Jakobshavn calves a(nother) big one

Greenland glacier guardian Espen Olsen informed us a couple of days ago on the Forum that Jakobshavn Isbræ - Greenland's fastest glacier draining 6.5 % of the Greenland ice sheet - has had another big bite taken out of its southern branch recently. Espen made this animation to show the difference between May 7th and June 1st (red circle added by me):

Estimates by Espen and other commenters vary from 5 to 10 km2 of ice lost (a couple of hundred times thicker than sea ice). Reading back the first blog post on Jakobshavn, not long after starting the blog back in 2010, it seems that this number is big enough to warrant some media attention. As NASA had it back then:

NASA-funded researchers monitoring Greenland's Jakobshavn Isbrae glacier report that a 7 square kilometer (2.7 square mile) section of the glacier broke up on July 6 and 7, as shown in the image above. The calving front – where the ice sheet meets the ocean – retreated nearly 1.5 kilometers (a mile) in one day and is now further inland than at any time previously observed. The chunk of lost ice is roughly one-eighth the size of Manhattan Island, New York.

Or maybe these things don't get noticed anymore as it has become 'normal'? Let's hope not.

Comments

[Martin Gisser]

The wikipedia image with calving fronts needs some serious update since a few years.

[Sourabh Jain]

Neven,

I think date on the second image is incorrect. It shows May 7th 2014.

I don't know if time also got scared of climate change and started moving backwards. :)

[Craig Merry]

The 2010 was made more famous by the coverage the Photographer James Balog in his Ted talk and "Chasing Ice" documentary video. Does anyone know how this event compares to that event?

[Neven]

I think date on the second image is incorrect. It shows May 7th 2014.

I don't know if time also got scared of climate change and started moving backwards. :)

Sourabh Jain, this is the first image. Of course, with only two images an animation can seem to start with either one of the two. Maybe I should've increased the duration of the June 1 image more.

[Hans Gunnstaddar]

The images and dates are correct. It's sort of an illusion as the switch seems more dramatic as it switches back to May 7th. The ice loss is however from left to right.

[Espen Olsen]

Thanks Neven for reporting, sorry about the confusion about the animation.
My bet is this calving event is larger than the calving shown in "Chasing Ice", primarily because the calving front is wider now than ever before and as Yuha pointed out at the ( https://forum.arctic-sea-ice.net/index.php/topic,154.msg27405.html#msg27405 ) including the flow rate which only adds to the size / volume it must be one of the top sized calvings.
I have to add that we are not at max. retreat, though depending on where one measures.

[Steve Bloom]

Espen, what's the actual retreat distance along the centerline, and how does that compare to the 2010 event?

[Sourabh Jain]

Thanks Neven and Hans for clarification.

I thought drainage was from right to left. Therefore, i got confused. If you watch it for the first time, it looks like May7th had a loss and 1st June, things returned to normal.

[LRC]

Comparing it to this map [img]http://www.geus.dk/viden_om/voii/ilulissat-uk/voii03_kort01.jpg[/img] are not the waters getting mighty close to the inland sea where things can go very bad very fast or are we still some distance from there?

[LRC]

[img]http://www.geus.dk/viden_om/voii/ilulissat-uk/voii03_kort01.jpg[/img]
fat fingers :D

[LRC]

http://www.geus.dk/viden_om/voii/ilulissat-uk/voii03_kort01.jpg
(not sure what it did not like)

[LRC]

On the note of media. Media only will write something if it can focus on a personality that is preferably on site at the time. On top of that Antarctica seems to be a juicier story talking about 15 ft. sea level rise over a 'small' calving.
Doing a quick google revels just blogs pointing to here.

[LRC]

If I am wrong sorry , but found this weather report.
http://www.wunderground.com/cgi-bin/findweather/getForecast?query=69.166664,-49.833332&cm_ven=googleonebox
Appears to be within norm but note for today indicates has been a lot warmer.

[Fwmbrown]

I suspect the media are wise to the fact that they can't link this to a hypothetical 'alarm', since SLR levels aren't sufficiently Diluvian. In addition, the story needs a better graphic representation to grab attention, eg, a polar bear falling off the top...

[Jim Hunt]

@LRC - You need to use proper HTML tags instead of BBCODE like you would on the ASIF. Note what it says under the comment box! e.g.

Then of course you have to worry about the size of the image you link to!

[Espen Olsen]

Steve,

I am not sure when that calving mentioned in "Chasing Ice" happened, too many dates are mentioned, so it is hard to quantify the calving?

But I have made an animation showing what I believe is the furthest retreat observed at Jakobshavn (Sept 27 2013):

https://forum.arctic-sea-ice.net/index.php/topic,154.msg27775.html#msg27775

[Clive Mitchell]

I think the trouble with the animation is the light appears to be coming from the bottom right. Turn your head (or the monitor) upside-down to see normal shadows for the end of the glacier.

[LRC]

Thanks Jim. Still getting used to this. Most times think I am little slow on up take.

[Glacierchange.wordpress.com]

Nice work as always by Espen Olsen. In looking at the Landsat images more closely for the southern portion of the terminus on May 9 and june 1. It is apparent that limited transverse surface rifting is evident. This would suggest a calving event due to a bottom crevasse or a progressive number of smaller iceberg calving events in quick sequence.

[TenneyNaumer]

Mauri, on the north fork is there some sort of underlying topographical feature that is preventing the terminus from retreating?

[LRC]

@TM: If you check this https://skitch-img.s3.amazonaws.com/20101026-jip6n4px828amdaf2i8ard4k1p.jpg you will see that topography is straight east and that north arm has a hump to work around. Water likes to go down and that is where the heat where the glacier is getting to calve.
The scary part we could see the beginnings of the same scenario we were given for the WAIS

[VaughnA]

There appears to be a bit of quite warm water along the southwest coast of Greenland:

http://polar.ncep.noaa.gov/sst/ophi/

I believe this is contributing to the calvings in the area. This map also shows anomalously warm water around the fringes of much of the Arctic Ice. Even though the temperatures have been cool so far the ice looks really "rotten." It appears to me that warmer water is contributing a lot to this appearance. Has anyone made definite connections between water temperature and this appearance?

[Gerhard Trausner]

Neven
I think there were at least 15 km ². Including their own speed.

[Raenor Shine]

RobertScribbler's blog has picked this up from here also

http://robertscribbler.wordpress.com/2014/06/06/ten-cubic-kilometers-of-ice-lost-from-jakobshavn-glacier-in-less-than-one-month/#comments

How large is a cubic kilometer? Think of something the size of a mountain. Now multiply that by ten and you end up with a veritable mountain range. Think of it. An entire mountain range of ice. That’s a good rough comparison to the volume of ice lost from just a single Greenland glacier over the course of a mere 26 days from May 7 to June 1 of 2014.

For according to reports from expert sea ice observer Espen over at the scientist and ice researcher camp that is Neven’s Arctic Ice Blog, about 7.5 square kilometers over an ice face about 1,300 meters tall (when including the above and below sea level ice front) shoved off from the great Jakobshavn Ibrae glacier during the past month. It was a period of time well before peak Greenland warming and one that featured a collapse of ice into the heating ocean even larger than the epic event caught on film during the seminal documentary Chasing Ice.

[Glacierchange.wordpress.com]

Tenney good question the fjord does not extend below sea level more than a few kilometers under the northern branch. Whereas the southern branch remains quite deep for at least 75 km. The issues is not meltwater, but flotation. The more of the glacier that is floated by the water depth the more tidal flexure and the less of a pinning point the glacier base is. This arm will retreat toward the lip of fjord certainly but the main action is the southern arm.

[john_mann]

There also seems to be a fair chunk gone from that region towards the bottom left. Is that significant?

[Glacierchange.wordpress.com]

The bottom left is an area of sea ice, so not important. This was glacier ice during my first visit to the glacier in 1985.

[Yuha]

Probably the currently most accurate map of the bed topography of Jacobshavn is on page 15 in this paper:

http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf

It's a supplement to a recent paper by Morlighem et al in Nature Geoscience (doi:10.1038/ngeo2167). The main paper is behind a paywall but the supplement is free.

[Lynn Shwadchuck]

Thanks, Yuha, for those images. Looking at them I wondered... well I kind of thought exactly what the paper's abstract says: "We detect widespread ice-covered valleys that extend significantly deeper below sea level and farther inland than previously thought. Our findings imply that the outlet glaciers of Greenland, and the ice sheet as a whole, are probably more vulnerable to ocean thermal forcing and peripheral thinning than inferred previously from existing numerical ice-sheet models."

[Glacierchange.wordpress.com]

Jakobshavn is the one glacier where the deep connection was well known. is a glacier where the deep connection was not. The width of these valleys is often deeper but also narrower than envisioned in older maps.

[Lynn Shwadchuck]

Mauri, something got lost in that post – the glacier name, the link. Thanks for being here!

Thanks to Yuha's post about the Nature paper I found the Nasa site on the Ice Sheet System Model, of which the paper's lead author is webmaster. http://issm.jpl.nasa.gov/

[Espen Olsen]

Maybe we should use Manhattan NV as a reference point in the future?

http://en.wikipedia.org/wiki/Manhattan,_Nevada

[Twemoran]

Is there any evidence of the composition of what is shown as bedrock? What I'm concerned with is the possibility that some of the valley floors past the fjords might be comparable to morain or esker gravel and sand deposits as opposed to solid rock.
I'd hate to trust future sea level rise to the ability of sand hills to impede glacial flow.
Terry

[Neven]

The glacier is not done as of yet. Massive calving continues.

[LRC]

@Terry Based on my readings what the bedrock is makes little difference as most is below sea level and going down hill.The important part is how strongly bound the ice is at the moment it appears the front line of the glacier is very weak. The longer the goes the more trouble it is going to have to hold back the influence of the warm waters.

[Glacierchange.wordpress.com]

The link must have calved off earlier today. It is the Upernavik Glacier that I was calling attention to that has a deeper-longer valley than we knew

[TenneyNaumer]

Thanks LRC and Mauri.

The second retreat is stunning! Would it be too much trouble to add that to the gif? Any idea of the volume of the second retreat?

[A-Team]

Whoa, this is getting interesting. The image below shows the starting position and two calving events of this month, overlaid on the position of maximum retreat attained at end of season last year.

Despite some enhancement, the second image gives no indication of an impending 3rd calving event. Indeed as MPelto notes above, "Lack of surficial transverse crevassing is unusual before a large calving event. Basal crevassing may be key."

The trick here, on these overly blue Landsat-8 images, is decompose into CMY and fade the equalize of the magenta layer. The speed of this glacier is such that if we could get 3 more or less consecutive clear days, a follow-on 'interferometric' RGB would show the relative velocities above the calving line. (The DMI ASAR images lack sufficient resolution.)

The 3rd image shows, among other things, the bed profile and historical seasonality of retreat. Note the maximal fjord overdeepening about where the calving front is today. It is taken from Joughin 2014 'Further summer speedup of Jakobshavn Isbræ' http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.html

[Neven]

Nice to see you again, A-Team.

I will follow up on this blog post if and when Jakobshavn moves past last year's retreating line.

[Steve Bloom]

Just re-read all of the foregoing and I still have no sense of how unusual this event might be. Size aside, is the calving front even at record retreat for the date?

Sometimes this site resembles a weather blog more than is helpful, IMO.

[LRC]

@SB point #1 see
Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #244 on: Today at 05:13:13 PM » here http://forum.arctic-sea-ice.net/index.php/topic,154.200.html#lastPost
and it shows you that the calving front equals max last Sept. We could see major calving still with 3 months to go. As for point 2. weather plays a major roll on ice melt. For those interested in how much melt is going to happen in the next few weeks, predicting the weather also involves predicting ice melt.

[A-Team]

Neven writes, "I will follow up on this blog post if and when Jakobshavn moves past last year's retreating line."

Ok, the 'if' part is a done deal -- Jakobshavn Isbrae sets a new record every year. None of that annoying 'natural variability' like we have with the Arctic sea ice death spiral.

The 'when' of the maximum retreat is hard to predict. While the two massive calving events noted by Espen seem awful early, the recent historical record shows the maximal retreat (or near-maximal) can occur quite early. The graphic shows this with dotted white boxes. (Here I selected colored circles on the far right for each year, requiring that that color selection also show up in the terminus position bar.)

The 'when' of the next calving event could be predicted from real time laser altimetry. The calving front rises some 15 m while the back sags ahead of the event, with only the first km affected. However the lead time of the prediction would be quite short.

The 'how much' of a new record set is the interesting part. I have a queasy feeling about Greenland overall, that it is becoming unglued ahead of schedule. But here, the ice stream is coming off a sharp turn with lateral constraints and also ending its run over the deepest part of its channel so even if we see say 3x the km of average recent retreat, that will still need interpretation.

Fortunately Jakobshavn Isbræ is heavily instrumented as poster child of Greenland glaciers (though not representative of all) and a major current contributor to sea level rise.

It's a credit to Espen and this blog to be the first to report these calving events that contribute directly to this year's SLR, though it would be great if someone would calculate the volume more carefully along with the associated uncertainty. Wipneus posted the pixel scale for these Landsat-8's over on the forum.

Graphic adapted from http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.html
See also http://students.washington.edu/kpoinar/Presentations/AGUposter_kpoinar_2011.pdf
and http://www.igsoc.org:8080/journal/57/204/j10J070.pdf

[Steve Bloom]

OK, the forum photo shows the current calving front position already very close to last September's minimum, and so well past its position in June of earlier years indicated by A-Team's graph, which answers my question, so thanks to both.

But A-Team, if I'm interpreting your graph correctly, it looks as if this year has already seen a distinct acceleration. Eyeballing, I would put this year's first early June (magenta) dots more or less where the m's are in "summer." Does that seem right to you?

Plus, every past year, even 2010, looks to have had a significant amount of further loss beyond early June, such that 2014 seems almost guaranteed to set a substantial new minimum record. Now I stick my neck out: Averaging the retreat beyond early June for all years and adding that to the current position gives a new minimum point (I place it more or less above the 1 in "2013") such that, if a curve is plotted using the minima of all six years (yes, six, count 'em, six whole data points -- I'm aware of my problem here), it forms a smoothish curve that's starting to bend to the right pretty sharply.

Not quite a hockey stick, but maybe one is on the way. Interesting times.

[Neven]

Sometimes this site resembles a weather blog more than is helpful, IMO.

Steve, the ASIB is mostly of a weather blog (watching the melting season unfold). I do try to report on the science and some of the Greenland stuff, because it's interesting, but I'm not good at science and I'm not the kind of person who keeps track of everything and then remembers it all.

I'm a muddler, and not ashamed of it. :-)

[LRC]

@Neven I must say for a muddler you have brought together and have kept running the best Arctic Ice forum on the planet. To the point many educational expert sites use many of the things your forum has pulled together. That is an accomplishment that is unique for an open free forum on a topic full of (the name their given escapes me right now) those who like getting forums off the main points.
If you google arctic ice your forums are almost always at or near the top and most of the rest have links to you and/or your images. For that you must be heartily commended. Keep up with your muddling we truly need more of you.

[A-Team]

Steve, good points -- the data here are under-analyzed. (The authors say it was intended only as a brief update to their 2012 paper, http://onlinelibrary.wiley.com/doi/10.1029/2011JF002110/abstract.)

There's more data on velocity speed-up in Fig 2 of this paper. Fig 1 has the TerraSAR-X image for 20 Sep 13 maximum retreat that goes with Espen's Landsat-8 visible bands.

Astonishingly, despite hundreds of journal articles on Jakobshavn Isbrae, no one ventures much by way of validatable predictions (this fall, not end-of-century). You can see timidity alternatives play out between reviewers (it's speculation) and authors (no it's hypothesizing) in the Cryosphere Today discussion section for this article. Yet expert opinion from folks who have devoted entire careers to this particular glacier would have a lot of value.

I'll post a graphic shortly showing my business-as-usual maximal retreat prediction for Sept 14 as well as a drama queen 2x version. Discharge volume (km^3 or as microns of sea level rise) is a little tricky because of thinning.

The way raster images are handled in a pdf is very complicated (see https://en.wikipedia.org/wiki/Pdf#Raster_images). The best way to extract them at optimal (author-supplied) resolution is not via a rescaled (dithered) screenshot off your pdf reader but rather by http://www.extractpdf.com/ (or similar). Once you're sure the display is right, a screenshot or crop will be lossless.

For everyone's convenience, I collected the native width x height of these graphics and displayed that of the synthetic aperture radar. They will be right-truncated by the blog so 'view image' in a separate browser tab. You'll get cheated within a pdf viewer.

1033 x 1204 TerraSAR-X imag
1033 x 1008 Fig 2 speeds at various distances from terminus
1033 x 770 Fig 3 seasonality of calving

[Jim Hunt]

Great stuff A-Team. It's good to have you back!

Where have you been hiding all winter?

[Neven]

NASA now has an article on this.

Oh wow, I just noticed that they link to the ASIB at the end of the article. Well done, Espen!

[Espen Olsen]

Neven,

At least this proves someone from NASA read about it? ;)Thanks for your and others comments.
By the way I have posted my impression of Jakobshavn vs. Zachariae Isstrøm

What is all the fuss about?:

https://forum.arctic-sea-ice.net/index.php/topic,400.msg28208.html#msg28208

[Blaine]

With daily change evident from satellite images, the speed is most impressive, isn't it? The annual advance/retreat cycle is huge too.

SharedHumanity has already pointed this out on the forum, but I also independently noticed that a large portion of ice to the northeast of the main Jakobshavin calving front appears to have come unstuck from its bed and formed a new tributary ice stream in a place where the bed depth makes it seem likely for one to appear. There are no large canyons feeding this stream, so it should not have a large flow for very long. The calving event is proceeding to the east, as much into this stream as southeast along the Jakobshavn trough.

With the grounding line now down into much deeper water, even the return of 50s-70s weather wouldn't stop a further retreat of around 75km to a shallower bed topography.

The main Jakobshavn trough makes a significant chicane near the current calving front, running westsouthwest, then northwest, and then west again, with the current calving front located in the portion running northwest. Further retreat of around 8-10km beyond the 2013 minimum, representing around 5 years so melting will eliminate this turn, removing back stress from the turn and essentially pulling the cork from the bottle. See A-team's link here. I expect the calving front to slow or stall here for a bit as glacier speed rises to a maximum.

[Lennartvdl]

The NASA-post being picked-up:
http://www.livescience.com/46264-greenland-glacier-loses-ice-photo.html

[A-Team]

Heraclitus said something to the effect you can't step into the same isbrae twice. The Jakobshavn Isbrae is a case in point, moving 17 km/yr = 326 m/week = 46.6 m/day = 1.94 m/hr upstream of the calving front at marker M6 (shown above) on 15 June 2012.

Consequently the calving front must break off this much ice just to hold the line (which sometimes it doesn't). Given Landsat-8 images with 250 meter pixels, a pixel at the calving front is replaced by one of upstream ice every 5.3 days.

Thus I've been casting around looking for better quality imagery so that we can better monitor calving events, measure glacier thinning and speed-up, determine shearing across the centerline, animate a year of melt and predict terminal position for 2014 and coming years.

Some of Espen's imagery seems to be better quality but I've not seen a link to it. I've been using the one below, refreshng the day (166 is 15 June) mid-morning Pacific coast time.

http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2014166.terra.721.250m.jpg

None of our usual products at DMI, Jaxa, WorldView are satisfactory -- clouds can mask visible imagery; the ASAR radar has insufficient resolution, sporadic coverage and does not come with pixel-perfect co-registration.

Google Map today provides a very high resolution image in the visible. However it is a mosaic of different dates and time of day; further, it is not current and we have no idea when the next update will arrive.

Google Earth (separate freeware) does archive a half-dozen very high resolution images from 2008-2012. To access, click on the alarm clock icon in the tool bar. These give a much better feel for seracs, crevasses, dynamic melt lakes, ridges and flow lines upstream of the calving front itself. The images are rather large at native resolution so the slide show below shows just a fraction of what is out there.

The hands-down winner is TerraSAR-X and its companion satellite TanDEM-X, operated by DLR (the German NASA). These are not free (200 euros a pop). Luckily, speedup of Jakobshavn Isbrae was an featured project for 2013, and a couple of incredible images are provided in their gallery, http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10460/685_read-9450/year-all/#gallery/13588.

The first image is a truly astonishing digital elevation map of the glacier rendered in perspective from the south, 2222 x 1250. It looks so much like an aerial photograph that I had to decompose it into CYMK color space to convince myself it is totally synthetic (no yellow). Can you imagine using a time series of these to animate the ice stream!

The second image is a hideous overhead grayscale from 08 Jan 14 useful as a base layer, similar to the 20 Sept 13 image of maximal calving retreat shown above but without its ruinous overlays.

http://www.dlr.de/dlr/en/Portaldata/1/Resources/bilder/portal/oberpfaffenhofen/2014/JakobshavnIsbrae_TDX.jpg

Very few climate scientists 'get it' in terms of image layering despite arcGIS etc being around since forever:
https://en.wikipedia.org/wiki/Geographic_information_system
http://researchguides.dartmouth.edu/content.php?pid=6723&sid=788288.

NASA is the only place I've seen doing image overlays correctly (as separate, co-registered files). I myself have stuck an extra 120 pages of journal techno into supplemental -- the journals don't care so what is the excuse here?

Turns out the authors of that key Cryosphere article(free http://www.the-cryosphere.net/8/209/2014/tc-8-209-2014.html) did all their velocity measurements on six years using TerraSAR-X speckling.

The trick to free imagery must be to co-author your paper with someone who works for DLR in SAR signal processing (http://www.researchgate.net/profile/D_Floricioiu). I'll write to request a 2013 animation and see if we can host free summer 2014 imagery.

Nukefix posted a fine animation of Kangerdluqssuaq from a different SAR satellite at the forum, noting Jakobshavn is an ESA Sentinel-1 "supersite" that will be imaged on a 6 day return by fall (if not sooner) Free. http://forum.arctic-sea-ice.net/index.php/topic,154.msg27707.html#msg27707

[A-Team]

The slide show below compares Jakobshavn Isbrae in June for 2013 and 2014. It is not so easy to find cloud-free days on the same date for both years. (The dates match except for the first pair.) The main things to see: mélange (ice jam of calved-off ice) is still blocking the channel in mid-June 2014 and the calving front is farther advanced.

I'm skeptical that the mélange is currently providing significant back pressure to glacier advance, though it may in mid-winter when frozen or when iceberg bottoms are caught on the terminal moraine off Illulisat. The tide at the calving front can be three meters -- the 2013 series flushes out on the time scale of a day.

There's an active webcam on the NE shore aimed at the calving front (not to be confused with Hotel Arctic webcam at Illulisat). Camera A takes hourly shots; you can roll your own animation or step through one frame at a time (eg to get daily series at noon). It's been operated by David M. Holland at NYU for 7 years. I made the animation below -- sort of a low budget Chasing Ice -- for 1 Jun 14. Note it shows air temperature too.

The camera is too far from the current front to capture calving events. Holland is best known for a 2008 paper relating abrupt warming of offshore waters in 1997 with the onset of rapid glacier retreat, diving seals with sat phones, and a more recent poster on fjord waters coming to resemble those of Disco Bay.

poster: http://www.usclivar.org/sites/default/files/meetings/Gladish_GRISO2013_Poster.pdf
cam: http://efdl_5.cims.nyu.edu/animations/animation_JIG_A.html

[A-Team]

I looked into quick exits from the quirky Landsat-8 interfaces (eg http://earthexplorer.usgs.gov/ and http://landsatlook.usgs.gov/). In a November forum post, Wipneus provided an excellent way of doing this primarily in terminal mode (ImageMagick).

The issues here are five-fold: getting the most recent image without delay (here the calving front), dealing with gigabyte file sizes of high resolution images, taking advantage of the extra data in NASA's '16 bit' Tiff format, best 3 of the 12 bands for an RGB, and pipelining for a seasonal time series animation.

I found a day or so delay in image availability -- they're still on yesterday. The GeoTiff folder arrives rapidly enough from EarthExplorer on a home 17 Mbps downlink, giving individual bands as 145 MB grayscales. There is no need for 16 megs of computer RAM, 4 works fine.

The visible bands B2-4 make exceedingly poor use of the available dynamic range (histogram). Opening them in Gimp cuts them down to 8 bit, meaning subsequent contrast expansion will posterize them severely vs doing that step within the native 12 bit.

However ImageJ -- which is highly developed NIH biomedical freeware -- can import and adjust contrast natively at 16 bits, then conveniently export the stack to Gimp as a gif animation which can then be cropped (vastly reducing file size) and composited as a color image at Gimp, best done with B5, B4, B2.

For purposes of the watching the calving front, little is gained by this. Both ImageJ and Gimp have batch processing which do all these steps in the background for a time series.

The 15m resolution panchromatic is still the crazy-making 17061 × 17161 pixels, one pixel less than 2x the band sizes of 8531 × 8581. Dumbing up, the 15 m can be used as the V or L in HSV or HSL color space when the 15m ground resolution is informative.

In summary, capturing high resolution Landsats are easier than when Wipneus wrote about them 8 months ago. Still, the interface is like the proverbial dog walking on its hind legs, not done well but we can applaud that the imagery is available at all.

800 x 450 DEM of calving front:

[A-Team]

Espen wrote about an apparent calving event on June 13 that needs confirmation by better than 250m resolution imagery: "... I can't figure out Landsat-8 release schedules and priorities."

Me either. Aggravating, inexplicable delays in providing data (or non-acquisition thereof). The USGS interface http://landsatlook.usgs.gov/ is very peculiar, maybe an unpaid summer intern's first venture into programming. Today I came across something a lot better -- Reverb -- a really first-rate unified portal not just to Landsat-8 but to all of EOS (including IceBridge).

The satellite itself orbits every 99 minutes, with the latest orbit displacing the previous one to the east. USGS promises a one day turnaround on imagery. So how can June 10th still be the most recent image on June 21st?

Landsat-8 is not part of the A-train like Terra and GCOM-W1. You can follow its position in real time http://www.n2yo.com/?s=39084. I just watched it go over Petermann Glacier so last time around it swung over Jakobshavn Isbrae. Well, not quite:

Modis Terra/Aqua stalled for 4 days on 17 June, then grudgingly updated itself four days later. This imagery shows skies were clear over the Jakobshavn Isbrae calving front on June 1, 2, 8, 10-16, and 20. Thus clouds cannot be the explanation for the missing Landsat coverage.

When I upsample and animate 250m June (not shown), the images are slightly out of register. That jiggle could be due to satellite orbit not quite repeating itself, the timing or lookdown not quite giving the same coverage, or something not done right in processing. Between this and 250m resolution for something on a km scale, the apparent calving event of June 13 is still up for grabs.

However Terra/Aqua do give a very satisfactory account of the abrupt development of melt lakes to the south. The grayish tone may represent bare ice (loss of snow). Jakobshavn Isbrae does *not* respond notably to sub-glacial lubrication by meltwater reaching the bedrock via moulins. This was worth animating the aforementioned cloud-free days:

The downstream fjord mélange is cannot really being providing much back-pressure during calving season. Full height icebergs break off with the bottom ice rolling out.

Since the ice at the calving front today is 1179 m thick (1075m below sea level, 104 m above) according to fig 2 of Joaghin 2014, the mélange gets bumped 3686 feet out to sea during rather short-lived events (which rules out significant back-pressure), as you can see in the 4 calving event videos for 2008.

Incidentally, the dramatic 'Chasing Ice' calving at Jakobshavn Isbrae was filmed in 2008. I believe it matches the May 10th one below.

time-lapse video of a calving event on 10 May 2008
time-lapse video of a calving event on 16 May 2008
time-lapse video of a calving event on 15 July 2008
time-lapse video of a calving event on 24 July 2008

For that year, a fantastic graphic showing terminal speed-up at Jakobshavn Isbrae appears in David Podarski's dissertation. I consolidated the color key and cropped; otherwise it is worth seeing as he presented it (which requires native image extraction at https://smallpdf.com/pdf-to-jpg.

[Espen Olsen]

A-Team wrote :"So how can June 10th still be the most recent image on June 21st?"

I have a feeling they are being kept away for some reasons?

[Wipneus]

Landsat 8 orbits are repeated exactly every 16 days. So if you have a successful image look for image 16 (32,...) days later.

Places in the polar regions appear in multiple paths, also the ascending (night) half of each orbit can be used in summer. So there may be more image series to be found. Because the position of the satellite differs, there will be distortions with the elevation of the surface.

I don't know if you have already found this.
The acquisition schedule (for June) is here:
http://landsat.usgs.gov/tools_pend_acq_l8.php?path=/L8_Pend_Acq/y2014/Jun

Last time I looked the usefulness was very limited: many images on the list are don't become available but also the reveres is true.

[Espen Olsen]

Wipneus wrote:

"I don't know if you have already found this.
The acquisition schedule (for June) is here":

LANDSAT 8 SCENE CAPTURE SCHEDULE
Inclusion on this list does not guarantee that a scene will actually be received by EROS.

Or released. That we know!

[Espen Olsen]

Anyway it is frustrating to know we had one or more major calvings between June 8 and June 21, probably beyond the maximum retreat point set in September 2013, but we don't have proper documentation, it is only based on ASAR and Modis 250m images.

[A-Team]

These folks have grant access to much better imagery. AGU abstracts fall 2013, not yet published. And when they are, the underlying imagery still won't be available.

Still, we can muddle along in real-time with our low-res freebies to report breaking news, summer 2014.

Analysis of the seasonal and interannual evolution of Jakobshavn Isbrae from 2010-2013 using high spatial/temporal resolution DEM and velocity data

DE Shean, IR Joughin, BE Smith et al

Greenland's large marine-terminating outlet glaciers have displayed marked retreat, speedup, and thinning in recent decades. Jakobshavn Isbrae, one of Greenland's largest outlet glaciers, has retreated ~15 km, accelerated ~150%, and thinned ~200 m since the early 1990s.

Here, we present the first comprehensive analysis of high spatial (~2-5 m/px) and temporal (daily-monthly) resolution elevation and velocity data for Jakobshavn from 7/2010 to 7/2013.

We have developed an automated processing pipeline using open-source software (Ames Stereo Pipeline, GDAL/OGR, NumPy/SciPy, etc.) to produce orthoimage, digital elevation model (DEM), and surface velocity products from DigitalGlobe WorldView-1/2 stereo imagery (~0.5 m/px, ~17 km swath width).

Our timeseries consists of 35 WorldView DEMs (~2-4 m/px) covering the lower trunks of the main+north branches and fjord, but also extending >110 km inland. We supplement this record with 7 TanDEM-X DEMs (~5 m/px, ~35 km swath width) between 6/2011-9/2012.

Elevation data from IceBridge ATM/LVIS, ICESat GLAS, and GPS campaigns provide absolute control data over fixed surfaces (i.e., exposed bedrock).

Observed WorldView DEM offsets are consistent with DigitalGlobe's published value of 5.0 m CE90/LE90 horizontal/vertical accuracy. After DEM co-registration, we observe sub-meter horizontal and vertical absolute accuracy.

Velocity data are derived from TerraSAR-X data with 11 day repeat interval. Supplemental velocity data are derived through correlation of high-resolution WorldView DEM/image data.

The contemporaneous DEM and velocity data provide full 3D displacement vectors for each time interval, allowing for the analysis of both Eulerian and Lagrangian elevation change.

The lower trunk of Jakobshavn displays significant seasonal velocity variations, with recent rates of ~8 km/yr during winter to >17 km/yr during summer. DEM data show corresponding elevation changes of -30 to -45 m in summer and +15 to +20 m in winter, corresponding to integrated volumes of -1.0 to -1.5 km3 and +0.3 to +0.6 km3 for the lower ~20 km of the main trunk.

The DEM time series shows a net interannual thinning trend of -15-20 m/yr for lower Jakobshavn, with decreasing magnitude upstream. This is consistent with long-term altimetry records. Interannual thinning of ~2 m/yr and lateral retreat is also observed for grounded ice sheet margins.

/*/*/*/*

We're obsolete!

Automated tracking of changes to terminus and mélange position in Greenland's marine outlet glaciers

F Seifert, JN Bassis et al

Mass loss from the Greenland ice Sheet is primarily through the dynamic changes of its marine terminating outlet glaciers. Understanding the behavior of these glaciers is therefore key to understanding how much the ice sheet will contribute to sea level in the next century. Glacier behavior is, however, complex, with wide disparities in behavior even between glaciers that occupy adjacent fjords. Deciphering the multitude of factors that control glacier behavior requires a comprehensive dataset of near daily changes in terminus position for a large set of glaciers over many years.

The creation of this dataset has been difficult due to the time required to process the changes manually. Evolution in computational methods allows the creation of an automated algorithm, using a combination of filtering techniques and edge detection, which ingests MODIS imagery and tracks changes to (i) the terminus position and (ii) the areal extent of melange downstream of the terminus. We tested the algorithm on several well-studied glaciers including Jakobshavn, Helheim, and Kangerdlugssuaq.

Comparison with manually identified terminus positions proved the algorithm accurate to within +/- 2 pixels (500 m). The validated model was then applied to a larger set of Greenland's marine terminating outlet glaciers. We use this higher temporal resolution dataset to determine statistical patterns to the calving events and ask whether these patterns are linked to mélange extent, fjord geometry, and any seasonal component affecting the regularity of the events.

[Espen Olsen]

I am not surprised?

[A-Team]

Here is the latest synthesis of ice-penetrating radar bedrock recent analysis (free) from Gogineni and coworkers.

Here I wanted to see at a glance what was below sea-level. However the authors provided a jpg'ed tinted and tilted shaded relief, causing the color key to get out of synch with the image itself.

The second slide shows a cure for this: pass to HSV color space and toss the S and V components. Then return to RGB and additively color-pick the key to create a mask for the land above sea level. I made the mask slightly translucent.

The bedrock under Jakobshavn Isbrae has numerous ups (sills) and downs (overdeepenings) along its course. Calving depends to a considerable extent on the position of the front relative to this profile.

[A-Team]

TL;DR: Landsat-8 is unsuitable for calving front time series.

Very helpful link to June Landsat-8 acquisition schedule, Wipneus.

Despite being a small ~5km feature, the Jakobshavn calving front is situated very unfavorably with respect to orbital scenes. The corners of path 7, row 11 appear in the middle of this scene; note the apparent drift.

Tomorrow 24 June may provide the long-awaited updates to 10 June. Then again the calving front could be covered by a small cloud like yesterday.

row path scene
10 11 LC80100112014175LGN00
83 233 LC80832332014175LGN00

Here (path, row) appear between LC80 and the date (day 175) in the scene names. LC80 and LGN00 (Landsat Global Network) do not seem informative. The SvalSat ground station in Svalbard will be receiving (10,11) and (83,233). Maybe.

[A-Team]

Nukefix has posted some early ESA Sentinel-1 polarized radar imagery of Epiq Sermia and nearby glaciers to the north (described at Glacier's perspective).

The graininess can be removed either by Fourier frequency splitting, followed by blurring of the high frequency component (Gimp --> G'MIC) or by wavelet decomposition with discard of first level or two (Gimp --> Filters --> Generic). HH and VV are nearly identical, as can be seen from grain extract after RGB decomposition. It's not entirely clear what the polarizations tell us about ice properties per se.

This resolution will allow us to follow calving at Jakobshavn Isbrae at 6-12 day repeat intervals. The imagery is free and puts us back in the ball game. Here we'll want to make a rolling RGB 'interferometric' animation to see which parts of Jakobshavn ice stream are moving at which relative velocities.

The position of the calving front has been vacillating in accord with the trade-off between westward glacier advancement and eastward calving loss. So far, the calving front has not ventured up the narrow ice stream channel as it did last fall. Espen posted a very nice image for June 24 at the forum. (To recover individual frames, open animation in a separate tab, save, open gif in Preview or Gimp as layers.)

[A-Team]

Below is a schematic cutaway in longitudinal profile of how Jakobshavn Isbrae ice sits over bedrock. More realistically it would show meltwater along the bottom and perhaps deep erosional till cut from headwalls in the trough bottoms (per Tremoran above) as well as temperature and ice rheology profiles. Ice stratification layers may also deformed on Jakobshavn, though not to the extremes seen on Petermann or nearby Epiq.

We need Andy Lee Robinson again to illustrate this properly:

If the ice were taken away, the remaining glacial valley would be U-shaped in cross-sectional profile, other than some possible bumps (local pinning points that retard glacial advance). The bedrock form does not resemble a valley cut by a river because river longitudinal profiles do not have sills and troughs except at plunge pools, the counterpart of glacier overdeepenings.

The next image shows the actual bed profile determined by ice-penetrating radar, as well as the position of the centerline of the calving front in recent years (from Joaghin 2014 linked above). Note the graphic shows the terminus retreating out of a -1300 m trough to the next sill at -950 m below sea level. There's an even deeper trough farther inland.

The position of the terminus relative to the deep trough may explain the speed-up in recent years to a certain extent, indeed this year's early retreat to an approaching sill. That sill may diminish future warming of the base from waters of Baffin Bay.

So well do we really know the bedrock profile? Here Gogineni himself says ice-penetrating radar is not reliable on narrow fast-moving ice streams.
Echoes from the bed can be masked by surface debris and watery inclusions volume scatter. Trailing radar antenna wires on P3's cannot provide the optimal 14 and 35 MHz probes.

The bigger problem though has been mis-interpretation of bottom freeze-on and consequent upward deformation as side-scatter from hills. This was recently disproven by gravity measurements showing no Greenland rock (2.67 gm/cm^3) in the vicinity.

Meanwhile, Kansas group has developed a greatly improved instrument, a drone with antennas embedded in the airframe. This is capable of flying on a 5m grid cross-track, enabling 2D synthetic aperture radar, as described in a free article in the March 2014 issue of IEEE Geoscience and Remote Sensing. They've announced a field deployment on Jakobshavn Isbrae for this summer.

Meanwhile Operation IceBridge flew straight up the channel this spring presumably for the same purpose.

These two efforts should result in a greatly improved understanding of this ice stream's stratigraphy and so predictions of its future retreat and attributable sea level rise.

[Espen Olsen]

Great work A-Team, please co-write on Arctic Sea Ice Forum: https://forum.arctic-sea-ice.net/index.php/topic,154.250.html

Espen

[A-Team]

So folks don't have to wrestle with a gigabyte images at 12 bit resolution, here is a piece of the 15 m Landsat-8 band B8 (panchromatic) of 24 June 14, namely LC80832332014175LGN00 as provided by http://earthexplorer.usgs.gov/

I normalized and equalized the contrast histogram within ImageJ at 16 bit depth before export to your 8 bit monitor.

Espen has posted 30 m bands 2,3,4 with a calving front comparison over at the forum.

Even with 15 meter pixels, there's no forewarning of the next big calving event. The front is about to enter the narrow part of the ice stream.

[Espen Olsen]

To add to your work, there is is still a lot we don't know anything about?

[A-Team]

Espen, agree it's better to consolidate these over in your Jakobshavn forum. However my registration there is hopelessly screwed up and there's no email for a forum admin. I'll see if Neven can help.

Yes indeed, a century of observations on Jakobshavn Isbrae ... and it takes awhile even to digest the 2013-14 journal articles on it.

Awright, I've finally managed a decent correlation map of bedrock depth with surface imagery:

This represents a kridged CReSIS 2008 digital elevation map (from pdf after unzipping: ftp://data.cresis.ku.edu/data/grids/old_format/) rescaled 4.167:1 to overlay the 30 meter 24 June 14 Landsat-8. It is the DEM thought best by Joughin et al 2014.

The transparency is set to ~30% so that ice stream features show through. The animation pauses at the last frame but will loop again.

The big hole (~1300 m below sea level) co-locates with a standing wave feature in the surface imagery. Coincidence? You'll see something very similar as an ordinary river passes over a pothole.

[Espen Olsen]

Yes it is very much like the scenes I see / watch when fishing trouts/salmons in rivers in Norway.

[Blaine]

ATeam:

You have now posted 3 different versions of the CReSIS data, (Hughes, Gogineni, & others, Joughin and others from gridded data, and from some other CReSIS PDF you found), and none of them agree at all closely with each other. In particular, along the rather quirky line of Joughin, according to the PDF you found the 2013 maximal retreat is near the bottom of a trench and not near the top of a ridge as it is in Joughin.

The figure from Hughes and Gogineni states that it is along the line of the previous figure, but doesn't explain well what they've done. It appears to be using non-orthognal axes with the x axis being across the trench, the y axis along it, and with these axes having a different scale. Presumably if you've been staring at a bed map of Jakobshavn non-stop for a couple years, this would seem to be obvious. Since the x and y axes have different scales, the scale indicator which you have rotated is no longer valid.

We really should take these disagreements amongst different versions of what are all nominally the CReSIS data set as indicating that the uncertainties of this data are rather large, which none of the principals appear to disagree with.

In trying to figure out what's going on, I found myself comparing the polarized radar with the velocity map in Podarski's thesis. Disturbed flow is evident on the southwest side of the channel in both, indicating that it is relatively shallow. Around 55-60% of the way downstream between bends, the flow is squeezed but does not accelarate indicating that the channel must be deep. I realized that I was doing an eyeball flow-balance method and considering my results to be more reliable than the radar results. We just had a recent paper doing flow-balance based estimates systematically that has to be much more accurate than anything I can eyeball, so I find that I trust figure S11B from here more than any of the radar estimates. Much of the map is clipped at maximum scale depth, and the region of interest is about 20x20 pixels in the PDF, but it probably has better fundamental resolution than radar data.

If you're going to do more image processing, I find I'm curious whether any information can be extracted from Hughes and Gogineni with a more reasonable colormap. The colors for everything deeper than around -550m are all virtually indistinguishable, for no good reason.

[A-Team]

Blaine, a lot of good points. Briefly, we've moved over to the forum and I'm on my 5th post there.

The Joughin article is based almost entirely on analysis of proprietary TerraSar imagery. You and I do not have access to it, neither did the referees. There is no way anyone can reproduce the figures when underlying data and methods are not provided.

The best we can do is reverse-engineer figures -- count pixels in photoshop to re-create the missing numerical data and dissect their underlying DEM file (the Cresis ftp link above) which I did over at the forum in the course of making a bedrock flythru.

The Gogineni group drastically binned the bedrock depth data, eg -1512 to -1103 navy blue, -1103 to -819 mid-blue, -819 to -535. That's why you can't resolve the colors. There's arguably heuristic value to these illustrations -- they get the main idea across without burdening the reader with scientific detail on troughs, pinning points and sills along the bottom of the channel.

The temptation on a coordinate system is to take a central flowline of the main ice stream, because the best data comes from flight lines that follow it and velocities and mass fluxes are naturally measured across surfaces orthogonal to the velocity field. Earlier flights went after overall Greenland bed topography so rectangular grid lines made more sense.

However there are problems using an ephemeral surface feature to define coordinates. This flowline may or may not lie over the lowest point in bedrock. Joughin uses the long-gone calving front of 2003 as origin of coordinate system origin and not quite a central streamline -- figure 1 starts out as an oblique line, changes to a curve, then cuts cross-channel between M9 and M10.

It's also tempting to run the coordinate system through emplaced instrumentation, though that too is ephemeral. Because the ice stretches, they need both Eulerian and Lagrangian reference frames here. The latter means GPS or theodolite targets going along for the ride.

Along-track coordinates could have been correlated to lat,lon but that was not done as a Fig.3 scale. So we have to put km coordinates along the photo track or determine from the DEM where the trough lies relative to the calving front on the image.

I can't get too exercised over older inaccurate depth profiling when both IceBridge and the new radar drone are out there now updating glacial thinning (the part above sea level) and determining fine-grain features of channel bedrock (needed to model resistance flow).

Inverse methods, deducing the bottom from deformations on the ice stream surface, have severe limitations as Sidd discusses over at the main Jakobshavn forum. There have to be consequences of something this massive and moving so rapidly while making a 43º turn. A huge new issue, freeze-on of meltwater leading to drastic deformations of overhead ice stratigraphy, may also be applicable to Jakobshavn.