynamics have started to hit north Greenland."

Better late than never ;)
« Last Edit: November 10, 2014, 09:42:23 PM by Espen »
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sidd

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #331 on: November 10, 2014, 11:32:49 PM »
"We reconstruct the sea floor bathymetry beneath the former ice shelves for the first time using OIB gravity data. The results reveal the natural passages of subsurface warm waters and help constrain the simulation of ice shelf melt rates."

I suspected as much. But (and I dont know why) Nioghalvfjerdsfjorden scares me more than Zach.

sidd

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #332 on: November 11, 2014, 05:04:30 PM »
We should get off our butts and process the OIB bathymetry ourselves instead of waiting for journal articles to dribble out. It's readily available and not particularly gnarly in size or column interpretation. ftp://n5eil01u.ecs.nsidc.org/SAN2/ICEBRIDGE/IGBTH4.001/   The lat,lon could be stripped out for a GoogEarth kml path file; for an unknown reason xml format is provided. Not rocket science to inter-convert these in a plain text editor.

#Bathymetry models from the inversion of Operation IceBridge gravity anomalies measured from Sander Geophysics Ltd AIRGrav
# LINE      XX.YYZ XX denotes individual glacier, YY denotes year of flight (20YY), Z greater than zero denotes repeat tracks
# FAG070_mGal   Observed Free air gravity anomaly (mGal)
# FAG_calc_mGAL Calculated gravity anomaly (mGal)
# LON      Longitude on WGS84 ellipsoid
# LAT      Latitude on WGS84 ellipsoid
# X      X co-ordinate in EPSG3413 (polar stereographic, true at 70N, 45W down, WGS84 ellipsoid)
# Y      Y co-ordinate in EPSG3413 (polar stereographic, true at 70N, 45W down, WGS84 ellipsoid)
#BATHY   Modelled bathymetry from gravity inversion. All depths reported in meters with positive downwards and with respect to WGS84 ellipsoid.
#LINE, FAG070_mGal, FAG_calc_mGal, LON, LAT, X, Y, BATHY_m
14.100,49.4,57.4,-49.2,71.54,-147685,-2011087,924
14.100,49.4,57.3,-49.2,71.54,-147685,-2011087,923
14.100,49.4,57.2,-49.2,71.54,-147685,-2011087,922
14.100,49.4,57.1,-49.2,71.54,-147685,-2011087,921
14.100,49.4,57.1,-49.2,71.54,-147685,-2011087,920
...etc etc ...
Quote
Bathymetry in fjords of Northwestern Greenland from Operation IceBridge aerogravity.
Kirsty Tinto

Understanding of the influence of water circulation on the melting and dynamics of Greenland glaciers is hampered by a lack of basic information on fjord bathymetry. Here we present results from Operation IceBridge aerogravity surveys along the axes of the fjords of northern Greenland and in a coast-parallel grid across the northwestern fjords in order to provide bathymetric models for this difficult to access region.

Fjord axis profiles reveal the depth and shape of the bed in front of the grounding line for nine glaciers around the northern coast of Greenland. Sills are revealed approximately 20 km offshore of the grounding lines of Petermann, Steensby and Ryder glaciers, with depths similar to those of their grounding lines.

Sills have not been identified in the other northern fjords. In Northwest Greenland, the recently released IBCAO v3 shows deep troughs in the continental shelf but does not resolve the connection between these troughs and the channels of the outlet glaciers that cut the coast. The changes observed in velocity and surface elevation of these glaciers does not follow a simple spatial pattern, and the influence of ocean waters is not fully understood.

The new IceBridge survey provides a bathymetry model of the area between the marine IBCAO data and the grounded glaciers and shows for the first time the linking pathways at depth of individual outlet glaciers to shelf troughs.

Quote
Bathymetry and geology of Greenlandic fjords from Operation IceBridge airborne gravimetry
Tinto, KJ et al 2011 AGU

The Greenland Ice Sheet is drained by outlet glaciers that commonly flow into long, deep fjords. Glacier flow is controlled in part by the topography and geology of the glacier bed, and is also affected by the interaction between ice and sea water in the fjords. This interaction depends on the bathymetry of the fjords, and particularly on the presence of bathymetric sills, which can control the influx of warm, saline water towards the grounding zone.

The bathymetry and geology of these fjords provide boundary conditions for models of the behaviour of the glaciers and ice sheet. Greenlandic fjords can be over 100 km long and up to 1000 m deep, with sills a few hundred metres above the bottom of the fjord.

Where bathymetry is not well known, the scale of these features makes them appropriate targets for aerogravity surveys. Where bathymetry is known, aerogravity can provide information on the geology of the fjord, but the sometimes narrow, sinuous fjords present challenges for both data acquisition and interpretation.

In 2010 and 2011 Operation IceBridge flew the Sander Geophysics AIRGrav system along the axes of more than 40 outlet glaciers distributed around the coast of Greenland. The AIRGrav system has high precision, fast recovery from turns and the capacity for draped flights, all of which improve the quality of data acquisition along fjord axes.

Operation IceBridge survey flights are conducted at or lower than 500 m above ground surface, at speeds of ~140 m/s, allowing full amplitude resolution of features larger than ~5 km, and detection of smaller scale features.

Fjord axis data are commonly of lower quality than data from grid-based gravity surveys. Interpretation of these data is improved by combining repeated survey lines from both seasons as well as incorporating other datasets, such as radar, and magnetic data from Operation IceBridge, digital elevation models and geological maps.

While most fjords were surveyed by a single axial track, surveys of Petermann Glacier include parallel flow lines, allowing new constraints on the bathymetry under its floating ice to be more reliably modelled. This work is a preliminary review of the fjord axes surveyed by Operation IceBridge and presents models of representative fjords. The surveys include major features, such as the fjord in front of Kangerdlugssuaq Glacier and under the the floating ice in front of Petermann, 79 N and Zachariae Glaciers and results identify the limits and applications of IceBridge aerogravity in the Greenland fjords.

sidd

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #333 on: November 12, 2014, 05:44:25 AM »
there are antarctic tracks in there also

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #334 on: November 12, 2014, 12:12:59 PM »
Right, they have gotten remarkable results from Operation IceBridge in Antarctica (first two images below). Oddly, for Greenland, the only previous use of airplane-borne OIB gravity seems to have been the Bell 2014 paper on basal freezeups (3rd image, see also Storstrømmen).

Note that radar can penetrate freshwater ice but not seawater, so in terms of floating iceshelves or mélange-covered outlet fjords only gravity can find the topography of bedrock. Farther to sea, side-looking towed sonar has better resolution.

Note NASA maintains quite a nice bibliography of all journal articles based on Operation IceBridge data from 2014- back to 2010. These are linked to the journal (which may or may not be paywalled). These mostly concern Greenland and Antarctica; 3-4 specifically Northeast Greenland (ie Zachariae). http://icebridge.gsfc.nasa.gov/?page_id=596

There is only so much that can be done from surface observations (eg Lidar dynamic thinning, Landsat calving, Modis albedo, GPS glacial isostatic adjustment, RadarSat surface velocity). While these remain important, Greenland research is shifting more to measurements of the interior, even though seeing into 3000 meters of solid ice seems at first problematic.

To date, the main observational techniques have been 9 boreholes and 21 years of airborne radar; these are now being supplemented with airborne and satellite gravity, seismic reflection, magnetic susceptibility, rapid mobile coring, refined radar, and mass conservation constraints.

These will improve bedrock topography, map variations in the basal geothermal gradient, determine thickness and location of pressure-melted temperate ice (resp. ice frozen to bed), date and map radar stratigraphy and heat content of deformations, global mass balance measurement, and above all measure the internal temperature profile that largely governs ice flow (4th image, my attempt at color temperature overlay on dated radar deformation).

There is a tremendous amount of ice sheet history carried in the contemporary internal conditions. For example, Zachariae fjord gravity connects sills that today block ocean heat exchange to continental shelf troughs ground out during the height of the ice age.

The past and present are both needed to estimate future sea level rise from Greenland. Modelling will be that informative until internal conditions are better constrained factually.
« Last Edit: November 12, 2014, 01:57:26 PM by A-Team »

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #335 on: November 23, 2014, 01:26:32 PM »
An odd coincidence, I met a member of the Zachariae family the other day, and explained him my interest in the Zachariae Isstrøm, first he was not aware of the glacier named after one of his earlier family members, but was rightly proud afterwards (thanks to smartphones and quick internet searches).

This also shows how little is known about this giant glacier?
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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #336 on: November 30, 2014, 08:00:33 PM »
Zachariae Isstrøm is still breathing, in the dark arctic winter:

(I dont think this was common just a few years ago?)
« Last Edit: November 30, 2014, 08:06:12 PM by Espen »
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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #337 on: December 11, 2014, 09:27:00 AM »
The number of publicly available Sentinel-1 L1 data of the Zachariae/N79 area has been fairly disappointing until now. After the first batch of images acquired in the first half of October, nothing  new appeared for weeks. This week new software was activated on the ESA site that promises an increase of more promptly data, it will take some time for the backlog to be filled in.
One image has come available until now, acquired in December 4. Its is of comparative low resolution (40m) and taken from a different orbital position than the ones I have archived. It has dual polarization ( H and V reflection from a Horizontally polarized beam). I created a false color image (HH-amplitude=Red, HV-amplitude=Green and HH-amplitude+HV-amplitude=Blue) using the Sentinel-1 toolbox and reduced the resolution to 80m for the attached image.

(click to see the 1.9MB image)


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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #338 on: December 13, 2014, 09:21:14 AM »
A sequence of two images from Nov 29 and December 11 (Sentinel is in the same orbital postion every 12 days). Resolution is 40m, not good enough for an accurate estimate of the movement.

(click for the 1.6MB animation)

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #339 on: December 13, 2014, 04:52:42 PM »
Quote
Resolution is 40m, not good enough for an accurate estimate of the movement.

Right. I rotated by -23º to make the movement horizontal, then started subtracting the images holding one fixed and bumping the other until a visual minimum was reached, 2 pixels ± 0.5 too much error.

The issue here is really calculating the velocity field, which cannot be assumed uniform for a glacier terminus. This turns out to be super-easy using Fiji (aka ImageJ2) using the built-in plugin bUnwarpJ under Registration as discussed in #msg41327. I first cropped the two images above, moved out of indexed color into grayscale, evened out the contrast and imported the two images into Fiji, ran the plugin using the defaults, and made a simple animation out of the products in Gimp. Elapsed time, including finding a download for Fiji, about five minutes.

bUnwarpJ finds a lot of match points and determines the deformation (b as in Bezier) of a rectangular grid necessary to bring one image into the other. The vectors simply connect before and after grid points. Software like this has been developed to the nth degree for the needs of biomedical imaging (eg tracking cell migrations, straightening out electrophoretic gel lines).

If we had a year's sequences of 30 Sentinel images, the change in the vector field over time would be easy to animate. It also outputs a very extensive text log of what it did. It would also work out of the box on pairs of Landsat images, say two a year apart for slow moving regions near the headwall of NEGIS.

The analog of an SDS gel is straightening out radar stratigraphy, not so much as flattening isochrons as capturing the deformation that does it -- fitting them with b splines as 2D analytic surfaces, Greenland's internal fonts. There are a lot of advantages in getting out of raster into ordinary calculus as the differential geometry of manifolds is exceedingly well-developed especially when that surface is described by splines.

http://forum.arctic-sea-ice.net/index.php/topic,867.msg41327.html#msg41327

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #340 on: December 13, 2014, 07:55:56 PM »
ESA is planning a full coverage of Greenland with three consecutive cycles during winter, which should allow for feature-tracking everywhere.

Wipneus

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #341 on: December 16, 2014, 08:16:32 AM »
The backlog for this area seems to be filled backward, about two days per 24 hours, and is now at November 21.

Unfortunately only medium resolution data.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #342 on: December 16, 2014, 11:43:11 AM »
The announced campaign will be in the IW-mode with higher resolution, not sure whet it will begin but not before cycle 37:

https://sentinel.esa.int/web/sentinel/missions/sentinel-1/observation-scenario

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #343 on: December 16, 2014, 03:41:25 PM »
The announced campaign will be in the IW-mode with higher resolution, not sure whet it will begin but not before cycle 37:

https://sentinel.esa.int/web/sentinel/missions/sentinel-1/observation-scenario

Thanks, that explains a lot.

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #344 on: December 23, 2014, 09:25:45 AM »
Filling the backlog continues slowly (we are at Nov 9th) but new additions for the Zachariae outlet are very rare. Bad luck probably, the neighborhood is much better served.
Any way an image from Dec 22 came in, half sized: the Nioghalvfjerdsfjorden has been cut off. With one acquired on Nov 16, three 12 day cycles ago, this leads to the following animation, 80m resolution to show more of the bigger picture. The glacier is moving fast as ever but calvings seem to get increasingly stuck.

(click to see the 1.8MB animation)

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #345 on: December 23, 2014, 04:10:19 PM »
The announced campaign will be in the IW-mode with higher resolution, not sure whet it will begin but not before cycle 37:

https://sentinel.esa.int/web/sentinel/missions/sentinel-1/observation-scenario

Thanks, that explains a lot.
Now the new planning is in, the Greenland campaign will start on cycle 38 and run for three consecutive cycles in IW HH:

https://sentinel.esa.int/documents/247904/1685281/Cycle-38.jpg

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #346 on: January 05, 2015, 08:53:43 AM »
Zachariae Dec 23-> Jan 4.

(must click)

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #347 on: January 16, 2015, 09:11:32 AM »
Zachariae was under the antenna once again. I created a sequence from the medium resolution EW product. I reduced the resolution even further for an overview and used the HH and HV polarizations (by amplitudo) as Red and Green channels. This seems to be what the quick-look images do.

No major calving has taken place since mid October, the pre-cracks of new ones are visible for a while though. I think the back-pressure of the sea ice is holding it back. The glacier itself  is of course unaffected.

(click to see animation)

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #348 on: January 16, 2015, 07:41:13 PM »
That is nice. 22 Dec - 15 Jan = ~24 days seems to be a decent interval. What other 2014 dates are available should you wish to make a longer animation?

Would we see something similar at Jakobshavn? See about nothing at Petermann?

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Re: Zachariae Isstrøm / Nioghalvfjerdsfjorden / North East Greenland
« Reply #349 on: January 19, 2015, 11:18:57 PM »
The linked reference discusses sustained ice mass loss from the Northeast Greenland ice sheet triggered by regional warming, and which show signs of accelerating:

Shfaqat A. Khan, Kurt H. Kjær, Michael Bevis, Jonathan L. Bamber, John Wahr, Kristian K. Kjeldsen, Anders A. Bjørk, Niels J. Korsgaard, Leigh A. Stearns, Michiel R. van den Broeke, Lin Liu, Nicolaj K. Larsen, & Ioana S. Muresan, (2014), "Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming", Nature Climate Change, Volume: 4, Pages: 292–299, doi:10.1038/nclimate2161

http://www.nature.com/nclimate/journal/v4/n4/full/nclimate2161.html


Abstract: "The Greenland ice sheet has been one of the largest contributors to global sea-level rise over the past 20 years, accounting for 0.5 mm yr−1 of a total of 3.2 mm yr−1. A significant portion of this contribution is associated with the speed-up of an increased number of glaciers in southeast and northwest Greenland. Here, we show that the northeast Greenland ice stream, which extends more than 600 km into the interior of the ice sheet, is now undergoing sustained dynamic thinning, linked to regional warming, after more than a quarter of a century of stability. This sector of the Greenland ice sheet is of particular interest, because the drainage basin area covers 16% of the ice sheet (twice that of Jakobshavn Isbræ) and numerical model predictions suggest no significant mass loss for this sector, leading to an under-estimation of future global sea-level rise. The geometry of the bedrock and monotonic trend in glacier speed-up and mass loss suggests that dynamic drawdown of ice in this region will continue in the near future."
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