Arctic Sea Ice : Forum

Cryosphere => Greenland and Arctic Circle => Topic started by: Laurent on December 15, 2014, 08:45:03 PM

Title: What's new in Greenland?
Post by: Laurent on December 15, 2014, 08:45:03 PM
Greenland ice melt underestimated, study says
http://www.theguardian.com/environment/2014/dec/15/greenland-ice-melt-underestimated-study-says (http://www.theguardian.com/environment/2014/dec/15/greenland-ice-melt-underestimated-study-says)
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on December 16, 2014, 12:57:11 PM
And also according to another recent paper in PNAS:
http://www.washingtonpost.com/blogs/wonkblog/wp/2014/12/15/scientists-are-worried-greenland-might-melt-even-faster-than-expected/ (http://www.washingtonpost.com/blogs/wonkblog/wp/2014/12/15/scientists-are-worried-greenland-might-melt-even-faster-than-expected/)
Title: Re: what's new in Greenland ?
Post by: Sigmetnow on December 16, 2014, 02:02:08 PM
Hidden Movements of Greenland Ice Sheet, Runoff Revealed
New NASA video has a nice overview of Greenland topography, satellite and Ice Bridge data collection, and glacier melt.
http://www.nasa.gov/content/goddard/hidden-movements-of-greenland-ice-sheet-runoff-revealed/ (http://www.nasa.gov/content/goddard/hidden-movements-of-greenland-ice-sheet-runoff-revealed/)
Title: Re: what's new in Greenland ?
Post by: Laurent on December 18, 2014, 06:00:14 PM
The Greenland Ice Sheet: Now in HD
http://phys.org/news/2014-12-greenland-ice-sheet-hd.html (http://phys.org/news/2014-12-greenland-ice-sheet-hd.html)
Title: Re: what's new in Greenland ?
Post by: Laurent on December 19, 2014, 11:24:52 AM
Greenland’s Ice Sheet Shifts Could Speed Melt
http://www.climatecentral.org/news/greenland-ice-sheet-shifts-melt-18448 (http://www.climatecentral.org/news/greenland-ice-sheet-shifts-melt-18448)
Title: Re: what's new in Greenland ?
Post by: A-Team on December 19, 2014, 04:52:50 PM
Whoa, this is really sensational to have access to 0.5 m WorldView panchromatic -- three cheers for DigitalGlobe and NGI for not hoarding Greenland imagery! After processing stereo pairs 45 seconds apart in satellite travel time into DEMs, it is 2 m resolution; the spectacular sample image of the west central Greenland coast is hill-shaded from that.

I located the region covered by the image in google earth -- quite the difference. The caption mentions Sermeq Silardleq (Silarleq) and Kangigdleq (Kangilleq). I added the available CReSIS radar tracks and a bit of the surface velocity map.

 the researchers are steadily processing it all with new Ohio State software called SETSM (for Surface Extraction from TIN-based Search Minimization). Ohio State research associate Myoung-Jong Noh created the software, which builds 1-gigabyte "tiles" representing regions 7 kilometers on a side and assembles them into mosaics depicting land, sea and ice elevation.

It seems at the meeting that Howat also showed Jakobshavn imagery having cracks hundreds of kilometers inland. The location and rate of widening indicates the direction and magnitude of ice accleration. 

Ohio State has finished only a quarter of the Greenland Ice Sheet which has taken a year of computing time using MJ Noh software called SETSM (Surface Extraction from TIN-based Search Minimization) where TIN stands for Triangulated Irregular Network. The tiles are 7 x 7 km but already 1-gigabyte in size.  Greenland is ~2.3 million sq km, so that amounts to 47,000 tiles. 

Commercial imagery vendor DigitalGlobe licensed it for U.S. federal use via the NSA's National Geospatial Intelligence Agency, which sends it to the Polar Geospatial Center at the University of Minnesota. At any given time, the Ohio Supercomputer Center is processing a 30-terabyte.

It seems that U Minn hosts a publicly accessible website off http://www.pgc.umn.edu/. (http://www.pgc.umn.edu/.) I don't know if that is up and running yet or whether the interface requires whole tile downloads at full resolution or is more like EarthExplorer. 7 km doesn't get you very far up Jakobshavn for a gigabyte.

The full size resolution of the sample imagery is online at 1440 x 3093 pixels, mysteriously as a color jpg (it is 8-bit grayscale). The second image below shows a small piece of it, the full image is at http://cdn.phys.org/newman/gfx/news/hires/2014/thegreenland.jpg (http://cdn.phys.org/newman/gfx/news/hires/2014/thegreenland.jpg)
Title: Re: what's new in Greenland ?
Post by: A-Team on December 19, 2014, 07:33:23 PM
I found the SETSM site and got registered; no password, products are free. I am not sure if the Greenland forums are a proceeding or just a blog -- maybe if we have a dedicated forum to SETSM it would be worth a head's up:

Quote
I agree to inform Dr. Ian Howat if this dataset is to be presented in any publication, presentation or proceeding and to acknowledge the Byrd Polar Research Center (BPRC) Glacier Dynamics Research Group, Ohio State University by name in presentations and publications arising from use of these data.
http://www.pgc.umn.edu/elevation/stereo (http://www.pgc.umn.edu/elevation/stereo)

The portal is well designed and provides enough levels of preview that you don't have to download a large pig in a poke only to find you wanted the next one over. They have quite a good gallery. http://www.pgc.umn.edu/elevation/stereo/gallery (http://www.pgc.umn.edu/elevation/stereo/gallery) These are also available as kmz for layering onto Google Earth, hooray.
Title: Re: what's new in Greenland ?
Post by: A-Team on December 20, 2014, 02:42:19 PM
The new PNAS paper Lennart mentions above is available there as full free text, which will give a clearer account than newspaper feeds. The authors have a long track record of research in what might be called fusion geomatics, putting together information from a mix of disparate, temporally spotty, terrestrially sparse remote sensing data.

Here they are after Greenland's contribution to sea level rise (taken as ice sheet mass loss), a sore point with researchers because best estimates were blown off by an IPCC 2007 panel as too uncertain (though today seen as spot-on).

There was enough radar altimetry to develop a time series for ice thickness of Greenland and partition that into contributions from surface mass balance (snowfall accumulation minus melt etc) and ice dynamics (gravity-driven flow, ie calving). However satellite coverage issues (ICESat ended Oct 2009; IceBridge tracks are sparse, ICESat 2 not launching until 2017) meant no annual updates for the 5 most recent years -- SETSM might help but all-Greenland processing is still a year off.

Greenland is best broken up into lots of individual iceshed basins; the 3-4 largest contributors cannot really serve as proxies because each represents a one-off situation, eg NEGIS icestreaming or Jakobshavn overdeepening. The authors make the important point that since physical inter-basin couplings are weak across ice divides,  annual changes in tandem must be attributable to climate.

The main internal products of the study are first the behavioral classification of individual glaciers (Fig.2, a portion shown below) which prove surprisingly heterogenous, and second the annual time series for six consecutive years 2004-2009.

The latter result is fairly difficult to convey effectively via scientific illustration. It involves 18 images representing SMB + Dynamic = Total for the six years. The authors provide these at low resolution and as a movie (blended slide show) whose frames are high resolution. The color palette is not completely satisfactory; a log scale might have better represented big coastal vs small interior changes. I tried a couple of things below but didn't improve conveyance greatly.

http://www.pnas.org/content/early/2014/12/12/1411680112.full.pdf+html?with-ds=yes (http://www.pnas.org/content/early/2014/12/12/1411680112.full.pdf+html?with-ds=yes)
Title: Re: what's new in Greenland ?
Post by: sidd on December 21, 2014, 07:45:34 AM
Greenland section from nsidc report card
http://www.arctic.noaa.gov/reportcard/greenland_ice_sheet.html (http://www.arctic.noaa.gov/reportcard/greenland_ice_sheet.html)

two points the struck me
a)albedo continues to drop
b)GRACE mass loss is only 6 Gton for June2013-June2014, as compared to nearly 500 the previous year. A reprieve, but for how long ?

sidd
Title: Re: what's new in Greenland ?
Post by: Wipneus on December 21, 2014, 07:47:45 AM
I did not see this mentioned elsewhere.

The Danish Polar Portal (http://polarportal.dk/en/home/) has issued a 2014 season report (http://polarportal.dk/en/nyheder/arkiv/2014-season-report/), available in Danish, English and Greenlandic.

The summary:
Quote
Year 2014 comes in above average for the amount of melting from the Greenland Ice Sheet in the period since 2002. On the other hand, Arctic sea ice was strengthened in 2014.

The most important results of climate
monitoring in the Arctic in 2014 are:

• The Greenland Ice Sheet contributed
approximately 1.2 mm to sea-level rise;
• Below average reflection of sunlight is
associated with increased melting from the
Greenland Ice Sheet in 2014;
• The surface mass balance of the Greenland
Ice Sheet was lower than normal, but not
record low;
• Arctic sea ice strengthened in 2014;
• A new temperature record was established
in west Greenland in June 2014;
• There were no exceptional changes in the
movements of glacier fronts in Greenland.

About Zachariae:

Quote
Zachariae Glacier is one of the 20 largest
glaciers that changed the most during the 2014
melt season. Already in April several km2 had
broken off the terminus, but were nonetheless
partially rebuilt by the glacier flow from the ice
sheet. However, between July and August an
additional roughly 20 km2 of the glacier’s
terminus was broken off to form floating
icebergs. This especially affected the central
and northern parts of the glacier, which lost 4
km between June and September.

Even though there were no major changes in
the terminus of 79N Glacier, there were both
more and larger meltwater lakes on the surface
of the glacier in the middle of August in
comparison with the same period in 2013.
Title: Re: what's new in Greenland ?
Post by: Wipneus on December 21, 2014, 10:04:41 AM
In The Cryosphere Discussion Brief Communication: 2014 velocity and flux for five major Greenland outlet glaciers using mGRAFT and Landsat-8 (http://www.the-cryosphere-discuss.net/8/6235/2014/tcd-8-6235-2014.html) by A. Messerli, N. B. Karlsson, and A. Grinsted.

Quote
Abstract. This study presents average velocity fields, mass flux estimates and central flowline profiles for five major Greenland outlet glaciers; Jakobshavn Isbræ, Nioghalvfjerdsbræ, Kangerdlugssuaq, Helheim and Petermann glaciers, spanning the period (August) 2013–(September) 2014. The results are produced by the feature tracking toolbox, ImGRAFT using Landsat-8, panchromatic data. The resulting velocity fields agree with the findings of existing studies. Furthermore, our results show an unprecedented speed of over 50 m day−1 at Jakobshavn Isbræ as it continues to retreat. All the processed data will be freely available for download at http://imgraft.glaciology.net (http://imgraft.glaciology.net).

ImGRAFT is (unfortunately for me) written in matlab, otherwise I would love to apply it at Zachariae.
Title: Re: what's new in Greenland ?
Post by: A-Team on December 21, 2014, 05:21:46 PM
Quote
ImGRAFT is (unfortunately for me) written in matlab, otherwise I would love to apply it at Zachariae.
You might email the authors and ask them to please run your favorite pair of Zachariae Landsat-8's (matched viewing geometry, minimal clouds, id numbers like LC80090112014040LGN00 supplied). Explain that you plan to write a blog article on Zachariae citing their software. Myself, I hope they start to offer this as an online service (like the 301 G'Mac filters), running matlab in the background.

Or try ImageJ2 (FIJI). It comes pre-loaded with automatic feature-tracking plugins and can process Landsat8 in 12-bit mode (32 bit mode supported for SETSM above, 64-bit supported for a few things).

It is becoming possible to run a pair of Landsat-8's with a full year of separation (good for slower moving upstream and peripheral areas. T Scambos AGU 2014 abstract indicates this has been done already far upstream for Jakobshavn with yet other software. More ambitiously, run all of them, compare and contrast algorithm output.

Meanwhile, back at 0.6 m DigiGlobe and really high resolution velocity maps, I've made some inroads downloading and processing the 32-bit SETSM DEMs from Noh and Howat which in some cases use WorldView 1 and 2 of different dates.

Here even the sub-tiles (20 km x 20 km) would benefit from a wall-sized monitor (in a room with a tall ceiling) being 10,100 pixels on a side. So far I have just tried shadowing (poor man's hill shading), contouring, norm gradient and jakobean.

The  ImGRAFT paper makes some interesting points. Note flux gates have been "constructed" elsewhere at both 1700 and 2000 m contours around the whole of Greenland.

Quote
Our data indicate yet a further speedup of Jakobshavn Isbræ in July 2014 peaking at a record 52 meters per day. This was manually verified using a simple triangulation of selected features near the terminus ... The current flux gate at the grounding line for Jakobshavn Isbræ sees ~30 cubic km per year go by... Joughin 2014 suggest that a tenfold increase in this estimate in the future is plausible.

A noticeable observation at Petermann is the distinct separation between the main trunk and the northern marginal slower flow which has been described in Münchow 2014. The large tributary that flows into the main glacier forms a slower flowing part of the glacier tongue. Petermann and Nioghalvfjerdsbræ display highest speeds not at the terminus but at approximately 45 and 70 km from the calving front respectively

Below Jakobshavn and Nioghalvfjerdsbræ are shown bumped up slightly from native submitted resolution. Below that, ImGRAFT and IceTools together in GoogleEarth.

Below that, a gradient of a SETSM tile with middle Jakobshavn lower left; and lastly an animation shadowing 32-bit Noh and Howat DEM, more rounds of shadowing bring out relief in low-relief areas (at the same time overdoing it in moderate relief areas). The direction of light chosen, from the NE, is roughly a flow line so orthogonal to surface wave features. With incredible resolution comes incredible file sizes ... hopefully we little desktops can stay in the game.
Title: Re: what's new in Greenland ?
Post by: sidd on December 21, 2014, 09:33:26 PM
Re;Matlab

Try Octave. I have translated some fairly complicated Matlab code to run on Octave, with small difficulty.

sidd
Title: Re: what's new in Greenland ?
Post by: sidd on December 21, 2014, 09:39:33 PM
That report fron Denmark polar portal does not agree with the NSIDC report i linked to, which shows only 6Gton for 2013-2014 mass loss for GRIS from GRACE data. Nebbe because the former is based on   reflectivity based studies, the latter on gravitational signal ?

Maybe Prof. Box will chime in. His name is on the NSIDC report, and he works at GEUS i think these days.

sidd
Title: Re: what's new in Greenland ?
Post by: A-Team on December 22, 2014, 01:54:43 PM
Quote
With incredible resolution comes incredible file sizes ... hopefully we little desktops can stay in the game.
Improving ground resolution is very important to more reliable modelling of the Greenland Ice Sheet -- but file sizes go as the square (from 5km --> 1 km is 25x the pixels). A time series of Landsat-8s is already a full plate; the new SETSM DEM is 10 GB per tile x 2300 tiles.

At what point will we lose the ability to replicate results and just have to take them on faith?

If someone should steal my current computer so I could rationalize getting a new one, would newer capabilities make any difference? For $3k, there has been a huge improvement in the screens: the current 27" iMac has 5120 x 2880 = 14.7 million pixels (218 ppi pixel density), a 7x improvement but it can also supports an external display of 3840 by 2160 resolution, another 8.3 million pixels. There is a big productivity improvement from getting the operational interface off the main screen.

The graphics card offers 3.5 teraflops -- large resolution raster image manipulation has benefited from the video gamer market. Yosemite OS can take advantage of high-end displays. The quad-core 4.0GHz Intel Core i7 processor can be overclocked to 4.4GHz, not much of an improvement over the 3.1 GHz I have now. The RAM limit is 32 GB (vs 16 MB now) though some sites are saying 64. I don't really store much locally but the 1.0 TB drive has faster retrieving. The 802.11ac supports data rates of 1.3 Gbps which is a mismatch to my mediocre connection and data plan.

There is a happy coincidence in that Greenland in polar stereographic projection has height:width ratio of 1.84 which, viewed sideways, is an excellent match to the 1.77 of the monitor. The icesheet itself covers 1,755,637 km^2 so a sq km could be represented by 3 x 3 pixels. How though would a neat image be shared -- at 700 pxl blog width?
Title: Re: what's new in Greenland ?
Post by: A-Team on December 22, 2014, 02:46:07 PM
Quote
Might try matLab in Octave
Interesting suggestion, sidd. Octave just thinks of images as matrices, stacked one per color channel. This makes sense as a lot of raster image processing amounts to very basic matrix manipulations. As mentioned before, the BMP file format interconverts image display on the monitor with its numerical matrix equivalent. Octave now has a GUI to get out of command line; I haven' tried it.
https://www.gnu.org/software/octave/doc/interpreter/index.html#SEC_Contents (https://www.gnu.org/software/octave/doc/interpreter/index.html#SEC_Contents)

Quote
report from Denmark polar portal does not agree with NSIDC which shows only 6 Gton for 2013-2014 mass loss from GRACE data.
Indeed, something is not right here. The polar portal offers an explanation in Box 2, page 3: power was shut off to the GRACE satellite in July to spare the battery which couldn't have come at worse time for Greenland mass balance. I'm inclined to go with the graph in Fig.3 below. The pdf also has a good summary of weather aspects.

Quote
Satellite observations since 2002 show that the Greenland Ice Sheet is not in balance and that the loss of ice from calving of icebergs and surface melting exceeds the overall mass input from snowfall. The Greenland Ice Sheet has lost about 250 Gt/year of mass over the past decade. One Gt is 1 billion tonnes and is equivalent to 1 cubic kilometer of water. A loss of mass of 100 Gt of ice corresponds to a sea level rise of 0.28 mm.

The annual melting season is normally at its peak in July or at the beginning of August, and 2014 was a year with greater melting than normal—although less than the highest level so far, 2012. According to our reflectivity based estimate, the ice sheet lost mass equivalent to approximately 1.7 mm sea-­‐level rise during the period of greatest sunlight from May to September 2014.

This is about 50% more than the average for the years 2002 to 2013 and only about 5% less than the loss of mass in the record year 2012. This loss of mass puts the year 2014 in third place in relation to melting since 2002. Second place is year 2010. When the average addition of mass equivalent to 0.4 mm during the winter period from October to March is considered, it is estimated that in 2014 the Greenland Ice Sheet contributed about 1.2 mm to sea-­‐level rise over the entire period.

Changes in the overall mass of the ice sheet are determined by two different methods. One method builds on measurements from the GRACE satellite of changes in the gravitational pull of the ice sheet, which decreases when there is less ice. However, it takes up to two to three months to analyze these data and GRACE data are unavailable mid-­‐2014 due to satellite power problems.

Therefore, researchers from GEUS have developed a supplementary method that is faster but not quite as precise as measurements of the gravity. This method is based on measurements of the albedo effect, that is, the reflection of sunlight from the ice sheet. This can be used because a statistical relationship has been found between the albedo effect and the gravity of the ice sheet. In this way a rapid, but provisional assessment can be made of the loss of mass from the ice sheet, while the more precise data are being analyzed.
http://polarportal.dk/fileadmin/user_upload/PolarPortal/season_report_2014/PolarPortal2014-EN.pdf (http://polarportal.dk/fileadmin/user_upload/PolarPortal/season_report_2014/PolarPortal2014-EN.pdf)
Title: Re: what's new in Greenland ?
Post by: Wipneus on December 22, 2014, 07:40:45 PM
Before shutting down, this is what I did today:

- borrowed a matlab installation
- installed the ImGRAFT software and figured out how to run a demo example
- got two Landsat B&W images with the same path and row (July 17 and August 29)
- played with the parameters to improve the picture

Latest result is attached. Scale is in meters/day.
Title: Re: what's new in Greenland ?
Post by: A-Team on December 22, 2014, 10:49:47 PM
Bravo! Do we know of some reason for enhanced motion in the area outlined below? (Please excuse the blur but it seems to give an overall picture.)
Title: Re: what's new in Greenland ?
Post by: Laurent on December 23, 2014, 12:40:13 PM

Greenland's Ice Loss Now Comes from Surface

http://www.livescience.com/49224-greenland-ice-sheet-melt-changing.html (http://www.livescience.com/49224-greenland-ice-sheet-melt-changing.html)
Title: Re: what's new in Greenland ?
Post by: A-Team on December 23, 2014, 03:22:50 PM
The AGU has not concerned itself greatly with providing online resources covering the meeting. I cannot understand how uploading slides can be optional for presenters since their research, salary, retirement, medical, meeting expenses etc etc are done entirely on the taxpayers' dime -- in terms of disadvantaging the competition (does this even make sense in a climate crisis), the audience has lots and lots of camcorders.

Even the poster session posters were not posted!!! (4 out of 30 below). Those posters had to have been finalized at the time of submission to the session. I'd say automatically upload those at the close of the meeting and let authors over-write with any corrections and updates. Topics like cryosphere -- wouldn't a tar.zip of the whole package be vastly more efficient than pecking through one pdf at a time?

I looked for a list of Cryosphere posters and panel talks which were either video-archived online or where the authors had uploaded a pdf or ppt.  This simple task proves to be a total nuisance, clicking through the entire archive one session at a time looked for 'ePoster' links. A lot of the main Greenland players appear not to have submitted anything -- or rather, name search failed to link up their ePosters (often submitted under unknown grad student name).

I did find two relevant to Laurent's newsy link above but the AGU did not have the pdf links formatted correctly (as far as Chrome or Firefox were concerned)! I eventually did get them open, very worthwhile. It is not possible to walk up their file system from the initial ePoster. In fact I haven't seen a pattern yet in their ePoster directory system.

Quote
C21B-0329 Firn and percolation conditions in the vicinity of recently formed high elevation supra-glacial lakes on the Greenland Ice Sheet assessed by airborne radar
ePoster - https://agu.confex.com/data/handout/agu/fm14/Paper_24929_handout_1496_0.pdf

The western region of the Greenland Ice Sheet around and above the equilibrium line is characterized by relatively high accumulation rates with short-lasting melt events of variable intensity during the summer months. During melt season, supra-glacial lakes are formed at least temporarily in depressions found in the topography of the ice.

These ponds can form and drain rapidly, affecting the dynamics of the ice below. Recent warming trends have gradually increased the amount of meltwater found every summer over the ice sheet, with melt regimes migrating to higher altitudes. Consequentially, supra-glacial lakes are being found at higher elevations, yet it is unclear what mechanisms control their formation over firn.

We used data from different radar systems acquired by Operation Icebridge around and over lakes formed above the equilibrium line of the Greenland Ice Sheet to study internal features of identified frozen/drained supra-glacial lakes, and to investigate near-surface snow and firn conditions in the vicinity of the ponds by radar-mapping internal snowpack structure. Airborne radar and additional field observations revealed extensive and impermeable ice layers 20-70 cm thick formed at elevations between 1500 m and 2200 m.

Buried by winter accumulation, these ice layers prevent further meltwater to percolate deeper during melt season, limiting firn capacity to absorb meltwater and causing near-surface snowpack saturation, thus facilitating the transport of meltwater to newly-formed basins above the equilibrium line. Ice penetrating capabilities from the different radar systems allow the survey of different firn layers and internal features created by refrozen meltwater. IceBridge data is acquired in early spring, when no liquid water content is found over this region ensuring adequate radar response.

Quote
C21B-0316Massive Perched Ice Layers in the Shallow Firn of Greenland's Lower Accumulation Area Inhibit Percolation and Enhance Runoff
ePoster - https://agu.confex.com/data/handout/agu/fm14/Paper_10527_handout_506_0.pdf

Greenland's recent trend of record-breaking melt seasons (2012, 2010, 2007, 2002, et al.) have substantially increased the amount of melt water generated in the ice sheet's lower accumulation area. Due to this enhanced refreezing in the firn, regions with low accumulation rates have formed multi-annual ice layers 5-10+ meters thick in the thermally active shallow firn that overlies porous firn at depth.

The loss of pore space in the firn prevents the majority of melt water from percolating to depth and results in surface runoff where water previously would have refrozen. Here we present evidence from in situ ground-penetrating radar, firn cores and airborne radar from NASA's Operation IceBridge, collected both before and after Greenland's 2012 melt season, to illustrate the mechanism by which southwest Greenland's runoff zone in 2012 extended 20 kilometers inland from the long-term saturation line.

Additional evidence from satellite imagery, firn temperature profiles and modeling support the notion that these layers blocked percolation and contributed to Greenland's record runoff in 2012. Should Greenland's trend of anomalously warm summers persist, these massive lenses are likely to grow thicker and extend further inland, resulting in enhanced runoff and rapid upslope migration of the equilibrium line. These results illustrate the vital importance of understanding subsurface firn changes in order to accurately predict Greenland's future runoff in a changing climate.
Title: Re: what's new in Greenland ?
Post by: Wipneus on December 24, 2014, 07:44:53 PM
Reporting on my progress with the ImGRAFT software.
This time I tried the Sentinel images, these are lower in resolution (as currently available) 40m and more of the 'SAR quality'. More high frequency noise than in optical images.
So this was more a challenge but I think I get reasonable result now.
What was done:
- filtered the input images in matlab using hi- and lo-pass filters (with the help of some suggestions in ImGRAFT documentation);
- Used quite a large 'template size', the pieces in the source image for which a match is sought in the target. It is about 140 pixels wide, judge by the left marging in the attached picture;
- Did away with the signal/noise filtering used in the examples;
- Probed a piece of solid rock to measure the alignment of the two images, used this to correct the flow field. As the pixel offset was not a whole number this is not an easy job (for me) in the Gimp;

The result has some encouraging things to say:
- the speed near the calving front is about 6m/day, just what we expected;
- part of the  Nioghalvfjerdsfjorden looks quite good;
Other localized aberrations in the flow field are visible, hopefully we can say more about these when we follow the glacier longer and in better resolution.
 
Title: Re: what's new in Greenland ?
Post by: A-Team on December 25, 2014, 02:01:46 PM
Nice! It would take n well-distributed rocks to really rectify image geometry (ImageJ2 distortion plugin) -- even when orbital parameters are 'known' they have too much uncertainty for geodesy (Howat 2014).

The ImGRAFT output is an evenly gridded vector field yet it can only find corresponding features in the two images here and there. Can it also output just the primary match arrows it uses to make the grid? Can it output RGB where as HSV the V is velocity magnitude and H is 360º direction? With 3 successive image dates, can it display acceleration dv/dt?

I rescaled and rotated imagery from Latour 2014 which uses Zachariae velocities from Rignot 2012 which uses InSar from still earlier to more or less fit the ImGRAFT scene above. Nothing there corresponds to the upstream oddities which ImGRAFT is reporting from both Landsat and Sentinel.
Title: Re: what's new in Greenland ?
Post by: nukefix on December 25, 2014, 04:54:34 PM
If the S-1 images are from the same track they are already in the same sensor geometry and should match very well after just applying a shift (no rotation needed). If we had a DEM it should be possible to geocode images from different tracks to map coordinates without having to use GCPs...
Title: Re: what's new in Greenland ?
Post by: Wipneus on December 26, 2014, 11:07:37 AM
Nice! It would take n well-distributed rocks to really rectify image geometry (ImageJ2 distortion plugin) -- even when orbital parameters are 'known' they have too much uncertainty for geodesy (Howat 2014).

From the Sentinel-1 User Handbook (https://sentinel.esa.int/documents/247904/685163/Sentinel-1_User_Handbook/06fa0b55-9eca-47ff-a45f-242012951564):

Quote
In particular for interferometry, SENTINEL-1 requires stringent orbit control. Satellite positioning along the orbit must be accurate, with pointing and timing/synchronisation between interferometric pairs. Orbit positioning control for SENTINEL-1 is defined using an orbital Earth fixed "tube", 50 m (RMS) wide in radius, around a nominal operational path. The satellite is kept inside this "tube" for most of its operational lifetime.

50m/693km seems to me impressive, does Howat consider such precision?

The ImGRAFT software contains a module "camera.m" that can rectify for differences in cameras (focal length, distortions) and positions. They don't use it on the Landsat images though, neither do I.
Title: Re: what's new in Greenland ?
Post by: Wipneus on December 26, 2014, 11:41:35 AM
The ImGRAFT output is an evenly gridded vector field yet it can only find corresponding features in the two images here and there. Can it also output just the primary match arrows it uses to make the grid? Can it output RGB where as HSV the V is velocity magnitude and H is 360º direction? With 3 successive image dates, can it display acceleration dv/dt?

Core of the ImGRAFT software is "templatematch.m" (http://imgraft.glaciology.net/documentation/functions/templatematchm) a routine that give 2 images, an array of x,y coordinates in the first image will calculate the displacements to matching point in the second image. Everything else is a demo: the evenly grid, the output image with colors and arrows. The user can  change those as you like it, as long as it is programmable.
Moreover there is nothing in the software that is aware that the displacements are a (u,v) vector field with some (dictated by physics) continuity in space and time (when more than 2 images are available). Those features seem desirable but non-trivial to add.
Title: Re: what's new in Greenland ?
Post by: A-Team on December 26, 2014, 05:26:51 PM
Quote
Everything else is add-on: the evenly grid, the output image with colors and arrows. The user can change those as long as it is programmable. nothing in the software is aware displacements are a (u,v) vector field with dictated by physics)
This modularity is a good thing ... users can build various paths through various options for interpolation and display in something like a PENTAHO drag'n'drop environment. Whether you end up with something the corresponds to reality as well as interferometric SAR (which inherently provides continuous velocity contours) isn't frequently validated on the ground (eg fiberglass pole array to 80 m depth Swiss Camp flow line).

On bringing in ice physics (see 14 talks of Morlighem at AGU 2014), for me the question is what we can measure with surface displacements versus what we want to measure, namely how the velocity and acceleration fields in 3D are responding to climate change, without just assuming surface motion is a satisfactory proxy for them.
 
Quote
The ImGRAFT software contains a module "camera.m" that can rectify for differences in cameras (focal length, distortions) and positions. They don't use it on the Landsat images though, neither do I.
The Landsat-8 has a group of image geometric attributes, things like ROLL_ANGLE = -0.001 which I've never seen vary to any interesting extent.

What got my attention above was Poh and Howat 2014, mss in prep http://www.pgc.umn.edu/system/files/SETSM_Product_Sheet_v1.1.pdf, (http://www.pgc.umn.edu/system/files/SETSM_Product_Sheet_v1.1.pdf,) which seeks to "extract a stereo-photogrammetric DEM from pairs of images without any user-defined or a-priori information and using only the [satellite] sensor Rational Polynomial Coefficients (RPC) for geometric constraints."

Quote
Surface Extraction with TIN-based Search-space Minimization (SETSM)
Fully automatic stereo-photogrammetric Digital Elevation Model (DEM) extraction from pushbroom satellite imagery

Since the geolocation accuracy of RPCs without ground control for WorldView-1 and 2 is 5m CE90 (DigitalGlobe, 2013), there is an offset between corresponding points projected by the vertical line locus. Where large enough, this offset can result in matching failure. Relative RPC updating provides an adaptive method for mitigating this error.

For any RPC-constrained DEM extraction algorithm there will be two common and dominant sources of error: blunders and RPC errors. Blunders are caused by incorrect matching of features between images, resulting in surface outliers. The iterative restriction of the search area in SETSM, as well as the blunder detection algorithm in step 4 above, substantially reduce blunders.

RPC errors are typically the result of errors in satellite positioning and look geometry, increasing with sensor look angle. These errors have two main effects: First, they result in misalignment of the stereo pair in the matching routine, resulting in poor match returns, which is mitigated in SETSM through iterative refinement of the search space.

The second effect is a bias in DEM elevations. Cheng and Chappel (2008), found an average bias of 5 m in several test DEMS extracted from WorldView-1 imagery. We are still testing for this bias using both Worldview 1 and 2 image pairs ... We anticipate further accuracy gains by determining which look geometries result in the best RCP determinations. The most effective way to reduce geometrically induced error, however, is by using ground control points (GCP).
The interometric velocity  below is adapted from http://posters.unh.edu/gallery/view/3177/ (http://posters.unh.edu/gallery/view/3177/)  "Investigating the cause of the 2012 Acceleration of Jakobshavn Isbrae, Greenland Using High Resolution Observations of the Glacier Terminus" by Ryan Cassotto
Title: Re: what's new in Greenland ?
Post by: A-Team on December 27, 2014, 01:04:45 PM
I collected all the Greenland and Arctic talks at AGU 2014 that had an attached pdf poster. Less than 1 in 10 offered anything beyond an abstract; whole poster sessions went by without a single poster posted! Worse, the .php formatting prevented advance google search from seeing the abstracts or finding the ePoster attachments; some talks had an attached graphic not listed anywhere.

This is about the lamest excuse for a scientific meeting I have ever come across, unless it be AGU 2013.

https://agu.confex.com/data/handout/agu/fm14/Paper_28053_handout_1869_0.pdf # Greenland # Saturated Crevasses along Shear Margins of Jakobshavn # A Ring # "temporal increase in lateral drag seems to indicate  long-­‐term stress loading of the shear margins as the ice  stream response to down stream mass perturbaAons at  the terminus. Differences in transects indicate that  regions where water-­‐filled crevasses are found the  magnitude of lateral drag is less and the rate of drag  increase is smaller than regions without water. Given  this, preliminary results suggest that water-­‐filled  crevasses are weakening the shear margins and likely  resulAng in enhanced stress loading in other parts of  the shear margins that are devoid of water."

https://agu.confex.com/data/handout/agu/fm14/Paper_10527_handout_506_0.pdf # Greenland # Perched Ice Layers In Shallow Firn Inhibit Percolation And Enhance Runoff # MJ MacFerrin # "mapping: some regions have formed multi-annual ice layers several meters thick in the top 20 meters of firn. When such layers grow thick enough to be impermeable, they prevent water from percolating to depth and cause surface runof. thick refrozen ice layers in the top 20 meters of firn in Greenland’s lower accumulation zone. •   When thick enough, these perched layers become impervious to further melt and quickly migrate the runoff line inland, even when pore space still exists below that could otherwise absorb water. If warming continues, these layers are expected to grow inland. Radar enables us to map and monitor these massive perched ice layers

https://agu.confex.com/data/handout/agu/fm14/Paper_24929_handout_1496_0.pdf # Greenland # Firn and percolation in high elevation supra-glacial lakes # Peña Howat # "assessment of percolation in  accumulation zone of western Greenland after the intense melt episodes of 2010 and 2012. Concentrations of ice has increased dramatically over the firn of the GIS, limiting the buffering capacity of the firn and facilitating meltwater transport and retention as ponds. The area covered by percolation features has expanded more than twice in 10 years, and melt intensity above 2000 m in 2012 was found to be an order of magnitude greater than at the end of the 20th Century... abrupt densification due to percolation processes a larger factor in altimetry–derived studies."

https://agu.confex.com/data/handout/agu/fm14/Paper_8948_handout_2231_0.pdf # Greenland # Disko Bay icebergs # J Scheick # "algorithm to delineate and extract quantitative information (location, geometry) about icebergs in optical satellite imagery. Future work will improve the cloud mask apply the algorithm to a long time series of Landsat images (1994-present), map changes in iceberg distributions with time (do export pathways remain constant or change depending on iceberg size?)"

https://agu.confex.com/data/handout/agu/fm14/Paper_11555_handout_734_0.pdf # Greenland # Rapid drainage of supraglacial lakes # S Adhikari # "Some Greenland Ice Sheet supraglacial lakes drain rapidly within the timescale of a few hours. The vertical discharge of water during these events may find a pre-­existing film of water potentially within a system of linked cavities. Here, we present a model for subglacial flooding in these circumstances."

https://agu.confex.com/data/handout/agu/fm14/Paper_17159_handout_1223_0.pdf # Greenland # Snow/firn density distribution on Devon Ice Cap, Canadian Arctic from airborne radar reflectometry # A Rutishauser # "Scattering and reflectivity distributions demonstrate the potential of using RES data to characterize the near-surface snow/firn properties. We hypothesize that the scattering values indicate a pseudo dry snow zone above ~1800 m asl, and the transition between the SI and glacier ice zone at ~1300 m asl. From the reflectivity values, we estimate the winter snow pack thicknesses, showing highest snow accumulation (~70-120 cm) in the southeast sector of DIC. The derived RSR dataset might help understanding the complex nature of the internal layering pattern. Especially the distribution of refrozen ice lenses/layers might explain complex internal layers resulting from a distorted snow/firn deposition pattern."

https://agu.confex.com/data/handout/agu/fm14/Paper_17824_handout_1269_0.pdf # Greenland # High frequency seismic waves recorded by the greenland ice sheet monitoring network (glisn) during the drainage of a supraglacial lake # EJ Orantes # "Supraglacial lake drainage is a major source of subglacial water under the Greenland Ice Sheet, impacting the ice dynamics at different temporal and spatial scales. Previous studies have shown that fast drainage of a supraglacial lake can produce high frequency seismic waves that are detected by local seismometers; however, little work has been done on the regional detection of such waves. Here we present the results of a study focusing on seismic data and their potential linkage to the drainage of a supraglacial lake (Lake Ponting) in the Paakitsoq region of the West Greenland ice sheet. The corrected seismograms show similar waveforms for arrivals on a single line supporting the idea that each line represents a traveling wave. The velocities derived from the trendlines are too low for the waves to be traveling through either the rock or the solid ice. Our current hypothesis is that they are traveling in a low-velocity channel of till underneath the ice. This would be consistent with the low attenuation required for the propagation of high frequency energy over regional distances."

https://agu.confex.com/data/handout/agu/fm14/Paper_19489_handout_1454_0.pdf # Greenland # Modeling of subaqueous melting in Petermann fjord, northwestern Greenland using an ocean general circulation model # C Cai # "Petermann Glacier drains approximate 6.1% (73,927k m2 of total 1,209,280 km2) of Greenland Ice Sheet. Basal melting of the floating tongue of Petermann Glacier is by far the largest process of mass ablation. Melting of the floating tongue is controlled by the buoyancy of the melt water plume, the pressure dependence of the melting point of sea ice, and the mixing of warm subsurface water with fresh buoyant subglacial discharge. In prior simulations of this melting process, the role of subglacial discharge has been neglected because in the Antarctic surface runoff is negligible; this is however not true in Greenland. In this work, we simulate the melting process of the ice shelf by MITgcm) at high resolution including outflow. We use varying oceanic thermal forcing and new bathymetry from Operation IceBridge.

The shape of the ice shelf cavity influences the ice shelf melt rate, especially in summer. ith the OIB-derived bathymetry, the melt rate is 34% higher in summer compared to winter. Between the 1990s and the 2010s, runoff increased by 20% and ice shelf melting should have increased by 16%. Between the 1990s and the 2010s, ocean temperature warmed by 0.5-0.9 C, the melt rate should have increased by 7%~20% . Taken together, these numbers may explain the recent break up of Petermann ice tongue, which is indicative of ice thinning. We will pursue this work in 3-D to include the assymetry in the bathymetry of Petermann Fjord.
"
https://agu.confex.com/data/handout/agu/fm14/Paper_24220_handout_713_0.pdf # Greenland # Predicting the stability of ice sheets with crevasses: a numerical experiment # Y Ma # "Iceberg calving accounts for ~50% of the mass lost from the Greenland Ice Sheet. Increased calving rates can lead to rapid sea level rise. Calving is not well parameterized in numerical ice sheet models. Water plays a negative role in the growth of crevasses and thus calving events, by both creating a more negative largest principle stress field and slowing down both the thinning process and flow speed of the glacier. The depth of a crevasse is inversly related to water depth but calving rate can be directly related to flow speed. The same buttressing effect applies to ice shelves, melange, etc. When water is absent, surface crevasses may reach the bed."

https://agu.confex.com/data/handout/agu/fm14/Paper_24717_handout_1434_0.pdf # Greenland # Improving estimates of cloud radiative forcing over Greenland # W Wang # "Larger uncertainty in SW, especially in Shelf and Coastal areas.  Positive (warm the surface). Negative (cool the surface): Shelf Average total forcing over both Inland: ~28 W/m2 ≈ 0.89 m snowmelt (liquid water) from May to Aug Low Clouds: liquid-only clouds High Clouds: mixed and ice clouds. Surface Ratidation Fluxes > Cloud Radiative Forcing because CRF bias is partially reduced when clear-sky fluxes are removed from the all-sky fluxes. No dataset is outstanding in all fluxes: CERES does a fairly good job in CRF. In Inland areas (warming area), low clouds warm the surface better than high clouds."

https://agu.confex.com/data/handout/agu/fm14/Paper_26038_handout_952_0.pdf # Greenland # Thermo-­mechanically coupled modeling of high elevation regions of the Greenland Ice Sheet # A Sommers # "Thermo-mechanical simulations were conducted on 54 flowlines in western and southeastern Greenland (shown on map) from the main divide past the 2,000 m elevation PARCA stake location. The mean absolute velocity difference between modeled and observed surface velocity at each PARCA stake is 21 m/a. Geothermal heat flux To examine the sensitivity of model results to the magnitude of prescribed geothermal heat flux, simulations were conducted with the geothermal heat flux increased or decreased. Surface velocity decreases in cases with lower geothermal heat flux (colder ice, lower viscosity). Quite surprisingly, surface velocity also decreases as the geothermal heat flux is increased for stake locations with temperate bed. The driving mechanism for this behavior may be that when the viscosity very near the bed is decreased, higher advection rates of cold ice from upstream result, producing colder temperatures and thus smaller velocity gradients in the slightly higher locations in the ice column. Bedrock elevation To examine the influence of uncertainty in bedrock elevation, the prescribed data (Bamber et al., 2013) were perturbed by adding Gaussian white noise (with standard deviation of 125 m) and smoothing using a moving average function to generate ‘similar but different’ bed profiles. Importance of thermo-mechanical coupling A substantial underestimation of surface velocities results from isothermal calculations (assuming ice temperature -5°C) with no enhancement to the flow law parameter for Wisconsin ice. The isothermal model tends to overpredict surface velocity when the enhancement factor is included."

https://agu.confex.com/agu/fm14/meetingapp.cgi#Paper/21416 # Greenland # Isochronal Ice Sheet Model: a new approach to tracer transport by explicitly tracing accumulation layers # A Born # "The long, high-resolution and largely undisturbed depositional record of polar ice sheets is one of the greatest resources in paleoclimate research. The vertical profile of isotopic and other geochemical tracers provides a full history of depositional and dynamical variations. Numerical simulations of this archive could afford great advances both in the interpretation of these tracers as well as to help improve ice sheet models themselves, as show successful implementations in oceanography and atmospheric dynamics. However, due to the slow advection velocities, tracer modeling in ice sheets is particularly prone to numerical diffusion, thwarting efforts that employ straightforward solutions. Previous attemps to circumvent this issue follow conceptually and computationally extensive approaches that augment traditional Eulerian models of ice flow with a semi-Lagrangian tracer scheme. Here, we propose a new vertical discretization for ice sheet models that eliminates numerical diffusion entirely. Vertical motion through the model mesh is avoided by mimicking the real-world ice flow as a thinning of underlying layers (see figure). A new layer is added to the surface at equidistant time intervals (isochronally). Therefore, each layer is uniquely identified with an age. Horizontal motion follows the shallow ice approximation using an implicit numerical scheme. Vertical diffusion of heat which is physically desirable is also solved implicitly. A simulation of a two-dimensional section through the Greenland ice sheet will be discussed."
Title: Re: what's new in Greenland ?
Post by: A-Team on December 29, 2014, 03:10:44 PM
ImGRAFT so far has gotten two anonymous reviews, one a bit cantankerous and the other constructive, which could lead to (needed) substantive improvements in the paper. http://www.the-cryosphere-discuss.net/8/6235/2014/tcd-8-6235-2014-discussion.html (http://www.the-cryosphere-discuss.net/8/6235/2014/tcd-8-6235-2014-discussion.html)

Quote
... if the center of the displacement vector is used versus the vector tail (starting center point of the source sub-scene), here glaciers flow a kilometer between image pairs – enough so that the strain field traversed by the tracked features becomes important.

On errors, a single value of ±2 m/d is used, for the 16-day repeat pairs using the same path-row, a systematic error based on geo-location issues. However, adjacent (non- identical) path-rows were used, with time-separations varying quite a bit. The greater error with non-identical viewing geometry is mentioned, but without elaboration.

Error bars need to be shown in Figure 2 - and this will show that 2m/d error will blur quite a bit of the seasonal signal you appear to be mapping. Also show the seasonal variation relative to the merged mean Landsat 8 velocity or to the InSAR mean. But this will point out uncorrected errors in the Landsat 8 mapping. 

Figure 2: should really re-design Fig2 for Niog and Petermann – there’s no detail visible, and a lot of white space.
On Figure 1, are the centerlines correct? picking centerlines with some of the data having systematic errors in flow direction is risky. The centerline for Niog seems off?  it appears as though nunataks are sitting within the ice stream.

Results are like those already reported with the exception of the slightly greater flow speed for Jacobshavn (±2m/d makes this suspect). How about differencing the new map with the InSAR data -- it would reveal errors, but might reveal evolution.
Meanwhile, never mind this vector cross-correlation software, here is NASA printing out DEM slope vectors and drawing drainage divides by hand, then re-digitizing: http://icesat4.gsfc.nasa.gov/cryo_data/ant_grn_drainage_systems.php (http://icesat4.gsfc.nasa.gov/cryo_data/ant_grn_drainage_systems.php)

Quote
Drainage divides were digitized using ArcGIS v 9.3. For the majority of the divides, the digitization was done from paper maps of the slope vectors via an Altek Datatab Pro Line puck digitizer. However, in regions where the slope vectors did not yield useful information, imagery was used as a guide. Vector maps showing the downslope maximum-gradient direction were generated from this DEM.

Drainage system divides were drawn on these maps, primary divides along major ridges, and secondary divides starting at points of interest, drawn upslope until meeting a primary divide or another secondary divide. The drainage systems and sub-systems include all basins and sub-basins in each.

The drainage system outlines used here are defined in WGS84 coordinates. This was ignored in this work, and the coordinates were treated as if they were Topex coordinates. The maximum difference between Topex and WGS84 latitude occurs at a latitude of 45° and is approximately 1.37 cm.
Title: Re: what's new in Greenland ?
Post by: Laurent on December 30, 2014, 12:10:30 PM
Bad News for Florida: Models of Greenland Ice Melting Could Be Way
http://www.nbcnews.com/science/environment/bad-news-florida-models-greenland-ice-melting-could-be-way-n268761 (http://www.nbcnews.com/science/environment/bad-news-florida-models-greenland-ice-melting-could-be-way-n268761)
Title: Re: what's new in Greenland ?
Post by: A-Team on December 30, 2014, 04:47:05 PM
Quote
Models of Greenland Ice Melting Could Be Way Low

We've now covered these same two campus press releases a dozen times beginning on 15 Dec (top). Headlining Florida is odd as the climate model re-runs have not yet been performed and neither paper mentioned this topic. Ditto sled dog video.

NBC does add value with 3rd party interviews -- commenter T Scambos has been at this too for decades: "What Csatho's group has done," he said, "is truly admirable — marshaling a huge amount of data to reveal not just where, but when and how much, ice is being lost from every glacier system in Greenland."

Quote
Nukefix writes, Hmmm box-plots still for SMB, I think more research is needed to produce plots with mass-balance each year.
I chased down where this all stood back in 1998-2001. As it happens, B Csatho, the lead author of the PNAS paper above co-authored three earlier versions of Greenland surface mass balance:

Thickening of the western part of the Greenland Ice Sheet.
R Thomas, B. Csatho, S. Gogineni, K. Jezek, and K. Kuivinen.
Journal of Glaciology 44: 653-658 1998 http://www.igsoc.org:8080/journal/44/148/igs_journal_vol44_issue148_pg653-658.pdf (http://www.igsoc.org:8080/journal/44/148/igs_journal_vol44_issue148_pg653-658.pdf)

Mass Balance of the Greenland Ice Sheet at High Elevations
R. Thomas, T. Akins, B. Csatho, M. Fahnestock,  P. Gogineni et al
Science 21 July 2000: DOI: 10.1126/science.289.5478.426 (registration req'd)

Greenland Ice Sheet: High-Elevation Balance and Peripheral Thinning
W. Krabill et al
Science 21 July 2000 http://www.uio.no/studier/emner/matnat/geofag/GEO4420/h06/undervisningsmateriale/papers/Krabill.pdf (http://www.uio.no/studier/emner/matnat/geofag/GEO4420/h06/undervisningsmateriale/papers/Krabill.pdf)

Mass balance of higher-elevation parts of the Greenland ice sheet
R. Thomas, B. Csatho, C. Davis, C. Kim, W. Krabill, S. Manizade, J. McConnell  and J. Sonntag
JGR 106 707-33,716 2001 http://onlinelibrary.wiley.com/doi/10.1029/2001JD900033/pdf (http://onlinelibrary.wiley.com/doi/10.1029/2001JD900033/pdf)
Title: Re: what's new in Greenland ?
Post by: Espen on December 30, 2014, 05:07:35 PM
As I think I have mentioned some times before, I believe more interest, for reasons, is now centering around the situation at Zachariae (Shfaqat A. Khan from DTU Space) , where there is big changes ahead this map below (from the new studies) shows how big the catchment area is compared to other more prominent places:
Title: Re: what's new in Greenland ?
Post by: Laurent on December 30, 2014, 05:30:01 PM
Hello Espen,

What did you say is the flow of ice of zachariae compare to Jakobshavn ?
Title: Re: what's new in Greenland ?
Post by: Espen on December 31, 2014, 10:11:58 AM
Hello Laurent,

I have mentioned the great changes seen at Zachariae since the early 2000s, and I expect far more to come in the next few years, probably a retreat of 25 - 50 km from the current position:

https://forum.arctic-sea-ice.net/index.php/topic,400.msg14600.html#msg14600

https://forum.arctic-sea-ice.net/index.php/topic,400.msg11377.html#msg11377
Title: Re: what's new in Greenland ?
Post by: A-Team on December 31, 2014, 11:00:18 AM
It's a good idea not to mix up the overall Zachariae basin with NEGIS, the Northeast Greenland Ice Stream that, today, provides almost all the ice passing through the flux gate near Zachariae's calving front.

NEGIS is the only feature of its type on Greenland. It is narrow, fast-moving and completely lacking in contributing tributaries due to its sharp shear walls, often attributed to an elevated geothermal gradient in the bedrock below the summit ridge. Three important field studies on upper NEGIS were published this summer -- those results have been reviewed multiple times on other forums.

The other 85% of the iceshed draining to Nioghalvfjerdsfjorden or Zachariae may be waking up as well but at this point is still in slow motion and not contributing much quantitatively to ice discharge.

Even though 79N seems like too far north to play an early role in Greenland's contribution to sea level rise, two other factors come into play: warming of the Fram Strait seas (which may have more dramatic climatic consequences than more southerly Baffin Bay) and markedly less net snow accumulation NE of the summit ridge (which means more pronounced ice sheet thinning and so faster discharge). So I'm on the same page with Espen in terms of this area's importance.

However to predict the near-term future with any degree of reliability, we need to have a better factual understanding of basal and englacial conditions under this sector of Greenland. Until that arrives, it's worth looking at various models (and their conflicts with received wisdom).

Figures below adapted from a 2012 Aschwanden paper (http://www.iac.ethz.ch/doc/publications/andy3.pdf (http://www.iac.ethz.ch/doc/publications/andy3.pdf)) treating latent heat in temperate ice ('enthalpy') are used in the blockbuster AGU 2014 ePoster of Sommers above that provides the first 3D model of englacial temperature isotherms above the PARCA flux gate perimeter. Sommers also had access to the LAYERMAP paper, J MacGregor et al. (in revision, not yet online), Radiostratigraphy and age structure of the Greenland Ice Sheet, J. Geophys. Res. Earth Surf.

This will be a game-changer to have a 3D coordinate system of isotherms, isochrons and slope/elevation/thickness ... 2015 will be the year of foliations, principal curvatures and moving Darboux frames.
Title: Re: what's new in Greenland ?
Post by: Espen on December 31, 2014, 05:07:55 PM
A-Team,

I completely agree with you conclusion, however, my gut feeling tells me something big is on ( not very scientific though) :

"However to predict the near-term future with any degree of reliability, we need to have a better factual understanding of basal and englacial conditions under this sector of Greenland. Until that arrives, it's worth looking at various models (and their conflicts with received wisdom)." 

Happy New Year from Berlin! ;)
Title: Re: what's new in Greenland ?
Post by: A-Team on December 31, 2014, 06:26:04 PM
Quote
however, my gut feeling tells me something big is on -- though it might just be those Jägermeisters
Below is a crumpled handout that supposedly a janitor picked up after a secretive closed-door AGU14 session that predicts something big going on at Zachariae ... can you make out what it is saying???
Title: Re: what's new in Greenland ?
Post by: Espen on January 01, 2015, 01:11:08 AM
Yeah right, that's how I read it,

Espen reporting from Berlin, just came from a +1 million party, now waiting for the hang-over to arrive ???
Title: Re: what's new in Greenland ?
Post by: A-Team on January 01, 2015, 07:00:19 PM
Greenland in 3D has arrived! At least for the west central Greenland. Soon we will be able to fly through the interior enjoying the temperature display, ice velocities, colored markups of the slush, and times of deposition (thanks to a mashup of Sommers modelling and MacGregor's stratigraphy) at least for the area above the 2000 m Parca stake gate.

So far only 5 of the Parca transects have been released. They, like Cresis radargrams, come packed in a fixed sized box which forces them all to have different scales both horizontally and vertically. I resized three of them to a constant physical scale suitable for our around-the-island tour of the interior. Only 5 of the 161 slices have been released to date.

The first image finds the radar flight lines that best approximate the Parca flow lines. The second is from Sommers AGU 2014 ePoster, and the third is a fix for that. I do not yet have access to the kml files for the ice flow lines terminating at the Parca ice stakes (still offline and unpublished, 18 years and counting); their length and elevations are needed to script rescaling.

While 'just' a model, it will provide us with a concrete picture of englacial conditions. I myself would not have chosen te 2005 geothermal heat model since a suite of more recent (see above) only means more operator-unattended runs. Ditto for only using the first of the Aschwanden diagrams and skimping on basal sliding regime.

They do bring in a very significant result from MacGregor's forthcoming radar stratigraphy paper, the scalar constant in Glen's Law (enhancement factor) of 3 being said appropriate to softer pre-11 kyr ice (not to be confused with the 3 taken by convention in the exponent).

They did not simply accept the new bedrock DEM as if it were written in stone but instead looked at model sensitivity to bedrock re-sampling (adding Gaussian white noise of appropriated radius to generate equally probable bed profiles).

The 2000 m perimeter flux gate is a very good idea because it isolates the mostly orderly behavior of the main body of the ice sheet from the case-by-case situations at the ocean margins. As mentioned earlier, B Csatho hosts csv files tantamount to the Paca stake kml polygon, whose interior area then follows from an online GoogE auxillary tool and whose ice volume results from masking the thickness DEM and toting up with the ImageJ2 volume plugin.
Title: Re: what's new in Greenland ?
Post by: A-Team on January 02, 2015, 02:57:23 PM
During the 21 years of pursuit of bedrock topography, surprisingly very few flight lines followed either the Parca perimeter polygon or flowlines ending to the Parca stakes (which were placed in the ice in 1995 or so and their movement measured a year later).

However 5 segments beginning with Cresis 20130409_01_052 do follow Parca #foo7 up to the summit divide. Recall #foo7 was one of 4 examples provided in the Sommers ePoster above.

I rescaled the radar stratigraphy imagery to a depth of 2500 m which suffices to catch bedrock the entire way, then rescaled to match the temperature prediction for #foo7 (which did not go to bedrock). The image below shows, rather provisionally, the temperature isotherms overlying the stratigraphic isochrons. Ice velocity isotachs could be done as well.

All of these will need interpolating between the 161 flow lines to actually build the 3D englacial model showing these intersecting surfaces (whose principal curvatures tell almost the whole story). The only intermediate data consists of measured surface elevation and velocity, ice thickness, and the sometimes sparse radar tracks. However, after carving out upheavals, NEGIS and the SE margin, the ice above the 2000 m contour is fairly well behaved.
Title: Re: what's new in Greenland ?
Post by: A-Team on January 03, 2015, 02:50:33 PM
I located a 5th Parca flowline output graphic on the Boulder website of the ePosters. The Parca stake wasn't labelled but stated to be on west Greenland. I measured the elevation at the stake from their graphic (which is reversed relative to the others); by sorting B Csatho's stake elevation database, the mystery stake turned out to be wpo7, way to the north.

It would be a good idea to re-name the stakes more systematically and stick with upper or lower case; 'wp' -- used for 31 stakes in 2.5 drainages -- was a poor choice because kml file readers mistake it for way point which it probably meant originally.

I rescaled horizontally and vertically it to fit the west side Parca graphics above. The flow line is the longest of the set, over 400 km to the summit ridge. Distortion of the letters gives some sense of the rescalings.

 
Quote
Temperature and velocity profiles inferred by thermal flowline modeling for high elevation regions of the Greenland Ice Sheet
AN Sommers, H Rajaram,  WT Colgan
http://hydrosciences.colorado.edu/symposium/abstract_details.php?abstract_id=7 (http://hydrosciences.colorado.edu/symposium/abstract_details.php?abstract_id=7)

...Most recent changes in the surface mass balance and ice dynamics of the Greenland ice sheet have been restricted to elevations below 2,000m. Substantial computational efficiency can be gained by limiting numerical modeling efforts to this lower elevation periphery, where changes in ice sheet form and flow are most pronounced, rather than modeling the entire ice sheet from the main divide to the margin. Accurately modeling the lower elevations with this approach is dependent on prescribing accurate velocity and temperature profiles at the upstream boundary... Without corresponding velocity and temperature profiles, however, these data alone are insufficient to serve as upstream boundary conditions for lower elevation thermo-mechanical modeling.

Using a two-dimensional, enthalpy-based thermal flowline model, we generate velocity and temperature profiles across the ice sheet depth at the PARCA stake locations. While prescribing ice surface and bedrock elevation, observed surface velocities at the stake locations and the ice discharge calculated from surface mass balance serve as modeling targets. We employ an iterative procedure between mechanical and thermal calculations; ice velocities found by solving the momentum equation (via the Shallow Ice Approximation, which is valid for these high-elevation domains) inform the energy equation to solve for temperature and liquid water content, which then inform the velocity calculations, and so on until convergence.

Preliminary results suggest that observed surface velocities in some regions of Greenland can only be reproduced with a temperate bed at high elevations...
Title: Re: what's new in Greenland ?
Post by: A-Team on January 05, 2015, 01:58:18 PM
The graphic below shows that the Parca stake boundary at ~2000 m served as a Cresis ice penetrating radar flight line in multiple years. This means a continuous radar 'curtain' could be constructed from the surface down to bedrock around the entire perimeter.

Unfortunately flights up the flow lines through the flux gate stations were never a specific goal and are rarely available as noted above, that stratigraphy can be filled in by interpolation from nearby (oblique) tracks.

Jakobshavn is an especially favorable case because of gridded 2008 flight coverage including the Parka flux gates and continuing ~200 km up towards the summit. Some of these could be 'held back' to test the accuracy of interpolation schemes. However this is a plain vanilla layer cake region of the ice sheet so would not validate the procedure for more complex sites with upheaval features.
Title: Re: what's new in Greenland ?
Post by: A-Team on January 06, 2015, 02:04:53 PM
I located a set of Cresis ice penetrating radar scenes that furnish a curtain around the whole island at the 2000 m Parca stake perimeter. Actually, as shown below, that perimeter was only nominally at 2000 m -- it varied from 1637 to 2878 averaging 2164 m (sd dev 358), I suppose to avoid crevasses and exposed rock.

These are not so easy to combine into a single image as they come from different years and are of vastly different scales and resolution -- not to mention gigantic image dimensions if all tiled up together. Perhaps LAYERMAP will provide a convenient way of this in terms of lines of dated stratigraphy.

At the time the Parca stakes were placed, there was not comprehensive information available on ice thickness or depth to bedrock. Today, we might choose the perimeter along a contour of equal driving stress, which amounts to thickness and density profile of the ice adjusted for buttressing slope.

Everything being the same, it will take quite a few iso's from geology, geometry, meteorology, glaciology, and related fields to describe the various substructures of englacial Greenland. These include isobar, isobathytherm, isocaloric, isocheimal, isochor, isochron, isoclinal, isocontour, isocurvature, isodensity, isodiabatic, isodiffusivity, isodrosotherm, isoelastic, isoelectric, isoenergetic, isoenthalpic, isogeotherm, isohel, isohyet, isointensity, isokinetic, isomagnetic, isometric, isopach, isophot, isopleth, isopotential, isopycnal, isospectral, isostasy, isostress, isosurface, isotach, isothere, isotherm, isovelocity, isoviscous, isovolumetric.

Here are the specific scenes needed from Cresis for the Parca curtain: it is easy to build out the urls from https://data.cresis.ku.edu/data/rds

20100513_04_004_2echo_picks.jpg   19970521_01_024_2echo_picks.jpg   19950524_01_003_2echo_picks.jpg
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Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on January 06, 2015, 11:36:37 PM
Applegate et al 2014:
http://link.springer.com/article/10.1007/s00382-014-2451-7 (http://link.springer.com/article/10.1007/s00382-014-2451-7)

Abstract
"Damages from sea level rise, as well as strategies to manage the associated risk, hinge critically on the time scale and eventual magnitude of sea level rise. Satellite observations and paleo-data suggest that the Greenland Ice Sheet (GIS) loses mass in response to increased temperatures, and may thus contribute substantially to sea level rise as anthropogenic climate change progresses. The time scale of GIS mass loss and sea level rise are deeply uncertain, and are often assumed to be constant. However, previous ice sheet modeling studies have shown that the time scale of GIS response likely decreases strongly with increasing temperature anomaly. Here, we map the relationship between temperature anomaly and the time scale of GIS response, by perturbing a calibrated, three-dimensional model of GIS behavior. Additional simulations with a profile, higher-order, ice sheet model yield time scales that are broadly consistent with those obtained using the three-dimensional model, and shed light on the feedbacks in the ice sheet system that cause the time scale shortening. Semi-empirical modeling studies that assume a constant time scale of sea level adjustment, and are calibrated to small preanthropogenic temperature and sea level changes, may underestimate future sea level rise. Our analysis suggests that the benefits of reducing greenhouse gas emissions, in terms of avoided sea level rise from the GIS, may be greatest if emissions reductions begin before large temperature increases have been realized. Reducing anthropogenic climate change may also allow more time for design and deployment of risk management strategies by slowing sea level contributions from the GIS."

Supplementary material:
http://link.springer.com/content/esm/art:10.1007/s00382-014-2451-7/file/MediaObjects/382_2014_2451_MOESM1_ESM.pdf (http://link.springer.com/content/esm/art:10.1007/s00382-014-2451-7/file/MediaObjects/382_2014_2451_MOESM1_ESM.pdf)

GIS could be gone in three centuries, it seems, if we keep forcing it hard enough.
Title: Re: what's new in Greenland ?
Post by: A-Team on January 07, 2015, 02:23:03 PM
The authors have chosen to bury their publication behind the largest paywall I have ever seen, declining the open access option. Instead of doing science, grant money is going to this. Very few universities can subscribe to this journal -- and a personal subscription is unheard of. Has anyone in the history of the universe ever paid $39.95 for an itty-bitty pdf?

The article seems directed to policymakers but these people won't have access at all, much less read about scenarios 300 years in the future, much less take action based on what somebody says is revealed by many runs of complex model code.

For blog suitability (everyone has google abstract alerts), readers here need to not only have access but some ability to replicate the results locally (doable on a desktop) or at least look under the hood at the long list of underlying assumptions and simplifications. And I don't mean commented code with that.

The question to ask about these sweeping models of Greenland is: what exactly do they descend to, in terms of predictions or assumption, about particular glaciers in coming years? I don't doubt that Greenland will melt out on the course the planet is on but where are the testable predictions here? That means next 5-10 years, not 300.

Greenland cannot be taken as one big ice sheet -- it can only be understood as the sum of individual glacial parts. And these have very heterogeneous behavior indeed, for example very little seasonal synchronicity. Englacial melt lakes and re-frozen blobs in the firn -- good luck modelling the consequences of that even this coming year.

We've been struggling mightily, even with great access to Landsat8 and Sentinel data, to understand what happened to Jakobshavn, Zachariae, Petermann etc in summer 2014. How could these guys go out to 2314? Could I actually learn how much Jakobshavn will accelerate even in 2015 from taking apart their models?  I sincerely doubt it.

What happens three years from now at Jakobshavn when the calving front retreats past the Big Bend resistance and then the entrance of the first sub-stream? Do they incorporate the speed-up in their 300 year model? I sincerely doubt it.

Let's look at an open source article published the same day concerning the Store Glacier. It's very well-written and provides clear explanations, diagrams and discussion of the future consequences of the one-off (aren't they all) geometry of the Store sill, stoss-side stress, buttressing, throttling and ice convergence.

J Todd and P Christoffersen
http://www.the-cryosphere.net/8/2353/2014/tc-8-2353-2014.pdf (http://www.the-cryosphere.net/8/2353/2014/tc-8-2353-2014.pdf)
Are seasonal calving dynamics forced by buttressing from ice mélange or undercutting by melting?

I've always wondered about sub-stream convergence at Jakobshavn (that is, wondered why it was never discussed). The fast branch is only contributing a third of the calving front width. How are the two main side streams brought up to a common speed where they come in, does not this generate a truly massive amount of frictional heat, how is the extra volume accommodated given steep bedrock variance underneath and incompressibility of ice without giving rise to an overt surface feature?

The authors wonder too about this absence of prior discussion and respond with a Stokes model term to amend it in section 3.3:
Quote
This convergence term represents an important 3-D effect, ensures that mass balance is maintained throughout the model domain, and allows for realistic evolution of mass and momentum near the terminus. We note that this prescribed flux convergence differs from implementation of flow convergence in earlier work with flow line models, where the additional mass is added as an input to the surface mass balance. Although the latter will result in correct flux, it neglects the direct effect of the additional flux on the velocity field and may consequently underestimate velocity change while overestimating elevation change.
Title: Re: what's new in Greenland ?
Post by: sidd on January 07, 2015, 09:34:36 PM
The mechanism is interesting, i speculated a few years ago that steepening slopes would increase driving stress, the authors seem to agree.

Applegate(2014):
" ... small to moderate increases in surface temperatures result in a progressive and accelerating surface lowering near the ice sheet margins (Born and Nisancioglu 2012), which steepens ice surface slopes near the margin of the ice sheet. This steepening increases the driving stress, which speeds ice flow into the ablation zone and generates a wave of thinning that propagates toward the central parts of the ice sheet (Huybrechts and de Wolde 1999; Parizek and Alley 2004)."

I enclose a copy of Fig 2a, showing the decrease in e-folding time with global average temperature increase.

For those who want a copy call or email the corresponding author: patrick.applegate@psu.edu
at Penn State. Or call Alley, he is on the paper, and quite responsive.

Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on January 08, 2015, 05:41:46 PM
Applegate et al 2014 assumes a polar amplification factor of 1.5 for Greenland, with a range up to about 2. See their fig.2 attached below.

But could this factor not be significantly higher? Say up to 3 or even 4? See for example fig.3a in Masson-Delmotte et al 2006 (also attached below):
http://pubs.giss.nasa.gov/docs/2006/2006_MassonDelmotte_etal_1.pdf (http://pubs.giss.nasa.gov/docs/2006/2006_MassonDelmotte_etal_1.pdf)

Or would that imply lower global mean warming? Does anyone have more (recent) info about potential polar amplification factors?
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on January 08, 2015, 08:29:48 PM
Just wondering if for example Brigham-Grette et al 2013 could be reason to assume the possibility of an amplification factor of maybe 2.5 to 3:
http://www.researchgate.net/profile/Volker_Wennrich/publication/236872407_Science-2013-Brigham-Grette-science.1233137/links/00b7d519c6bd6f3c93000000 (http://www.researchgate.net/profile/Volker_Wennrich/publication/236872407_Science-2013-Brigham-Grette-science.1233137/links/00b7d519c6bd6f3c93000000)

Maybe not, but if so, then even 3-4C global warming could possibly cause very rapid deglaciation of GIS, it seems.

From a risk perspective we should maybe need to take a risk into account of almost full deglaciation within 5-7 centuries in such a case? Average discharge could then be 1-1.4m per century, with peak discharge maybe up to 1.5-2 meters in a century?

I speculate that the first 1-2m SLR-contribution from GIS could be discharged at faster speed than the next 5-6m, because the forcing would be strongest in the beginning and the most vulnerable, marine based ice would go first, together with the most vulnerable non-marine based ice.

So peak discharge over a century, say from 2100-2200, could be some more than the average over full deglaciation, I suppose.

Or would that not be a plausible line of reasoning?
Title: Re: what's new in Greenland ?
Post by: sidd on January 08, 2015, 08:34:00 PM
Polar Amplification from IPCC AR5 Fig 12.41 attached. 2 looks better than 1.5 for Greenland

sidd
Title: Re: what's new in Greenland ?
Post by: sidd on January 08, 2015, 08:47:48 PM
In the previous post, I should have written, 2 looks better for the zonal mean and 1.5 for Greenland. Personally, I think both those numbers are optimistic. The projected amplification is already huge for the peripheral ice shelf northwest of GRIS

sidd
Title: Re: what's new in Greenland ?
Post by: AbruptSLR on January 09, 2015, 01:48:45 AM
The link leads to an article about GISS measured global temperatures that includes the attached 2008-2012 temperature change map that shows measured Arctic Amplification around Greenland.

http://www.giss.nasa.gov/research/news/20130115/ (http://www.giss.nasa.gov/research/news/20130115/)
Title: Re: what's new in Greenland ?
Post by: Martin Gisser on January 09, 2015, 03:10:28 PM
Quote
2015 will be the year of foliations, principal curvatures and moving Darboux frames
Holla! Differential geometers to Greenland! While I'm not into data crunching, I'd love to see some details of this real application of diff. geometry.

A propos: How is the melt data doing? I'm actually just interested in a sum of 3-4 exponential functions (summing the different melt basins) to extrapolate the Greenland melt trend and the ensuing sea level rise -- just like wipneus's famous sea ice melt trend graphs. (The Frobenius theorem applied to foliated ice can wait.) Some years back my back-in-the head exponential estimamate was 1-2m SLR by 2100 from Greenland. Gavin was shocked ("that would be catastrophic"). Is there meanwhile enough data to justify a more elaborate graph, something to become wipneus' other world-famous graph, updated every year? It would be a "terrific" service for the lay audience.
Title: Re: what's new in Greenland ?
Post by: A-Team on January 09, 2015, 06:10:08 PM
 
Quote
Differential geometers to Greenland! While I'm not into data crunching, I'd love real application of diff. geometry.
Martin, that's fantastic to hear some interest in this! A day or two delay before I can back to you on melt and sea level rise.

I am planning to start a separate forum for 'Englacial Greenland or maybe 'Greenland in 3D + T' the very minute two key papers from AGU2014 become available. These would be the MacGregor database LAYERMAP of 21 years of radar stratigraphy and the Sommers PARCA flow lines from the summit. Lots of the forum will be coverage of published papers, no math for math's sake.

It seems to me we initially find ourselves not only in low dimensions but also strictly concerned with a specific embedding in R3xT so that much of the fancy geometry after Gauss/Riemann is either not applicable or collapses to something more familiar. There are some tensor bundles in the picture but no real topology; I'm not sure yet about a significant role for connections; for Lie groups, just SO(3), no finite groups really, but maybe dilational symmetry for time behavior of isochrons.

I am interested in efficient analytic expressions that keep track of these intersecting surfaces to replace pixel arrays. The main nuance here is catching layer deformation over bedrock. I don't anticipate too much along the lines of singularities or even complications like umbilical points.

Picking 3 foliations, say isotherm, isochron and isostress, they are going to intersect in a lattice. The main idea is a coordinate system may exist in which the Navier-Stokes equation is well-behaved (as an expression of conservation laws, aka symmetries, Noether). Developing the ice sheet on in lattice coordinates will then be vastly more computationally efficient. At any rate, saying goodbye to xyz numerical approximation theory and crunching of tesselation meshes.

This has to kept accessible to everyone who happens by. And that can only be done with pictures, we are not a math forum. However intuitive visualizations not only become more difficult to make with open source software, but also to share within the confines of the blog  (eg, no 3D interactive mousing).

So, one step at time, let's see how far it gets.

Meanwhile, take a look at this amusing piece at wikipedia -- it may come in handy for Greenland ice: https://en.wikipedia.org/wiki/Streamlines,_streaklines,_and_pathlines (https://en.wikipedia.org/wiki/Streamlines,_streaklines,_and_pathlines) 

Did you ever see this thesis by Ed Boring on "Visualization of tensor fields". It gets pretty good toward the end.
http://www.ann.jussieu.fr/frey/papers/scientific%20visualisation/Boring%20E.,%20Visualization%20of%20tensor%20fields.pdf (http://www.ann.jussieu.fr/frey/papers/scientific%20visualisation/Boring%20E.,%20Visualization%20of%20tensor%20fields.pdf)
Title: Re: what's new in Greenland ?
Post by: Martin Gisser on January 09, 2015, 07:07:27 PM
Hi A-Team, thanks! Will have a look at the Boring thesis Sunday night. I've studied stricly pure mathematic and as a hobby horse am currently putting Riemannian calculus on it's feet (physicist abstract index calculus with abstract indices replaced by uncompromising abstract multilinear algebra, plus doing the LeviCivita on cotangent space with a new fundamental lemma of Riemannian Geometry working with differentials...).

While I have a keen interest in physics I have always hated physicist math. The only thing I get is Einstein's field equation in vacuum :-). In geometry I even hate most of the mathematicians math, so I do my own tensor calculus now, so I can translate lots of superfluous mess to fit my low-IQ brain.

So, I am a total newbie to applied math and numerics (except that I've written the world's first raytracing graphics for toy computers of the 1980ies and attended a boring Fortran numerics class in the 1990ies). But maybe here's a point of entry. I hope this year to get a job as farm hand, to keep my brain power for myself to learn and work out some interesting stuff.

Another thing I want to extend this year is statistics (mostly for energy markets incl. grid balancing). Methinks for modelling of greenland ice dynamics this is as important as differential geometry. Alas I bet mostly Poissonian cracking and flushing. Apropos, my main subject of study in the 1990ies was stochastic diff. geom. i.e. Brownian motion. I have a purely abstract hunch (dream) this could help in numerics.
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on January 13, 2015, 08:41:33 AM
New paper by Smith et a 2015 on Greenland drainage:
http://www.pnas.org/content/early/2015/01/07/1413024112.full.pdf+html (http://www.pnas.org/content/early/2015/01/07/1413024112.full.pdf+html)
Title: Re: what's new in Greenland ?
Post by: Martin Gisser on January 13, 2015, 04:33:39 PM
New paper by Smith et a 2015 on Greenland drainage:
http://www.pnas.org/content/early/2015/01/07/1413024112.full.pdf+html (http://www.pnas.org/content/early/2015/01/07/1413024112.full.pdf+html)
Video interview and some spectacular scenes from 2012 melt: http://www.latimes.com/science/sciencenow/la-sci-sn-catastrophic-greenland-melt-20150112-story.html (http://www.latimes.com/science/sciencenow/la-sci-sn-catastrophic-greenland-melt-20150112-story.html)

From paper abstract:
Quote
Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056–0.112 km3⋅d−1 vs. ∼0.103 km3⋅d−1), and when integrated over the melt season, totaled just 37–75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean.
Open question: Duration of this
Quote
nontrivial subglacial water storage
Title: Re: what's new in Greenland ?
Post by: A-Team on January 14, 2015, 12:55:57 AM
Unexpected outcome from the new 0.5 m WorldView academic license:

Quote
The mapped river channels only nominally followed topographic relief, often breaching ice divides. Runoff flowing to lower elevations did not first fill topographic depressions, contrary to a key assumption of terrestrial watershed models, that depressions must fill with meltwater before overtopping

Quote
Martin writes my main subject of study in the 1990ies was stochastic differential geometry, Brownian motion
Did you ever do anything with Ricci flow? It is like the heat equation only for diffusing the metric tensor. I wish there was more 19th century math online -- what was Ricci's physical motivation? Nice treatment at wiki: https://en.wikipedia.org/wiki/Ricci_flow. I have been thinking about the z in ice xyz ... seems like height is a start on a natural metric (leading to driving stress) but then over a 450 km flow line, that subtends quite an angle on S2 so really should be using r. Then the Bouguet gravity varies quite a bit too, so much for a simple ice weight calc.

I'd say my top visualization priority is  of invariants of the deviatoric stress tensor. We need an intuitive exposition with simple pictures like the one the Brazilian prof wrote for the strain rate tensor. https://en.wikipedia.org/wiki/Strain_rate_tensor  See also https://en.wikipedia.org/wiki/Cauchy_stress_tensor
 
There is a very low level of pathology in the otherwise nice ice layering. The case below shows the oldest consistently traceable triple that we know from NEEM are ~85,000 years old. These are hugely important to the study of paleo-stability of the Greenland ice sheet.
Title: Re: what's new in Greenland ?
Post by: Martin Gisser on January 14, 2015, 02:50:46 AM
Hi A-Team, thanks for the fascinating images!

What are these vertical white blurred stripes? Moulins? In the video interview on the paper mentioned above it was said the GIS is "Swiss cheese". Are there any radar images/sections where the cheese holes (moulins) are visible?

----------------
On Ricci flow: I haven't yet looked into the hard technical details. (The soft stuff, like evolution of curvature, is a paradigmatic example of mathematicians tensor calculus mess where you waste 90% of your IQ...) Why Ricci invented his tensor is a bit messy. He certainly wasn't thinking about Hamilton's Ricci flow or Einstein's field equation. Looks like Ricci wasn't even aware of the geometric meaning of the Ricci tensor: It is the quadratic approximation of the volume form - just like Riemann curvature is the quadratic approximation of the metric - in normal coordinates. Ricci flow looks like heat flow but is a very difficult nonlinear PDE that can blow up. (It took a crazy genius like Perelman to get the final knack.) Brownian motion may be of some use there, but extremely technical: diffusion on infinite dimensional (path) space.

------------------
Hmmm... so you are looking for some Riemannian metric for the ice sheet? And perhaps the best one could be approximated by Ricci flow? As I said me dunno anything almost of elasticity/fluid physics. But like to get there.

(Ha! My most reality based life dream is to find and marry a rich farmer girl and open a carbon negative dairy cow farm on Greenland. No kidding.)
Title: Re: what's new in Greenland ?
Post by: Neven on January 14, 2015, 07:56:40 AM
Thanks for making me feel stupid, guys.  ;D
Title: Re: what's new in Greenland ?
Post by: icefest on January 14, 2015, 01:01:59 PM
Thanks for making me feel stupid, guys.  ;D
I feel the same.
The more I learn the stupider I feel.
Title: Re: what's new in Greenland ?
Post by: A-Team on January 14, 2015, 02:34:01 PM
Neven/Icefest, don't worry, this will end up reading like a comic book. We are just thrashing around trying to figure which 0.00001% of modern geometry is applicable.

Martin, I have not see moulins in radar yet. The horizontal resolution of the main radar program is typically 1000 pixels for 50 km so a pixel column represents 50 m. The flight tracks are also fairly sparse. The moulins are mostly found south-centrally below the 2000 m contour, not the region with the most interesting radar stratigraphy. Snowmobile-drawn radar might have better resolution but they would not knowingly drive over a snow covered moulin.

So, to answer your question, personal drone radar can fly a tight 5 m grid but it has not yet been deployed in Greenland for this purpose (as far as we've been told). There must be quite a network of new and old moulins but there may not be enough contrast for them to stand out. If a barrel of sea salt had been added to the melt lake -- and the moulin water refroze in place -- that might provide enough dielectric.

Radar unfortunately does not go straight down like a focused laser beam; the return signal has reflected to various extents off everything in a fairly wide cone, so even if they chop to specified return times expected for a given reflector depth, other things can contribute, beyond what is directly below at that depth. So a 1-pixel vertical column is not fully separated from its adjacent pixels in some information-theoretic sense.

The worst-case scenario -- the white vertical flares that you see in the Petermann radar scan above -- arise from steep bedrock topography which the radar is striking obliquely; the slope is adding too much backscatter. The question is, since they are determining this topography on the fly, why don't they use it in buffered real time to dial back the flare where it is anticipatable?

They'll say it comes down to unfavorable signal to noise ratio. I'm not thrilled with that answer because it implies, wrongly, that the flare can't be reduced at all by after-the-fact digital imaging enhancement (photoshopping). Here adaptive (locally defined) contrast adjustment as in ImageJ2 can help with tracing stratigraphy layers continuously through the flares.

The imagery was never despeckled properly either. The whole 21 year Cresis archive needs to be reprocessed. I presume that was done in the course of developing the LAYERMAP dbase.

The backstory here: radar was initially tasked with just getting the bedrock topography and locating the oldest ice (flat deep thick isochrons along summit ridge). The electronics was optimized for that.

The goals have changed today (basal melt, isochronal surfaces, ice upheavals, englacial lakes) but the data archive has not. It is what it is; nobody is going to re-fly the grid.

The englacial radar is a seriously under-analyzed data set, maybe the worst case in the history of science. However people have caught on to the opportunities and the situation may be rectified in a year or so.

Below is a flare off a steep-walled ice upheaval (with some bedrock contribution). If these images were rescaled to 1:1, the horizontal would be ~25 x wider. They're very distorted as they stand.

This is most disturbing in the case of Greenland's so called Grand Canyon. How could they fill in the blanks between radar tracks? These are very sparse even in the most intensely surveyed regions -- even at a generous 100 m width, 98% of the tightest grid (Petermann) is completely devoid of observational data. Yet a whole lot of topography can and does happen over this 10 km gap scale. More on this shortly!
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on January 18, 2015, 12:39:56 PM
From Applegate et al 2014:
"Our ice sheet model experiments represent crudely, or neglect, many processes that are important on the real ice sheet. In particular, both of the models we apply here use the positive degree-day method for calculating surface melt. Previous studies have shown that the positive degreeday method has shortcomings relative to more-sophisticated melt calculation schemes (e.g. Braithwaite 1995; van de Wal 1996; Bougamont et al. 2007; Robinson et al. 2010; van de Berg et al. 2011). We have not explored the effects of albedo feedbacks (Robinson et al. 2012), or changes in the distribution of temperature or precipitation over the year, on our model output. However, the ranges of the positive degree-day factors that we investigated in the SICOPOLIS ensemble are quite large (Applegate et al. 2012), suggesting that we have adequately explored possible variations in melt over the Greenland Ice Sheet’s surface.

Other processes that we parameterize or neglect include surface meltwater-driven lubrication of the ice-bed interface (this process is implicitly included in the profile model simulations; Zwally et al. 2002; Parizek and Alley 2004; Bartholomew et al. 2010; Shannon et al. 2013) and the penetration of warm ocean waters into fjords, accelerating the drawdown of ice through outlet glaciers (Joughin et al. 2008; Straneo et al. 2010). Including these processes in our simulations would likely shorten our estimated e-folding times, rather than lengthen them (e.g. Parizek and Alley 2004)."
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on January 18, 2015, 02:50:29 PM
Applegate et al also say:
"It might be argued that the plausible range of temperature changes is smaller than the one we report, because some models in the CMIP5 ensemble show less skill over Greenland than others (Belleflamme et al. 2013; Fettweis et al. 2013) and thus yield temperature changes that are too high or low. However, the CMIP5 ensemble provides only a limited sampling of uncertainties associated with model parameter values and initial conditions, which can be substantial (e.g. Stainforth et al. 2005; Deser et al. 2012; Olson et al. 2013). Thus, the range of plausible Greenland temperature changes that we derive from the CMIP5 ensemble might be too narrow, rather than too wide. Climate model calibration (e.g., Bhat et al. 2012) could help to reduce the range of plausible future temperature increases; such a calibration is beyond the scope of the present study."
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on January 18, 2015, 03:00:57 PM
And their last paragraph on policy implications:
"We speculate that near-term reductions in greenhouse gas emissions could pay large dividends in terms of avoided sea level rise. Our results suggest that the relationships between temperature change, GIS response time scale, and GIS equilibrium sea level contribution are approximately exponential (Fig. 2). Thus, the benefit, in terms of avoided sea level rise contributions from the GIS, of a unit of avoided emissions is greatest if emissions reductions are begun before much temperature change has already happened. Alternatively, one could say that mitigation becomes less effective in preventing or delaying sea level rise contributions from the Greenland Ice Sheet as temperature rises. Near-term reductions in greenhouse gas emissions may also buy time to design and implement improved strategies for adapting to sea level change."
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on January 18, 2015, 06:49:50 PM
From Todd & Christoffersen 2014 on Store Glacier, linked by A-Team earlier:
"Inland of Store’s stable frontal pinning point is a 28km long overdeepening reaching 950m below sea level (Fig. 2), which could make Store susceptible to sudden retreat, i.e. if the terminus becomes ungrounded from its current pinning point at 113km. We found that, by forcing the model with unphysically large values for submarine melt rate (not shown), we were able to force the terminus back off its pinning point, which led to rapid retreat through this trough. However, none of our climate forcing scenarios were able to trigger such a retreat, which suggests that the current configuration of Store is stable and will most likely remain so in the near future... Our model excludes the effect of water in surface crevasses, which may conceivably affect calving due to hydrofracture if water levels are high (Benn et al., 2007a). Although recent work included this effect (Nick et al., 2010), we ignore it because high-resolution images captured in repeat surveys of Store with an unmanned aerial vehicle in July 2013 detected water in only a small number of surface crevasses near the terminus (Ryan et al., 2014).Although we cannot exclude the possibility that undetected water is contributing to crevasse penetration, it is not necessary to invoke this process to explain the observed behaviour of Store."

So if in the future more melt water on the glacier would cause hydrofracture, calving may increase and maybe less (submarine) climate forcing is needed for the terminus to become ungrounded from its pinning point, possibly leading to rapid retreat.
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on January 18, 2015, 10:57:00 PM
I think this has been posted earlier in one of the Greenland threads, but for a good overview of the many marine based GIS-glaciers see (again) the supplement to Morlighem et al 2014:
http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf (http://www.nature.com/ngeo/journal/v7/n6/extref/ngeo2167-s1.pdf)

They find more vulnerable (marine based) ice then estimated before.
Title: Re: what's new in Greenland ?
Post by: A-Team on January 21, 2015, 07:00:12 PM
Big news conference coming up tomorrow, Thursday 21 Jan 15. It involves the long-awaited paper by JA MacGregor sorting out 21 years the radiostratigraphic age structure of Greenland. There will be a press release from U Texas and simultaneous release of a sophisticated narrated animation by NASA Visualizations.

This is a huge breakthrough for Greenland glaciology and I'll be cross-posting about it for the rest of the month, mostly over at the Greenland subglacial topography forum.

The paper was released yesterday  in the 'reviewed, accepted" section of the Journal of Geophysical Research Earth Surface. The doi:10.1002/2014JF003215 is paywalled but the three animations are freely available from journal supplemental.
 
Alternatively, you can download an open source .zip file containing the 37 page article pdf, its 13 figures and 3 mp4 animations courtesy of the lead author. Getting the full 285.8 MB file to download caused me some esoteric unpacking grief in Chrome and Firefox but Safari worked right away. Below I've explained a few things in brackets and trimmed down the text:

283MB  ftp://ftp.ig.utexas.edu/outgoing/joemac/gris_strat_rev2.zip folder of pdfs

Quote
Radiostratigraphy and age structure of the Greenland Ice Sheet
JA MacGregor, MA Fahnestock, GA Catania, JD Paden, S Goginen, SK Young, SC Rybarski, AN Mabrey, BM Wagman, M Morlighem

We present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by U Kansas between 1993 and 2013 [2014 added very little]. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflector slope from the phase recorded by coherent radars. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet.

When integrated along-track, these slope fields predict the radiostratigraphy and simplify semi-automatic reflection tracing. The stratigraphy was dated via synchronized depth–age relationships for the six deep Greenland ice cores [Camp Century, NEEM NGRIP, GRIP, GISP2, DYE3].

Additional reflections were dated by matching reflections between transects and by extending depth–age relationships using the local effective vertical strain rate [see http://gravity.ucsd.edu/pub/2004_elsberg.pdf (http://gravity.ucsd.edu/pub/2004_elsberg.pdf)].

The oldest reflectors (Eemian) are found mostly [but not entirely] in the northern part of the ice sheet. Reflections do not conform to the bed topography within the onset regions of fast-flowing outlet glaciers and ice streams. Disrupted radiostratigraphy is also observed in a region north of NEGIS that is not presently flowing rapidly.

Dated reflections are used to make a 3D gridded age product for the ice sheet and to determine the depths of key climate transitions that were not observed directly.

They are not calling it LAYERMAP any more -- that name is being reserved for a forthcoming project in Antarctica. The database of grids and traced reflections are headed to the NSIDC repository but they're not posted yet. However you can download them for now from the two ftp sites below. 

[I don't recommend these links. Better to wait a week for NSIDC to host urls and final data revisions].
1.5GB  ftp://ftp.ig.utexas.edu/outgoing/joemac/Greenland_radiostratigraphy.mat crashes Octave, should open QGIS
2.4GB  ftp://ftp.ig.utexas.edu/outgoing/joemac/Greenland_age_grid.nc opens in QGIS and Pandora

The raw layer data is in MATLAB HDF5 (for which you do not need $matlab). Due to gaps in layer tracing, this data may be split into multiple divisions which do not exactly correspond to CReSIS frame numbers. However you can go to the appropriate Cresis frame using the provided GPS time.

The layer data include the age that we assigned to the layer which from either from the 6 main drill cores or quasi-Nye strain law dating (Nye was a 1950's contemporary of Glen). For an example of the internal notation, gris_strat.campaign(17).segment(110).division(1) maps to Cresis 20110506_01 along the northwestern ice divide.

The age volumes and depths of specific isochrons -- obtained by IDW (inverse distance weighting) which they are calling kriging -- are in NetCDF. It's most convenient to view .nc files in Panoply freeware -- I gave the link a couple days back. The normalized age volume (age_norm) is the age of 25 thickness-normalized depths throughout the ice sheet. The isochron depths (depth_iso) include 11.7, 29, 57 and 115 kyr bands.

I've attached Fig3d -- a spectacular enhancement coming off NGRIP.
Title: Re: what's new in Greenland ?
Post by: AbruptSLR on January 21, 2015, 10:40:26 PM
The linked reference (with an open access pdf) documents that two subglacial lakes suddenly drained (see attached image) beneath the GIS (that had previously been stable for at least decades), indicating that the GIS is sensitivity to climate change:

Howat, I.M., C. Porter, M.J. Noh, B.E. Smith, S. Jeong, Brief Communication: Sudden drainage of a subglacial lake beneath the Greenland Ice Sheet, The Cryosphere, 9,103-108, doi:10.5194/tc-9-103-2015

http://www.the-cryosphere.net/9/103/2015/tc-9-103-2015.html (http://www.the-cryosphere.net/9/103/2015/tc-9-103-2015.html)

Abstract. We report on the appearance of a 2 km wide, 70 m deep circular depression located 50 km inland of the southwestern margin of the Greenland Ice Sheet that provides the first direct evidence for concentrated, long-term storage, and sudden release, of meltwater at the bed. Drainage of the lake may have been triggered by the recent increase in meltwater runoff. The abundance of such lakes and their potential importance to the ice sheet's hydrologic system and flow regime remain unknown.

See also:
http://www.cbsnews.com/news/the-case-of-greenlands-disappearing-lakes/ (http://www.cbsnews.com/news/the-case-of-greenlands-disappearing-lakes/)
Title: Re: what's new in Greenland ?
Post by: werther on January 21, 2015, 11:41:16 PM
Thanks, ASLR. I think I located the little bastard on the 10072012 MODIS tile in my CAD-grid. It is high up in the bare ice slope, about 8 km from the snow-line further up. From that line upwards, the melting snow slope continued for another 70 km. G.Earth indicates a height of 1850 m1 for the 'dry' snow line. The 'little bastard' lies on 1350 m1 asl.
On MODIS there are lots of features like that.
I remember one of the posters on the blog having suggested that these 'swiss cheese' moulins could deliver a lot of dynamic warmth to the whole ice sheet depth. At the time, I suggested there could be a time when we may witness karst-like collapses. In this article I read a sort of confirmation. This could be a beginning.
Title: Re: what's new in Greenland ?
Post by: sidd on January 22, 2015, 03:56:27 AM
Re:MacGregor(2015)

small warning:
the nc file is 2.4 gig and the mat file is 1.5 gig. the first opens fine is qgis and is fascinating. octave crashes and burns on the latter. qgis should open hdf5 but i havent bothered bcoz nc is all good.

o that i had time

sidd
Title: Re: what's new in Greenland ?
Post by: AbruptSLR on January 22, 2015, 10:20:15 PM
The following reference discusses how the GIS was formed:

Bernhard Steinberger, Wim Spakman, Peter Japsen, Trond H. Torsvik, (2014), "The key role of global solid-Earth processes in preconditioning Greenland's glaciation since the Pliocene", Terra Nova, DOI: 10.1111/ter.12133
Title: Re: what's new in Greenland ?
Post by: A-Team on January 23, 2015, 03:31:34 PM
Quote
how tectonic motion northward of Greenland set the stage for ice sheet formation

True polar wander is an interesting idea, slippage relative to the mantle followed by readjustment of the rotation axis to the new moment of inertia. I have to say that a wide swath of geologists do not subscribe to the coincidence of the Iceland hot spot sitting on the center of a rifting axis. In this view, Iceland is not a conventional mantle plume (a slippery term with dozens of published definitions), has produced no track of islands like other hotspots, was never under Greenland influencing its geothermal regime, and indeed is unsuitable for inclusion inthe hot spot coordinate reference system.

The closing of the Panama Strait at 2.5 myr end-Pliocene is the 800 lb gorilla here in terms of oceanic circulation -- there had to have been massive consequences, along the lines of Tasman Strait much earlier. Note once  over-turned geology exposed at the canal was revealed by recent field work, oft-claimed discrepancies have evaporated.

The northern hemisphere goes 400 myr without significant glaciation, then a one-off closing of the straits (requiring major equatorial heat redistribution mechanisms), and right away the glaciation cycles commence. Coincidence? No thanks.

The authors here desperately needed to discuss equatorial glaciers such as Rwenzori, Kilimanjaro and the Andes that do have glaciers despite their low latitude plus all the regions in Siberia, Alaska and Canada that don't have glaciers despite Greenlandic latitudes.
Title: Re: what's new in Greenland ?
Post by: A-Team on January 23, 2015, 03:41:54 PM
Here's a youtube release of NASA's new visualization of MacGregor 2015. It comes with a voice-over narration (rather basic from our perspective).

https://www.youtube.com/watch?v=u0VbPE0TOtQ (https://www.youtube.com/watch?v=u0VbPE0TOtQ)
 
Quote
"Peering into the thousands of frozen layers inside Greenland’s ice sheet is like looking back in time. Each layer provides a record of not only snowfall and melting events, but what the Earth’s climate was like at the dawn of civilization, or during the last ice age, or during an ancient period of warmth similar to the one we are experiencing today. Using radar data from NASA’s Operation IceBridge, scientists have built the first-ever comprehensive map of the layers deep inside the ice sheet. This video is public domain and can be downloaded at: http://svs.gsfc.nasa.gov/goto?4249 (http://svs.gsfc.nasa.gov/goto?4249) [dead link]"

That link should be http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4249&button=recent (http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4249&button=recent) where much more detailed information, the text of the narration etc etc are provided. Very much worth a look. Hopefully meant as artwork, look at that same image reprocessed for isochrons.)
Title: Re: what's new in Greenland ?
Post by: Jim Hunt on January 23, 2015, 08:48:01 PM
I think the NSIDC have been plagiarising ASIF techniques! See their "2014 melt season in review (http://nsidc.org/greenland-today/)" then scroll to the bottom. The abstract is as follows:

Quote
Melt extent in Greenland was well above average in 2014, tying for the 7th highest extent in the 35-year satellite record. Overall, climate patterns favored intense west coast and northwest ice sheet melting, with relatively cool conditions in the southeast.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fnsidc.org%2Fgreenland-today%2Ffiles%2F2015%2F01%2FGrnToday_20Jan2015_Fig6b_lakes.gif&hash=a1ec572a00349bc52d319b86c9fd2263)

Title: Re: what's new in Greenland ?
Post by: A-Team on January 23, 2015, 11:02:02 PM
Below I took some screen grabs from the Goddard animation. The image shows three frames of the Greenland ice sheet slumping from the summit to the sea. This gives you some idea what models calculate but never display. It is done much better in the actual video.

The other image displays for the very first time the highly contoured subglacial thickness surfaces, starting with the usual contemporary view, followed by stripping off Holocene ice to reveal the 11.7 kyr surface, and finishing with the Eemian ice which is much more extensive than previously thought.

Again, we don't need this fancy perspective view and hopefully we can replace it soon with a higher resolution scientific grayscale, from which anyone can produce their own bump map in a few seconds. The reason for going scientific is the asymmetry: it's all but impossible to recover underlying data from a perspective.

There is some confusion here between portraying the isochronal surface by its elevation relative to sea level (or bottom of NGRIP) vs portraying its thickness, which will differ according to ± departure of bedrock topography from sea level. The former smooth surface is what you'd see in an ice core; the latter bumpy surface is wanted for gravitational driving stress.

The 'age volume' is an interesting concept. This takes any two dated surfaces and computes the volume of ice between them over all Greenland. Fitting this data to per-year volume then measures net retained accumulation over the 100 kyr available. The newtonian volume integrals can be done in Gimp simply by subtracting the two grayscale surface elevations and summing via the histogram and mean value theorem.

A good quote from lead author MacGregor:
Quote
“Prior to this study, a good ice-sheet model was one that got its present thickness and surface speed right. Now, they’ll also be able to work on getting its history right, which is important because ice sheets have very long memories.”
http://www.nasa.gov/content/goddard/nasa-data-peers-into-greenlands-ice-sheet/#.VMK3dWTF-QM (http://www.nasa.gov/content/goddard/nasa-data-peers-into-greenlands-ice-sheet/#.VMK3dWTF-QM)

This is neat quote too:
Quote
Flying over northern Greenland during the 2011 Ice Bridge season, Kirsty Tinto, a geophysicist at Lamont-Doherty, sat up straight when the radar images began to reveal a deformed layer-cake structure. “When you’re flying over this flat, white landscape people almost fall asleep it’s so boring—layer cake, layer cake, layer cake,” said Tinto, a study coauthor of Bell 2014.  “But then suddenly these things appear on the screen. It’s very exciting. You get a sense of these invisible processes happening underneath.”
MacGregor's online CV suggests two follow-up papers are coming soon. These had to await prior publication of the isochron database paper under discussion here. If they have actually been able to wring some experimental temperature data out of the radar archive, that would be huge news. MacGregor has 5 previous publications on englacial radar attenuation, mostly in Antarctica.

MacGregor, J.A., J. Li, J.D. Paden, G.A. Catania, G.D. Clow, M.A. Fahnestock, S. Gogineni,
R.E. Grimm, M. Morlighem, S. Nandi, H. Seroussi and D.E. Stillman,
Radar attenuation and temperature within the Greenland Ice Sheet,
Journal of Geophysical Research Earth Surface (same journal, in press)
 
MacGregor, J.A., W.T. Colgan, M. Morlighem, M.A. Fahnestock, G.A. Catania, J.D. Paden and S. Gogineni
Holocene deceleration of the Greenland Ice Sheet
Journal not specified  (in review)
Title: Re: what's new in Greenland ?
Post by: A-Team on January 24, 2015, 01:45:30 PM
AbruptSLR quite rightly calls our attention to one of the two Greenland lake stories that appeared Thursday, namely 'Sudden drainage of a subglacial lake beneath the Greenland Ice Sheet' which is open source at http://www.the-cryosphere.net/9/103/2015/tc-9-103-2015.html (http://www.the-cryosphere.net/9/103/2015/tc-9-103-2015.html)

The other paper -- and even its graphics -- are paywalled but Andrea Thompson wrote up a nice review at
http://www.climatecentral.org/news/surprise-lake-sheds-light-on-underbelly-of-greenland-ice-18580 (http://www.climatecentral.org/news/surprise-lake-sheds-light-on-underbelly-of-greenland-ice-18580)

It's all about heat: whether solar and atmospheric energy (meltwater) runs off harmlessly into the sea as surface rivers or efficient under-glacier tunnels, or stays behind on, in or under the ice sheet thus softening or lubricating it to faster calving (sea level rise). Since the meltwater is already at 0º C, it comes down to glacial capture (or not) of latent heat.

Quote
Abstract. In a warming climate, surface meltwater production on large ice sheets is expected to increase. If this water is delivered to the ice sheet base it may have important consequences for ice dynamics. For example, basal water distributed in a diffuse network can decrease basal friction and accelerate ice flow whereas channelized basal water can move quickly to the ice margin, where it can alter fjord circulation and submarine melt rates.

Less certain is whether surface meltwater can be trapped and stored in subglacial lakes beneath large ice sheets. Here we show that a subglacial lake in Greenland drained quickly, as seen in the collapse of the ice surface, and then refilled from surface meltwater input.

We use digital elevation models from stereo satellite imagery and airborne measurements to resolve elevation changes during the evolution of the surface and basal hydrologic systems at the Flade Isblink ice cap in northeast Greenland [81.3º latitude].

During the autumn of 2011, a collapse basin about 70 meters deep and about 0.4 cubic kilometers in volume formed near the southern summit of the ice cap as a subglacial lake drained into a nearby fjord. Over the next two years, rapid uplift of the floor of the basin (which is approximately 8.4 square kilometers in area) occurred as surface meltwater flowed into crevasses around the basin margin and refilled the subglacial lake.

Our observations show that surface meltwater can be trapped and stored at the bed of an ice sheet. Sensible and latent heat released by this trapped meltwater could soften nearby colder basal ice and alter downstream ice dynamics. Heat transport associated with meltwater trapped in subglacial lakes should be considered when predicting how ice sheet behaviour will change in a warming climate.
The first page of the article is offered by readcube, the whole article for $4. Helpfully, supplemental data is free.
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14116.html (http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14116.html)
Title: Re: what's new in Greenland ?
Post by: Espen on January 24, 2015, 02:01:36 PM
These unplugging happens now and then, there was a huge one prior to 1984 in North Greenland:
https://forum.arctic-sea-ice.net/index.php/topic,335.msg6224.html#msg6224
Title: Re: what's new in Greenland ?
Post by: Espen on January 25, 2015, 10:36:06 AM
The Steensby Depression:

The above mentioned depression / unplugging from 1984 can still be seen, if any interest we might be able to convince Wipneus to convert a landsat image from 2014 to real colors and higher resolution?

Title: Re: what's new in Greenland ?
Post by: A-Team on January 25, 2015, 01:32:49 PM
We should be paying some attention to the Dec 2014 release from the INTIMATE (INTegration of Ice-core, MArine and TErrestrial records) project. Although  committee proceedings and protocols are tediously pedantic, they do amount to careful expert review of the timing and best-practice nomenclature for the major climatic and volcanic events that show up in the Greenland ice cores (and sometimes in Antarctica's as well), and by extension explain some aspects of radar stratigraphy as pulled together in MacGregor 2015.

Quote
North Atlantic area experienced a series of dramatic climatic fluctuations known as Dansgaard-Oeschger events, during which oceanic and atmospheric conditions alternated between full glacial (stadial) and relatively mild (interstadial) conditions. Ice-core records resolve the most recent of the D-O events in sub-annual detail, and analysis of these high-resolution records suggests that fundamental atmospheric circulation changes took place in just a few years.

About 25 abrupt transitions from stadial to interstadial conditions took place during the Last Glacial period and these vary in amplitude from 5ºC to 16ºC, each completed within a few decades. The interstadials vary in duration from around a century to many millennia, with surface air temperature (as reflected in d18O values) decreasing gradually before each interstadial ended in a less pronounced but nevertheless abrupt transition to stadial conditions. The alternating pattern of stadials and interstadials is reflected in many different palaeoclimatic records from diverse archives, but is particularly clear in the Greenland ice-core records.

The first image below from Rasmussen 2014 only shows about 10% of their overall timeline, which extends back from 8-123 kyr. The table is very clumsily done in the pdf but is promised soon in xls format at the fifth link; a small part of it is shown in the second image.

The Blockley chronology focuses on tephra events of the last 8-60 kyr; these will correspond better to ice core conductivity (~radar permitivity) and so the calcium dust trace might be fitted to the MacGregor 2015 isochronal dating scheme. The 18O line could tie in to englacial temperature profiles which may have also been determined in a second MacGregor article "Radar attenuation and temperature within the Greenland Ice Sheet" caught up in peer review.

http://forum.arctic-sea-ice.net/index.php/topic,984.msg36237.html#msg36237 (http://forum.arctic-sea-ice.net/index.php/topic,984.msg36237.html#msg36237) initial chronology
http://tinyurl.com/lsn5hkk (http://tinyurl.com/lsn5hkk) Rasmussen 2014
http://tinyurl.com/opwrmw4 (http://tinyurl.com/opwrmw4) Seierstad 2014
http://tinyurl.com/k46z598 (http://tinyurl.com/k46z598) Blockley 2014
http://www.iceandclimate.nbi.ku.dk/data (http://www.iceandclimate.nbi.ku.dk/data) Data Archive
Title: Re: what's new in Greenland ?
Post by: A-Team on January 27, 2015, 09:05:08 PM
The 4th new article on Greenland paleo-tephra seems to be paywalled but I found a copy soon enough via ResearchGate, which is quite a nice way to get in touch with authors. This issue in Quaternary Science Reviews is incredibly convenient for us, coming as it does at the same time as the newly dated radarstratigraphy tied in to the same ice cores in MacGregor 2015.

If someone reading this post has a knack for extracting clean excel text files out of these nasty journal pdfs, that would be a great public service to grab the ones above and below so we have a decent searchable chronology of the Greenland ice sheet.

Quote
A tephra lattice for Greenland and a reconstruction of volcanic events spanning 25e45 ka b2k
Quaternary Science Reviews
AJ Bourne 2014
http://dx.doi.org/10.1016/j.quascirev.2014.07.017 (http://dx.doi.org/10.1016/j.quascirev.2014.07.017)

Tephra layers preserved within the Greenland ice-cores are crucial for the independent synchronisation of these high-resolution records to other palaeoclimatic archives. Here we present a new and detailed tephrochronological framework for the time period 25,000-45,000 a b2k that brings together results from 4 deep Greenland ice-cores.

In total, 99 tephra deposits, the majority of which are preserved as cryptotephra, are described from the NGRIP, NEEM, GRIP and DYE-3 records. The major element signatures of single glass shards within these deposits indicate that 93 are basaltic in composition all originating from Iceland.

Specifically, 43 originate from Grimsvotn, 20 are thought to be sourced from the Katla volcanic system and 17 show affinity to the Kverkfjoll system.

Robust geochemical characterisations, independent ages derived from the GICC05 ice-core chronology, and the stratigraphic positions of these deposits relative to the Dansgaard-Oeschger climate events represent a key framework that provides new information on the frequency and nature of volcanic events in the North Atlantic region between GS-3 and GI-12.

Of particular importance are 19 tephra deposits that lie on the rapid climatic transitions that punctuate the last glacial period. This framework of well-constrained, time-synchronous tie-lines represents an important step towards the independent synchronization of marine, terrestrial and ice-core records from the North Atlantic region, in order to assess the phasing of rapid climatic changes during the last glacial period.
I wondered how they could determine that it all came from Iceland (and indeed which volcano there) rather than some big stratovolcano far far away. The answer is plotting ash composition in spaces that resolve the potential sources.

In practice this means plotting percent weights of sodium plus potassium oxides vs silicon dioxide, titanium oxide vs aluminum oxide, ferrous oxide vs calcium oxide (lime), and FeO/Ti02 vs SiO2 as in Fig 5, 6, and 7.

There is no way of knowing a priori which combinations (if any) would have the necessary resolving power and no doubt many other things were tried but didn't work out.

The temptation for me is to plot the data in the higher dimensional spaces for which these biplots are just sections (projections on axial pairs), then do principal component analysis to bring it all back to dimension 2 or 3. Or go with support vector machines. Either would give much better separation of volcanoes and higher statistical confidence. But I would say they didn't need anything more than their biplots here.
Title: Re: what's new in Greenland ?
Post by: Laurent on February 06, 2015, 12:45:34 AM
(Already known on this forum)
Greenland’s hidden meltwater lakes store up trouble
http://www.theguardian.com/environment/2015/feb/05/greenlands-hidden-meltwater-lakes-store-up-trouble (http://www.theguardian.com/environment/2015/feb/05/greenlands-hidden-meltwater-lakes-store-up-trouble)

Quote
“If we are going to do something to mitigate sea level rise, we need to do it earlier rather than later,” Dr Applegate said. “The longer we wait, the more rapidly the changes will take place and the more difficult it will be to change.”
Title: Re: what's new in Greenland ?
Post by: A-Team on February 06, 2015, 02:52:22 AM
Save yourself the €34.95 and get the Applegate full text at http://tinyurl.com/oadcjlj (http://tinyurl.com/oadcjlj) -- this is quite cool how younger scientists have taken to ResearchGate to get their work out there where everyone can access it, even as the older ones still defer to journal MBAs.

If you wanted to dig into the modelling, this research was based on open source Sicopolis which has its own web page: http://www.sicopolis.net/ (http://www.sicopolis.net/)

Quote
The model is based on the shallow ice approximation for grounded ice and the shallow shelf approximation for floating ice. It is coded in Fortran 90 and uses finite difference discretisation on a staggered (Arakawa C) grid, the velocity components being taken between grid points. Its particularity is the detailed treatment of basal temperate layers (that is, regions with a temperature at the pressure melting point), which are positioned by fulfilling a Stefan-type jump condition at the interface to the cold ice regions. Within the temperate layers, the water content is computed, and its influence on the ice viscosity is taken into account.
Required model forcing:

    Surface mass balance
    (precipitation, evaporation, runoff).
    Mean annual air temperature
    above the ice.
    Eustatic sea level.
    Geothermal heat flux.
Output (as functions of position and time):

    Extent and thickness of the ice sheet.
    Velocity field.
    Temperature field.
    Water content field (temperate regions).
    Age of the ice.
    Isostatic displacement and temperature of the lithosphere.
This seems bizarre at first in that 3 of the outputs are already known for Greenland and the others don't seem subject to experimental validation anytime soon. I suppose the idea is to keep tweaking inputs until something emerges that matches the outputs.

Here you will find Cuffey & Paterson 4th edition, a required text for every budding glaciologist ($75 at Amazon), providing a blunt cautionary statement already on page 5 about accidental agreements (non-uniqueness of solutions):

Quote
A model explanation may sometimes be illusory; the fact that a model with adjustable parameters gives plausible numerical values does not prove the validity of the underlying assumptions ... use of all the data to 'tune' model parameters precludes a proper assessment of its abilities.
Title: Re: what's new in Greenland ?
Post by: Sleepy on February 22, 2015, 05:42:26 AM
I certainly appreciate when I can access the papers for free, as their much appreciated work is about my home and my kids future, earth.

IRIs seasonal forecast for this summer, that broken fridge can't escape. Only it's contents.
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on July 15, 2015, 08:22:18 PM
New paper by Rignot et al on depth of Greenland fjords:
http://blogs.agu.org/geospace/2015/07/15/greenlands-fjords-are-far-deeper-than-previously-thought-and-glaciers-will-melt-faster-researchers-find/#.VaadhJ2OWMI.twitter (http://blogs.agu.org/geospace/2015/07/15/greenlands-fjords-are-far-deeper-than-previously-thought-and-glaciers-will-melt-faster-researchers-find/#.VaadhJ2OWMI.twitter)
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on July 15, 2015, 08:29:58 PM
Record heat in north of Greenland:
http://www.thelocal.dk/20150714/greenlands-ice-melting-at-rapid-pace (http://www.thelocal.dk/20150714/greenlands-ice-melting-at-rapid-pace)
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on July 15, 2015, 08:49:27 PM
Western Greenland melting:
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2015196.terra.250m (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2015196.terra.250m)
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on July 15, 2015, 08:55:21 PM
Eastern Greenland melting:
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c03.2015196.terra.250m (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c03.2015196.terra.250m)

Northern Greenland melting:
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2015196.terra.250m (http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r03c03.2015196.terra.250m)
Title: Re: what's new in Greenland ?
Post by: Andreas Muenchow on July 16, 2015, 01:55:12 AM
Open Water != Melting

Differential advection (divergence) of ice can and does cause open water.
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on July 19, 2015, 10:26:06 PM
Colgan et al on potential Thermal Viscous Collapse of GIS:
http://onlinelibrary.wiley.com/doi/10.1002/2015EF000301/full (http://onlinelibrary.wiley.com/doi/10.1002/2015EF000301/full)

Abstract
We explore potential changes in Greenland ice sheet form and flow associated with increasing ice temperatures and relaxing effective ice viscosities. We define “thermal-viscous collapse” as a transition from the polythermal ice sheet temperature distribution characteristic of the Holocene to temperate ice at the pressure melting point and associated lower viscosities. The conceptual model of thermal-viscous collapse we present is dependent on: (1) sufficient energy available in future meltwater runoff, (2) routing of meltwater to the bed of the ice sheet interior, and (3) efficient energy transfer from meltwater to the ice. Although we do not attempt to constrain the probability of thermal-viscous collapse, it appears thermodynamically plausible to warm the deepest 15% of the ice sheet, where the majority of deformational shear occurs, to the pressure melting point within four centuries. First-order numerical modeling of an end-member scenario, in which prescribed ice temperatures are warmed at an imposed rate of 0.05 K/a, infers a decrease in ice sheet volume of 5 ± 2% within five centuries of initiating collapse. This is equivalent to a cumulative sea-level rise contribution of 33 ± 18 cm. The vast majority of the sea-level rise contribution associated with thermal-viscous collapse, however, would likely be realized over subsequent millennia.
Title: Re: what's new in Greenland ?
Post by: Tor Bejnar on July 21, 2015, 03:51:54 PM
See Discovery News:  Weakened Solar Activity Could Speed Greenland Ice Melt (http://news.discovery.com/earth/global-warming/weakened-solar-activity-could-speed-up-greenland-ice-melt-150717.htm)

The following is from E&E’s publishing service – subscription required
http://www.eenews.net/climatewire/2015/07/21/stories/1060022132 (http://www.eenews.net/climatewire/2015/07/21/stories/1060022132)
Quote

"Greenland temperatures are quite strongly related to solar activity," Takuro Kobashi, the lead author of the study and a researcher at the University of Bern, Switzerland, said. They looked at temperature trends over a 2,000 year period and showed that temperatures in Greenland had a negative relationship with solar activity.

A public debate between scientists was spurred by findings presented at the Royal Astronomical Society in the United Kingdom by a mathematics professor, Valentina Zharkova, that solar activity will decrease drastically during the 2030s, reaching what is popularly known as the solar minimum.

[D]iminishing solar activity could be more worrying, because it would mean that Greenland would heat up more than expected in those years and predictions about the melting of ice sheets may be off the mark. "If predictions about the diminishing solar activity are true, then we can expect the Greenland ice sheet to melt faster as temperatures there remain higher than the average in the Northern Hemisphere," Kobashi said.
...
Title: Re: what's new in Greenland ?
Post by: A-Team on July 21, 2015, 05:21:19 PM
The article is paywalled but it takes but minutes to get a copy by email from the AGU secretariat. Temperatures and argon and nitrogen isotopes at NGRIP and GISP2 have been determined previously but here they added NGRIP2. These are not new firn cores but the top 400 m of main cores. It's not clear whether this entailed destructive sampling.

The resolution sounds somewhat sketchy (10 years per sample) and the time span a bit short at 2100 years out of 10,700. I would like to have seen more predictions, say of Renland profiles. Renland may be more informative than these summit ridge sites being adjacent to the North Atlantic conditions under discussion.

This is a sophisticated paper that is well worth reading past the counter-intuitive headlined aspects of AMOC  and Greenland temperatures. However that involves also reading all of the 17 MB supplemental as well as 6 previous Kobashi papers in this series.

The authors here do not delve into future variations in total solar irradiance, though the publisher may be playing off the Sarkova PCA dynamo paper to generate publicity. That paper is actually from November, 2014 which in turn is a re-hash of a 2012 paper. These are interesting technically but attracted minimal interest; the furor came from her recent meeting talk and careless comments about climate, a field in which she is unqualified, unfamiliar and unpublished. The Kobashi paper shows how complicated the latter analysis really is.

https://www.researchgate.net/profile/Valentina_Zharkova/publications (https://www.researchgate.net/profile/Valentina_Zharkova/publications) free full text

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064764/full?campaign=wlytk-41855.5282060185 (http://onlinelibrary.wiley.com/doi/10.1002/2015GL064764/full?campaign=wlytk-41855.5282060185)

Quote
The abrupt Northern Hemispheric (NH) warming at the end of the 20th century has been attributed to an enhanced greenhouse effect. Yet, Greenland and surrounding subpolar North Atlantic remained anomalously cold in 1970s- early 1990s. Here, we reconstructed robust Greenland temperature records (NGRIP and GISP2) over the past 2100 years using argon and nitrogen isotopes in air trapped within ice cores, and show that this cold anomaly was part of a recursive pattern of antiphase Greenland temperature responses to solar variability with a possible multidecadal lag. We hypothesize that high solar activity during the modern solar maximum (ca. 1950s-1980s) resulted in a cooling over Greenland and surrounding subpolar North Atlantic through the slow-down of Atlantic Meridional Overturning Circulation (AMOC) with atmospheric feedback processes.

Quote
The new study concludes that high solar activity starting in the 1950s and continuing through the 1980s played a role in slowing down ocean circulation between the South Atlantic and the North Atlantic oceans. Combined with an influx of fresh water from melting glaciers, this slowdown halted warm water and air from reaching Greenland and cooled the island.

But that mitigation from global warming didn’t last, and it’s actually reversed itself. Conversely, the researchers’ findings also suggest that weak solar activity, as the sun is currently experiencing, could slowly fire up the ocean circulation mechanism, increasing the amount of warm water and air flowing to Greenland. Starting around 2025, temperatures in Greenland could increase more than anticipated and the island’s ice sheet could melt faster than projected.

This unexpected ice loss would compound projected sea-level rise expected to occur as a result of climate change, Kobashi said. The melting Greenland ice sheet accounted for one-third of the rise in global sea level every year from 1992 to 2011.
http://news.discovery.com/earth/global-warming/weakened-solar-activity-could-speed-up-greenland-ice-melt-150717.htm (http://news.discovery.com/earth/global-warming/weakened-solar-activity-could-speed-up-greenland-ice-melt-150717.htm)

The green shaded area (late 20th century) is when the modern solar maximum had strong negative influence (red circle) on the Greenland temperature.
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on July 23, 2015, 12:06:32 PM
New paper on Greenland ice velocities:
http://www.mdpi.com/2072-4292/7/7/9371 (http://www.mdpi.com/2072-4292/7/7/9371)
Title: Re: what's new in Greenland ?
Post by: AbruptSLR on July 23, 2015, 06:40:06 PM
While somewhat old news, the following link leads to an Arctic Report Card on the Greenland Ice Sheet through the end of 2014:

http://www.arctic.noaa.gov/reportcard/greenland_ice_sheet.html (http://www.arctic.noaa.gov/reportcard/greenland_ice_sheet.html)
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on July 27, 2015, 05:14:03 PM
Furst et al 2015 find a maximum 16-17 cm of SLR contribution from GIS by 2100 under RCP8.5:
http://www.the-cryosphere.net/9/1039/2015/tc-9-1039-2015.pdf (http://www.the-cryosphere.net/9/1039/2015/tc-9-1039-2015.pdf)

Haven't read the paper yet, so wondering what their assumptions are.
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on July 27, 2015, 05:48:18 PM
In any case Applegate et al 2014 found much higher potential ice loss from Greenland:
http://link.springer.com/article/10.1007%2Fs00382-014-2451-7 (http://link.springer.com/article/10.1007%2Fs00382-014-2451-7)

In their supplementary fig1, attached below, all ice from GIS could be gone in as little as 300 yrs under a worst-case high warming scenario (6-8C global warming, 12C warming over GIS; amplification factor 1.5-2.0). This would mean a maximum SLR-contribution from GIS of 2-3m/century.
Title: Re: what's new in Greenland ?
Post by: Stephen on July 29, 2015, 02:50:05 PM
In any case Applegate et al 2014 found much higher potential ice loss from Greenland:
http://link.springer.com/article/10.1007%2Fs00382-014-2451-7 (http://link.springer.com/article/10.1007%2Fs00382-014-2451-7)

In their supplementary fig1, attached below, all ice from GIS could be gone in as little as 300 yrs under a worst-case high warming scenario (6-8C global warming, 12C warming over GIS; amplification factor 1.5-2.0). This would mean a maximum SLR-contribution from GIS of 2-3m/century.

But with 6-8C of warming will there be anyone left alive to measure it?
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on July 29, 2015, 03:32:42 PM
Good question. Maybe a few million/billion people would still be around...
Title: Re: what's new in Greenland ?
Post by: cats on July 29, 2015, 11:59:35 PM
This project - http://www.nature.com/news/nasa-launches-mission-to-greenland-1.18085?WT.mc_id=TWT_NatureNews (http://www.nature.com/news/nasa-launches-mission-to-greenland-1.18085?WT.mc_id=TWT_NatureNews) sounds interesting and should produce some interesting data. 
Excerpt:
"Called Oceans Melting Greenland (OMG), the US$30-million NASA project will help scientists to predict the future of the Greenland ice sheet, which holds enough water to boost sea levels by around 6 metres and already seems to be melting more rapidly in response to increasing air temperatures. But it is not clear how much the oceans affect the rate of melting along the island’s edges, which depends on poorly known variables such as how warm, saline water interacts with the glaciers."
Title: Re: what's new in Greenland ?
Post by: notjonathon on July 30, 2015, 02:35:33 AM
re: OMG

NASA meets The Onion?

Some dark humor over there.
Title: Re: what's new in Greenland ?
Post by: sidd on August 01, 2015, 07:38:26 AM
lurking about byrd polar research center bprc.osu.edu brought me to this paper by the redoubtable Ellen Mosley-Thompson, Howat and others

snow turning to ice in greenland, reduced melt buffer and such

" ... these huge ice reservoirs are the result of an intense melting process of the same order of magnitude as the total mass imbalance of the GrIS ... "

thats about 400 GT

http://www.the-cryosphere.net/9/1203/2015/tc-9-1203-2015.html (http://www.the-cryosphere.net/9/1203/2015/tc-9-1203-2015.html)

open access

many nice videos at bprc too

sidd
Title: Re: .what's new in Greenland ?
Post by: Lennart van der Linde on August 05, 2015, 11:19:50 PM
Here an attempt by Calov et al 2015 to model GIS in the Eemian:
http://www.the-cryosphere.net/9/179/2015/tc-9-179-2015.pdf (http://www.the-cryosphere.net/9/179/2015/tc-9-179-2015.pdf)

They find an estimated average contribution of about 1.4m from GIS to Eemian-SLR (range 0.6-2.5m).
Title: Re: what's new in Greenland ?
Post by: Lennart van der Linde on September 03, 2015, 07:52:40 PM
Discussion paper by Mikkelsen et al on extreme GIS-runoff in 2012:
http://www.the-cryosphere-discuss.net/9/4625/2015/tcd-9-4625-2015.html (http://www.the-cryosphere-discuss.net/9/4625/2015/tcd-9-4625-2015.html)
Title: Re: what's new in Greenland ?
Post by: sidd on September 04, 2015, 02:17:27 AM
I see Box is an author. The results show the firn layer is now saturated. Apart from the loss of the 3.6mm SLR buffer, so that all melt now discharges, i wonder about structural effects and cryohydrologic warming softening ice.

Every new result we see disquiets me.
Title: Re: what's new in Greenland ?
Post by: skanky on September 15, 2015, 03:44:58 PM
Don't know if this is the best thread for this, but ARS have a good interview with Marco Tedesco on the equipment they use to study Greenland:

http://arstechnica.co.uk/science/2015/09/tools-of-the-trade-when-your-trade-is-studying-the-greenland-ice-cap/ (http://arstechnica.co.uk/science/2015/09/tools-of-the-trade-when-your-trade-is-studying-the-greenland-ice-cap/)

Title: Re: what's new in Greenland ?
Post by: Laurent on October 27, 2015, 04:43:49 PM
Greenland Is Melting Away
http://www.nytimes.com/interactive/2015/10/27/world/greenland-is-melting-away.html?_r=0 (http://www.nytimes.com/interactive/2015/10/27/world/greenland-is-melting-away.html?_r=0)
Quote
“No one has ever collected a data set like this,” Asa Rennermalm, a professor of geography at the Rutgers University Climate Institute who was running the project with Dr. Smith, told the team over a lunch of musk ox burgers at the Kangerlussuaq airport cafeteria.
Title: Re: what's new in Greenland ?
Post by: Laurent on November 12, 2015, 09:37:03 PM
Scientists say Greenland just opened up a major new ‘floodgate’ of ice into the ocean
https://www.washingtonpost.com/news/energy-environment/wp/2015/11/12/scientists-say-greenland-just-opened-up-a-major-new-floodgate-of-ice-into-the-ocean/ (https://www.washingtonpost.com/news/energy-environment/wp/2015/11/12/scientists-say-greenland-just-opened-up-a-major-new-floodgate-of-ice-into-the-ocean/)
Quote
“Collapse of the entire basin is going to take a long time, it’s not going to happen tomorrow,” says Mouginot. “But it’s a process, when you start, it’s like Jakobshavn — [you don’t] see the glacier recovering from that.”
Title: Re: what's new in Greenland ?
Post by: AbruptSLR on November 13, 2015, 06:12:04 PM
Per the linked reference, ice mass losses (and associated loss acceleration rates) reported by the GRACE satellite when the measured losses are corrected for "land-ocean leakage effects":

Shuanggen Jin and Fang Zou (2015), "Re-estimation of glacier mass loss in Greenland from GRACE with correction of land-ocean leakage effects", Global and Planetary Change, doi: 10.1016j.gloplacha.2015.11.002


http://www.sciencedirect.com/science/article/pii/S0921818115301168 (http://www.sciencedirect.com/science/article/pii/S0921818115301168)

Abstract
The Gravity Recovery and Climate Experiment (GRACE) satellites can estimate the high-precision time-varying gravity field and the changes of Earth's surface mass, which have been widely used in water cycle and glacier mass balance. However, one of larger errors in GRACE measurements, land-ocean leakage effects, restricts high precision retrieval of ocean mass and terrestrial water storage variations along the coasts, particularly estimation of mass loss in Greenland. The land-ocean leakage effect along the coasts in Greenland will contaminate the mass loss signals with significant signal attenuation. In this paper, the precise glacier mass loss in Greenland from GRACE is re-estimated with correction of land-ocean leakage effects using the forward gravity modeling. The loss of Greenland ice-sheets is − 100.56 ± 8.86Gt/a without removing leakage effect, but − 171.56 ± 19.24Gt/a after removing the leakage effect from September 2003 to March 2008, which has a good agreement with ICESat results of − 184.8 ± 28.2 Gt/a. From January 2003 to December 2013, the total Greenland ice-sheets is losing at − 254.10 ± 6.90Gt/a from GRACE measurements with removing the leakage effect by 43.15%, while two-thirds of total glacier melting in Greenland is occurred in southern Greenland for the past 11 years. The secular leakage effects on glacier melting estimate mainly locate in the coastal areas, where larger glacier signals are significantly attenuated due to leaking out into the ocean. Furthermore, the leakage signals also have remarkable effects on seasonal and acceleration variations of glacier mass loss in Greenland. More significantly accelerated loss of glacier mass in Greenland is found by − 12.11 Gt/a2 after correcting leakage effects.
Title: Re: what's new in Greenland ?
Post by: sidd on November 13, 2015, 11:40:46 PM
That Jin (2015) paper shows doubling in 7 years then for GIS mass waste.
Title: Re: what's new in Greenland ?
Post by: sidd on November 15, 2015, 01:44:13 AM
GRACE, from polarportal, Barletta's analyses i think.



Title: Re: what's new in Greenland ?
Post by: alataristarion on November 20, 2015, 08:38:47 PM
This is my first post, but I've been reading as a guest for a long time now. I hope this is the appropriate forum for this!

I've created an animation using the IceBridge bedrock data overlaid with the new image of the Sentinel data that A-Team. For me at least, this really helps highlight how the ice movement lines up with the underlying bedrock.

I find it particularly interesting that the NE Greenland Ice Stream moves quickly very near the deep bedrock canyon underlying the Storstrømmen glacier, and then stops. I wish the directional data on the ice movement were preserved, but if the ice is moving toward the canyon and then stopped by the pining of the islands near the calving face, it will be very interesting to see what happens if the calving face retreats northwest slightly.

Title: Re: what's new in Greenland ?
Post by: Neven on November 24, 2015, 05:03:43 PM
I've created an animation using the IceBridge bedrock data overlaid with the new image of the Sentinel data that A-Team.

Hi, alataristarion. Unfortunately your animation isn't playing (I fear because it's too big). Could you post another, slightly smaller one?
Title: Re: what's new in Greenland ?
Post by: alataristarion on November 24, 2015, 06:56:35 PM
Absolutely! Here is one that is under 1MB, so hopefully it will play properly. I have the higher resolution version (and the source file) that I can email if anyone wants to look at them.
Title: Re: what's new in Greenland ?
Post by: Neven on November 24, 2015, 07:36:20 PM
Yup, that one works (when clicked). Thanks!
Title: Re: what's new in Greenland ?
Post by: Espen on November 24, 2015, 08:28:57 PM
Absolutely! Here is one that is under 1MB, so hopefully it will play properly. I have the higher resolution version (and the source file) that I can email if anyone wants to look at them.

Great animation! ;)

Zachariae Fjord will be a serious contender to world largest fjord system title in the future, this now belongs to Scoresby Sund (a bit further south).
Title: Re: what's new in Greenland ?
Post by: alataristarion on November 24, 2015, 10:04:14 PM
Quote
Great animation! ;)

Zachariae Fjord will be a serious contender to world largest fjord system title in the future, this now belongs to Scoresby Sund (a bit further south).

Thanks!

I also like how this image makes clear what the rough structure of ice streams must have been during the last glacial maximum, in particular in Scoresby Sund and Disko Bay.

Does anyone know if there have been any sea floor cores drilled in Disko Bay? I would not be surprised to learn that there was once a Disko Bay Ice Shelf that was bifurcated around Disko Island like the Ronne-Filchner Ice Shelf in Antarctica, but I'd be interested to see if that has been confirmed scientifically.
Title: Re: what's new in Greenland ?
Post by: oren on November 24, 2015, 11:30:11 PM
Great animation indeed. And welcome to the forum as a poster.
Title: Re: what's new in Greenland ?
Post by: Sleepy on November 25, 2015, 05:03:23 AM
Quote
Does anyone know if there have been any sea floor cores drilled in Disko Bay? I would not be surprised to learn that there was once a Disko Bay Ice Shelf that was bifurcated around Disko Island like the Ronne-Filchner Ice Shelf in Antarctica, but I'd be interested to see if that has been confirmed scientifically.

Both of these mention MSM343300.
http://www.archipel.uqam.ca/6996/1/M13491.pdf (http://www.archipel.uqam.ca/6996/1/M13491.pdf)
www.uib.no/sites/w3.uib.no/files/attachments/kelley_13.pdf (http://www.uib.no/sites/w3.uib.no/files/attachments/kelley_13.pdf)
A quote from Kelley et al.
Quote
6. Conclusions
New 10Be ages from around Disko Bugt, western Greenland,
place the deglaciation of western Disko Bugt at 10.8  0.5 ka, with
the ice margin reaching the eastern coast of Disko Bugt near Ilulissat
at 10.1 0.3 ka and in southeastern Disko Bugt at 9.2  0.1 ka.
This chronology yields a retreat rate between w50 and 450 m a1
across central Disko Bugt. This rate indicates that w25% of the
overall retreat between the shelf edge and the current position
occurred in as little as 700 years. We suggest this retreat was the
result of internal ice dynamics acting upon an ice sheet driven out
of equilibrium by climatic factors. These findings further emphasize
the ability of marine sectors of ice sheets to change rapidly due to
ice dynamics in warming climates (e.g. Kjær et al., 2012). Our
chronology fills a gap in the current understanding of the early
Holocene behavior of the GrIS in Disko Bugt, and provides a dataset
that completes a history of a western GrIS margin spanning from
the continental shelf to the present ice position, and from the latest
Pleistocene through the Holocene.
Picture with locations from Kelley et al attached.
Title: Re: what's new in Greenland ?
Post by: nukefix on November 25, 2015, 11:11:43 AM
I find it particularly interesting that the NE Greenland Ice Stream moves quickly very near the deep bedrock canyon underlying the Storstrømmen glacier, and then stops. I wish the directional data on the ice movement were preserved, but if the ice is moving toward the canyon and then stopped by the pining of the islands near the calving face, it will be very interesting to see what happens if the calving face retreats northwest slightly.
Storströmmen has been slowing down, or at least ice has been piling up there according to altimetry. The Ice Velocity data does contain the direction so I expect it to be there once the S-1 Greenland-product is officially released by the project:

http://products.esa-icesheets-cci.org/ (http://products.esa-icesheets-cci.org/)

ps. Kick-ass animation, thanks!
Title: Re: what's new in Greenland ?
Post by: alataristarion on November 25, 2015, 04:27:38 PM
@Sleepy

Thanks! I have now fallen down a rabbit hole of research papers that will occupy me throughout the long Thanksgiving weekend here in the US.

@nukefix

That will be very interesting to see. And thanks!
Title: Re: what's new in Greenland ?
Post by: Sleepy on November 26, 2015, 08:08:18 AM
alataristarion, it's not a rabbit hole. It's more like passing the event horizon of a black hole, if one consider all of the papers out there associated with AGW.  ;D

I've tried to stop reading, but I can't.
Title: Re: what's new in Greenland ?
Post by: A-Team on November 26, 2015, 04:39:59 PM
Nice effort at overlaying surface velocity onto bedrock! Below are a couple of variations, first with blended frames of variable intermediate percentages and second similar but with color conflicts reduced by desaturating the bedrock layer.

These include the other glaciers of northern greenland. To optimize to NEGIS only and stay within our 700 pixel width, the second animation can be cropped, rotated sideways and enlarged to fit (3rd animation).

The NASA visualization center would do this differently: the bedrock DEM would be displayed in hill-shaded perspective grayscale with the speeds put on as an over-tint. This can be done in open freeware discussed on this forum but the catch will be finding the raw data, getting it out of its obtuse NSIDC storage format, cropping to the desired area, maybe exponentiating to get out of log compression, and recovering the grayscales that are needed for input to draped hill-shades.

In all this, it is crucial not to forget the actual resolution of the data and the associated error. In the words of R Feynman, it's easy to fool people and the easiest person of all to fool is yourself, as in the recent Zwally paper.

For example the bedrock had to be heavily kriged to interpolate from the sparse ice penetrating radar tracks which themselves have ~50 m error. The Sentinel velocity magnitudes -- well, you can see swath artifacts everywhere not to mention big blank places on the map.
Title: Re: What's new in Greenland?
Post by: Laurent on December 10, 2015, 10:29:49 PM
Greenland glaciers melt rate hits 9,500 year record
http://www.theecologist.org/News/news_round_up/2986640/greenland_glaciers_melt_rate_hits_9500_year_record.html (http://www.theecologist.org/News/news_round_up/2986640/greenland_glaciers_melt_rate_hits_9500_year_record.html)

Quote
As Arctic Peoples at COP21 in Paris appeal for unity to halt global warming, writes Tim Radford, scientists report that Greenland's glaciers are now melting at a speed not seen since the last Ice Age almost 10,000 years ago.

Quote
The glaciers of Greenland are retreating two to three times faster now than at any time since the last Ice Age ended 9,500 years ago, according to new research.

The news comes as indigenous peoples from the northern polar region staged an Arctic Day at the COP21 climate change summit in Paris.

Leaders of Greenland peoples, the Nunavut region of Canada and the Inuit Circumpolar Council appealed to the governments of the world to unite to dramatically reduce greenhouse gas emissions and keep global warming to between 1.5C and 2C.

That is because the Arctic is now warming faster than almost anywhere else on Earth, and both human settlements and natural ecosystems are vulnerable.

That the Greenland glaciers are in retreat is itself not news. Satellite data and measurements on the ground have repeatedly confirmed the retreat of the glaciers, the loss of ice and the acceleration of flow. The Jakobshavn Isbrae glacier has even reached a speed of 17 kilometres a year.

Sediment cores

But US scientists report in Climate of the Past journal that the present rate of loss is without precedent.

They analysed sediment cores from a lake bed fed by two Greenland glaciers and built up a record reaching back nearly 10,000 years, charting the advance and retreat of the ice in response to natural cycles. And they found evidence of climate change triggered by the human combustion of fossil fuels imposed upon the natural pattern.

"Two things are happening", says one of the report's authors, William D'Andrea, a paleoclimatologist at Columbia University's Lamont-Doherty Earth Observatory.

"One is you have a very gradual decrease in the amount of sunlight hitting high latitudes in the summer. If that were the only thing happening, we would expect these glaciers to very slowly be creeping forward, forward, forward.

"But then we come along and start burning fossil fuels and adding carbon dioxide to the atmosphere, and glaciers that would still be growing start to melt back because summer temperatures are warmer."

The evidence lies in the erosion rates revealed by the lake silts. Colder climates mean more ice, which means heavier glaciers, which then grind and erode more rock. Cores of sediment preserve the annual record of seasonal change, and radiocarbon dating techniques can provide a calendar of melting and freezing periods.

The record reveals that erosion decreased 8,500 years ago, increased again, and then around 8,000 years ago the glaciers began almost to waste away. There was very little evidence of erosion, and the lake silt incorporated evidence that plants once bloomed around the lake.

Around 4,000 years ago, the glaciers grew again, and - with intervals of retreat - continued to grow until 100 years ago.

Pattern of retreat

Although the evidence comes from a small area confined to the southeastern part of Greenland, it remains a guide to the bigger picture. The same pattern of advance and retreat is matched by evidence from ocean sediments and cores of ice from Greenland and Baffin Island.

"This shows that there are internal responses within the climate system that can make glaciers grow and shrink on very short timescales", Dr D'Andrea says. "They're really dynamic systems, which we have not had much evidence for prior to this."

Greenland's minister of industry, labour, trade and foreign affairs, Vittus Qujaukitsoq, one the Arctic voices appealing for strong and effective action in Paris, said: "Greenland has an important responsibility in promoting international climate research.

"Greenlandic climate research combines international cutting-edge research with an Arctic human dimension. Our joint Inuit voice and our traditional know-how from across the Arctic should be heard and included in international policy-making."
Title: Re: What's new in Greenland?
Post by: A-Team on December 11, 2015, 02:37:24 PM
The article is open access:

Glacier response to North Atlantic climate variability during the Holocene
NL Balascio, WJ D'Andrea, RS Bradley
http://www.clim-past.net/11/1587/2015/cp-11-1587-2015.html (http://www.clim-past.net/11/1587/2015/cp-11-1587-2015.html)

Kulusuk Lake is a small cirque 0.8 km2, 69 m depth in southeastern Greenland as shown in the first image. While the study is quite interesting, I wonder how safe it is to extrapolate to the whole of Greenland from this one particular lake (or rather its two tiny contributing glaciers) adjacent to a coastal ocean current. The glaciers themselves were not studied in tandem; no cores were taken; no ice-penetrating radar tracks are mentioned.

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in many Northern Hemisphere regions glacier advances of the past few hundred years were the most extensive and destroyed the geomorphic evidence of ice growth and retreat during the past several thousand years. Thus, most glacier records have been of limited use for investigating centennial scale climate forcing and feedback mechanisms.

Here we report a continuous record of glacier activity for the last 9.5 ka from southeast Greenland, derived from high-resolution measurements on a proglacial lake sediment sequence. Physical and geochemical parameters show that the glaciers responded to previously documented NH climatic excursions, including the 8.2 ka cooling event, the Holocene Thermal Maximum, Neoglacial cooling, and 20th century warming.

... declining summer insolation caused long-term cooling and glacier expansions during the late Holocene [but] climate system dynamics resulted in repeated episodes of glacier expansion and retreat on multi-decadal to centennial timescales. These episodes coincided with ice rafting events in the North Atlantic Ocean and periods of regional ice cap expansion, which confirms their regional significance and indicates that considerable glacier activity on these timescales is a normal feature of the cryosphere. The data  indicate that recent anthropogenic-driven warming has already impacted the regional cryosphere in a manner outside the natural range of Holocene variability.

Bedrock erosion at the base of glaciers provides sediment supply for meltwater transport to proglacial lakes. In catchments where other sources of sediment are limited, such as from mass wasting or the release of stored sediment, there is a strong relationship between sediment properties and glacier size; large glaciers produce more minerogenic material than small glaciers. Measurements of physical and geochemical properties of proglacial lake sediments can therefore be used to reconstruct records of past glacier size.

The methods used these days to study sediment cores include scanning XRF for elemental analysis (xray fluorescence of K Ca Ti Mn Fe Zn Rb Sr in bedrock flour), magnetic susceptibility (proxy for changes in paleoclimate-driven depositional processes such as preferred orientation, distribution or shape of ferromagnetic or paramagnetic minerals associated with bottom currents, compaction, and deformation), net organic matter (whatever is burnt off at 4 hrs at 550ºC), and visual stratigraphy (gravelly sand, clayey silt, brown, organic sediment, laminated sand).

We'll see these same methods applied at this summer's study of Petermann Glacier to determine its comings and goings, though at the bottom of the fjord rather than in the context of a cirque lake.
Title: Re: What's new in Greenland?
Post by: Lennart van der Linde on December 17, 2015, 09:07:11 AM
Kjeldsen et al 2015 on mass loss from GIS since 1900:
http://www.nature.com/nature/journal/v528/n7582/pdf/nature16183.pdf (http://www.nature.com/nature/journal/v528/n7582/pdf/nature16183.pdf)

Abstract
"The response of the Greenland Ice Sheet (GIS) to changes in temperature during the twentieth century remains contentious, largely owing to difficulties in estimating the spatial and temporal distribution of ice mass changes before 1992, when Greenland-wide observations first became available. The only previous estimates of change during the twentieth century are based on empirical modelling and energy balance modelling. Consequently, no observation-based estimates of the contribution from the GIS to the global-mean sea level budget before 1990 are included in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. Here we calculate spatial ice mass loss around the entire GIS from 1900 to the present using aerial imagery from the 1980s. This allows accurate high-resolution mapping of geomorphic features related to the maximum extent of the GIS during the Little Ice Age at the end of the nineteenth century. We estimate the total ice mass loss and its spatial distribution for three periods: 1900–1983 (75.1 ± 29.4 gigatonnes per year), 1983–2003 (73.8 ± 40.5 gigatonnes per year), and 2003–2010 (186.4 ± 18.9 gigatonnes per year). Furthermore, using two surface mass balance models we partition the mass balance into a term for surface mass balance (that is, total precipitation minus total sublimation minus runoff) and a dynamic term. We find that many areas currently undergoing change are identical to those that experienced considerable thinning throughout the twentieth century. We also reveal that the surface mass balance term shows a considerable decrease since 2003, whereas the dynamic term is constant over the past 110 years. Overall, our observation-based findings show that during the twentieth century the GIS contributed at least 25.0 ± 9.4 millimetres of global-mean sea level rise. Our result will help to close the twentieth-century sea level budget, which remains crucial for evaluating the reliability of models used to predict global sea level rise."
Title: Re: What's new in Greenland?
Post by: sidd on December 18, 2015, 07:03:56 AM
Thanks for the reference. I feel that Kjeldsen confirms what Enderlin proposed, that surface mass balance is driving Greenland mass waste. The thing is melting in place. We shall see if Greenland dynamic waste resurges, say in NEGIS, but i think we will see awful dynamic waste in Antarctica first.
Title: Re: What's new in Greenland?
Post by: A-Team on December 18, 2015, 09:36:36 PM
The Kjeldsen piece is open source thanks to a wonderful new policy adopted by Macmillan for across their scientific journal portfolio. This is html only, no pdf download without paying $6 to ReadCube. However -- and this astonished me -- full free access to figures at author-submitted size in permitted.

It's quite a decent article on the stereo photogrammetry processing side. It's not so surprising to see Melville Bay in far northwestern Greenland getting hammered. That area, despite its latitude, also jumps out on ocean current warming maps.

In terms of closing the sea level budget, that depends on the eye of the beholder (vis-a-vis Antarctica), be it that of the consensus or that of an obstinate 76-year old.

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Here we calculate spatial ice mass loss around the entire GIS from 1900 to the present using aerial imagery from the 1980s. This allows accurate high-resolution mapping of geomorphic features related to the maximum extent of the GIS during the Little Ice Age at the end of the nineteenth century.

We estimate the total ice mass loss and its spatial distribution for three periods: 1900–1983 (75.1 ± 29.4 gigatonnes per year), 1983–2003 (73.8 ± 40.5 gigatonnes per year), and 2003–2010 (186.4 ± 18.9 gigatonnes per year). Furthermore, using two surface mass balance models we partition the mass balance into a term for surface mass balance (that is, total precipitation minus total sublimation minus runoff) and a dynamic term.

We find that many areas currently undergoing change are identical to those that experienced considerable thinning throughout the twentieth century. We also reveal that the surface mass balance term shows a considerable decrease since 2003, whereas the dynamic term is constant over the past 110 years.

Overall, our observation-based findings show that during the twentieth century the GIS contributed at least 25.0 ± 9.4 millimetres of global-mean sea level rise. Our result will help to close the twentieth-century sea level budget
Title: Re: What's new in Greenland?
Post by: sidd on January 05, 2016, 01:16:26 AM
Firn is full, melt goes to ocean. This is why SMB began to dominate mass waste as Enderlin saw, no refreeze.


doi:10.1038/nclimate2899
Title: Re: What's new in Greenland?
Post by: Pmt111500 on January 11, 2016, 09:58:59 AM
The wettest snow is most often found deeper in the springtime. It either reaches ground or if there's an ice layer it will float on that. One friend (regular icefisher though) once walked 2km in 20cm water/slush layer on ice (40cm) to get back on land. This is common knowledge that the surface granular snow/deformed icecrystals is pretty dry. It's still nice to have some numbers concerning Greenland about this aspect of regular spring runoff.
Title: Re: What's new in Greenland?
Post by: A-Team on January 11, 2016, 02:48:25 PM
sidd is citing:

An improved mass budget for the Greenland ice sheet
E Enderlin
Geophys. Res. Lett., 41, 2014, doi:10.1002/2013GL059010
http://onlinelibrary.wiley.com/doi/10.1002/2013GL059010/pdf (http://onlinelibrary.wiley.com/doi/10.1002/2013GL059010/pdf) (paywalled, not on ResearchGate)

That paper has already been cited an astonishing 69 times (google-search with title in quotes). In fact Enderlin et al have a follow-up discussion paper now under contentious review which would bring in 2016 thinking. I actually prefer reading the back-and-forth with reviewers to reading a final published version (if there is one here).

The bottom line of these 70 papers? That seems a moving target but can't go on forever without some consensus being reached.

www.the-cryosphere-discuss.net/9/4661/2015 (http://www.the-cryosphere-discuss.net/9/4661/2015)

RC C1763: 'Review of Xu et al. (2015)', Anonymous Referee #1, 30 Sep 2015
  AC C2487: 'Response to referee#1 and updates', Zheng Xu, 14 Dec 2015 
 
RC C1925: 'Review of Xu et al.. (2015)', Anonymous Referee #2, 23 Oct 2015
  AC C2489: 'Response to referee#2 and updates', Zheng Xu, 14 Dec 2015
 
RC C2128: 'suggestions to improve clarity of GRACE vs IOM comparison', Anonymous Referee #3, 03 Nov 2015
  AC C2491: 'Response to referee#3 and updates', Zheng Xu, 14 Dec 2015
 
EC C2132: 'Major revisions required', Etienne Berthier, 03 Nov 2015
  AC C2493: 'rebuttal of the TCD paper " Improved GRACE regional mass balance estimates of the Greenland Ice Sheet cross-validated with the input-output method "', Zheng Xu, 14 Dec 2015
Title: Re: What's new in Greenland?
Post by: AbruptSLR on January 18, 2016, 09:47:19 PM
The linked (open access) reference discusses the use of GRACE to evaluate ice flow sensitivity in Greenland to climate change:

Schlegel, N.-J., Wiese, D. N., Larour, E. Y., Watkins, M. M., Box, J. E., Fettweis, X., and van den Broeke, M. R: Application of GRACE to the evaluation of an ice flow model of the Greenland Ice Sheet, The Cryosphere Discuss., doi:10.5194/tc-2015-224, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2015-224/ (http://www.the-cryosphere-discuss.net/tc-2015-224/)


Abstract. Quantifying the Greenland Ice Sheet’s future contribution to sea level rise is a challenging task that requires accurate estimates of ice flow sensitivity to climate change. Forward models of ice flow dynamics are promising tools for estimating future ice sheet behavior, yet confidence is low because evaluation of historical simulations is so challenging due to the scarcity of highly-resolved (spatially and temporally) continental-wide validation data. Recent advancements in processing of Gravity Recovery and Climate Experiment (GRACE) data using Bayesian-constrained mass concentration ("mascon") functions have led to improvements in spatial resolution and noise reduction of estimated monthly global gravity fields. Specifically, the Jet Propulsion Laboratory’s JPL RL05M GRACE mascon solution (GRACE-JPL) now offers an opportunity for ice sheet model evaluation within independently resolved 300 km mascons. Here, we investigate how Greenland Ice Sheet mass balance captured through observations - GRACE-JPL - differs from that simulated by the ice flow model - the Ice Sheet System Model (ISSM). For the years 2003-2012, ISSM is forced with regional climate model (RCM) surface mass balance (SMB), and resulting mass balance is directly compared against GRACE-JPL within individual mascons. Overall, we find good agreement in the Northeast, Southwest, and the interior of the ice sheet, where mass balance is primarily controlled by SMB. In the Northwest, seasonal amplitudes match well, but trends in ISSM are muted relative to GRACE-JPL. In the Southeast, GRACE-JPL exhibits larger seasonal amplitude than that predicted by SMB while simultaneously having more pronounced trends. These results indicate that discrepancies in the Northwest are controlled by changes in ice dynamics that are not currently modeled by ISSM, i.e. transient processes driven by ice sheet hydrology and ice-ocean interaction, while discrepancies in the Southeast are controlled by a combination of these missing dynamics and errors in modeled SMB. Along the margins, we find that transient dynamics are responsible for consistent intra-annual variations in regional mass balance that ultimately contribute to the steeper negative mass trends observed by GRACE-JPL. Consequently, ice-ocean interactions and hydrologically-driven processes at relatively high (monthly-to-seasonal) temporal resolutions must be considered for improving upon ice flow models.
Title: Re: What's new in Greenland?
Post by: AbruptSLR on January 23, 2016, 05:57:37 PM
The linked (open access) reference discusses the use of GRACE to evaluate ice flow sensitivity in Greenland to climate change:

Schlegel, N.-J., Wiese, D. N., Larour, E. Y., Watkins, M. M., Box, J. E., Fettweis, X., and van den Broeke, M. R: Application of GRACE to the evaluation of an ice flow model of the Greenland Ice Sheet, The Cryosphere Discuss., doi:10.5194/tc-2015-224, in review, 2016.

The process cited in the open access paper referenced below, should work well with the reference cited in Reply #128 (note overlap of Fettweis in the authorship)

Navari, M., Margulis, S. A., Bateni, S. M., Tedesco, M., Alexander, P., and Fettweis, X.: Feasibility of improving a priori regional climate model estimates of Greenland ice sheet surface mass loss through assimilation of measured ice surface temperatures, The Cryosphere, 10, 103-120, doi:10.5194/tc-10-103-2016, 2016

http://www.the-cryosphere.net/10/103/2016/ (http://www.the-cryosphere.net/10/103/2016/)

Abstract. The Greenland ice sheet (GrIS) has been the focus of climate studies due to its considerable impact on sea level rise. Accurate estimates of surface mass fluxes would contribute to understanding the cause of its recent changes and would help to better estimate the past, current and future contribution of the GrIS to sea level rise. Though the estimates of the GrIS surface mass fluxes have improved significantly over the last decade, there is still considerable disparity between the results from different methodologies (e.g., Rae et al., 2012; Vernon et al., 2013). The data assimilation approach can merge information from different methodologies in a consistent way to improve the GrIS surface mass fluxes. In this study, an ensemble batch smoother data assimilation approach was developed to assess the feasibility of generating a reanalysis estimate of the GrIS surface mass fluxes via integrating remotely sensed ice surface temperature measurements with a regional climate model (a priori) estimate. The performance of the proposed methodology for generating an improved posterior estimate was investigated within an observing system simulation experiment (OSSE) framework using synthetically generated ice surface temperature measurements. The results showed that assimilation of ice surface temperature time series were able to overcome uncertainties in near-surface meteorological forcing variables that drive the GrIS surface processes. Our findings show that the proposed methodology is able to generate posterior reanalysis estimates of the surface mass fluxes that are in good agreement with the synthetic true estimates. The results also showed that the proposed data assimilation framework improves the root-mean-square error of the posterior estimates of runoff, sublimation/evaporation, surface condensation, and surface mass loss fluxes by 61, 64, 76, and 62 %, respectively, over the nominal a priori climate model estimates.

Title: Re: What's new in Greenland?
Post by: ms on February 03, 2016, 05:55:09 PM
I just saw this news (in danish).
http://videnskab.dk/miljo-naturvidenskab/oprab-til-alle-laenestolsforskere-esa-frigiver-satellitdata-over-gronland
 (http://videnskab.dk/miljo-naturvidenskab/oprab-til-alle-laenestolsforskere-esa-frigiver-satellitdata-over-gronland)

A call to armchair-scientists, that ESA has launched a new home-page with data on the Greenland Ice sheet.

http://esa-icesheets-cci.org/ (http://ttp://esa-icesheets-cci.org/)
Title: Re: What's new in Greenland?
Post by: A-Team on February 03, 2016, 07:54:34 PM
Make that http://esa-icesheets-cci.org/ (http://esa-icesheets-cci.org/) as the 'h' didn't make it into the url.
Title: Re: What's new in Greenland?
Post by: sidd on February 05, 2016, 12:08:42 AM
MacGregor(2016) doi:10.1126/science.aab1702 "Holocene deceleration of the Greenland Ice Sheet"

indicates that a la Bamber in Antarctica, GRIS interior is also thickening. The MacGregor paper led to to a nice paper by the Paterson in 1991, and thence to a nice paper by the Alley in 1986 ... whereupon i ran out of time, so sad.

sidd
Title: Re: What's new in Greenland?
Post by: A-Team on February 05, 2016, 05:17:25 PM
The article is an important follow-up on the MacGregor 2015 digest of Greenland isochrons. The illustrations are available in high resolution pngs from the UT press release, which also gives a good account of the paper.

http://www-udc.ig.utexas.edu/external/joemac/publications.html (http://www-udc.ig.utexas.edu/external/joemac/publications.html) free full text
http://science.sciencemag.org/highwire/filestream/673104/field_highwire_adjunct_files/0/MacGregor.SM.pdf (http://science.sciencemag.org/highwire/filestream/673104/field_highwire_adjunct_files/0/MacGregor.SM.pdf) supplemental details
http://science.sciencemag.org/content/351/6273/562 (http://science.sciencemag.org/content/351/6273/562) paywalled commentary by CS Hvidberg
http://news.utexas.edu/2016/02/04/scientists-map-movement-of-greenland-ice-sheet-over-time-0 (http://news.utexas.edu/2016/02/04/scientists-map-movement-of-greenland-ice-sheet-over-time-0)
http://williamcolgan.net/blog/?p=247 (http://williamcolgan.net/blog/?p=247)

Ouch: they had this ready about the same time as the isochron paper came out. Ten months in review is too long.
    Received for publication 23 March 2015.
    Accepted for publication 7 January 2016.

Quote
AUSTIN, Texas — Scientists have created the first paleo-velocity map that shows how the Greenland Ice Sheet has moved over time, revealing that ice in the interior is moving more slowly toward the edges than it has during the past 9,000 years.

Researchers said the findings don’t change the fact that the ice sheet is losing mass overall and contributing to sea level rise.

Along Greenland’s periphery, many glaciers are rapidly thinning. However, the vast interior of Greenland is slowly thickening.

The authors identified three causes for deceleration. First is that snowfall rates were generally higher during the past 9,000 years, second is the slow stiffening of the ice sheet over time, and third is the collapse of an ice bridge that used to connect Greenland’s ice across the Nares Strait to that of nearby Ellesmere Island. Of most interest were the last two.

“Like many others, I had in mind the ongoing dramatic retreat and speedup along the edges of the ice sheet, so I’d assumed that the interior was faster now too. But it wasn’t,” said MacGregor.

“The ice that formed from snow that fell in Greenland during the last ice age is about three times softer than the ice being formed today,” according to co-author William Colgan.

Because of this difference, the ice sheet is slowly becoming stiffer. As a consequence, the ice sheet is flowing more slowly and getting thicker over time. This effect is most important in southern Greenland, where higher snowfall rates have led to rapid replacement of ice from the last glacial period with more modern Holocene ice.

“But that didn’t explain what was happening elsewhere in Greenland, particularly the northwest, where there isn’t as much snowfall, so the stiffening effect isn’t as important,” said MacGregor.

The explanation of deceleration in the northwest lies in the collapse 10,000 years ago of an “ice bridge” across Nares Strait, which used to connect Greenland’s ice to that on Ellesmere Island. The collapse of the ice bridge at the end of the last ice age led to acceleration in the northwest, but the ice sheet has since returned to a slower pace.

“We’re saying that recent increases in snowfall do not necessarily explain present-day interior thickening,” said Colgan. “If you’re using a satellite altimeter to figure out how much mass Greenland is losing, you’re going to get the answer slightly wrong unless you account for these very long-term signals that are evident in its interior.”
Title: Re: What's new in Greenland?
Post by: A-Team on February 05, 2016, 08:54:52 PM
The authors are going to keep us busy with 4 other related papers In various stages of publication:

Reeh thickening: Ongoing deglacial stiffening of the Greenland Ice Sheet
W Colgan, JA MacGregor, SB Simonsen and KK Kjeldsen
Geophysical Research Letters (unavailable at this time)
http://williamcolgan.net/blog/?p=247 (http://williamcolgan.net/blog/?p=247)

A synthesis of the thermal state of the bed of the Greenland Ice Sheet
JA MacGregor, MA Fahnestock, GA Catania, A Aschwanden, GD Clow, W.T. Colgan, S.P. Gogineni, M. Morlighem, S.M.J. Nowicki, J.D. Paden, S.F. Price and H. Seroussi
Journal of Geophysical Research Earth Surface (unavailable at this time)
http://ig.utexas.edu/2015/12/09/utig-at-agu/ (http://ig.utexas.edu/2015/12/09/utig-at-agu/)
https://cires.colorado.edu/news/events/events/cryospheric-and-polar-processes-seminar2/?eID=380 (https://cires.colorado.edu/news/events/events/cryospheric-and-polar-processes-seminar2/?eID=380)

Annual Greenland accumulation rates (2009-2012) from airborne snow radar
LSKoenig, A Ivanoff, PM Alexander, JA MacGregor, X Fettweis, B Panzer, JD Paden, RR Forster, I Das, JR McConnell, C Leuschen and P Gogineni
Cryosphere Discussions
http://wwwthe-cryosphere-discussnet/tc-2015-211/ (http://wwwthe-cryosphere-discussnet/tc-2015-211/)

Deep radiostratigraphy of the East Antarctic plateau: connecting Dome C and Vostok ice core sites
MGP Cavitte, DD Blankenship, DA Young, DM Schroeder, F Parrenin, E Le Meur, JA MacGregor and MJ Siegert
Journal of Glaciology (accepted for 2016 #2915; unavailable at this time)
https://earth.stanford.edu/radio-glaciology/radar-sounder-data-analysis (https://earth.stanford.edu/radio-glaciology/radar-sounder-data-analysis)
Title: Re: What's new in Greenland?
Post by: sidd on February 05, 2016, 09:01:52 PM
I shall watch JGR for the digest of thermal state of GIS bed, that seems important to understand.
Title: Re: What's new in Greenland?
Post by: A-Team on February 06, 2016, 01:15:43 PM
Quote
watch JGR for the digest of thermal state of GIS bed, that seems important to understand.
Right. That and the status of basal till are the missing pieces. MacGregor 2016 above only went down to the 9000 kyr isochron which might be only the top quarter of ice thickness in central Greenland; MacGregor 2015a had no widespread isochrons to work with below 91 kyr and used a depth-age formula to locate Eemian. That paper deliberately sidestepped Greenland's basal deformations.

I was not thrilled with MacGregor 2015b per se but it likely lays the technical groundwork for the bed thermal synthesis paper we're awaiting (which will also sidestep the major deformation areas but probably still trip over the cryptic ones). They cannot get at till with radar yet seismic is terribly restricted with no prospects for islandwide coverage.

Radar attenuation and temperature within the Greenland Ice Sheet
JA MacGregor, J Li, JD Paden, GA Catania, GD Clow, MA Fahnestock, SP Gogineni, RE Grimm, M Morlighem, S Nandi, H Seroussi and DE Stillman
Journal of Geophysical Research Earth Surface, 120, 983–1008 2015b
http://www-udc.ig.utexas.edu/external/joemac/pdf/MacGregor_2015_JGR_2.pdf (http://www-udc.ig.utexas.edu/external/joemac/pdf/MacGregor_2015_JGR_2.pdf)

'Reeh thickening' plays an important role in the current paper. That has not surfaced before in the forums though it is covered in early editions of Cuffey and Paterson's textbook, not so much in the current. Oddly we were just talking about Paterson's 'soft ice' of the last glacial and legacy effects of temperate paleo-firn described by Luethi around Swiss Camp a few days ago in the NEEM forum.

It's all part of 'ice sheets have long memories'. It simply doesn't work to pull an era like the Eemian out of its context, saying the CO2 and solar were such-and-such yet this that and other didn't happen so let's all drive Hummers. See https://en.wikipedia.org/wiki/Hysteresis (https://en.wikipedia.org/wiki/Hysteresis)

The second image from MacGregor 2016 shows ice thickness in Greenland 9000 years ago. Here snow and firn are converted to their ice thickness equivalent. The data for this map were determined MacGregor 2015. The authors deserve high marks both for high quality images (import into ImageJ for full resolution) and public access to them.

Quote
MacGregor 2016: The millennial-scale evolution of GrIS rheology can partly explain this response. Ice deposited during the last glacial is approximately three times less viscous (“softer”) than ice deposited during the Holocene1. To explain observations of subtle thickening (1 cm per) at DYE-3, Reeh2 hypothesized that, as softer LGP ice is buried by stiffer Holocene ice, the GrIS interior will thicken (hereafter referred to as “Reeh thickening”).

Reeh thickening is distinct from that induced by increased accumulation rate, decreased rate of firn densification, post LGP isostatic adjustment, or horizontal deceleration due to other poorly constrained mechanisms (e.g., increasing basal friction). By continuity, it follows that this transient viscosity change would also have caused the GrIS interior to decelerate after deglaciation....

Corroborating and expanding upon Reeh’s original hypothesis, we suggest that downward advection of the LGP-Holocene transition partly explains the subtle deceleration we infer in the interior of the southern GrIS. The dynamic consequences of this effect are predicted to have in creased nonlinearly within the GrIS interior during the Holocene and to continue for tens of millennia.

Quote
1. Why ice-age ice is sometimes “soft”
WSB Paterson 1991 (doi:10.1016/0165-232X(91)90058-O  cited 121 times)  full text still paywalled

Data on the mechanical properties, texture, fabric, and impurity content of ice deposited during the last glaciation are reviewed. The conclusions are: (1) Chloride and possibly sulphate ions, in concentrations high relative to those in Holocene ice, impede grain-boundary migration and grain growth so that the crystals remain small. (2) Such ice, in shear parallel to the ice-sheet bed, develops a strong, near-vertical, single-maximum fabric. (3) This fabric favours further deformation and this, in turn, further strengthens the fabric and keeps the crystals small. (4) This is why the strain rate in ice-age ice, in simple shear, is some 2.5 times that in Holocene ice at the same stress and temperature. (5) Ice-age ice under other stress systems, such as ice in roughly the upper 60% of the ice thickness, in bedrock hollows, at a stationary ice divide, in ice streams and in ice shelves, will not have enhanced flow. (6) An anisotropic flow relation must be used for detailed modelling of polar ice sheets.

2. Was the Greenland ice sheet thinner in the late Wisconsinan than now?
Niels Reeh
Nature 317, 797 - 799 (31 October 1985); doi:10.1038/317797a0
http://www.nature.com/nature/journal/v317/n6040/abs/317797a0.html (http://www.nature.com/nature/journal/v317/n6040/abs/317797a0.html) full text still paywalled

Ice of Wisconsinan origin which constitutes the basal layers of the ice caps in arctic Canada and Greenland flows three to four times more readily than the Holocene ice above. A model based on simple ice sheet profile theory is set up for the thickness response of the interior ice sheet regions to the progressive thinning of this soft layer. The model is applied to calculate the thickness response of the Greenland ice sheet at the locations Dye 3 and Crête, and of the Devon Island ice cap in arctic Canada. It is concluded that the mechanism contributes significantly to the thickness change of the Greenland ice sheet, presently at a rate of about 1 cm yr−1 and that this rate of change will persist potentially over thousands of years to come. As regards the Devon Island ice cap, most of the estimated 15% thickness increase has already been accomplished. A further consequence is that in the late Wisconsinan, ice thicknesses of the interior regions of the Greenland ice sheet were likely to have been no greater and possibly even less than at present, in spite of the larger geographical extent of the ice sheet. It is argued that the glacial-interglacial cycles of accumulation rate and ice temperature are likely to enhance this ice thickness variation.
Title: Re: What's new in Greenland?
Post by: Sigmetnow on February 15, 2016, 04:07:03 PM
Hurricane force storm developing just south of Greenland.  Very strong flow of warm air with a second, intensifiying system.

https://www.facebook.com/NWSOPC/posts/1007203242671740 (https://www.facebook.com/NWSOPC/posts/1007203242671740)

Bottom image is surface air temperature with wind direction and speed.
Title: Re: What's new in Greenland?
Post by: AbruptSLR on February 29, 2016, 06:45:10 PM
The linked reference documents a positive feedback mechanism between Arctic sea-ice loss and increased surface melting of the Greenland Ice Sheet:

Jiping Liu, Zhiqiang Chen, Jennifer Francis, Mirong Song, Thomas Mote and Yongyun Hu (2016), "Has Arctic sea-ice loss contributed to increased surface melting of the Greenland ice sheet?", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-15-0391.1 (http://dx.doi.org/10.1175/JCLI-D-15-0391.1)

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0391.1 (http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0391.1)

Abstract: "In recent decades, the Greenland ice sheet has experienced increased surface melt. However, the underlying cause of this increased surface melting and how it relates to cryospheric changes across the Arctic remain unclear. Here we show that an important contributing factor is the decreasing Arctic sea ice. Reduced summer sea ice favors stronger and more frequent occurrences of blocking-high pressure events over Greenland. Blocking highs enhance the transport of warm, moist air over Greenland, which increases downwelling infrared radiation, contributes to increased extreme heat events, and accounts for the majority of the observed warming trends. These findings are supported by analyses of observations and reanalysis data, as well as by independent atmospheric model simulations using a state-of-the-art atmospheric model that is forced by varying only the sea ice conditions. Reduced sea ice conditions in the model favor more extensive Greenland surface melting. We find that a positive feedback between the variability in the extent of summer Arctic sea ice and melt area of the summer Greenland ice sheet, which affects the Greenland ice sheet mass balance. This linkage may improve the projections of changes in the global sea level and thermohaline circulation."
Title: Re: What's new in Greenland?
Post by: Laurent on March 04, 2016, 11:41:25 AM
Greenland's ice melt accelerating as surface darkens, raising sea levels
http://www.theguardian.com/environment/2016/mar/03/greenland-ice-sheet-melting-global-warming-feedback-loop (http://www.theguardian.com/environment/2016/mar/03/greenland-ice-sheet-melting-global-warming-feedback-loop)

Quote
The research, published in the European Geosciences Union journal The Cryosphere, looked at satellite data from 1981 to 2012. The drop in reflectivity from 1996 was probably due to a change in atmospheric circulation that favoured warmer, moist air from the south. The scientists found there was no significant increase in soot from forest fires since 1997 to explain the darkening of the surface.
Title: Re: What's new in Greenland?
Post by: Tealight on March 06, 2016, 03:38:10 AM
It looks like Sentinel 2A will will finally acquire images from Greenland. It will start on the 12th March with Greenland's east coast and the south-centre on the 14th of March.

I can't wait to finally get High-res images  :D

The Acquisition Plans can be downloaded here:
https://sentinel.esa.int/web/sentinel/missions/sentinel-2/acquisition-plans

The final images will be available at:
https://scihub.copernicus.eu/
Title: Re: What's new in Greenland?
Post by: A-Team on March 06, 2016, 02:00:58 PM
Quote
finally get Sentinel 2igh-res images... Acquisition Plans can be downloaded here:
https://sentinel.esa.int/web/sentinel/missions/sentinel-2/acquisition-plans
Yes, Sentinel 2 will be a great addition -- some of the longer wavelength bands are more interesting than those of Landsat. We don't know yet how useful these will be on the Greenland ice sheet. The 10 m resolution will also be a big plus for marine terminating glaciers. That link is a big improvement over slow, futile searches at their data portal.

My sense is that the Greenland glaciological research community has not been able to communicate their scientific interests to the Sentinel 2 committee. (The ESA overall is quite hostile to end-user feedback.) I could not imagine worse orbital choices than the ones that they are making available initially. What exactly do they expect to see in early March in the center of the ice sheet with visible and near IR?
Title: Re: What's new in Greenland?
Post by: Tealight on March 06, 2016, 03:16:07 PM
(The ESA overall is quite hostile to end-user feedback.) I could not imagine worse orbital choices than the ones that they are making available initially. What exactly do they expect to see in early March in the center of the ice sheet with visible and near IR?

Yeah their products are very unfriendly to small end users. I did send them an email a while ago, suggesting to allow downloads of individual tiles instead of these huge stripes. Most of us are just interested in a few square kilometer and not half of the continent. This could reduce the download size from 7-10Gb to just 1Gb, which also reduces the load of their servers.
Title: Re: What's new in Greenland?
Post by: Laurent on April 01, 2016, 01:16:00 PM
More Greenland melt under cloudy conditions
http://jasonbox.net/more-greenland-melt-under-cloudy-conditions/ (http://jasonbox.net/more-greenland-melt-under-cloudy-conditions/)

Quote
Not an April 1 joke: Our new study reveals that under warm and wet conditions, atmospheric heat can melt the lower 1/3 of the Greenland ice sheet more than under sunny conditions. This was especially so during the 2012 heat wave when a record warm North America loaded the air with heat and moisture that drifted to Greenland.
Title: Re: What's new in Greenland?
Post by: A-Team on April 01, 2016, 04:22:57 PM
Quote
Yeah ESA products are very unfriendly to small end users. I did send them an email suggesting to allow downloads of individual tiles  . Most of us are just interested in a few square kilometer and not half of the continent.
Just so it is on this thread too, little people can now grab just band 4 (red) with most of the benefit but none of the fou fou. It is 130 MB rather than 8300 MB which is 1.5%. Still, the micro preview is useless and does not indicate if your site is clouded over (scene percent is unsatisfactory). It is truly mystifying why they worry over another 100 KB in a multi GB context.

After much wrestling with their crazy-long file names that should have been in metadata like Landsat, the download drops the scene's date, time and location! So over time you will accumulate many dozen B04.jp2's that you better manually fix at the time of acquisition.

Once having drilled into the AWS file system to say the Jakobshavn calving front, it appears possible to keep the tab open and check daily or so for new scenes, then do a quickie download of band 1 (4 MB) for a cloud check or more ambitiously band 5 (33 MB) before bothering with the 10 m bands (2,3,4,8). It takes three bands to make 'true color', not of much use on ice sheets unless there's melt. Band 4 has a better histogram in shadowed regions.

These AWS bands are 16-bit jpeg2000 (jp2) but they will unfortunately open in most desktop software, without warning, as 8-bit. However all initial operations (contrast stretching, gamma, rotation, re-sizing) need to be done at 16-bit. The attached image shows the degradation of the image/histogram when processed at 8-bit.

It is very expensive to design, build, launch and support satellites, so it makes no sense to discard image quality by sloppy processing at the very end. Around here we say, "you don't put a two dollar saddle on a million dollar mule."

http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/22/W/EB/2016/3/26/0/ (http://sentinel-s2-l1c.s3-website.eu-central-1.amazonaws.com/#tiles/22/W/EB/2016/3/26/0/)
http://forum.arctic-sea-ice.net/index.php/topic,154.msg72793.html#msg72793 (http://forum.arctic-sea-ice.net/index.php/topic,154.msg72793.html#msg72793)
Title: Re: What's new in Greenland?
Post by: Martin Gisser on April 02, 2016, 01:03:41 AM
After much wrestling with their crazy-long file names that should have been in metadata like Landsat, the download drops the scene's date, time and location! So over time you will accumulate many dozen B04.jp2's that you better manually fix at the time of acquisition.
Wow. Sounds like Microsofty stone age. What system is doing this?
(Your reply could help me deciding: I'm thinking of getting me some new Computer thing. But I'm so thoroughly fed up with stupid design and never fixed elementary bugs. I've meanwhile quit on German IT industry. Maybe I even quit serious private useage, because the stuff seems getting hopeless. (What I'm using right now is even worse than Windoze 93 on an Intel 486. Feels not even like a Turing machine anymore...))

Quote
(...)
Around here we say, "you don't put a two dollar saddle on a million dollar mule."
Seems like classic business administration going on. They can formally work numbers, but lack any understanding. The numbers are in tidy boxes. Outside those boxes the numbers have no dimension, no strategical or any other value. Billions in this box, peanuts in the other. The good German MBA keeps them strictly separate, for anything else would require creative thinking. This is taboo when dealing with money numbers. -- Heck, why a two dollar saddle? Lets do it without because the corresponding box is almost empty. -- I've seen Software sellers trying to do without software engineers.


Title: Re: What's new in Greenland?
Post by: AbruptSLR on April 04, 2016, 03:47:12 AM
Rignot et al (2016) provides news measurements that many marine-terminating glaciers in Greenland has deeper water depths than previously realized; which could contribute to the relatively early acceleration of some of these glaciers with continued global warming:

E. Rignot, I. Fenty, Y. Xu, C. Cai, I. Velicogna, C. Ó Cofaigh, J. A. Dowdeswell, W. Weinrebe, G. Catania & D. Duncan (25 March 2016), "Bathymetry data reveal glaciers vulnerable to ice-ocean interaction in Uummannaq and Vaigat glacial fjords, west Greenland", Geophysical Research Letters, DOI: 10.1002/2016GL067832


http://onlinelibrary.wiley.com/doi/10.1002/2016GL067832/full (http://onlinelibrary.wiley.com/doi/10.1002/2016GL067832/full)

Abstract: "Marine-terminating glaciers play a critical role in controlling Greenland's ice sheet mass balance. Their frontal margins interact vigorously with the ocean, but our understanding of this interaction is limited, in part, by a lack of bathymetry data. Here we present a multibeam echo sounding survey of 14 glacial fjords in the Uummannaq and Vaigat fjords, west Greenland, which extends from the continental shelf to the glacier fronts. The data reveal valleys with shallow sills, overdeepenings (>1300 m) from glacial erosion, and seafloor depths 100–1000 m deeper than in existing charts. Where fjords are deep enough, we detect the pervasive presence of warm, salty Atlantic Water (AW) (>2.5°C) with high melt potential, but we also find numerous glaciers grounded on shallow (<200 m) sills, standing in cold (<1°C) waters in otherwise deep fjords, i.e., with reduced melt potential. Bathymetric observations extending to the glacier fronts are critical to understand the glacier evolution."
Title: Re: What's new in Greenland?
Post by: A-Team on April 04, 2016, 11:37:25 PM
This being Rignot's 4th substantive article for 2016 -- it is a full-time job just reading them. This one is the overview of west-central Greenland glaciers; we've been discussing the expanded version of Store Glacier over on that and the Jakobshavn forums. Basically these glaciers cannot be meaningfully modeled without this better data.

The article doesn't say who did the extraordinary graphics. I have not had a chance to see what is in th 100 m geotiff file  available at ess.uci.edu/group/erignot/node/1535

Atmospheric Chemistry and Physics Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous
James Hansen · Makiko Sato · Paul Hearty · Reto Ruedy · Maxwell Kelley · Valerie Masson-Delmotte · Gary Russell · George Tselioudis · Junji Cao · Eric Rignot · Isabella Velicogna ..

Bathymetry data reveal glaciers vulnerable to ice-ocean interaction in Uummannaq and Vaigat glacial fjords, West Greenland.
E. Rignot · I. Fenty · Y. Xu · C. Cai · I. Velicogna · C. Ó Cofaigh · J. A. Dowdeswell · W. Weinrebe · G. Catania · D. Duncan
 Geophysical Research Letters

A constitutive framework for predicting weakening and reduced buttressing of ice shelves based on observations of the progressive deterioration of the remnant Larsen B Ice Shelf
Chris Borstad · Ala Khazendar · Bernd Scheuchl · Mathieu Morlighem · Eric Larour · Eric Rignot

Modeling of Store Gletscher's calving dynamics, West Greenland, in response to ocean thermal forcing
M. Morlighem · J. Bondzio · H. Seroussi · E. Rignot · E. Larour · A. Humbert · S. Rebuffi
Title: Re: What's new in Greenland?
Post by: AbruptSLR on April 05, 2016, 01:11:26 AM
This being Rignot's 4th substantive article for 2016 -- it is a full-time job just reading them.

For those who do not need another full-time job, Rignot provides a nice overview of his many faceted (but interconnected) interests in the linked video of his AGU Dec 2015 presentation:

https://www.youtube.com/watch?v=3p9uRxX95f4 (https://www.youtube.com/watch?v=3p9uRxX95f4)
Title: Re: What's new in Greenland?
Post by: sidd on April 06, 2016, 12:56:17 AM
"The reconstruction of subglacial thermal conditions suggests that about half of the north-central GIS is now resting on a thawed bed ... "

Nice paper, I attach Fig. 3. Illuminates the question "Why NEGIS ?" and the basal melt in NEEM, and perhaps some basal melt refreeze structure. Also, now i have a strange urge to look at the interior pics of Greenland from Sentinel ...

doi: 10.1038/NGEO2689
Title: Re: What's new in Greenland?
Post by: johnm33 on April 06, 2016, 11:38:10 AM
IF [bigif] the west greenland slope current is driven north by the type of low presently in Labrador
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fpuu.sh%2Fo82dL%2F477cf2c77f.jpg&hash=3995342d53e0b6e0697897967c2d5f7e)
[nullschool] then come saturday/sunday we should see a lot of activity in most of those glaciers served by a channel out into deeper Baffin waters.
There was a less intense low, further south and less extreme tides last August 11-15
http://earth.nullschool.net/#2015/08/11/1200Z/wind/surface/level/orthographic=-46.03,68.03,299/loc=-74.468,75.769 (http://earth.nullschool.net/#2015/08/11/1200Z/wind/surface/level/orthographic=-46.03,68.03,299/loc=-74.468,75.769)
So could be an interestiing week in west Greenland we'll see.
Title: Re: What's new in Greenland?
Post by: A-Team on April 06, 2016, 02:02:02 PM
Quote
bigif west greenland slope current is driven north by low presently in Labrador  then  saturday/sunday we should see a  activity glaciers served by a channel out into deeper Baffin 
Good to get ahead of the curve. A validated prediction carries a lot more weight than a retro-fit.

I am skeptical of this whole paper, "Melting at the base of the Greenland ice sheet explained by Iceland hotspot history". Open peer review would have been much preferable. The actual core data is very sparse and ill-situated. The whole concept of an Iceland hot spot track has been very controversial -- the coincidence of sitting right on a rift and lack of island chain are too much for some to bear.

What here is explained vs conveniently fitted to long known observations and modelling (eg 2001 Fahnestock)? I don't see where the most striking feature of NEGIS ice stream -- the sharp and narrow boundaries are predicted. Note Jakobshavn's basin is shown as very cold yet it is an order of magnitude faster than than the others. The hottest area in east central Greenland hardly moves at all. The radar-based basal melt areas shown are problematic and unsubstantiated. How determinative is geothermal, even assuming the modest excursions over the mean are as shown?

It will be interesting to see what emerges from the current drill to bedrock project at the NEGIS ice stream.
Title: Re: What's new in Greenland?
Post by: AbruptSLR on April 06, 2016, 11:33:28 PM
The north-central Greenland ice sheet is melting from below due to an old tectonic hotspot:

Irina Rogozhina, Alexey G. Petrunin, Alan P. M. Vaughan, Bernhard Steinberger, Jesse V. Johnson, Mikhail K. Kaban, Reinhard Calov, Florian Rickers, Maik Thomas & Ivan Koulakov (2016), "Melting at the base of the Greenland ice sheet explained by Iceland hotspot history", Nature Geoscience, doi:10.1038/ngeo2689

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2689.html (http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2689.html)


Abstract: "Ice-penetrating radar and ice core drilling have shown that large parts of the north-central Greenland ice sheet are melting from below. It has been argued that basal ice melt is due to the anomalously high geothermal flux that has also influenced the development of the longest ice stream in Greenland. Here we estimate the geothermal flux beneath the Greenland ice sheet and identify a 1,200-km-long and 400-km-wide geothermal anomaly beneath the thick ice cover. We suggest that this anomaly explains the observed melting of the ice sheet’s base, which drives the vigorous subglacial hydrology and controls the position of the head of the enigmatic 750-km-long northeastern Greenland ice stream. Our combined analysis of independent seismic, gravity and tectonic data implies that the geothermal anomaly, which crosses Greenland from west to east, was formed by Greenland’s passage over the Iceland mantle plume between roughly 80 and 35 million years ago. We conclude that the complexity of the present-day subglacial hydrology and dynamic features of the north-central Greenland ice sheet originated in tectonic events that pre-date the onset of glaciation in Greenland by many tens of millions of years."
Title: Re: What's new in Greenland?
Post by: RaenorShine on April 09, 2016, 09:09:14 AM
Not strictly new in Greenland, but as a result of Greenland melt, the earths polar wobble as changed according to NASA.

http://www.theguardian.com/environment/2016/apr/09/melting-ice-sheets-changing-the-way-the-earth-wobbles-on-its-axis-says-nasa (http://www.theguardian.com/environment/2016/apr/09/melting-ice-sheets-changing-the-way-the-earth-wobbles-on-its-axis-says-nasa)

Quote
Global warming is changing the way the Earth wobbles on its polar axis, a new Nasa study has found.

Melting ice sheets, especially in Greenland, are changing the distribution of weight on Earth. And that has caused both the North Pole and the wobble, which is called polar motion, to change course, according to a study published on Friday in the journal Science Advances.

Original Paper is published here

http://advances.sciencemag.org/content/2/4/e1501693 (http://advances.sciencemag.org/content/2/4/e1501693)

Quote
Abstract
Earth’s spin axis has been wandering along the Greenwich meridian since about 2000, representing a 75° eastward shift from its long-term drift direction. The past 115 years have seen unequivocal evidence for a quasi-decadal periodicity, and these motions persist throughout the recent record of pole position, in spite of the new drift direction. We analyze space geodetic and satellite gravimetric data for the period 2003–2015 to show that all of the main features of polar motion are explained by global-scale continent-ocean mass transport. The changes in terrestrial water storage (TWS) and global cryosphere together explain nearly the entire amplitude (83 ± 23%) and mean directional shift (within 5.9° ± 7.6°) of the observed motion. We also find that the TWS variability fully explains the decadal-like changes in polar motion observed during the study period, thus offering a clue to resolving the long-standing quest for determining the origins of decadal oscillations. This newly discovered link between polar motion and global-scale TWS variability has broad implications for the study of past and future climate.
Title: Re: What's new in Greenland?
Post by: Cate on April 10, 2016, 06:52:09 PM
Severe Weather Europe on their FB page today:

maps from climatereanalyzer.org, showing temp anomalies for Greenland through Wednesday 13 April ranging 15C-20C above normal, with large areas of the ice sheet exposed to air temps above 0C.

https://www.facebook.com/severeweatherEU/posts/1796835510539542?pnref=story (https://www.facebook.com/severeweatherEU/posts/1796835510539542?pnref=story)

Tweeted here:
https://twitter.com/severeweatherEU/status/719115326705770496/photo/1 (https://twitter.com/severeweatherEU/status/719115326705770496/photo/1)
Title: Re: What's new in Greenland?
Post by: A-Team on April 13, 2016, 02:12:08 PM
I looked through the Greenland sector of abstracts from the EGU spring meeting, a similar event to the December AGU meeting. It provides a preview of ongoing cryosphere research that has not yet reached the journal submission stage. (A lot can change and even disappear by then.) 

The in-house search tool is poorly done but a key word search at google with url restricted to 'meetingorganizer.copernicus.org/' is effective. No posters are available even for the poster session but sometimes it pays to re-google the title. I came across a couple dozen items of interest ... just the titles are given below.

Pathways of Petermann Glacier meltwater, Greenland

SAFIRE 1: Borehole-based englacial and subglacial measurements from a rapidly-moving tidewater glacier: Store Glacier, Greenland

SAFIRE 2: High magnitude englacial strain detected with autonomous phase-sensitive FMCW radar on Store Glacier, West Greenland

Investigation of Greenland Russell glacier with remote sensing observations and ice sheet/hydrodynamic simulations

Modeling of subglacial water pressure on Russell glacier

Reconstructing the dynamics of the Greenland ice sheet during the last deglaciation

Modeling of subglacial water pressure on Russell glacier

Fluctuations of the Greenland Ice Sheet since the last ice age: comparisons of the response of marine and land-terminating ice margins to Holocene climate changes

Reconstruction of the Greenland ice sheet surface mass balance over 1900-2015 with the help of the regional climate MARv3.6 model

Moulin density controls subglacial drainage development under the Greenland Ice Sheet

Continuous monitoring of Greenland and Antarctic ice sheet velocities using Sentinel-1 SAR

An ice-sheet wide framework for englacial attenuation and basal reflection from ice penetrating radar data

Radar data offer insights into the state of the Greenland Ice Sheet in the 1970s

Snow stratigraphy on the Greenland Ice Sheet

Contrasting current and projected changes in surface mass balance components across the Greenland Ice Sheet
Title: Re: What's new in Greenland?
Post by: crandles on April 21, 2016, 08:19:02 PM
That's amazing, there is rain all other Greenland in the days to come !

I'm confused. I only see green and orange and (Edit: hardly any) blue which seems to indicate snow not rain if I am reading legend correctly.
Title: Re: What's new in Greenland?
Post by: Laurent on April 21, 2016, 08:22:35 PM
Ouppss big sorry !!! my mistake !!! Shame on me I remove that !
Title: Re: What's new in Greenland?
Post by: Laurent on April 22, 2016, 01:40:45 PM
A new portal for ice velocity for some glaciers in "real time" in Greenland and Antarctica.
http://www.cpom.ucl.ac.uk/csopr/iv/index.html (http://www.cpom.ucl.ac.uk/csopr/iv/index.html)
Title: Re: What's new in Greenland?
Post by: Sigmetnow on April 27, 2016, 05:44:39 PM
Climate change and extreme weather linked to high pressure over Greenland
Quote
Professor Hanna said: "Our research has found an increase in the incidence of high pressure weather systems remaining stationary over Greenland since the 1980s, which is having a significant impact on extreme weather and climate change in the region.

These weather systems are occurring in the area more often because of strong Arctic warming and changes in the atmospheric jet stream in recent years.

"This is resulting in an increase in the occurrence of warm air in the region and it is also affecting weather systems downstream of Greenland, such as over the UK. The unusually wet weather seen in the UK in the summers of 2007 and 2012, for instance, is linked to these stationary high pressure systems over Greenland."

The research team, which also includes a climate scientist John Cappelen from the Danish Meteorological Institute in Copenhagen, Denmark, found that Greenland 'blocking' pressure systems have become much more variable from year to year in December in recent decades. This reflects an increasing destabilisation of atmospheric weather systems in late autumn and early winter, which the team believe may be related, at least in part, to dramatic declines in sea-ice coverage in the Arctic region.

"Sea-ice coverage throughout the Arctic has significantly reduced in recent years, which we already know is having an amplifying effect on warming in the region. What this study now tells us is that changes in stationary high pressure over Greenland are adding to the change in polar climate," Professor Hanna added.
http://phys.org/news/2016-04-climate-extreme-weather-linked-high.html (http://phys.org/news/2016-04-climate-extreme-weather-linked-high.html)
Title: Re: What's new in Greenland?
Post by: DavidR on April 28, 2016, 07:08:39 AM
NSIDC brings more bad news for the melting season:

http://nsidc.org/greenland-today/ (http://nsidc.org/greenland-today/)

"An early melt event occurred on April 10 through April 15, encompassing the central western and southeastern Greenland coastal areas. The event was a result of a large pulse of mid-Atlantic air moving northward, bringing record warm air to the entire ice sheet and rain along the western coast. Approximately 10 percent of the ice sheet surface melted on April 11, dropping to 5 percent on April 12 and less on later days. A melt event of similar magnitude occurred on April 6 to 9 of 2012, which became the current record surface melt and melt-runoff season for the satellite era (since 1978). (These values and dates are slightly different from those reported in other news releases, because they are based on different snowmelt mapping methods). Early melt events are important as they lower the surface albedo by increasing the snow grain size. A lower albedo allows for more absorption of the sun’s energy, fostering more ice melt."
Title: Re: What's new in Greenland?
Post by: AbruptSLR on May 08, 2016, 09:34:50 PM
The linked reference discusses a technique that uses vibrations generated by crashing ocean waves to monitor southwest Greenland ice sheet’s seasonal changes and associated ice melting:

Aurélien Mordret, T. Dylan Mikesell, Christopher Harig, Bradley P. Lipovsky and Germán A. Preto (06 May 2016), "Monitoring southwest Greenland’s ice sheet melt with ambient seismic noise", Science Advances, Vol. 2, no. 5, e1501538 DOI: 10.1126/sciadv.1501538.


http://advances.sciencemag.org/content/2/5/e1501538 (http://advances.sciencemag.org/content/2/5/e1501538)


Abstract: "The Greenland ice sheet presently accounts for ~70% of global ice sheet mass loss. Because this mass loss is associated with sea-level rise at a rate of 0.7 mm/year, the development of improved monitoring techniques to observe ongoing changes in ice sheet mass balance is of paramount concern. Spaceborne mass balance techniques are commonly used; however, they are inadequate for many purposes because of their low spatial and/or temporal resolution. We demonstrate that small variations in seismic wave speed in Earth’s crust, as measured with the correlation of seismic noise, may be used to infer seasonal ice sheet mass balance. Seasonal loading and unloading of glacial mass induces strain in the crust, and these strains then result in seismic velocity changes due to poroelastic processes. Our method provides a new and independent way of monitoring (in near real time) ice sheet mass balance, yielding new constraints on ice sheet evolution and its contribution to global sea-level changes. An increased number of seismic stations in the vicinity of ice sheets will enhance our ability to create detailed space-time records of ice mass variations."
Title: Re: What's new in Greenland?
Post by: Sigmetnow on May 11, 2016, 07:08:28 PM
NOAA NWS Ocean Prediction Center:
Hurricane-force low west of Greenland.
https://www.facebook.com/NWSOPC/posts/1061059233952807 (https://www.facebook.com/NWSOPC/posts/1061059233952807)
Title: Re: What's new in Greenland?
Post by: Sigmetnow on May 13, 2016, 02:08:30 AM
Quote
Another large and unusually early #Greenland melt is occurring in response to anomalous warmth over the last month
https://twitter.com/zlabe/status/730803456689102848
Title: Re: What's new in Greenland?
Post by: sidd on June 02, 2016, 07:03:46 AM
van den Broeke et many usual suspects

http://www.the-cryosphere-discuss.net/tc-2016-123/ (http://www.the-cryosphere-discuss.net/tc-2016-123/)

open access and very nice. I recommend fig 3) (becoz it's pretty) but the meat is in figs 4,9 and 10.
Apparently mass waste accelerated since 1991 at 15-20 GT/yr^2, and SMB at 10 GT/yr^2. At this rate, sometime between 2024 and 2043 we reach the point when GIS declines  _even if discharge via calving and basal melt of marine terminated glaciers went to zero_

Uncomfortably close.

Read the whole thing.

sidd
Title: Re: What's new in Greenland?
Post by: sidd on June 10, 2016, 01:23:34 AM
http://nsidc.org/greenland-today (http://nsidc.org/greenland-today)

another melt spike. This year might see 2012 scale melt.
Title: Re: What's new in Greenland?
Post by: Espen on June 14, 2016, 08:38:27 PM
New temperature record!

24,8°C was measured at Nuuk Airport on June 10 2016, the previous record was only 24 hours old at 24,7°C measured at the same station.

http://www.dmi.dk/nyheder/arkiv/nyheder-2016/juni/groenland-faar-ny-varmerekord-for-juni/ (http://www.dmi.dk/nyheder/arkiv/nyheder-2016/juni/groenland-faar-ny-varmerekord-for-juni/)
Title: Re: What's new in Greenland?
Post by: A-Team on June 18, 2016, 02:49:41 PM
Quote
10 June 18 another melt spike. This year might see 2012 scale melt. http://nsidc.org/greenland-today (http://nsidc.org/greenland-today)
To be followed by a plunge on June 16th. I wonder if this will be accompanied by clear skies and sharp S2A images.

To be followed by more spiking? Not seeing any year-to-year volatility index, seems like they could just use the 'beta' volatility used in tracking stock prices.

The full resolution graphic is very peculiar in that someone (not at NSIDC) screwed up the placement of tick marks, ie days and weeks are non-integral numbers of pixels (and even the months are wrongly spaced). Thus it is not feasible to subdivide to melt date. Who would make such a stupid design choice when 4 pixels per day was so close? You won't see stuff like this from the Rignot group.
Title: Re: What's new in Greenland?
Post by: J Cartmill on June 18, 2016, 05:08:06 PM
For the "new normal"l 2016 looks to be under performing.
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fbeta.dmi.dk%2Fuploads%2Ftx_dmidatastore%2Fwebservice%2Fe%2Fn%2Fi%2Fb%2Fm%2FMelt_combine.png&hash=3da6c1fcbc3c20af9784c9770ff5ab83)

And as for mass balance it is way behind 2012:
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fbeta.dmi.dk%2Fuploads%2Ftx_dmidatastore%2Fwebservice%2Fb%2Fm%2Fs%2Fd%2Fe%2Faccumulatedsmb.png&hash=f00f7a297d3927e3b2b92e9b11e98dc4)

http://beta.dmi.dk/en/groenland/maalinger/greenland-ice-sheet-surface-mass-budget/ (http://beta.dmi.dk/en/groenland/maalinger/greenland-ice-sheet-surface-mass-budget/)

This image from NSIDC shows how spiky 2012 was:

(https://lh3.googleusercontent.com/3GtSJU3eSKpb1_mgs4MUhseZlUyhYLmdbll7T-WI6uaXLohn9pK1g2pID91RwgHn-XG3YWvpZZYpbpEgHFG_4nwy2b-YB24KFOx_YcrFdHobfwOaLdn1n5iLod7ZEcP25Tb35likmR5tjeqsbqoZVW7zPQbvn7YA2Dhiqycc6HzheYilT91iFgKHT7Xja_N1Rh9nn5o1f8wq9pzET5V2QSihDyz_RSy-7TZiUqPJN5WbGnJ-pku913p8HSIcny3LWZ1PHdzUHmAENUamuAl3T9vaZbbufsGXwdhmkM3AL81c5CRrw_5Oj3Z5cvC6yPhQMV_f6mq76geyCU98wJwy7gyEaCdP0r2Uoo33eOJhT9nWR5PXguiI9dubsADGEmDJx4jpidB0tlJnC5jHNPLgbXyRE-YtkjHEBHfa_PQHUXooOR-c7HcgcAx78p3nPYD-C8a_ivz3nvzXXOuGNtTjZDnBeaPxYKeF7cc0qzV0wc0QczLt8q57laycRwcqUcHVo6zdUI9WpMdV4doQcHawofbFlH4SuVBoVallW9050auRJiu2hOf_mJxZitkKVz8xepg1IfY4wyPwktl9tYjtyFvm0M5BHQ=w706-h432-no)
http://nsidc.org/greenland-today/files/2016/04/GT_Apr16_Fig1.png (http://nsidc.org/greenland-today/files/2016/04/GT_Apr16_Fig1.png)
Title: Re: What's new in Greenland?
Post by: Sleepy on June 19, 2016, 05:37:23 AM
.
Title: Re: What's new in Greenland?
Post by: Sleepy on July 05, 2016, 04:48:33 AM
Dark Snow Field Log 2016 First Entry, by Peter Sinclair.
http://youtu.be/06WIbz3MHN8 (http://youtu.be/06WIbz3MHN8)
Title: Re: What's new in Greenland?
Post by: Juan C. García on July 05, 2016, 06:10:05 AM
Climate Reanalyzer is forecasting High Sea Level Pressure at Greenland this week.

http://cci-reanalyzer.org/Forecasts/#ARC-LEA (http://cci-reanalyzer.org/Forecasts/#ARC-LEA)
Title: Re: What's new in Greenland?
Post by: A-Team on July 08, 2016, 08:53:41 PM
omg we have barely wrapped our heads around Sentinel 1A and now they've launched and re-maneuvered its twin Sentinel 2B to the same plane plus taken the first interferograms as of 22 June 2016. The satellites are on the opposite sides of the earth in sun-synchronous near-polar orbits at 693 km altitude with 175 orbits per 12 day repeat.

1B won't be 'commissioned' until mid-September. They may post initial imagery in the meantime so we need to look at the SNAP toolbox to see if it lets the average person make these interferograms (perhaps just using a graph that nukefix could provide), eg for Petermann,  Jakobshavn and Pine Island. (Recall we've seen Petermann done in emulation with Radarsat.)

The time available for glacier movement is half the orbital period (98.74 minutes) or 49.37 minutes for a single cycle. That pencils out to 3.57 m for Jakobshavn assuming peak velocity of 52 m/day, far less for Petermann.

"Sentinel 1AB are an ideal tool for monitoring glacier flow and changes in Arctic and Antarctic ice shelves.

Sentinel-1’s first such paired ‘interferogram’ combined a Sentinel-1A scan over southern Romania on 9 June with a Sentinel-1B acquisition over the same area just one day before reaching its target orbit position. A second interferogram over northwest Romania was produced shortly after Sentinel-1B reached its final orbit [below].

The rainbow-coloured patterns are related to topography, and they demonstrate that the two satellites’ identical radars are accurately synchronised, pointing in the same direction and that the satellites are in their correct orbits....

For interferometry, SENTINEL-1AB require stringent orbit control. Satellite positioning along the orbit must be accurate, with pointing and timing/synchronisation between interferometric pairs. Orbit positioning control for SENTINEL-1 is defined using an orbital Earth fixed "tube", 50 m (RMS) wide in radius, around a nominal operational path. The satellite is kept inside this "tube" for most of its operational lifetime."

Parameters shown in the diagram will prove critical to eliminating small errors from orbital wander   from the ground displacement interferogram. Presumably this metadata will be read in by
software and not require manual entry (or even understanding) by users.

http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Sentinel-1_satellites_combine_radar_vision (http://www.esa.int/Our_Activities/Observing_the_Earth/Copernicus/Sentinel-1/Sentinel-1_satellites_combine_radar_vision)
Title: Re: What's new in Greenland?
Post by: AbruptSLR on July 10, 2016, 11:58:21 PM
The linked websites provide ESA ice velocity information & images (currently only from Sentinel 1a, but after September hopefully from Sentinel 1b as well) about the three indicated Greenland glaciers:

http://www.cpom.ucl.ac.uk/csopr/iv/index.html (http://www.cpom.ucl.ac.uk/csopr/iv/index.html)

For Jakobshavn
http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=1 (http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=1)

For Petermann
http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=2 (http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=2)

For Nioghalvfjerdsfjorden
http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=0 (http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=0)

See also:
http://www.enveo.at/ (http://www.enveo.at/)

Title: Re: What's new in Greenland?
Post by: AbruptSLR on July 11, 2016, 12:04:58 AM
omg we have barely wrapped our heads around Sentinel 1A and now they've launched and re-maneuvered its twin Sentinel 2B to the same plane plus taken the first interferograms as of 22 June 2016. The satellites are on the opposite sides of the earth in sun-synchronous near-polar orbits at 693 km altitude with 175 orbits per 12 day repeat.

1B won't be 'commissioned' until mid-September. They may post initial imagery in the meantime so we need to look at the SNAP toolbox to see if it lets the average person make these interferograms (perhaps just using a graph that nukefix could provide), eg for Petermann,  Jakobshavn and Pine Island. (Recall we've seen Petermann done in emulation with Radarsat.)

A-Team,

As Sentinel 1b is also monitoring PIG and Thwaites Glaciers, it would be nice if after September you could post some related images in the Antarctic folder:

http://www.cpom.ucl.ac.uk/csopr/iv/index.html (http://www.cpom.ucl.ac.uk/csopr/iv/index.html)

For Thwaites
http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=4 (http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=4)

For PIG
http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=3 (http://www.cpom.ucl.ac.uk/csopr/iv/index.html?glacier_number=3)


See:
http://www.bbc.com/news/science-environment-36051112 (http://www.bbc.com/news/science-environment-36051112)

Extract: "The sextet - Pine Island and Thwaites in Antarctica; and Jakobshavn, Nioghalvfjerdsfjorden, Zacharae Isstrom and Petermann in Greenland - are major contributors to ongoing sea-level rise.

They are thinning and flowing faster, and scientists believe some of them have become unstable.

Routine observation should pick up any sudden changes in behaviour.

The data is currently being gathered by the Sentinel-1a spacecraft, but it will be assisted soon by a sister platform, Sentinel-1b, which the European Space Agency will launch on Friday.

Both have radar instruments that are able to see the glaciers' surfaces day or night, and in all weathers.

They can track activity by keeping a watch on the velocities of crevasses as they move towards the ocean."

Best,
ASLR

Edit: Note that the new satellite's name is Sentinel 1b
Title: Re: What's new in Greenland?
Post by: skanky on July 12, 2016, 04:56:18 PM
Sort of wonder if Dark Snow and Black & Bloom (see below) need their own thread, a la Icebridge, but as Dark Snow posts are in here....

Black & Bloom is a UK project that's working alongside (and with what appears some overlap) Dark Snow, on Greenland. Lots of info. and updates, etc. here:

https://blackandbloom.org/

h/t Peter Sinclair (https://climatecrocks.com/2016/07/11/fish-out-of-water-whats-a-marine-biologist-doing-on-the-ice-sheet/)
Title: Re: What's new in Greenland?
Post by: sidd on July 12, 2016, 10:29:58 PM
doi: 10.1002/2016GL069666

"Between January 2011 and December 2014 we estimate that the Greenland Ice Sheet lost an average of 269 ± 51 Gt/yr of snow and ice. The observed deficit indicates an annual contribution of 0.74 ± 0.14 mm/yr to global mean sea level, which is approximately double the 1992–2011 mean ..."

Doubling in a decade ?

Open access. Read all about it.
Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: Adam Ash on July 14, 2016, 11:11:24 AM
Can't see anywhere better to ask this...

Greenland ice sheet is estimated to contribute about 7.2 metres to global sea level when it melts away.

That contribution is due to the melting of all the ice above sea level becoming water, as all below sea level dose not contribute to sea level rise if it melts, apart from a small fraction due to thermal expansion.

But has anybody estimated what the effect on sea level rise will be from the resulting isostatic rebound?  Assuming it all rebounds to near or above present-day sea level, that displacement would add several metres more to the current maximum estimated sea level rise.  Same goes (much more, I imagine) for Antarctica too as it also has a massive ice overburden on top of land held below sea level which will no doubt rise (and hence displace ocean) when the load is removed.
Title: Re: What's new in Greenland?
Post by: nukefix on July 14, 2016, 12:33:34 PM
The time available for glacier movement is half the orbital period (98.74 minutes) or 49.37 minutes for a single cycle. That pencils out to 3.57 m for Jakobshavn assuming peak velocity of 52 m/day, far less for Petermann.
That's the orbital period in minutes but since the Earth is rotating under the orbit that translates to halving the 12-day repeat-period into six days.
Title: Re: What's new in Greenland?
Post by: skanky on July 14, 2016, 12:50:18 PM
Sort of wonder if Dark Snow and Black & Bloom (see below) need their own thread, a la Icebridge, but as Dark Snow posts are in here....

Black & Bloom is a UK project that's working alongside (and with what appears some overlap) Dark Snow, on Greenland. Lots of info. and updates, etc. here:

https://blackandbloom.org/

h/t Peter Sinclair (https://climatecrocks.com/2016/07/11/fish-out-of-water-whats-a-marine-biologist-doing-on-the-ice-sheet/)

Update from Sinclair: https://climatecrocks.com/2016/07/13/black-and-bloom-ramps-up-reflectivity-research/
Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: Stephen on July 14, 2016, 01:52:05 PM
Can't see anywhere better to ask this...

Greenland ice sheet is estimated to contribute about 7.2 metres to global sea level when it melts away.

That contribution is due to the melting of all the ice above sea level becoming water, as all below sea level dose not contribute to sea level rise if it melts, apart from a small fraction due to thermal expansion.

But has anybody estimated what the effect on sea level rise will be from the resulting isostatic rebound?  Assuming it all rebounds to near or above present-day sea level, that displacement would add several metres more to the current maximum estimated sea level rise.  Same goes (much more, I imagine) for Antarctica too as it also has a massive ice overburden on top of land held below sea level which will no doubt rise (and hence displace ocean) when the load is removed.

But that rebound volume has to come from somewhere. The surrounding  sea floor perhaps?  So the overall effect would be none.  Just a guess.
Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: Iceismylife on July 14, 2016, 06:15:06 PM

But that rebound volume has to come from somewhere. The surrounding  sea floor perhaps?  So the overall effect would be none.  Just a guess.
My guess is that the rebound deficit would be on the order of the density difference between the rock and the ice. Enough rock would go up to replace the push of the ice. The rock is much denser than ice and it takes a long time so...
Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: binntho on July 15, 2016, 09:04:15 AM
But has anybody estimated what the effect on sea level rise will be from the resulting isostatic rebound?  Assuming it all rebounds to near or above present-day sea level, that displacement would add several metres more to the current maximum estimated sea level rise.  Same goes (much more, I imagine) for Antarctica too as it also has a massive ice overburden on top of land held below sea level which will no doubt rise (and hence displace ocean) when the load is removed.

Someone already pointed out that isostatic rebound in one place leads to a lowering somewhere else - the volume of the lithosphere does not change. Isostatic rebound can be quite fast, in South-East Iceland it is currently measured in centimeters annually, due to melting glaciers in that area.

Apparently some areas of Greenland are rising by up to 15 mm annually (a quick Google search gave quite a lot of information).

Globally, isostatic rebound does not affect sea levels. Locally, sea levels may well fall along the Greenland coast, at least in the short run, both from isostatic rebound and from gravitational effects (the mass of the ice sheet pulls the surrounding ocean towards it).
Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: nukefix on July 15, 2016, 09:34:23 AM
Globally, isostatic rebound does not affect sea levels.
Glacial Isostatic Adjustment (GIA) - correction is used in altimetry when deriving global mean sea level:

http://sealevel.colorado.edu/content/what-glacial-isostatic-adjustment-gia-and-why-do-you-correct-it (http://sealevel.colorado.edu/content/what-glacial-isostatic-adjustment-gia-and-why-do-you-correct-it)
Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: RoxTheGeologist on July 16, 2016, 12:40:32 AM

Globally, isostatic rebound does not affect sea levels. Locally, sea levels may well fall along the Greenland coast, at least in the short run, both from isostatic rebound and from gravitational effects (the mass of the ice sheet pulls the surrounding ocean towards it).


Wow.. that raise a really interesting isostatic problem (Finally a post in my field).

Lets assume that the mass change in a column of the ocean with added water has to be isostatically balanced by a mass change in a column of continental rock (otherwise rock will flow from the high to low pressure as evidenced by post glacial rebound).

Adding 1m of water, density 1, with the density of ocean floor to be 2.9, and the density of continents to be  2.7 gives us

1+2.9Ho = 2.7Hl

Hl = height change of continent, Ho being height change of ocean floor.

However, a second assumptions is that the volume of rock does not change globally.
Ho = -0.3/0.7Hl (the continents occupy 3/7 of the globe) volume change of oceanic rock matches continental rock.

Solving these gives us that 1m of water added to the oceans causes the continents to raise 0.254m, and that the oceans floors drop by 0.109m, giving a net sea level increase of 0.637m

Of course, finding that perfect isostatic balance is going to take a lot longer than it takes the melt water to flow around the globe.






Thing of it as squeezing on a spot.. you apply pressure on a broad area to have high pressure in one spot. Yes. We are living on the spot.

 
Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: binntho on July 16, 2016, 08:55:45 AM
Globally, isostatic rebound does not affect sea levels.
Glacial Isostatic Adjustment (GIA) - correction is used in altimetry when deriving global mean sea level:

http://sealevel.colorado.edu/content/what-glacial-isostatic-adjustment-gia-and-why-do-you-correct-it (http://sealevel.colorado.edu/content/what-glacial-isostatic-adjustment-gia-and-why-do-you-correct-it)
Interesting - and makes sense. I stand corrected!
Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: binntho on July 16, 2016, 09:18:22 AM

Globally, isostatic rebound does not affect sea levels. Locally, sea levels may well fall along the Greenland coast, at least in the short run, both from isostatic rebound and from gravitational effects (the mass of the ice sheet pulls the surrounding ocean towards it).


Wow.. that raise a really interesting isostatic problem (Finally a post in my field).

Lets assume that the mass change in a column of the ocean with added water has to be isostatically balanced by a mass change in a column of continental rock (otherwise rock will flow from the high to low pressure as evidenced by post glacial rebound).
 ...

However, a second assumptions is that the volume of rock does not change globally. ... volume change of oceanic rock matches continental rock.
I don't really understand when you talk about the flow of "rock" - isostatic rebound is caused by magma in the mantle shifting about.  "Continental rock" presumably means continental crust, and "oceanic rock" ocean crust. Neither sees any volume change due to isostatic pressure changes. The density of the mantle is thought to be 3.3 in the top layers, probably slightly higher below the continental crust than under the oceanic crust.

The page that nukefix's post links to states that due to post-glacial isostatic rebound, the ocean basins are getting larger (deeper), causing a net effect on sea level of -0.3 mm annually. The Greenland glacier is much smaller than the Ice Age ice sheet, so any effects on sea level due to isostatic rebound from the melting of the former are going to be miniscule.
Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: RoxTheGeologist on July 16, 2016, 05:29:53 PM

I don't really understand when you talk about the flow of "rock" - isostatic rebound is caused by magma in the mantle shifting about.  "Continental rock" presumably means continental crust, and "oceanic rock" ocean crust. Neither sees any volume change due to isostatic pressure changes. The density of the mantle is thought to be 3.3 in the top layers, probably slightly higher below the continental crust than under the oceanic crust.


Rock does flow: Mantle convection is not from movement of magma, you only get melt where the solidus of the rock approaches the geotherm, such as mid ocean ridges, underneath hotspots, in thinning events or where fluids are injected, such as subduction zones. There is unlikely to be any partial melt underneath Greenland. Much of Greenland is (we believe) ancient shield rock.
Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: binntho on July 19, 2016, 08:20:51 AM

I don't really understand when you talk about the flow of "rock" - isostatic rebound is caused by magma in the mantle shifting about.  "Continental rock" presumably means continental crust, and "oceanic rock" ocean crust. Neither sees any volume change due to isostatic pressure changes. The density of the mantle is thought to be 3.3 in the top layers, probably slightly higher below the continental crust than under the oceanic crust.


Rock does flow: Mantle convection is not from movement of magma, you only get melt where the solidus of the rock approaches the geotherm, such as mid ocean ridges, underneath hotspots, in thinning events or where fluids are injected, such as subduction zones. There is unlikely to be any partial melt underneath Greenland. Much of Greenland is (we believe) ancient shield rock.
You are right of course - the mantle is rock, not magma. And the mantle does flow - and has a density of 3.3 in the top layers. Your previous use of the word "rock" seemed to indicate the crust given the density values you gave. The crust does not "flow", i.e. there is no shifting of material from oceanic to continental crust.

You calculated isostatic effects of raised sea levels based on the density of the crust which seems wrong to me. Also I'm not sure whether you are claiming that the volume of the lithosphere changes due to shifting of mass in the hydrosphere.
Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: RoxTheGeologist on July 22, 2016, 06:15:17 PM

The mantle and lithosphere are both comprised of rock. The rheology changes with composition, heat and pressure. The rheology of the rock beneath shields is actually not particularly well understood.

You are right, It would have been better to use the density of rock at which compensation happens in the asthenosphere, and that would scale the height changes that I made above by about 10%.

I'm using conservation of volume of rock to calculate how much the extra water in the oceans would push down of the ocean floors and thereby increase the height of the continents. Of course, that takes 1,000s or 10,000s of years to happen.

One further interesting point is that the water on the Greenland ice sheet is close to the axis of rotation of the earth. Distributing that mass over the oceans will cause the earths rotation to slow by a tiny amount.

Title: Re: What's new.?' A 'silly question' re effect of isostatic rebound on SLR est
Post by: binntho on July 25, 2016, 08:25:34 AM

I'm using conservation of volume of rock to calculate how much the extra water in the oceans would push down of the ocean floors and thereby increase the height of the continents. Of course, that takes 1,000s or 10,000s of years to happen.

One further interesting point is that the water on the Greenland ice sheet is close to the axis of rotation of the earth. Distributing that mass over the oceans will cause the earths rotation to slow by a tiny amount.

This is actually quite interesting - and it makes sense that more pressure on the ocean floors would lead to isostatic adjustment of the continents.

Sea level rise following the end of the last Ice Age was 120 m, if we assume that the -0.3 mm rebound currently measured worldwide can be extended linearly back 10.000 years that would result in some -30 m due to rising continents/sinking sea floor. Reconstructions of sea levels since the last Ice Age, on the other hand, show a steady (if small) increase in sea levels over the same period (see https://en.wikipedia.org/wiki/Sea_level_rise#/media/File:Post-Glacial_Sea_Level.png).

So I'm a bit confused - it makes sense logically that, after an initial surge, isostatic rebound should work to decrease sea levels over the last 10.000 years according to your calculations. But that didn't seem to happen?

As for the change in spin, I seem to remember seeing somewhere that this can already be measured as a result of the melt of the last 25 years of so.
Title: Re: What's new in Greenland?
Post by: Laurent on July 25, 2016, 10:57:39 AM
This graph does not reflect the reality of sea level rise around 7.000 years, that is because they soften too much the datas.
Title: Re: What's new in Greenland?
Post by: J Cartmill on July 30, 2016, 03:51:16 PM
Nature article with a short video about 180000 photos from the 1930's
http://www.nature.com/news/180-000-forgotten-photos-reveal-the-future-of-greenland-s-ice-1.20335 (http://www.nature.com/news/180-000-forgotten-photos-reveal-the-future-of-greenland-s-ice-1.20335)

Title: Re: What's new in Greenland?
Post by: Tor Bejnar on July 30, 2016, 07:35:27 PM
What a great find!  Thanks J Cartmill.  Or should I write "Great find, Anders Bjørk!"
Title: Re: What's new in Greenland?
Post by: sidd on August 04, 2016, 04:06:49 PM
MacGregor et al. 2016 doi:10.1002/2015JF003803 on the thermal state of the bed.

" The transition between a likely frozen bed and an uncertain basal thermal
state follows the western and northern boundaries of the NEGIS system."

And quite a bit under Jacobshawn. I attach a copy of fig 11.
Title: Re: What's new in Greenland?
Post by: A-Team on August 05, 2016, 02:31:39 PM
That's a very carefully written piece that makes a good effort on sparse data. Basal sliding and deformation of subglacial till, as discussed earlier for Jakobshavn, need a thawed bottom. This is not anything brought about or exacerbated by contemporary climate change but rather an inconvenient legacy condition that, unfortunately, would synergize with global warming above to raise sea level faster than a frozen legacy condition would have.

Although sidd already posted the bottom line (Fig.11), Table 1 provides a very useful compendium of known basal temperature data.

There's also a curious analysis of surface texture based on the MODIS mosaic of Greenland (MOG) said to delineate the ice sheet transition between a relatively smooth surface and prominent surface undulations corresponding to relative velocities and so presumably to basal melt status. Yet though shear margins of NEGIS are well defined its route is not distinguished by surface undulations and some adjacent regions don't fit the roughness paradigm. Fig.9 shows this below.

There don't seem to be an immediate prospects for resolving the status of uncertain areas, not plausibly by a massive drilling grid on the flanks because ice cores are more favorable on summit ridges even though these don't have representative bottom conditions. Coring is underway this summer about a third of the way down NEGIS (good twitter site); however no one is laying out exactly what they expect to find by way of temperature profile prediction or rates of bore hole deformation.

The 'companion' article of April 2016, treated neutrally by Macdonald et al, asserts that the anomaly of NEGIS is explained by northeastern Greenland warmed from below tens of millions of years prior by anomalous mantle heat associated with the Iceland hot spot.

There is no chain of islands or bathymetry otherwise indicative of a hot spot track; the North Atlantic initially began to open in Baffin Bay where older basaltic flows are still evident but the subsequent forking history and mid-Arctic Ocean stalling of the Gaekel Ridge are still in a state of scientific confusion (in my view).

Melting at the base of the Greenland Ice Sheet explained by Iceland hotspot history
I Rogozhina, AGPetrunin ... 2016
Nat. Geosci., 9, 366–369, doi:10.1038/ngeo2689 paywalled
https://www.sciencedaily.com/releases/2016/04/160404111603.htm (https://www.sciencedaily.com/releases/2016/04/160404111603.htm)

Quote
Ice-penetrating radar and ice core drilling have shown that large parts of the north-central Greenland ice sheet are melting from below. It has been argued that basal ice melt is due to the anomalously high geothermal flux that has also influenced the development of the longest ice stream in Greenland.

Here we estimate the geothermal flux beneath the Greenland ice sheet and identify a 1,200-km-long and 400-km-wide geothermal anomaly beneath the thick ice cover. We suggest that this anomaly explains the observed melting of the ice sheet's base, which drives the vigorous subglacial hydrology and controls the position of the head of the enigmatic 750-km-long northeastern Greenland ice stream.

Our combined analysis of independent seismic, gravity and tectonic data implies that the geothermal anomaly, which crosses Greenland from west to east, was formed by Greenland's passage over the Iceland mantle plume between roughly 80 and 35 million years ago.
Title: Re: What's new in Greenland?
Post by: bligh8 on August 05, 2016, 03:24:28 PM
The abandoned ice sheet base at Camp Century, Greenland, in a warming climate


.wiley.com/doi/10.1002/2016GL069688/full

"We first inventory the nature and quantity of abandoned wastes buried at the Camp Century site (supporting information). Physical waste, such as buildings and railway, is approximately 9.2 · 103 t. Chemical waste is an estimated 2.0 · 105 L of diesel fuel and a nontrivial quantity of polychlorinated biphenyls (PCBs). Biological waste consists of at least 2.4 · 107 L of grey water, including sewage, disposed in unlined sumps. Previously acknowledged radiological waste (coolant for the portable nuclear generator) had a bulk radioactivity of 1.2 · 109 Bq at the time of its disposal (1960–1963) in an unlined sump. While nontrivial in absolute terms, this radiological waste is small compared to the >4.6 · 1012 Bq accidentally dispersed in the vicinity of Thule AB in 1968 [Christensen, 2009]."
Title: Re: What's new in Greenland?
Post by: Tigertown on August 09, 2016, 04:33:00 AM
New map for bottom melt of Greenland Ice sheet. Article explains how it was derived.

www.space.com/33664-nasa-map-reveals-thawing-under-greenland.html (http://www.space.com/33664-nasa-map-reveals-thawing-under-greenland.html)

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2F&hash=35d7d5d7526c9897dfb55501e320295a)
Title: Re: What's new in Greenland?
Post by: Tealight on September 04, 2016, 08:29:23 PM
Evidence for oldest life found in southwest Greenland on newly exposed rock. I attached an image with the rough position using Google Earth.


Quote
Rapid emergence of life shown by discovery of 3,700-million-year-old microbial structures

Biological activity is a major factor in Earth’s chemical cycles, including facilitating CO2 sequestration and providing climate feedbacks. Thus a key question in Earth’s evolution is when did life arise and impact hydrosphere–atmosphere–lithosphere chemical cycles? Until now, evidence for the oldest life on Earth focused on debated stable isotopic signatures of 3,800–3,700 million year (Myr)-old metamorphosed sedimentary rocks and minerals1, 2 from the Isua supracrustal belt (ISB), southwest Greenland3. Here we report evidence for ancient life from a newly exposed outcrop of 3,700-Myr-old metacarbonate rocks in the ISB that contain 1–4-cm-high stromatolites—macroscopically layered structures produced by microbial communities. The ISB stromatolites grew in a shallow marine environment, as indicated by seawater-like rare-earth element plus yttrium trace element signatures of the metacarbonates, and by interlayered detrital sedimentary rocks with cross-lamination and storm-wave generated breccias. The ISB stromatolites predate by 220 Myr the previous most convincing and generally accepted multidisciplinary evidence for oldest life remains in the 3,480-Myr-old Dresser Formation of the Pilbara Craton, Australia4, 5. The presence of the ISB stromatolites demonstrates the establishment of shallow marine carbonate production with biotic CO2 sequestration by 3,700 million years ago (Ma), near the start of Earth’s sedimentary record. A sophistication of life by 3,700 Ma is in accord with genetic molecular clock studies placing life’s origin in the Hadean eon (>4,000 Ma)6.

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature19355.html (http://www.nature.com/nature/journal/vaop/ncurrent/full/nature19355.html)
Title: Re: What's new in Greenland?
Post by: ms on September 05, 2016, 04:23:12 PM
The danish professor of geology Minik Rosing, who has been studying the specific area for years is very sceptical of their findings.
http://videnskab.dk/naturvidenskab/forskere-verdens-aeldste-fossiler-er-fundet-i-groenland (http://videnskab.dk/naturvidenskab/forskere-verdens-aeldste-fossiler-er-fundet-i-groenland)
( in danish)
He is not convinced that the formations they found are a sign of life. But he does agree that the area has signs of early life ( http://science.sciencemag.org/content/283/5402/674 (http://science.sciencemag.org/content/283/5402/674) )
Title: Re: What's new in Greenland?
Post by: AbruptSLR on September 05, 2016, 04:42:40 PM
Per the linked reference the north-east sector of the GIS (GrIS) will experience the most rapid increasing in surface ice melting with continued global warming; however, if ECS is closer to 4.6 rather than 3.2 C, then the timeframe for the indicated melting will be too slow:

Ádám Ignéczi, Andrew J. Sole, Stephen J. Livingstone, Amber Leeson, Xavier Fettweis, Nick Selmes, Noel Gourmelen & Kate Briggs (31 August 2016), "North-east sector of the Greenland Ice Sheet to undergo the greatest inland expansion of supraglacial lakes during the 21st century", Geophysical Research Letters, DOI: 10.1002/2016GL070338


http://onlinelibrary.wiley.com/doi/10.1002/2016GL070338/abstract (http://onlinelibrary.wiley.com/doi/10.1002/2016GL070338/abstract)

Abstract: "The formation and rapid drainage of supraglacial lakes (SGL) influences the mass balance and dynamics of the Greenland Ice Sheet (GrIS). Although SGLs are expected to spread inland during the 21st century due to atmospheric warming, less is known about their future spatial distribution and volume. We use GrIS surface elevation model and regional climate model outputs to show that at the end of the 21st century (2070-2099) approximately 9.8 ± 3.9 km3 (+113% compared to 1980-2009) and 12.6 ± 5 km3 (+174%) of meltwater could be stored in SGLs under moderate (RCP 4.5) and high (RCP 8.5) climate change scenarios respectively. The largest increase is expected in the north-eastern sector of the GrIS (191% in RCP 4.5 and 320% in RCP 8.5), whereas in west Greenland, where the most SGLs are currently observed, the future increase will be relatively moderate (55% in RCP 4.5 and 68% in RCP 8.5)."
Title: Re: What's new in Greenland?
Post by: sidd on September 21, 2016, 11:33:40 PM
GRACE estimates for GIS mass loss are 10% too low because of flawed GIA model.  Many usual suspects on the author list. Open access. Read all about it.

doi: 10.1126/sciadv.1600931
Title: Re: What's new in Greenland?
Post by: Lennart van der Linde on September 22, 2016, 06:35:07 AM
Thanks, sidd.
It's about 7-8 percent more melt between 2003-2013 than thought earlier, according to:
https://www.sciencedaily.com/releases/2016/09/160921145338.htm (https://www.sciencedaily.com/releases/2016/09/160921145338.htm)

Here's the full article by Khan et al 2016,Geodetic measurements reveal similarities between post–Last Glacial Maximum and present-day mass loss from the Greenland ice sheet:
http://advances.sciencemag.org/content/2/9/e1600931.full (http://advances.sciencemag.org/content/2/9/e1600931.full)

Abstract
Accurate quantification of the millennial-scale mass balance of the Greenland ice sheet (GrIS) and its contribution to global sea-level rise remain challenging because of sparse in situ observations in key regions. Glacial isostatic adjustment (GIA) is the ongoing response of the solid Earth to ice and ocean load changes occurring since the Last Glacial Maximum (LGM; ~21 thousand years ago) and may be used to constrain the GrIS deglaciation history. We use data from the Greenland Global Positioning System network to directly measure GIA and estimate basin-wide mass changes since the LGM. Unpredicted, large GIA uplift rates of +12 mm/year are found in southeast Greenland. These rates are due to low upper mantle viscosity in the region, from when Greenland passed over the Iceland hot spot about 40 million years ago. This region of concentrated soft rheology has a profound influence on reconstructing the deglaciation history of Greenland. We reevaluate the evolution of the GrIS since LGM and obtain a loss of 1.5-m sea-level equivalent from the northwest and southeast. These same sectors are dominating modern mass loss. We suggest that the present destabilization of these marine-based sectors may increase sea level for centuries to come. Our new deglaciation history and GIA uplift estimates suggest that studies that use the Gravity Recovery and Climate Experiment satellite mission to infer present-day changes in the GrIS may have erroneously corrected for GIA and underestimated the mass loss by about 20 gigatons/year.
Title: Re: What's new in Greenland?
Post by: sidd on October 31, 2016, 11:07:34 PM
Nice recap of 2016 melt season at nsidc

http://nsidc.org/greenland-today/2016/10/2016-melt-season-in-review/ (http://nsidc.org/greenland-today/2016/10/2016-melt-season-in-review/)
Title: Re: What's new in Greenland?
Post by: charles_oil on November 04, 2016, 10:17:15 PM
At NSIDC there is now an interactive "chartic" style graph for the melting on Greenland - sadly its arrived just when they have stopped recording the melt so we wont catch any surprises in the current weirdly high temperatures.

As its real daily data rather than smoothed 5 day data the bands are a bit wide and rugged - so its harder to see what is going on than with the Chartic area/ extent one.

http://nsidc.org/greenland-today/greenland-surface-melt-extent-interactive-chart/ (http://nsidc.org/greenland-today/greenland-surface-melt-extent-interactive-chart/) - would this be a handy link for the ASI Graphs section ?
Title: Re: What's new in Greenland?
Post by: Anne on January 02, 2017, 11:25:42 PM
Using Landsat to Take the Long View on Greenland's Glaciers

A new publicly accessible data portal for analysing changes in outlet glacier flow velocities. EOS article from 29 December:
Quote
<snip>We based our project on more than 37,000 optical images collected by multiple sensors aboard the U.S. Geological Survey (USGS) and NASA’s Landsat satellites. The data span the period between 1972, when Landsat 1 was launched, and 2015, using data from Landsat 8 (launched in 2013), although most of the Landsat scenes were acquired after 1998.

We will continue to extend the database using new scenes recorded by the ongoing Landsat 7 and 8 missions. The USGS Landsat Global Archive Consolidation (LGAC) will add even more scenes, providing access to Landsat data that are archived at individual international ground stations [Wulder et al., 2016]. For Greenland, this could provide a considerable number of scenes from Landsat 4 and 5, dating back to 1982.

These additional images are valuable for extending the time span of the velocity time series. This greater time span is particularly important for inferring flow velocity variations that occur within the span of one season, and it may help to close observation gaps that occurred before 1999, when Landsat 7 was launched. Moreover, in regions of extensive cloud coverage, collecting Landsat scenes over a longer time span increases the chance of obtaining cloud-free data.

Enhanced Data Processing Provides a Clearer Picture
For 302 glaciers all around Greenland, we have processed more than 100,000 flow velocity fields from 1972 to 2012. We have extended this processing to include velocity fields for about 50 major glaciers up to 2015 so far.

By adding a quality flag that indicates the reliability of the data, we reduced the number of existing velocity fields with extensive outliers. We used an outlier detection strategy that compared the differences between each observed velocity product and a theoretically derived velocity field to compile the statistical parameters for our evaluation. Altogether, we have made more than 40,000 flow velocity fields accessible so far, and we continue to add new velocity fields as we process more data.

Rosenau et al. [2015] described a number of steps included in the processing procedure. We have improved the correction for tilt and terrain effects (orthorectification) using the Global Digital Elevation Map Version 2 (GDEM V2) from NASA’s Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). The improved orthorectification step, in particular, facilitates the usage of overlapping scenes from orbits that are not repeat passes. The ability to include these additional scenes provides a much higher effective sampling rate than would be provided by repeat-pass sampling, which is limited to the repeat orbit of 16 days (Landsat 4 to 8 ) or 18 days (Landsat 1 to 3).

In 2003, a small pair of mirrors (the scan line corrector) aboard Landsat 7 failed, introducing data gaps as well as small shifts between the scan lines. We applied a destriping correction to mitigate the impact on the resulting velocity fields. In addition, we removed outliers using an adaptive, recursive filter approach. The combination of all these improvements leads to higher accuracy of the inferred velocity fields.

Long-Term and Seasonal Trends in Flow Velocity
The long time span covered by the Landsat scenes allows us to determine long-term flow velocity trends. The high temporal resolution lets us analyze seasonal flow velocity variations of numerous outlet glaciers. However, the pattern of temporal and spatial distributions of the flow velocity changes is not uniform (Figure 1). The monitoring system provides a powerful tool to examine the flow velocity pattern throughout time and space, and we have detected an acceleration pattern for a number of outlet glaciers.
More at the link: https://eos.org/project-updates/using-landsat-to-take-the-long-view-on-greenlands-glaciers
and at Technische Universität Dresden’s site here: https://data1.geo.tu-dresden.de/flow_velocity/
Title: Re: What's new in Greenland?
Post by: Shared Humanity on January 20, 2017, 01:24:17 AM
Wasn't sure where to post this photo of a melt lake on Greenland but decided to post it here. The photo came, not from a science study but as more of an art project. The link to more photos is here.

https://www.theguardian.com/artanddesign/2017/jan/19/what-should-be-pristine-white-is-littered-with-blue-timo-liebers-arctic-photography (https://www.theguardian.com/artanddesign/2017/jan/19/what-should-be-pristine-white-is-littered-with-blue-timo-liebers-arctic-photography)

This one interested me because of what it suggests about these melt lakes. The fragmented floes look like something you would see in the CAB during the height of the melt season and suggests that this lake does not freeze completely in the winter. I wonder how many melt lakes are like this?
Title: Re: What's new in Greenland?
Post by: Milret2 on February 11, 2017, 07:49:58 AM
I just found this in today's Washington Post, am not entirely sure where the best place to put it is, and am not sure I know how to link so feel free to move it if I link properly but in a poor area and let me know if the link is bad.

A project started by NASA five years ago is starting to pay off. It is called OMG for "Oceans are Melting Greenland" and it is basically trying to see what temperature differentials are doing to underwater glacier masses at various levels. So far ... does not look very good but not enough data has been observed and I doubt that the current administration will allow much more to be collected.

Will try to leave a link here >>http://wapo.st/2lyasOz?tid=ss_mail (http://wapo.st/2lyasOz?tid=ss_mail)<<
Title: Re: What's new in Greenland?
Post by: oren on February 11, 2017, 11:58:48 AM
I just found this in today's Washington Post, am not entirely sure where the best place to put it is, and am not sure I know how to link so feel free to move it if I link properly but in a poor area and let me know if the link is bad.

A project started by NASA five years ago is starting to pay off. It is called OMG for "Oceans are Melting Greenland" and it is basically trying to see what temperature differentials are doing to underwater glacier masses at various levels. So far ... does not look very good but not enough data has been observed and I doubt that the current administration will allow much more to be collected.

Will try to leave a link here >>http://wapo.st/2lyasOz?tid=ss_mail (http://wapo.st/2lyasOz?tid=ss_mail)<<
The link worked for me with a slight modification http://wapo.st/2lyasOz (http://wapo.st/2lyasOz)
Title: Re: What's new in Greenland?
Post by: Tor Bejnar on February 11, 2017, 04:04:48 PM
Alas, it wasn't started 5 years ago - it started 2 years ago.  It was planned to be a 5-year study.
Here’s a figure that the scientists have produced, showing the overall flow of waters around the ice island:
(https://img.washingtonpost.com/news/energy-environment/wp-content/uploads/sites/43/2017/02/OMG-greenland-map-of-currents.png)
Quote
...
“It’s too early” to run the model, said Mathieu Morlighem, a researcher at the University of California and the lead author of one of the papers presenting the accumulating data. “I think you need to wait another year or two, maybe more. It was not possible at all before OMG.”

Still, the recently published findings mark a start. Morlighem’s study, for instance, looked at the depth and shape of the seafloor near the fronts of and beneath numerous Greenland glaciers. The research shows that numerous glaciers extend deeper beneath the surface of the ocean than previously thought.

For instance, Store Glacier in northwestern Greenland (at around 70 degrees North latitude in the image above) starts at 400 meters (around 1,300 feet) deep where its front touches the ocean, and then plunges to depths as high as 1,000 meters deep (3,280 feet) farther inland — making it quite vulnerable to the ocean. Prior research, however, had suggested the glacier was much shallower.

The same was true of numerous other glaciers, which also appear more vulnerable than previously thought.

“OMG is transforming our knowledge of which glaciers are vulnerable to more warming or not,” Morlighem said. “So I wouldn’t say we have been surprised; it’s more, we had no idea, for many of these fjords, what they were looking like.”

Overall, the data are also showing that Greenland’s west coast is far more vulnerable, in general, than its east, Morlighem said.

The second study, meanwhile, examines ocean circulation around the Greenland coast and finds, strikingly, that between 68 degrees North latitude along the coast and 77 degrees North (see above), the deepest warm layer of Atlantic water cools from 3.5 degrees Celsius down to 2.5 degrees Celsius. Moreover, it does so in part because the water busily melts away at a large and deep glacier called Upernavik at 73 degrees North, which touches the ocean in 675 meter (over 2,000 foot) deep waters. The cold meltwater from the glacier spills into the ocean and, through mixing, cools the warm Atlantic water somewhat.

“The glaciers there are actively losing enough ice, and enough fresh water, that it’s important for the oceanography, and how the water changes as it goes up the west coast of Greenland,” says Willis. That in itself is proof that Greenland is melting quite a lot.

The big picture is that NASA’s new data suggest — that’s right — new vulnerabilities.

“Overall, together I think these papers suggest that the glaciers as a whole are more vulnerable than we thought they were,” Willis said. He says that, of course, with the aforementioned caveat that NASA is not ready yet to feed the data into a model that actually shows how this could play out over the decades of our future.
...
Title: Re: What's new in Greenland?
Post by: Carex on February 12, 2017, 01:50:33 PM
Is their coastal topography available as a map, or has it been incorporated into any other bedrock/till models??
Title: Re: What's new in Greenland?
Post by: johnm33 on February 13, 2017, 01:14:14 AM
'coastal topography'
http://membrane.com/sidd/greenland-2013/45-270.jpg (http://membrane.com/sidd/greenland-2013/45-270.jpg)
http://membrane.com/sidd/greenland-2013/large-1-text.jpg (http://membrane.com/sidd/greenland-2013/large-1-text.jpg)
I've yet to find better detail.
Title: Re: What's new in Greenland?
Post by: Carex on February 13, 2017, 01:24:02 PM
Since the OMG study is mapping glacier mouths and according to press reports finding more deep channels underlying more west coast glaciers, I was wondering if they had produced/or are planing to produce an updated coastal topography/bathymetric map.  It seems like it would be a first step on which to present the rest of their work.   
Title: Re: What's new in Greenland?
Post by: Susan Anderson on February 13, 2017, 07:33:44 PM
Here's an article linked from the OMG article, apologies if someone else has already posted it:
http://www.tos.org/oceanography/assets/docs/29-4_morlighem.pdf (http://www.tos.org/oceanography/assets/docs/29-4_morlighem.pdf)

Authors/official citation (above link provides full content):
Morlighem, M., E. Rignot, and J.K. Willis. 2016. Improving bed topography mapping of Greenland glaciers using NASA’s Oceans Melting Greenland (OMG) data. Oceanography 29(4):62–71, https://doi.org/10.5670/oceanog.2016.99. (https://doi.org/10.5670/oceanog.2016.99.)

Title: Re: What's new in Greenland?
Post by: sidd on February 17, 2017, 07:45:17 PM
doi: 10.1002/2016PA003014

Interesting paper about meltwater from Greenland reaching as far south as Bermuda during the Eemian (120-130Kyr BP)

"Shells from Rocky Bay and Grape Bay populate two distinct temperature ranges. Temperatures in Rocky Bay are 16 to 27°C, ~2°C lower than modern on average, whereas temperatures recorded by Grape Bay shells are 8 to 20°C, averaging ~10°C colder than modern "

"This second sea level rise event likely included contributions from both the Greenland and West Antarctic Ice Sheets [Dutton et al., 2015]. The southern portion of the Greenland Ice Sheet in particular underwent substantial melting between ~122 and ~119 ka [Colville et al., 2011; NEEM Community Members, 2013]. Given the location of Bermuda in the North Atlantic and the time constraints on deposition, it is possible, and perhaps likely, that the meltwater pulse recorded by Grape Bay shells came from rapid melting of the Greenland Ice Sheet."

"This possibility makes our results particularly relevant for the future of the North Atlantic. It appears that substantial and rapid melting occurred after thousands of years of sustained interglacial climate, when global ice volume was even smaller than today [Dutton and Lambeck, 2012]."

The possibility of MWP1A scale sea level rise is sometimes discounted since the volume of available ice to melt is smaller today. In that context, that last sentence is the killer, " ... when global ice volume was even smaller than today ... "

sidd
Title: Re: What's new in Greenland?
Post by: P-maker on April 01, 2017, 10:10:35 PM
A new study just out about marginal Glaciers and Ice Caps (GICs) in Greenland, in which the authors managed to:

Quote
identify 1997 (±5 years) as a tipping point for GICs mass balance. That year marks the onset of a rapid deterioration in the capacity of the GICs firn to refreeze meltwater. Consequently, GICs runoff increases 65% faster than meltwater production, tripling the post-1997 mass loss to 36±16 Gt−1, or ∼14% of the Greenland total.”

See more at: http://www.nature.com/articles/ncomms14730 (http://www.nature.com/articles/ncomms14730)
Title: Re: What's new in Greenland?
Post by: sqwazw on April 04, 2017, 04:23:22 AM
NSIDC's greenland-today is back online for 2017. No action yet.

http://nsidc.org/greenland-today/ (http://nsidc.org/greenland-today/)
Title: Re: What's new in Greenland?
Post by: gerontocrat on April 13, 2017, 02:56:55 PM
NSIDC's greenland-today is back online for 2017. No action yet.

http://nsidc.org/greenland-today/ (http://nsidc.org/greenland-today/)

There has been a tiny bit of action. Look very carefully on Cumulative  Melt Days Jan 1 - Apr 11 at bottom SW corner and there are 2 light blue pixels !!!
Title: Re: What's new in Greenland?
Post by: DrTskoul on April 13, 2017, 03:00:50 PM
NSIDC's greenland-today is back online for 2017. No action yet.

http://nsidc.org/greenland-today/ (http://nsidc.org/greenland-today/)

There has been a tiny bit of action. Look very carefully on Cumulative  Melt Days Jan 1 - Apr 11 at bottom SW corner and there are 2 light blue pixels !!!


Yay... you pass the eye test...
Title: Re: What's new in Greenland?
Post by: Cate on April 21, 2017, 04:59:39 PM
NASA OMG blog by science communicator Laura Faye Tenebaum on Greenland: "A vast melting desert."

".....Over my headset, I can hear the pilots discussing the flight path with the instrument engineers. Out the window, I can see Greenland’s northernmost glaciers below us; white upon white upon white. They sure appear stable, still, enduring. But they’re not. They’re melting..."

https://climate.nasa.gov/blog/2578/a-vast-melting-desert/

Good read.

Title: Re: What's new in Greenland?
Post by: Reallybigbunny on April 24, 2017, 11:21:24 PM
I have been wondering how measures are being made/estimated of current Greenland ice melt rates. Can anyone tell me where to look?

Please see link below regarding Climate changes clues revealed by ice sheet collapse.

https://www.sciencedaily.com/releases/2017/04/170424093950.htm (https://www.sciencedaily.com/releases/2017/04/170424093950.htm) 
Title: Re: What's new in Greenland?
Post by: crandles on April 25, 2017, 12:36:38 AM
Try: Gravity Recovery and Climate Experiment (GRACE)

Greenland ice mass loss continued in 2016
https://www.climate.gov/news-features/featured-images/greenland-ice-mass-loss-continued-2016 (https://www.climate.gov/news-features/featured-images/greenland-ice-mass-loss-continued-2016)


Regional acceleration in ice mass loss from Greenland and Antarctica using GRACE time-variable gravity data (2014 paper)
http://onlinelibrary.wiley.com/doi/10.1002/2014GL061052/full (http://onlinelibrary.wiley.com/doi/10.1002/2014GL061052/full)

or search further for Gravity Recovery and Climate Experiment (GRACE)

HTH
Title: Re: What's new in Greenland?
Post by: Reallybigbunny on April 25, 2017, 03:52:46 AM
Thanks Crandles, perfect!  :)
Title: Re: What's new in Greenland?
Post by: budmantis on April 25, 2017, 07:41:10 AM
NASA OMG blog by science communicator Laura Faye Tenebaum on Greenland: "A vast melting desert."

".....Over my headset, I can hear the pilots discussing the flight path with the instrument engineers. Out the window, I can see Greenland’s northernmost glaciers below us; white upon white upon white. They sure appear stable, still, enduring. But they’re not. They’re melting..."

https://climate.nasa.gov/blog/2578/a-vast-melting-desert/

Good read.

Good article Cate. Thanks for the link.
Title: Re: What's new in Greenland?
Post by: iceman on April 28, 2017, 02:04:34 PM
I don't get the warm spell forecast for northerly Greenland around May 4-5.  The weak low moving in from Baffin doesn't seem to carry much atmospheric moisture, and it's a little early for the sun to have much warming power that far north.  Is it some unusual cloud condition causing increased downwelling ILR?
   If the forecast verifies, attendant surface melt will be quite early for that location.
Title: Re: What's new in Greenland?
Post by: AbruptSLR on May 02, 2017, 04:48:14 PM
I don't get the warm spell forecast for northerly Greenland around May 4-5.  The weak low moving in from Baffin doesn't seem to carry much atmospheric moisture, and it's a little early for the sun to have much warming power that far north.  Is it some unusual cloud condition causing increased downwelling ILR?
   If the forecast verifies, attendant surface melt will be quite early for that location.

The linked article is entitled: "Early Greenland Melt Spike Possible as Forecast Calls for Temperatures of up to 50 F Above Average".  The GIS melt season will likely start early this year.

https://robertscribbler.com/2017/05/01/early-greenland-melt-spike-possible-as-forecast-calls-for-temperatures-of-up-to-50-f-above-average/

Extract: "Greenland — a region vulnerable to the slings and arrows of human-forced climate change — appears set to experience both considerable warming and a significant melt spike this week.

Starting on Wednesday, May 3, a sprawling dome of high pressure is expected to begin to extend westward from the far North Atlantic and out over Iceland. As the high pressure dome builds to 1040 mb over the next couple of days, its clockwise flow will thrust abnormally warm and moist air northward out of the Atlantic. This air-mass is expected first to over-ride eastern Greenland, then run up into Baffin Bay, finally encompassing most of the island and its vast, receding glaciers."
Title: Re: What's new in Greenland?
Post by: Tealight on May 03, 2017, 10:02:38 AM
.... and it's a little early for the sun to have much warming power that far north.  Is it some unusual cloud condition causing increased downwelling ILR?
   If the forecast verifies, attendant surface melt will be quite early for that location.

Yes it is early, but solar radiation is equal to early August and with the right atmospheric conditions mentioned by AbruptSLR widespread melt can happen. It typically takes until June because the sun first has to melt all the snow and generally heat the land to freezing temperature.
Title: Re: What's new in Greenland?
Post by: gerontocrat on May 04, 2017, 03:35:07 PM
http://nsidc.org/greenland-today/ (http://nsidc.org/greenland-today/) shows some actual melting

Title: Re: What's new in Greenland?
Post by: gerontocrat on May 05, 2017, 03:29:19 PM
http://nsidc.org/greenland-today/ (http://nsidc.org/greenland-today/) shows some increased melting  May 3 (all on SE quarter coast).
Title: Re: What's new in Greenland?
Post by: AbruptSLR on May 05, 2017, 06:26:55 PM
The linked reference discusses the positive feedback mechanism between Arctic Sea Ice extent loss and ice mass loss from the GIS:

Stroeve, J. C., Mioduszewski, J. R., Rennermalm, A., Boisvert, L. N., Tedesco, M., and Robinson, D.: Investigating the Local Scale Influence of Sea Ice on Greenland Surface Melt, The Cryosphere Discuss., doi:10.5194/tc-2017-65, in review, 2017.

http://www.the-cryosphere-discuss.net/tc-2017-65/ (http://www.the-cryosphere-discuss.net/tc-2017-65/)

Abstract. Rapid decline in Arctic sea ice cover in the 21st century may have wide-reaching effects on the Arctic climate system, including the Greenland ice sheet mass balance. Here, we investigate whether local changes in sea ice around the Greenland ice sheet have had an impact on Greenland surface melt. Specifically, we investigate the relationship between sea ice concentration, the timing of melt onset and open water fraction surrounding Greenland with ice sheet surface melt using a combination of remote sensing observations, and outputs from a reanalysis model and a regional climate model for the period 1979–2015. Statistical analysis points to covariability between Greenland ice sheet surface melt and sea ice within Baffin Bay and Davis Strait. While some of this covariance can be explained by simultaneous influence of atmospheric circulation anomalies on both the sea ice cover and Greenland melt, within Baffin Bay we find a modest correlation between detrended melt onset over sea ice and the adjacent ice sheet melt onset. This correlation appears to be related to increased transfer of sensible and latent heat fluxes from the ocean to the atmosphere in early sea ice melt years, increasing temperatures and humidity over the ice sheet that in turn initiate ice sheet melt.
Title: Re: What's new in Greenland?
Post by: Jester Fish on May 05, 2017, 10:13:02 PM
Greenland melt lifting out of the Interdecile range   :'( for May 4 posting....
http://nsidc.org/greenland-today/ (http://nsidc.org/greenland-today/)
Title: Re: What's new in Greenland?
Post by: gerontocrat on May 09, 2017, 02:48:30 PM
Greenland melt continues (May 7 nsidc images)

Title: Re: What's new in Greenland?
Post by: silkman on May 11, 2017, 09:32:34 AM
Surface melt up and running in the SW:
Title: Re: What's new in Greenland?
Post by: magnamentis on May 11, 2017, 01:47:59 PM
absolutely and in reality it's even a bit more and longer than the low resolution illustrations show, like i.e. in ilulissat ice-fjord which is not THAT far south at all LOL

Title: Re: What's new in Greenland?
Post by: Forest Dweller on May 11, 2017, 05:51:41 PM
High temperatures up to 6.2 C now between Hudson and Baffin bay.
With southwestern Greenland still above freezing as well.

Title: Re: What's new in Greenland?
Post by: Reallybigbunny on May 13, 2017, 08:39:15 PM
I found the thread below very interesting. I haven't seen it posted elsewhere. Does anyone know if moulins are a common phenomena? I understood lakes form on top of glaciers, but I did not know about this mechanism for draining.


The Melting of Greenland: Prof Konrad Steffen (March 2017). Published on May 12, 2017


https://www.youtube.com/watch?v=8-0ynd1Vesk (https://www.youtube.com/watch?v=8-0ynd1Vesk)
Title: Re: What's new in Greenland?
Post by: magnamentis on May 13, 2017, 08:41:47 PM
very common indeed


https://www.google.es/search?q=moulins%2Bglaciers&oq=moulins%2Bglaciers&aqs=chrome..69i57j0.5383j0j9&sourceid=chrome&ie=UTF-8 (https://www.google.es/search?q=moulins%2Bglaciers&oq=moulins%2Bglaciers&aqs=chrome..69i57j0.5383j0j9&sourceid=chrome&ie=UTF-8)

https://www.google.es/search?q=gletscherm%C3%BChlen&num=100&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwj2tfaWw-3TAhXEBBoKHRGBAeEQsAQIPw (https://www.google.es/search?q=gletscherm%C3%BChlen&num=100&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwj2tfaWw-3TAhXEBBoKHRGBAeEQsAQIPw)
Title: Re: What's new in Greenland?
Post by: Reallybigbunny on May 13, 2017, 11:32:09 PM
Thanks Magnamentis. excuse my ignorance. In view of rising temperatures in the Arctic, there must be increasing numbers of moulins contributing to the destabilisation of the Greenland ice sheet? Another positive feedback factor? Or am I off track?
Title: Re: What's new in Greenland?
Post by: oren on May 14, 2017, 12:19:53 AM
Thanks Magnamentis. excuse my ignorance. In view of rising temperatures in the Arctic, there must be increasing numbers of moulins contributing to the destabilisation of the Greenland ice sheet? Another positive feedback factor? Or am I off track?
I would say the main factor is not the moulins themselves but the amount of surface melt and total meltwater. More meltwater will probably lead to more moulins. Surface melt in turn depends on the weather in Greenland which isn't necessarily in lockstep with the whole arctic.
The best way to track current season surface melt and compared to past behavior is using this NSIDC link
Greenland Ice Sheet Today (http://nsidc.org/greenland-today/)
Note 2012 was the top year in terms of surface melt over GIS.
Title: Re: What's new in Greenland?
Post by: Reallybigbunny on May 14, 2017, 01:52:51 AM
Thanks oren :) I was thinking that water drainage through moulins might cause heating of the ice sheet from below leading to destabilisation, in comparison to water that drained straight into the sea.
Title: Re: What's new in Greenland?
Post by: oren on May 14, 2017, 04:44:11 AM
Thanks oren :) I was thinking that water drainage through moulins might cause heating of the ice sheet from below leading to destabilisation, in comparison to water that drained straight into the sea.
You are indeed right AFAIK.
Title: Re: What's new in Greenland?
Post by: johnm33 on May 14, 2017, 11:04:43 AM
Thanks oren :) I was thinking that water drainage through moulins might cause heating of the ice sheet from below leading to destabilisation, in comparison to water that drained straight into the sea.
Something to think about, though I've never noticed it being considered, is that much of inland Greenland is well below sea level, I can't imagine any scenario where the salt from the ancient seas that covered it didn't end up in the lowest troughs, once these deposits begin to dissolve the melting temp. of that basal ice will be @ -5C. With more melt above we get more melt below.
Title: Re: What's new in Greenland?
Post by: TerryM on May 14, 2017, 02:08:39 PM
Thanks oren :) I was thinking that water drainage through moulins might cause heating of the ice sheet from below leading to destabilisation, in comparison to water that drained straight into the sea.
Something to think about, though I've never noticed it being considered, is that much of inland Greenland is well below sea level, I can't imagine any scenario where the salt from the ancient seas that covered it didn't end up in the lowest troughs, once these deposits begin to dissolve the melting temp. of that basal ice will be @ -5C. With more melt above we get more melt below.
A possibly interesting question:
We know that the ocean has become increasingly saline over time. Do we know how salty the ocean was when Greenland last sank beneath the waves? Since the weight of ice is what pushed the land beneath the waves, and the glaciers are basically fresh snow, would any water now beneath the ice be fresh?
Terry
Title: Re: What's new in Greenland?
Post by: Andreas T on May 14, 2017, 08:29:03 PM
observations of the land surface now below the ice suggest that there were river valleys before ice covered the land. If the weight of the ice pushed the land surface below the sea level there would not be salt below the ice.
Title: Re: What's new in Greenland?
Post by: VeliAlbertKallio on May 15, 2017, 12:12:29 AM
One of the biggest problems is of course that we cannot see through ice perfectly to assess the geology and its chemistry. When ice sheet mass balance changes, this can open old faults and close other ones in bedrocks (these tremors are called ice quakes). A far bigger problem could be if a new fault forms into rock salt containing minerals thus releasing and dissolving salt away, the saline brine might then get flushed out into the subglacial base together with warm water. Has there any hot springs in Greenland to support such a possibility (salt under ice)?

Yes, I am enclosing an example of one in Nanortalik. I doubt if anyone has ever measured a correlation of its hot water throughput (flow changes) as linked to nearby glaciers and ice sheet, but I am afraid that these will influence how much hot water comes out from Nanortalik hot spring. Get one Nanortalik-type thing forming under the ice sheet and lots of melting would occur due to hot water and this melting amplified by salt brine.

The glacial ice quakes could also start opening or forming deep faults and act like hydraulic press when moving ice opens and closes faults within rocks and in the process pushing water incursions deeper down into the crust and surface of the mantle.

This could lead into mud volcanoes up to 10 km depth (i.e. like those forming on the Caspian Sea) in clay based minerals.

The olivine group minerals (especially peridotite) within deeper rocks in the crust and on the surface of the mantle may get partially dissolved triggering a re-start of volcanism in the highly volcano-infested South East Greenland (which has so far sat quietly under thickening snow cap even until now despite all the melting already). But as ice thins, the nucleation of gasses in volcanic reservoirs turn them foamy and more voluminous - thus sending magma to the upward trajectory to form magma incursions beneath ice sheet. Further down mantle - and over the wider areas - the conversion of wet solidus into dry solidus can intensify the overall negative pressure of volcanic plume solids (due to disassociation of hydrogen and oxygen from the rock making it lighter like cork or sea ice that float on water and rise upwards towards the surface). 

The problem overall is the more aggressively we disturb Greenland Ice Sheet the more complex the possible processes become. But volcanism can become a major cause of sudden ice sheet loss once enough nucleation and disequilibrium and new faults in bed rocks form. I suspect that the Pine Island Glacier (PIG) might have hot water or magma incursions beneath ice - fed by the growing disequilibrium between ablating WAIS and accumulating EAIS both causing fluid displacements from higher pressure areas to the lower pressure areas, and wet solidus damage under whole of WAIS with localized pockets of ablation-induced nucleation of gases in volcanic reservoirs sitting beneath PIG. Greenland similar things could also happen. Grimsvotn under Vatnajokull in nearby Iceland is a result of ablation-induced nucleation also Eyjafjallajokull.

observations of the land surface now below the ice suggest that there were river valleys before ice covered the land. If the weight of the ice pushed the land surface below the sea level there would not be salt below the ice.
Title: Re: What's new in Greenland?
Post by: Tor Bejnar on May 17, 2017, 05:47:18 PM
Rain in forecast in parts of Greenland for each on the next several days, according to ASIG-Forecasts-Precipitation and Clouds (https://sites.google.com/site/arcticseaicegraphs/forecasts2) maps.  Here is the one for Friday.  (Okay, more snow than rain)
Title: Re: What's new in Greenland?
Post by: AbruptSLR on May 19, 2017, 05:16:48 PM
More details on albedo & 'Dark ice' in Southwest Greenland:

Tedstone, A. J., Bamber, J. L., Cook, J. M., Williamson, C. J., Fettweis, X., Hodson, A. J., and Tranter, M.: Dark ice dynamics of the south-west Greenland Ice Sheet, The Cryosphere Discuss., doi:10.5194/tc-2017-79, in review, 2017.

http://www.the-cryosphere-discuss.net/tc-2017-79/ (http://www.the-cryosphere-discuss.net/tc-2017-79/)

Abstract. Runoff from the Greenland Ice Sheet (GrIS) has increased in recent years due largely to declining albedo and enhanced surface melting. Some of the largest declines in GrIS albedo have occurred in the ablation zone of the south-west sector and are associated with the development of 'dark' ice surfaces. Field observations at local scales reveal that a variety of light-absorbing impurities (LAIs) can be present on the surface, ranging from inorganic particulates, to cryoconite materials and ice algae. Meanwhile, satellite observations show that the areal extent of dark ice has varied significantly between recent successive melt seasons. However, the processes that drive such large inter-annual variability in dark ice extent remain essentially unconstrained. At present we are therefore unable to project how the albedo of bare-ice sectors of the GrIS will evolve, causing uncertainty in the projected sea level contribution from the GrIS over the coming decades.

Here we use MODIS satellite imagery to examine dark ice dynamics on the south-west GrIS each year from 2000 to 2016. We quantify dark ice in terms of its annual extent, duration, intensity and timing of first appearance. Not only does dark ice extent vary significantly between years, but so too does its duration (from 0 % to > 80 % of June–July–August, JJA), intensity and the timing of its first appearance. Comparison of dark ice dynamics with potential meteorological drivers from the regional climate model MAR reveals that the JJA sensible heat flux, the number of positive minimum-air-temperature days and the timing of bare ice appearance are significant inter-annual synoptic controls.

We use these findings to identify the surface processes which are most likely to explain recent dark ice dynamics.We suggest that whilst the spatial distribution of dark ice is best explained by outcropping of particulates from ablating ice, these particulates alone do not drive dark ice dynamics. Instead, they may enable the growth of pigmented ice algal assemblages which cause visible surface darkening, but only when the climatological pre-requisites of liquid meltwater presence and sufficient photosynthetically-active radiation fluxes are met. Further field studies are required to fully constrain the processes by which ice algae growth proceeds and the apparent dependency of algae growth on melt-out particulates.
Title: Re: What's new in Greenland?
Post by: FishOutofWater on May 20, 2017, 05:23:50 AM
One of the biggest problems is of course that we cannot see through ice perfectly to assess the geology and its chemistry. When ice sheet mass balance changes, this can open old faults and close other ones in bedrocks (these tremors are called ice quakes). A far bigger problem could be if a new fault forms into rock salt containing minerals thus releasing and dissolving salt away, the saline brine might then get flushed out into the subglacial base together with warm water. Has there any hot springs in Greenland to support such a possibility (salt under ice)?
.....

The olivine group minerals (especially peridotite) within deeper rocks in the crust and on the surface of the mantle may get partially dissolved triggering a re-start of volcanism in the highly volcano-infested South East Greenland (which has so far sat quietly under thickening snow cap even until now despite all the melting already). But as ice thins, the nucleation of gasses in volcanic reservoirs turn them foamy and more voluminous - thus sending magma to the upward trajectory to form magma incursions beneath ice sheet. Further down mantle - and over the wider areas - the conversion of wet solidus into dry solidus can intensify the overall negative pressure of volcanic plume solids (due to disassociation of hydrogen and oxygen from the rock making it lighter like cork or sea ice that float on water and rise upwards towards the surface). 


[/quote]

Much of Greenland is billion year plus old pre-Cambrian shield. In southern Greenland the Iceland hot spot track is associated with relatively recent voluminous volcanism. Salt is not generally found in these types of rocks.

Peridotite may serpentinize under near surface conditions in the presence of water, but it has a very high melting point. Olivine has such a high melting point that it tends to form cumulates in the bottom of magma chambers. Olivine crystals sink to to bottom of magma chambers. The magnesium end member of the olivine group was one of the first solids to form out of the solar nebula. It has a ridiculously high melting point. Peridotites form from very hot volcanic systems.

Depressurizing an existing volcano can lead to additional magma production but it will not reactivate old dead systems that have solidified. So we might see glacial unloading increase Icelandic volcanism but it won't revive dead volcanoes in Greenland.
Title: Re: What's new in Greenland?
Post by: gerontocrat on May 21, 2017, 03:48:18 PM
Greenland melting quite high 18th & 19th May- especially on SW coast.

Does Greenland Melting Season deserve a thread of its own?

Title: Re: What's new in Greenland?
Post by: Shared Humanity on May 21, 2017, 04:40:42 PM
One of the biggest problems is of course that we cannot see through ice perfectly to assess the geology and its chemistry. When ice sheet mass balance changes, this can open old faults and close other ones in bedrocks (these tremors are called ice quakes). A far bigger problem could be if a new fault forms into rock salt containing minerals thus releasing and dissolving salt away, the saline brine might then get flushed out into the subglacial base together with warm water. Has there any hot springs in Greenland to support such a possibility (salt under ice)?
.....

The olivine group minerals (especially peridotite) within deeper rocks in the crust and on the surface of the mantle may get partially dissolved triggering a re-start of volcanism in the highly volcano-infested South East Greenland (which has so far sat quietly under thickening snow cap even until now despite all the melting already). But as ice thins, the nucleation of gasses in volcanic reservoirs turn them foamy and more voluminous - thus sending magma to the upward trajectory to form magma incursions beneath ice sheet. Further down mantle - and over the wider areas - the conversion of wet solidus into dry solidus can intensify the overall negative pressure of volcanic plume solids (due to disassociation of hydrogen and oxygen from the rock making it lighter like cork or sea ice that float on water and rise upwards towards the surface). 



Much of Greenland is billion year plus old pre-Cambrian shield. In southern Greenland the Iceland hot spot track is associated with relatively recent voluminous volcanism. Salt is not generally found in these types of rocks.

Peridotite may serpentinize under near surface conditions in the presence of water, but it has a very high melting point. Olivine has such a high melting point that it tends to form cumulates in the bottom of magma chambers. Olivine crystals sink to to bottom of magma chambers. The magnesium end member of the olivine group was one of the first solids to form out of the solar nebula. It has a ridiculously high melting point. Peridotites form from very hot volcanic systems.

Depressurizing an existing volcano can lead to additional magma production but it will not reactivate old dead systems that have solidified. So we might see glacial unloading increase Icelandic volcanism but it won't revive dead volcanoes in Greenland.
[/quote]

You guys are amazing. I learn so much here.
Title: Re: What's new in Greenland?
Post by: FishOutofWater on May 21, 2017, 07:28:40 PM
My PhD is in geochemistry so I know some pretty weird things. For a nice short write up about volcanic rocks in Greenland check out this NASA blog post.
https://blogs.nasa.gov/icebridge/2013/04/16/post_1366140794166/
Title: Re: What's new in Greenland?
Post by: crandles on May 22, 2017, 01:18:08 PM
Greenland melting quite high 18th & 19th May- especially on SW coast.

Does Greenland Melting Season deserve a thread of its own?

I suggest multiyear images from
http://nsidc.org/greenland-today/greenland-surface-melt-extent-interactive-chart/ (http://nsidc.org/greenland-today/greenland-surface-melt-extent-interactive-chart/)

such as attached
Title: Re: What's new in Greenland?
Post by: Neven on May 22, 2017, 01:51:19 PM
Greenland melting quite high 18th & 19th May- especially on SW coast.

Does Greenland Melting Season deserve a thread of its own?

Good idea. We've had one every year so far, I believe. Here it is: Greenland 2017 melt season (http://forum.arctic-sea-ice.net/index.php/topic,2054.0.html)
Title: Re: What's new in Greenland?
Post by: gerontocrat on May 22, 2017, 02:00:27 PM
Greenland melting quite high 18th & 19th May- especially on SW coast.

Does Greenland Melting Season deserve a thread of its own?

Good idea. We've had one every year so far, I believe. Here it is: Greenland 2017 melt season (http://forum.arctic-sea-ice.net/index.php/topic,2054.0.html)
Cor! Thanks. I hope there are chances of images where melting is biting hard.
Title: Re: What's new in Greenland?
Post by: VeliAlbertKallio on May 25, 2017, 04:19:04 AM
I was referring to this landscape on the Geikie Peninsula which is definitely volcanic as you can see (and NASA article put it quite nicely). What still bothers me is that these volcanoes go there beneath the ice sheet almost forever (!) and then you cannot see every volcano on the surface - much like the Gamburtseve Range they are hidden deep in Antarctic ice.

It bothers me how uniform the volcanic rocks there are and what faults in the rocks might be therein. Just like Toba and Yellowstone aren't really very active volcanic systems today to fear, there is some tiny bit of beast still left in them (this justifying some fear of future supereruptions).

My concern or fear is that if huge ablation of ice takes place stresses by ice-forced subsidence reverberates to the old faults or creates new ones and incursion of hot water or rocks would come active under ice just like Nanortalik hot springs. The partial melting of Peridotite isn't easy to come, I admit, but the weight of ice sheet influences bedrocks and has a very deep footprint which I think is generally underestimated:

I see here a clear connection between central Greenland subglacial depression, volcanic incursions on the east coast of Greenland and proximity of the vast volcanic shield of Iceland nearby all in connection. Whilst I am aware of the drifting of a volcanic hotspot and believe it to be the strongest today in Iceland, I do not see an absolute reason why not residual activity pockets could not exist in Greenland. True, in Hawaii the volcanic activity diminishes towards North East.

There are extinct volcanoes in Antarctica, but also some others that aren't and keep wondering if any system is left in limbo in Greenland that could start playing up due to wet solidus damage strengthening regional plumes in mantle due to ablation and then nucleation of gases within magma reservoirs (if there were any near surface).

After all, I also note that if these volcanoes really are so old (those NASA guys did not walk on the mountains but flew over in altitude, sic), in many of them appears far too little erosion if they were millions of years old as you follow NASA argument - but sharp volcanic forms appear not always planed smooth by ice. Long periods of ice and glaciation tends to smoothen the rocks round but I can't see often rocks smoothened by ice in this volcanic region, do you have any explanation to that? This isn't Grand Canyon region carved by river, but area which ought to be carved by ice. Look at the rocks elsewhere Greenland and see how rounded ice has made them.

So, I am still afraid that they could cause Jokullhaups and contribute as ice sheet mass balance is impacted. For example, looking at the Gamburtsev Range volcanoes profiles in ice, it has been claimed that the ice sheet on that region was "growing from bottom up" by ice upwell (ice sheet growing from its base upwards).

I have interpreted these Gamburtsev features the other way round: the volcanoes have dumped latent heat during the ice sheet by melting ice and so destroying the ice sheet stratification there as the compacted snow melted and then turned next into frozen water ice (rather than compacted snow what it was before the heat incursion event I suspect occurring there). I support heat possibility because we have seen Vatnajokull producing Jokullhaups with huge bursts of water by volcano melting, but if the water could not escape out and once the effusive eruption fizzles out the water will freeze just the way the Gamburtsev Range soundings look like.

I would not take NASA airborne people's expedition at face value, I would rather see them going on foot and kicking stones around to come to conclusions like mine that the ice has not sufficiently shaped the mountains to justify them a greatly different age and origins to those in Iceland. I did not say that I have seen live volcanoes, but can feel suspicious of lack of planing effect of ice.

My PhD is in geochemistry so I know some pretty weird things. For a nice short write up about volcanic rocks in Greenland check out this NASA blog post.
https://blogs.nasa.gov/icebridge/2013/04/16/post_1366140794166/
Title: Re: What's new in Greenland?
Post by: FredBear on May 25, 2017, 12:12:44 PM
VeliAlbertKallio, the landscape looks similar to Spitsbergen (pointed mountains) and the "layer-cake" of rocks have obviously been eroded for some considerable time. In my opinion the layers are not distorted as they might  be in more active zones (but this is just a snap-shot)?
Title: Re: What's new in Greenland?
Post by: lifeblack on May 25, 2017, 07:35:59 PM
VelliAlbertKallio, while the peaks in the picture have an overall shape that suggests they are younger than suggested elsewhere, the features that are visible are clearly all erosional, and none of the pyramidal shapes in view were erupted as cone shaped mountains  (ie, none of the features are from a partially eroded cascade-type stratovolcano).  As evidence, look at the stacked layers of lava that are visible - they were clearly emplaced as (apparently) continuous sheets on a nearly level landscape, and they remain nearly horizontal today.
As for the height of the mountains after so many millions of years of glaciation, I might be going out on a limb here, but I think that as the rock gets eroded away, the crust will rebound upwards in response to the removal of the top layers.

I would definitely be interested in whether there are any moribund volcanic sources in Greenland that may be reactivated by decompression melting, but the landscape in  the picture doesn't seem to be good evidence of anything recent
Title: Re: What's new in Greenland?
Post by: Tor Bejnar on May 25, 2017, 08:34:08 PM
The following information is from a geologic map of Greenland (http://www.geus.dk/program-areas/raw-materials-greenl-map/greenland/gr-map/anhstart-uk.htm), with my leading comments:
It appears the youngest igneous rocks in Greenland are on the order of 50 million years old.  I wouldn't expect the removal of all Greenlandic ice to re-energize significant (or actually any) volcanic activity. From here (https://www.wired.com/2015/08/tell-volcano-active-dormant-extinct/): "Extinct: It takes a lot to be an “extinct” volcano. The rule of thumb I use is about 1 million years since the last eruption … "


Chart describing last 100 million years of igneous rocks in Greenland (see time line screen shots):
(references are to time line reference numbers)

 
[6] Paleocene tholeiitic lavas, central West Greenland.
[7] Paleocene picritic lavas, central West Greenland.
[48] Eocene tholeiitic plateau basalts in East Greenland.
[49] Paleocene–Eocene tholeiitic basalts with picritic intervals. East Greenland.
[53] Tertiary felsic intrusions in East Greenland.
[57] Tertiary mafic to intermediate intrusive complexes in East Greenland.
[58] Upper Cretaceous gabbroic intrusion. Pearya terrane, Ellesmere Island (Canada).
Title: Re: What's new in Greenland?
Post by: VeliAlbertKallio on May 26, 2017, 04:48:40 AM
Very many thanks for the highly constructive points raised! Please note that  I raise these here as highly speculative stipulations and as a sort of brainstorming attempt and I do not see - at least for now any evidence - of geological activity. Yet, I wish to raise further detailed points for your consideration.)

I'm enclosing a very typical scenery of glacier-shaped rocks and boulders from Greenland. Even volcanic rocks, as hard they may be, are impacted and subjected to the milling of ice domes from above (if rocks were covered by one). I have seen many volatile structures on that region (unlike the Svalbard) that do not appear in any way round but look like a frozen in time, a still frame. The overall appearance is similar to water-flooding impacted strata of the Grand Canyon region, not an ice sheet gourged one. For me, the region has perhaps undergone strong isostatic uplift, but it was impacted by water floods, Jokullhaups, turning it to the Grand Canyon of Greenland. It is not geomorphic according to the ice sheet planing, if it were the volcanic mountains would have a distinctive smooth rise facing the direction ice sheet had flowed, with steep rear sides.

Source of these floods would then be Jokullhaups.

The volatile structures preserved is, therefore, suggestive to me that the rocks were hot when the ice sheet was forming (and hence expelling the local ice development unlike elsewhere). As Jokullhaups periodically discharged water and lahar, the loose, slushy stratum eroded rapidly.

If so, then the volcanic incursion is associated with the Central Greenland's subsidence when the ice dome was being deposited onto the Precambrian granites across Greenland. Thus, the incursion of magma is a result of ice sheet compressing subglacial magma reservoir and driving a partial melting of asthenosphere beneath the glaciating region - with the partial melting breakdown products being driven out here near this edge area of Greenland continental plate (where plate's weaknesses are greatest). The only option is for me to go and collect more volatile rock structure evidence which would dispel the idea of ice having carved out this peculiar area. That's a future project for me and these expeditions are costly!

There are earthquakes and the Nantortalik hot spring. I suspect that there must be more hot springs hidden beneath ice sheet as the faults are myriad. Hot springs could be behind some of the subglacial heat anomalies are found in various parts of Greenland. Today more pressurized water is fed into subglacial faults by water from moulins that are becoming increasingly active over perimetrical subglacial bedrock. Moulins one day number in millions over perimeter shield.

I expect the volcanic region (potentially) evolving to the Mascarene volcanism. A two-phase volcanism where a low viscosity, vast lava floods are followed by a long non-active interval to the previous episodes of vast effusive volcanic eruptions. Then a smaller secondary episode re-emerges a new bout of different type of volcanism which shatters the old crust and causes mountain incursions to pierce the old, lava field by the extremely high viscosity (cool) secondary lavas. This renewal of eruptivity thus shatters the solidified ('extinct') flat lava volcano field. The secondary volcanism in the Mascarene volcanos had so high viscosity that many eruptions caused vertically rising lava floods (like a toothpaste comes out of the tube when it is pointed upwards).

In the Mascareane volcanism, the force of high viscous rock oozing through flat lava field was so great that nearly all secondary volcanoes go vertigo through the plain, lava rising vertically skyward. Even parts of the old solidified lava crust sitting as a tip of the newly oozing highly viscous lava with the old solid blocks of lava becoming a mushroom-like 'hat' shapes for the volcano, i.e. Peter Both 'hat' cap. https://upload.wikimedia.org/wikipedia/commons/b/b3/Pieter_Both%2C_mountain.jpg These vertical formations rising from flat lava landscapes.

The question is of course how solid is the high viscous incursion and whether such incursions could make way up once Greenland ice sheet melts. What drives high viscous lava up is not exactly clear but some disassociation of gases must have happened, maybe further afield, pressure change reverberated from nucleating lavas elsewhere to make cool rocks to cause secondary Mascarene eruptivity. In the case of deglaciation, this could be the secondary trigger, whereas the low viscous eruptivity would have been the primary trigger, a forming ice sheet.

It is my view that the secondary Mascarene volcanism was driven by gaseous disassociating within low viscous magmas in long distance, perhaps when the hot spot was already transiting from Mauritius to nearby Reunion. Events in Iceland and/or deep partial melting in asthenosphere under Greenland could be the source to force old cool lavas in Greenland once the ice sheet mass balance losses become large enough to create Mauritian style new volcanic life on the old volcanic region.

By the way, whilst climbing to study Mount Lepus I came also across old continental blocks of rock embedded in these high viscous plumes of semi-solid rocks that had broken through the primary plain of solidified lavas and seabed. (Only years after people theorized this sunken continent.)


Title: Re: What's new in Greenland?
Post by: Hyperion on May 26, 2017, 12:22:47 PM
(https://upload.wikimedia.org/wikipedia/commons/8/89/Greenland%27s_Geikie_Peninsula.jpg)

Certainly some spectacular igneous pancaking in the Geike Area.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fl7.alamy.com%2Fzooms%2Ffe3e79dde1b74ea3ac4dff06494af796%2Fgeikie-plateau-peak-d4bcxm.jpg&hash=c064b180e65e3b33256e6e3a2906b05e)

This seems to be the Skaergaard intrusion some 55 million years ago. Possibly ASSOCIATED with the PETM.
Wikipedia:
Quote
The Skaergaard intrusion is a layered igneous intrusion in the Kangerlussuaq area, East Greenland. It comprises various rock types including gabbro, ferro diorite, anorthosite and granophyre.

Discovered by Lawrence Wager[1] in 1931 during the British Arctic Air Route Expedition led by Gino Watkins, the intrusion has been important to the development of key concepts in igneous petrology, including magma differentiation and fractional crystallisation[2][3] and the development of layering.[4][5] The Skaergaard intrusion formed when tholeiitic magma was emplaced about 55 million years ago,[6] during the initial opening of the North Atlantic Ocean. The body represents essentially a single pulse of magma, which crystallized from the bottom upward and the top downward. The intrusion is characterized by exceptionally well-developed cumulate layering defined by variations in the abundance of crystallizing olivine, pyroxene, plagioclase and magnetite.

The Skaergaard is perhaps the simplest and smallest of a group of gabbroic complexes of similar age that occur along the central coast of East Greenland, which together with coeval flood basalts are part of the North Atlantic large igneous province.

I say associated because looking at the some 50ma glaciated alternating with some 100ma hothouse approximate periodicity of the last about 500ma. These Large Igneouse events seem very much clustered in the transition of meltdown. Quite plausibly causation is the deglaciation. rather than the result. Or more precisely a cyclic melt loading and unloading process causing the repeated addition of sills. Both under the ice sheets during mass loss cycles. And at distances where the super heated fluid basalt emerges through deep dyke conduits from the glaciated continent keels as hot spots or super-swells. Or from rift zones to allow spreading  when the rebuilding of icecaps as ice mass starts to destabilize and oscillate.

Heres a list from wikipedia. And a picture of the Longest seamount chain in the world left by the hotspot thats thought to have caused the biggest eruption we know of. The Ontong-Java event. The Louisville hotspot probably connects with central West Antarctica. And whats left of WAs bum is the Hikurangi,  Manihiki, Ontong Java Plateaus, and Sth Pacific Superswells. Whether Greenlands bum is going to keep feeding Iceland, or Nth Canada and Iceland feed Greenlands bum in the near future, who can say.



Title: Re: What's new in Greenland?
Post by: RoxTheGeologist on May 26, 2017, 04:43:59 PM

I think Palaeomagnetic evidence places East Greenland at around 60N when the hotspot was causing volcanism.  Is there any evidence of glaciation from that period in Greenland, or the extent of ice sheets if any? I think that the earth was pretty hot at that time, there was a long term warming event that covered the period when Greenland moved over the hotspot, so there was unlikely to be an ice sheet at all.

The North American plate is moving north west relative to the hot spot frame of reference, away from the Icelandic hotspot. Greenland has been moving in the same direction pretty much since the opening of the North Atlantic. The magma chambers that were created in Greenland by the hotspot are cold and eroded, as evidenced from the pictures. Ice unloading will not reawaken any volcanism associated with that hotspot in Greenland. It might increase the activity in Iceland.
Title: Re: What's new in Greenland?
Post by: RoxTheGeologist on May 26, 2017, 04:49:32 PM

This is worth reading, and shows how the lithosphere below Greenland is now high density, and therefore cold:

https://www.researchgate.net/figure/33681824_fig7_Figure-5-Present-day-tomographic-image-c-of-the-Iceland-hotspot-plume-modified-from (https://www.researchgate.net/figure/33681824_fig7_Figure-5-Present-day-tomographic-image-c-of-the-Iceland-hotspot-plume-modified-from)
Title: Re: What's new in Greenland?
Post by: sidd on May 26, 2017, 07:56:51 PM
Fascinating soliton in ice stream going down Rink. May be associated with hi-melt summers. Requires only one bedrock GPS station time series (and some orbiting satellites ...).  The authors clearly share some of Saruman's [1] traits. Wonder if such events can be teased out by ground GPS around Jacobshawn.

Very pretty paper. Read all about it:

https://www.jpl.nasa.gov/news/news.php?feature=6857 (https://www.jpl.nasa.gov/news/news.php?feature=6857)

open access  doi:10.1002/2017GL073478

I attach Fig 3c), 3d) and S11

The captions for 3c) and d) are

"(c) Pattern of mass deficit transiting the Rink Glacier during 2012 summer. About − 7.1 m of monthly thinning over the optimal domain (blue fill within the glacier trunk outlined by white line) is required to explain the mean monthly displacement (red arrow). Plotted are also the magnitudes and fulcrum positions of monthly mass anomalies (circles) that satisfy the measured monthly displacements (arrows). Notice the down glacier propagation of (negative) mass anomaly that represents the negative phase of mass transport wave. Mean monthly SMB loads are shown in the background. (d) Same as Figure 3c but for the fall/midwinter season that follows. It requires about 2.8 m of monthly thickening over the optimal domain (red fill within the glacier trunk) to explain the mean monthly displacement (blue arrow)."

The caption for S11 is in the image

sidd

[1] "His knowledge was deep, his thought was subtle, and his hands marvellously skilled ... " Tolkien, Lord of the Rings, v III, Ch. X, 1954

Title: Re: What's new in Greenland?
Post by: Reallybigbunny on May 27, 2017, 12:40:21 PM
Very interesting indeed  :o

https://www.jpl.nasa.gov/news/news.php?feature=6857 (https://www.jpl.nasa.gov/news/news.php?feature=6857)

Title: Re: What's new in Greenland?
Post by: johnm33 on May 27, 2017, 12:53:44 PM
With animation https://scitechdaily.com/nasa-scientists-reveal-a-new-mode-of-ice-loss-in-greenland/
is there a bedrock map?
Title: Re: What's new in Greenland?
Post by: Hyperion on May 31, 2017, 04:20:45 PM
Dang! This "new mode of glacial acceleration" seems like the slushalanche effect I've been predicting from the spreading and thickening sub surface slushifer discovered in 2011. If this starts to be the new normal behaviour of glacial outflows in Greenland and WA we are looking at big trouble. If a big late summer weather system rains heavily over Greenland. say from a stuck planetary wave in the jets, and a big low in the fram vicinity lifting surfacing gulfstream heat and moisture, with a Greenland/ CAA high. its not difficult to imagine a whole lot going at once. Perhaps 40 days and nights of rain COULD cause abrubt slr.  :o
Title: Re: What's new in Greenland?
Post by: Jester Fish on June 06, 2017, 01:09:40 AM
Above normal temps forecast for June, July, August for Greenland.  I haven't checked out the forecasting verification.
 
http://iri.columbia.edu/our-expertise/climate/forecasts/seasonal-climate-forecasts/ (http://iri.columbia.edu/our-expertise/climate/forecasts/seasonal-climate-forecasts/)
Title: Re: What's new in Greenland?
Post by: solartim27 on August 07, 2017, 08:11:21 PM
Wildfires?  (Cross post from Wildfire thread)
And now Greenland is burning, though it has happened before.
More pics here:  https://twitter.com/Pierre_Markuse/status/894461039609352192
Title: Re: What's new in Greenland?
Post by: Tor Bejnar on August 07, 2017, 08:31:05 PM
Greenland burning:  see also posts in Greenland 2017 melt... thread starting here (http://forum.arctic-sea-ice.net/index.php/topic,2054.msg123633.html#msg123633).
Title: Re: What's new in Greenland?
Post by: nukefix on August 11, 2017, 11:41:04 AM
A beautiful Sentinel-1 track crossed Greenland yesterday...while sightseeing I managed to spot both the Greenland summit site and the NEGIS coring site on the imagery. Images downloaded from PolarView.
Title: Re: What's new in Greenland?
Post by: Tor Bejnar on August 11, 2017, 07:22:21 PM
The biggest fire continues to spread.  Image from Sentinel Playground August 8 (http://apps.sentinel-hub.com/sentinel-playground/?lat=67.85690144960271&lng=-51.55319021665491&zoom=12&preset=CUSTOM&layers=B02,B08,B12&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01|2017-08-08&cloudCorrection=none&atmFilter=&showDates=false).  I'm showing the color bands choices. (8/8/17 image is latest.) Note scale in lower left corner.  (click if you like)
Title: Re: What's new in Greenland?
Post by: be cause on August 11, 2017, 07:57:00 PM
http://www.seaice.dk/latest/feature4.jpg (http://www.seaice.dk/latest/feature4.jpg)
Title: Re: What's new in Greenland?
Post by: solartim27 on August 16, 2017, 05:44:32 AM
New Olympic sport
https://www.instagram.com/p/BXx1yjgjpXK/ (https://www.instagram.com/p/BXx1yjgjpXK/)
Title: Re: What's new in Greenland?
Post by: nukefix on August 16, 2017, 11:23:50 AM
Amazing blue iceberg spotted in Jakobshaven icefjord:

http://apps.sentinel-hub.com/sentinel-playground/?lat=69.16542768047643&lng=-49.78935241699219&zoom=12&preset=1_NATURAL_COL0R&layers=B02,B08,B12&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01 (http://apps.sentinel-hub.com/sentinel-playground/?lat=69.16542768047643&lng=-49.78935241699219&zoom=12&preset=1_NATURAL_COL0R&layers=B02,B08,B12&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01)|2017-08-10&cloudCorrection=none&atmFilter=ATMCOR&showDates=true&evalscript=
Title: Re: What's new in Greenland?
Post by: sidd on August 18, 2017, 12:09:21 AM
A paper by Kulessa et al is pessimistic on future sedimentary control on glacier veelocity as melt season lengthens and enroaches deeper into the ice sheet. Some modelling using CISM, bed hydro is finally being cracked. Open access. read all about it.


DOI: 10.1126/sciadv.1603071

http://advances.sciencemag.org/content/3/8/e1603071 (http://advances.sciencemag.org/content/3/8/e1603071)

sidd
Title: Re: What's new in Greenland?
Post by: Juan C. García on October 05, 2017, 08:55:32 PM
Washington Post: Scientists mapping Greenland have produced some surprising – and worrying – results (https://www.washingtonpost.com/news/energy-environment/wp/2017/10/04/scientists-mapping-greenland-have-produced-some-surprising-and-worrying-results/?utm_term=.61be3f8edaab&wpisrc=nl_green&wpmm=1)

Quote
Two new studies of Greenland, using sophisticated technologies and large scientific teams to pull together and process the data, have now gone further in taking the full measure of the island through that ever-so-basic scientific act: mapping.

The first, a comprehensive seabed mapping project, relying in part on new data from NASA’s OMG (“Oceans Melting Greenland”) mission, concludes that the Greenland ice sheet is far more exposed to the planet’s warming oceans than previously known — and has more ice to give up than, until now, has been recognized.

Quote
Meanwhile, on Wednesday, a separate team of scientists used another quite different large-scale mapping exercise to document a surprising — but closely related — change in Greenland’s above-water topography. Publishing in the journal Nature, they showed that the contours of the huge island are changing because with all the ice melt rushing from glaciers to the sea, river deltas are expanding outward — a rare occurrence these days when deltas around the world are generally retreating, threatened by rising seas (think of the Mississippi River delta, for instance, and its vanishing wetlands).
Title: Re: What's new in Greenland?
Post by: A-Team on October 13, 2017, 01:59:44 PM
The first article mentioned in the post above, Morlighem 2017, represents a very substantial refinement in mapping of Greenland fjords whose bathymetry is key to warm ocean water access to the grounding lines of the glaciers.

The article is open access and even better, so is the data. That's a first. It's all packaged as a single giant 2.5 GB netCDF file and stored at NSIDC at the link below (nuisance registration req'd). The download opens readily as seven Panoply map options despite the immense grid of 18346 x 10218 = 187,459,428 cells.

BedMachine v3: Complete bed topography and ocean bathymetry mapping of Greenland from multi-beam echo sounding combined with mass conservation
M. Morlighem et al 2017  open source 8.5 MB
http://onlinelibrary.wiley.com/doi/10.1002/2017GL074954/full (http://onlinelibrary.wiley.com/doi/10.1002/2017GL074954/full)
http://sites.uci.edu/morlighem/dataproducts/bedmachine-greenland/ (http://sites.uci.edu/morlighem/dataproducts/bedmachine-greenland/)
http://nsidc.org/data/IDBMG4# (http://nsidc.org/data/IDBMG4#) netCDF file 2.5 GB
https://icdc.cen.uni-hamburg.de/1/daten/land/geoid-eigen.html (https://icdc.cen.uni-hamburg.de/1/daten/land/geoid-eigen.html) EIGEN-6C4
https://www.nytimes.com/2017/09/12/magazine/what-could-we-lose-if-a-nasa-mission-goes-dark.html (https://www.nytimes.com/2017/09/12/magazine/what-could-we-lose-if-a-nasa-mission-goes-dark.html) GRACE replacement

This frees us from external dependencies on map generation for favorite forum areas such as Petermann, Jakobshavn and Zachariae. We can likely improve on journal illustrations using the seven mappable GEO2D files. The authors' motivation for netCDF is to enable Greenland-wide forecasting models such as ISSM which is far too computationally intensive for us.

A post on another forum complains about ESRL using a spherical earth approximation instead of the ellipsoid WGS84 approximation (these differ by 1 part in 300) but the authors here are dismissive of WGS84  and use an earth geoid, a 2014 product called EIGEN-6C4, a high-resolution global gravitational field model. It's a correction on EGM2008. WGS84 is off by as much as 64 m error in Greenland which defeats the whole purpose of OMG fjord bathymetry.

The European Improved Gravity model of the Earth by New techniques includes data from the Gravity field and Ocean Circulation Explorer (GOCE) satellite. While its role is fundamental in geodesy, the importance for Greenland arises from improved orbital description of the failing GRACE satellite which is critical to mass balance measurements.
Title: Re: What's new in Greenland?
Post by: Tealight on October 14, 2017, 11:25:46 PM
The new BedMachine v3 is really great for marine terminating glaciers. Finally the bedrock map is not cropped anymore in the important terminus region.

For Petermann and Zachariae not much has changed since version 2, but Jakobshavn looks quite different. I wonder if a slower flow speed influenced the mass conversion calculations.

The bedrock beneath the wedged part of Spaltegletscher is modeled as above sea level, which obviously can't be right. One of the weak spots of the mass conversion model.

click on images to animate
Title: Re: What's new in Greenland?
Post by: oren on October 15, 2017, 12:04:49 AM
@Tealight, thank you. Very interesting.
Title: Re: What's new in Greenland?
Post by: sidd on October 15, 2017, 09:41:30 PM
Sejr et al. on a 13 year hydrographic record from NE greenland, not quite as far north as the Flade Isblink papers i posted earlier on that thread.

DOI:10.1038/s41598-017-10610-9

Open access. Read all about it.

sidd
Title: Re: What's new in Greenland?
Post by: A-Team on October 17, 2017, 03:11:29 PM
Nice, T-lite! If you have that gif in a linear grayscale palette, it would be easy to make 3D surfaces of the trough. The newer over older below shows that depths at the calving front and preceding trough are now substantially shallower than in version 2.

Also adding below the best overall geoid I could locate for Greenland and the Arctic Ocean. Seems like there should be an interactive version or global geolocated netCDF and indeed finally located the former.

http://www.gfz-potsdam.de/en/section/global-geomonitoring-and-gravity-field/topics/terrestrial-and-airborne-gravimetry/icgem/ (http://www.gfz-potsdam.de/en/section/global-geomonitoring-and-gravity-field/topics/terrestrial-and-airborne-gravimetry/icgem/)

http://icgem.gfz-potsdam.de/vis3d/series (http://icgem.gfz-potsdam.de/vis3d/series) visualization service
Title: Re: What's new in Greenland?
Post by: AbruptSLR on November 02, 2017, 10:31:55 PM
The linked open access reference presents Bed Topography and Ocean Bathymetry that is useful in highlighting Greenland marine glaciers that are at risk of accelerated ice mass loss due to continued global warming:

M. Morlighem et. al. (1 November 2017), "BedMachine v3: Complete Bed Topography and Ocean Bathymetry Mapping of Greenland From Multibeam Echo Sounding Combined With Mass Conservation", Geophysical Research Letters, DOI: 10.1002/2017GL074954

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074954/full

Abstract: "Greenland's bed topography is a primary control on ice flow, grounding line migration, calving dynamics, and subglacial drainage. Moreover, fjord bathymetry regulates the penetration of warm Atlantic water (AW) that rapidly melts and undercuts Greenland's marine-terminating glaciers. Here we present a new compilation of Greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach. A new 150 m horizontal resolution bed topography/bathymetric map of Greenland is constructed with seamless transitions at the ice/ocean interface, yielding major improvements over previous data sets, particularly in the marine-terminating sectors of northwest and southeast Greenland. Our map reveals that the total sea level potential of the Greenland ice sheet is 7.42 ± 0.05 m, which is 7 cm greater than previous estimates. Furthermore, it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which AW can access glaciers with marine-based basins, thereby highlighting sectors of Greenland that are most vulnerable to future oceanic forcing."
Title: Re: What's new in Greenland?
Post by: Juan C. García on November 03, 2017, 10:48:31 AM
Quote
Global sea level rise will be one of the major environmental challenges of the 21st Century. Oceans Melting Greenland (OMG) will pave the way for improved estimates of sea level rise by addressing the question: To what extent are the oceans melting Greenland’s ice from below?

https://omg.jpl.nasa.gov/portal/ (https://omg.jpl.nasa.gov/portal/)
Title: Re: What's new in Greenland?
Post by: johnm33 on November 03, 2017, 01:55:34 PM
The thought crossed my mind that the changes in Jacobshavn may be due to the dissolving of ice welded rock/permafrost, or even a salt deposit being dissolved.
Title: Re: What's new in Greenland?
Post by: Adam Ash on November 08, 2017, 02:06:37 AM
https://www.nasa.gov/feature/jpl/new-greenland-maps-show-more-glaciers-at-risk (https://www.nasa.gov/feature/jpl/new-greenland-maps-show-more-glaciers-at-risk)

'New maps of Greenland’s coastal seafloor and bedrock beneath its massive ice sheet show that two to four times as many coastal glaciers are at risk of accelerated melting as previously thought.'

Sigh.
Title: Re: What's new in Greenland?
Post by: AbruptSLR on November 10, 2017, 05:43:26 PM
The linked open access reference provides updated information about the dynamics of dark ice in south-west Greenland:

Tedstone, A. J., Bamber, J. L., Cook, J. M., Williamson, C. J., Fettweis, X., Hodson, A. J., and Tranter, M.: Dark ice dynamics of the south-west Greenland Ice Sheet, The Cryosphere, 11, 2491-2506, https://doi.org/10.5194/tc-11-2491-2017, 2017.

https://www.the-cryosphere.net/11/2491/2017/

Abstract. Runoff from the Greenland Ice Sheet (GrIS) has increased in recent years due largely to changes in atmospheric circulation and atmospheric warming. Albedo reductions resulting from these changes have amplified surface melting. Some of the largest declines in GrIS albedo have occurred in the ablation zone of the south-west sector and are associated with the development of dark ice surfaces. Field observations at local scales reveal that a variety of light-absorbing impurities (LAIs) can be present on the surface, ranging from inorganic particulates to cryoconite materials and ice algae. Meanwhile, satellite observations show that the areal extent of dark ice has varied significantly between recent successive melt seasons. However, the processes that drive such large interannual variability in dark ice extent remain essentially unconstrained. At present we are therefore unable to project how the albedo of bare ice sectors of the GrIS will evolve in the future, causing uncertainty in the projected sea level contribution from the GrIS over the coming decades.

Here we use MODIS satellite imagery to examine dark ice dynamics on the south-west GrIS each year from 2000 to 2016. We quantify dark ice in terms of its annual extent, duration, intensity and timing of first appearance. Not only does dark ice extent vary significantly between years but so too does its duration (from 0 to > 80 % of June–July–August, JJA), intensity and the timing of its first appearance. Comparison of dark ice dynamics with potential meteorological drivers from the regional climate model MAR reveals that the JJA sensible heat flux, the number of positive minimum-air-temperature days and the timing of bare ice appearance are significant interannual synoptic controls.

We use these findings to identify the surface processes which are most likely to explain recent dark ice dynamics. We suggest that whilst the spatial distribution of dark ice is best explained by outcropping of particulates from ablating ice, these particulates alone do not drive dark ice dynamics. Instead, they may enable the growth of pigmented ice algal assemblages which cause visible surface darkening, but only when the climatological prerequisites of liquid meltwater presence and sufficient photosynthetically active radiation fluxes are met. Further field studies are required to fully constrain the processes by which ice algae growth proceeds and the apparent dependency of algae growth on melt-out particulates.
Title: Re: What's new in Greenland?
Post by: Juan C. García on December 05, 2017, 08:11:11 PM
An interesting view of "before and after the inclusion of new OMG data" of Greenland bed floor, given on NASA page:

https://climate.nasa.gov/news/2646/new-greenland-maps-show-more-glaciers-at-risk/ (https://climate.nasa.gov/news/2646/new-greenland-maps-show-more-glaciers-at-risk/)
Title: Re: What's new in Greenland?
Post by: Juan C. García on December 05, 2017, 08:34:05 PM
Maybe you already know about these tools.
They are new for me...

Virtual Earth System Laboratory: https://vesl.jpl.nasa.gov/

Specially for Greenland:
Greenland Basal Friction.

Quote
This simulation of Greenland is the result of work carried out by the ISSM team for the SeaRISE experiments (Bindschadler et al., 2013, Nowicki et al. I, 2013, Nowicki et al. II, 2013) in which modeling teams from around the world compared their simulations against one another. One goal among others was to understand the impact of lubrication/friction at the ice/bedrock interface, and how the ice would speed-up if the friction coefficient α was reduced by a factor of two. Here, you will be able to replicate this experiment and play with a global reduction of Greenland friction coefficient up to 5% of its 2010 value.

https://vesl.jpl.nasa.gov/research/ice-sheets/giscui/ (https://vesl.jpl.nasa.gov/research/ice-sheets/giscui/)
Title: Re: What's new in Greenland?
Post by: AbruptSLR on December 14, 2017, 04:34:09 PM
Title: "New map reveals landscape beneath Greenland's ice sheet"

https://phys.org/news/2017-12-reveals-landscape-beneath-greenland-ice.html
Title: Re: What's new in Greenland?
Post by: Tor Bejnar on December 14, 2017, 08:39:56 PM
I wonder what is the relationship between the "new Greenland map" Adam Ash reported on above (November 7) and this one ["published this week (Thursday 14 December 2017)"].

From November 7 linked article:
Quote
Researchers at the University of California at Irvine (UCI), NASA and 30 other institutions have published the most comprehensive, accurate and high-resolution relief maps ever made of Greenland's bedrock and coastal seafloor. Among the many data sources incorporated into the new maps are data from NASA's Ocean Melting Greenland (OMG) campaign.
From today's linked article:
Quote
Produced by researchers at British Antarctic Survey (BAS), University of Bristol and University of California at Irvine (UCI), the printed map is unveiled this week at the American Geophysical Union meeting in New Orleans.

"Greenland Basal Topography BedMachine v3" is the new 1:3,500,000 scale map created from data collected by over 30 institutions.


 Read more at: https://phys.org/news/2017-12-reveals-landscape-beneath-greenland-ice.html#jCp
Title: Re: What's new in Greenland?
Post by: JMP on December 15, 2017, 06:13:33 AM
I wonder what is the relationship between the "new Greenland map" Adam Ash reported on above (November 7) and this one ["published this week (Thursday 14 December 2017)"].

From November 7 linked article:
Quote
Researchers at the University of California at Irvine (UCI), NASA and 30 other institutions have published the most comprehensive, accurate and high-resolution relief maps ever made of Greenland's bedrock and coastal seafloor. Among the many data sources incorporated into the new maps are data from NASA's Ocean Melting Greenland (OMG) campaign.
From today's linked article:
Quote
Produced by researchers at British Antarctic Survey (BAS), University of Bristol and University of California at Irvine (UCI), the printed map is unveiled this week at the American Geophysical Union meeting in New Orleans.

"Greenland Basal Topography BedMachine v3" is the new 1:3,500,000 scale map created from data collected by over 30 institutions.


 Read more at: https://phys.org/news/2017-12-reveals-landscape-beneath-greenland-ice.html#jCp

This probably has more to do with the different meanings of the word published.  What was published in scientific articles has now been printed by a publishing company. 
Title: Re: What's new in Greenland?
Post by: ms on December 15, 2017, 08:17:37 PM
New paper from a danish/greenlandish team: Abrupt shift in the observed runoff from the southwestern Greenland ice sheet

From the abstract: "We present for the first time a 40-year (1975–2014) time series of observed meltwater discharge from a >6500-km2 catchment of the southwestern Greenland ice sheet. We find that an abrupt 80% increase in runoff occurring between the 1976–2002 and 2003–2014 periods is due to a shift in atmospheric circulation..."

http://advances.sciencemag.org/content/3/12/e1701169

Two articles in danish about the project:
https://www.dr.dk/nyheder/viden/miljoe/40-aars-maalinger-det-gik-allerede-galt-med-indlandsisen-i-2003
http://www.geus.dk/cgi-bin/webbasen_nyt.pl?id=1513242866&cgifunction=form
Title: Re: What's new in Greenland?
Post by: sidd on December 19, 2017, 01:14:07 AM
Wilson et al, 79N ice tongue is thinning, Peterman and Ryder tongues close to balance:

"We also show that PG and RG are in their current geometries close to maintaining their total volume, with grounding line influxes balancing inferred melting ... We find that in spite of
apparently minor changes in surface area in recent decades at 79N, net mass losses there are the highest of the remaining large ice tongues in Greenland. While our mass deficit estimates are based on an average over a relatively short (4 year) time span, high rates of mass loss lead us to speculate that major changes will take place at 79N in the future as the ice tongue thins and eventually becomes ungrounded at its terminus. This could have important implications for buttressing of the inland portion of the outlet glacier that is the exit of the northeast Greenland ice stream."

doi: 10.5194/tc-11-2773-2017

Open access. Read all about it.

https://www.the-cryosphere.net/11/2773/2017/

sidd
Title: Re: What's new in Greenland?
Post by: Espen on December 21, 2017, 09:14:46 PM
I dont think so ???
Title: Re: What's new in Greenland?
Post by: AbruptSLR on December 22, 2017, 12:35:42 AM
The linked reference finds that algae driven darkening of bare ice in Greenland reduced albedo more than nonalgal impurities.  Furthermore, they find that a global warming continues the impact of the algae on albedo will also increase:

Marek Stibal et al. (18 November 2017), "Algae Drive Enhanced Darkening of Bare Ice on the Greenland Ice Sheet", Geophysical Research Letters, DOI: 10.1002/2017GL075958

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075958/full

Abstract: "Surface ablation of the Greenland ice sheet is amplified by surface darkening caused by light-absorbing impurities such as mineral dust, black carbon, and pigmented microbial cells. We present the first quantitative assessment of the microbial contribution to the ice sheet surface darkening, based on field measurements of surface reflectance and concentrations of light-absorbing impurities, including pigmented algae, during the 2014 melt season in the southwestern part of the ice sheet. The impact of algae on bare ice darkening in the study area was greater than that of nonalgal impurities and yielded a net albedo reduction of 0.038 ± 0.0035 for each algal population doubling. We argue that algal growth is a crucial control of bare ice darkening, and incorporating the algal darkening effect will improve mass balance and sea level projections of the Greenland ice sheet and ice masses elsewhere."
Title: Re: What's new in Greenland?
Post by: sidd on December 22, 2017, 05:41:41 AM
"I don't think so."

If this is in reference to Wilson, which bit don't you agree with ? I thought the mass balance study from DEM was plausible, but i am willing to be convinced otherwise.

sidd
Title: Re: What's new in Greenland?
Post by: sidd on December 22, 2017, 11:57:29 PM
I quite like the Cullather paper, probably because it agrees with me. Here is a bit of evidence that downwelling longwave from clouds is tied to melt in greenland. But even recognizing my bias, I do think the whole paper is quite good, and they have done some painstaking work. I would have bowed to their analysis if they had come to another conclusion.

"Melt area is enhanced in the presence of increased cloudiness and a large downwelling longwave radiative flux."

The paper is quite interesting. I attach fig 6 and since the caption turns out to be complicated, i retype:

Fig 6 caption:

Regression of passive microwave-derived daily melt area for basins indicated in green to de-trended MERRA-2 surface downwelling longwave radiative flux anomalies, in W/m^2 at each grid point for 1980-2012, in °C. The melt area time series is normalized by the total area of the basin and is restricted to values greater than 5 percent of the basin area. The center panel denotes the regression pattern for daily melt area summed over the entire ice sheet. Hatched areas denote regression significance at the 99 percent confidence level.

doi: 10.1175/JCLI-D-17-0447.1

sidd
Title: Re: What's new in Greenland?
Post by: Espen on December 26, 2017, 04:19:23 PM
"I don't think so."

If this is in reference to Wilson, which bit don't you agree with ? I thought the mass balance study from DEM was plausible, but i am willing to be convinced otherwise.

sidd

Simply because Zachariae Gletscher became unplugged over the last decade and redirected the whole pressure regime. The movement at 79 is almost zero now, even a big story last year about Spaltegletscher emminent calving and the consequenses was an overkill, 79 today more or less behaves like the former ice tonque of Zachariae Gletscher.

https://forum.arctic-sea-ice.net/index.php/topic,400.msg89757.html#msg89757

https://www.youtube.com/watch?v=QzKTIgRW-j8
Title: Re: What's new in Greenland?
Post by: sidd on December 26, 2017, 07:44:17 PM
I think i agree with you that 79N does not provide much backpressure, but i also think that Wilson et al. are correct in the 79N will continue to thin.

sidd
Title: Re: What's new in Greenland?
Post by: Espen on December 26, 2017, 08:03:49 PM
I think i agree with you that 79N does not provide much backpressure, but i also think that Wilson et al. are correct in the 79N will continue to thin.

sidd

Yes it will continue to thin like almost anything else in Greenland these days, provided we follow our path of "self-realization".
Title: Re: What's new in Greenland?
Post by: Anne on January 10, 2018, 02:57:00 PM
GEM Data project now publicly available (http://cphpost.dk/news/gem-project-makes-data-on-greenland-freely-available-to-all.html)
Quote
A treasure trove of information about Greenland and the Arctic is now at the disposal of the world’s researchers, thanks to a project under the auspices of Aarhus University.

The database is part of the Greenland Ecosystem Monitoring (GEM) project and the data has been collected by researchers who have returned again and again to the same places to measure the same things in the same way, reports Videnskab.dk.

A treasure trove of information about Greenland and the Arctic is now at the disposal of the world’s researchers, thanks to a project under the auspices of Aarhus University.

The database is part of the Greenland Ecosystem Monitoring (GEM) project and the data has been collected by researchers who have returned again and again to the same places to measure the same things in the same way, reports Videnskab.dk.

And here's the link to the site: http://data.g-e-m.dk/
Title: Re: What's new in Greenland?
Post by: solartim27 on January 18, 2018, 05:33:22 PM
What's new is very old

https://www.nationalgeographic.com/adventure/contributor-drafts/world_s-oldest-fossils-discovered-due-to-climate-change/

Edit:  Turns out it's an old story, but here is a link to a better one from last March
http://www.sciencemag.org/news/2017/03/377-billion-year-old-fossils-stake-new-claim-oldest-evidence-life
Title: Re: What's new in Greenland?
Post by: AbruptSLR on February 09, 2018, 06:29:17 PM
The linked reference provides a nice review of outlet glaciers in northern Greenland:

Hill, E. A., Carr, J. R., Stokes, C. R., and Gudmundsson, G. H.: Dynamic changes in outlet glaciers in northern Greenland from 1948 to 2015, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-17, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-17/

Abstract. The Greenland Ice Sheet (GrIS) is losing mass in response to recent climatic and oceanic warming. Since the mid-1990s, marine-terminating outlet glaciers across the GrIS have retreated, accelerated and thinned, but recent changes in northern Greenland have been comparatively understudied. Consequently, the dynamic response (i.e. changes in surface elevation and velocity) of these outlet glaciers to changes at their termini, particularly calving from floating ice tongues, remains unknown. Here we use satellite imagery and historical maps to produce an unprecedented 68-year record of terminus change across 18 major outlet glaciers and combine this with previously published surface elevation and velocity datasets. Overall, recent (1995–2015) retreat rates were higher than at any time in the previous 47 years, but change-point analysis reveals three categories of frontal position change: (i) minimal change followed by steady and continuous retreat, (ii) minimal change followed by a switch to a period of short-lived rapid retreat, (iii) glaciers that underwent cycles of advance and retreat. Furthermore, these categories appear to be linked to the terminus type, with those in category (i) having grounded termini and those in category (ii) characterised by floating ice tongues. We interpret glaciers in category (iii) as surge-type. Glacier geometry (e.g. fjord width and basal topography) is also an important influence on the dynamic re-adjustment of glaciers to changes at their termini. Taken together, the loss of several ice tongues and the recent acceleration in the retreat of numerous marine-terminating glaciers suggests northern Greenland is undergoing rapid change and could soon impact on some large catchments that have capacity to contribute an important component to sea level rise.
Title: Re: What's new in Greenland?
Post by: sidd on February 20, 2018, 09:25:57 AM
That Hill paper is brilliant. Check out figs 7,8,9. Open access.

sidd
Title: Re: What's new in Greenland?
Post by: Espen on February 20, 2018, 10:20:29 PM
That Hill paper is brilliant. Check out figs 7,8,9. Open access.

sidd

Not so in my oppinion according to the paper Steensby Gletscher should be advancing, that is not true the glacier retreated more than 20 km over the last decade??
Title: Re: What's new in Greenland?
Post by: sidd on February 21, 2018, 05:36:56 AM
That figure is odd considering this statement on pg 8:

"Steensby Glacier underwent minimal change during the study period (1 m a -1 : 1948–2015), but
with a high rate of retreat from 1978 to 2015 (-366 m a -1 )."

Fig 4 shows Steensby at +104m/yr till 2010 or later, but then retreating at 3Km/yr

Perhaps you should post a comment there. the paper is still in discussion, i think.

sidd

P.S. : I think i figured it out fig3 is the average from 1948, and the rapid recent retreat has not swung the average yet.
Title: Re: What's new in Greenland?
Post by: sidd on March 01, 2018, 12:30:00 AM
Nice paper by Joughin, Smith and Howat with new velocity maps.

"It is unclear whether external forcing, internal dynamics, or some combination of both have contributed to the changes in terminus extent that have produced the recent slowdown. Temperature records from the nearby coastal station at Egedesminde 20 indicate that 2017 was the second coldest year, behind 2015, in the 21 st Century (GISS, 2018). Thus, one plausible hypothesis is that the recent colder temperatures may have contributed to the advance and slowdown, although if there were cooler water at the terminus it could have played a role as well. Whether this slowdown could reduce summer thinning and increase winter thickening sufficiently to stabilize the glacier over scales of years to decades is unclear."

...

"If the recent slowdown is not the beginning of a period of stabilization, then the terminus of Jakobshavn Isbrae likely will continue to retreat at least 60 km inland until it recedes from the trough’s deeper parts (Joughin et al., 2012)"

Open access. Read the whole thing.

doi: 10.5194/tc-2018-40

sidd

Title: Re: What's new in Greenland?
Post by: sidd on March 03, 2018, 02:54:16 AM
Bamber and the usual suspect have a paper out on Arctic freshwater flux:

doi: 10.1002/2017JC013605

"The cumulative freshwater flux anomaly exceeded 6300±316 km^3 by 2016. This is roughly twice the estimate of a previous analysis that did not include glaciers and ice caps outside of Greenland and which extended only to 2010. From 2010 onward, the total freshwater flux is about 1300 km 3 /yr, equivalent to 0.04 Sv, which is roughly 40% of the estimated total runoff to the Arctic for the same time period. Not all of this flux will reach areas of deep convection or Arctic and Sub-Arctic seas. We note, however, that the largest freshwater flux anomalies, grouped by ocean basin, are located in Baffin Bay and Davis Strait ... "

"The total cumulative FWF anomaly is close to reaching a value where it will be comparable to the interannual
variability in FWF driven by other processes in the climate system [Boning et al., 2016]."

I attach a figure

sidd
Title: Re: What's new in Greenland?
Post by: AbruptSLR on March 14, 2018, 11:02:48 PM
If the findings of the linked reference are correct then "chain-reactions of fast draining lakes" could threaten the stability of key portions of Greenland's ice sheet over the coming 50 years:

Poul Christoffersen et al, Cascading lake drainage on the Greenland Ice Sheet triggered by tensile shock and fracture, Nature Communications (2018). DOI: 10.1038/s41467-018-03420-8

http://www.nature.com/articles/s41467-018-03420-8

Abstract: "Supraglacial lakes on the Greenland Ice Sheet are expanding inland, but the impact on ice flow is equivocal because interior surface conditions may preclude the transfer of surface water to the bed. Here we use a well-constrained 3D model to demonstrate that supraglacial lakes in Greenland drain when tensile-stress perturbations propagate fractures in areas where fractures are normally absent or closed. These melt-induced perturbations escalate when lakes as far as 80 km apart form expansive networks and drain in rapid succession. The result is a tensile shock that establishes new surface-to-bed hydraulic pathways in areas where crevasses transiently open. We show evidence for open crevasses 135 km inland from the ice margin, which is much farther inland than previously considered possible. We hypothesise that inland expansion of lakes will deliver water and heat to isolated regions of the ice sheet’s interior where the impact on ice flow is potentially large."

See also:

Title: "Chain reaction of fast-draining lakes poses new risk for Greenland ice sheet"

https://phys.org/news/2018-03-chain-reaction-fast-draining-lakes-poses.html

Extract: "A growing network of lakes on the Greenland ice sheet has been found to drain in a chain reaction that speeds up the flow of the ice sheet, threatening its stability."
Title: Re: What's new in Greenland?
Post by: litesong on March 16, 2018, 05:26:27 PM
Yes, that is a lollapalooza! I just read about it from this Science Daily: https://www.sciencedaily.com/releases/2018/03/180314092305.htm
But I see I'm already late, here. ha ha ha
It almost sounds like the stress-tensor theory they expounded in our 1970's aeronautical structures classes.
Title: Re: What's new in Greenland?
Post by: gerontocrat on March 20, 2018, 10:52:25 AM
http://spacenews.com/iridium-raising-new-debt-to-cover-late-aireon-payments/

Iridium raising new debt to cover late Aireon payments
by Caleb Henry — February 26, 2018


You might be asking what on earth has Iridium's debts got to do with Greenland ?

Once upon a time there was the GRACE project (US & Germany) that gave us the data on ice mass loss in Greenland (and Antarctica and loads of other data used in more than 6000 scientific papers). It lasted much longer than its design life but NASA finally took it off life support in January 2017.

Do not despair - the new improved GRACE Follow-on project is due to happen this spring (and the specs look great). But the private sector are doing the launch with Iridium satellites also involved. Things have got messy - see below.

This project has major importance. The data will be (amongst other things) the definitive record of ice mass change of the ice-sheets, eliminating uncertainty, speculation and denial.

Quote

WASHINGTON — A company that fleet operator Iridium formed to help finance its second-generation satellite constellation is taking longer than expected to pay Iridium back for carrying its sensor network to orbit.

McLean, Virginia-based Iridium said Feb. 22 that to avoid counting on aircraft-tracking startup Aireon for liquidity, Iridium went back to its lenders to raise additional debt to finish the $3 billion Iridium Next constellation it’s in the midst of deploying.

Next SpaceX launch in late March

Iridium CEO Matt Desch said the successful Feb. 22 launch of a SpaceX Falcon 9 from Vandenberg Air Force Base cleared the way for greater schedule certainty with Iridium Next, which is launching entirely from the California facility. So far SpaceX has completed four Falcon 9 launches for Iridium, and has four more to go, though the original launch campaign was supposed to have been completed in 2017.

The fifth Iridium Next launch will likely occur March 29, he said. Subsequent missions should follow every five to six weeks until the constellation is complete, he said. Each launch carries 10 satellites at a time, with the exception of the sixth launch, which will carry five Iridium Next satellites and two U.S.-German science satellites called GRACE-FO.

The GRACE-FO, or Gravity Recovery and Climate Experiment Follow-On satellites, were originally supposed to launch on a Dnepr rocket through the Russian-Ukrainian joint venture Kosmotras, but the mission never happened. Iridium had two satellites slated to launch on Dnepr as well, but booked a shared Falcon 9 after Russian red tape left the launch, once forecast for 2015, on indefinite hold.

What a complicated world we live in. ("Oh! what a tangled web we weave" Sir Walter Scott 1808 - not the Bard).

PS Ice-Sat 2 - will look at ice thickness - launch in September 2018 (We hope). A definitive measurement of ice thickness would be a big plus?
http://environmentalresearchweb.org/cws/article/news/70881
Title: Re: What's new in Greenland?
Post by: sidd on March 29, 2018, 08:08:36 PM
Paper by Graeter et al on increasing melt in Greenland over the last twenty years. They looked at cores from the percolation zone, and it is clear from the ice left behind by melt evetns that melt frequency has been increasing over the last two decades. I attach fig 1.

doi:10.1002/2017GL076641

sidd
Title: Re: What's new in Greenland?
Post by: gerontocrat on April 11, 2018, 02:21:03 PM
GRACE FOLLOW-ON LAUNCH AT LAST -

https://www.prnewswire.com/news-releases/nasa-invites-media-to-launch-of-grace-follow-on-spacecraft-300627660.html

Quote
GRACE-FO will launch as part of a commercial rideshare mission with five Iridium Communications Inc. satellites aboard a SpaceX Falcon 9 rocket. The Iridium-6/GRACE-FO launch is scheduled for no earlier than 1:03 p.m. PDT (4:03 p.m. EDT) May 19 from Vandenberg Air Force Base in California.

Read all about it on https://gracefo.jpl.nasa.gov/ from the jet propulsion lab. Also about ICE-SAT-2
Title: Re: What's new in Greenland?
Post by: gerontocrat on April 18, 2018, 11:43:14 AM
A paper on Glacier Calving in Greenland from October 2017. Certainly improved my understanding of the subject.
https://link.springer.com/content/pdf/10.1007%2Fs40641-017-0070-1.pdf

And an older one from 2012 also giving me a bit more insight.
http://www.pnas.org/content/109/49/19934
Mapping Greenland’s mass loss in space and time

See map below - how to find an up-to-date equivalent?


Title: Re: What's new in Greenland?
Post by: Juan C. García on July 03, 2018, 02:43:03 PM
OMG, the water's warm! NASA study solves glacier puzzle
By Carol Rasmussen,
NASA's Earth Science News Team

Quote
Tracy and Heilprin were first observed by explorers in 1892 and have been measured sporadically ever since. Even though the adjoining glaciers experience the same weather and ocean conditions, Heilprin has retreated upstream less than 2.5 miles (4 kilometers) in 125 years, while Tracy has retreated more than 9.5 miles (15 kilometers). That means Tracy is losing ice almost four times faster than its next-door neighbor.

Quote
Using ocean data from NASA's Oceans Melting Greenland (OMG) campaign, the study documents a plume of warm water flowing up Tracy's underwater face, and a much colder plume in front of Heilprin.

https://climate.nasa.gov/news/2754/omg-the-waters-warm-nasa-study-solves-glacier-puzzle/ (https://climate.nasa.gov/news/2754/omg-the-waters-warm-nasa-study-solves-glacier-puzzle/)
Title: Re: What's new in Greenland?
Post by: solartim27 on July 03, 2018, 05:51:34 PM
Nice overview of what you can find on Cryoportal from this thread.
Ruth Mottram (@ruth_mottram) Tweeted:
The final meeting for phase 2 of the @esaclimate #CCI #Greenland #icesheet project showing the evolution of the #icevelocity data with improvements to coverage and algorithms from #Sentinel1

Data: https://t.co/Tu4tdFe3kq https://t.co/iLrq1wUElg https://twitter.com/ruth_mottram/status/1014089754839744513?s=17

http://cryoportal.enveo.at
Title: Re: What's new in Greenland?
Post by: gerontocrat on July 14, 2018, 11:02:50 AM
A nice reminder that when Greenland's glaciers calve, big stuff falls off.
Title: Re: What's new in Greenland?
Post by: Shared Humanity on July 14, 2018, 05:06:04 PM
Great photo.
Title: Re: What's new in Greenland?
Post by: gerontocrat on July 14, 2018, 08:03:12 PM
More about that iceberg

https://www.bbc.co.uk/news/world-europe-44831663

Huge iceberg threatens Greenland village
Quote
A huge iceberg has drifted close to a village in western Greenland, prompting a partial evacuation in case it splits and the resulting wave swamps homes. The iceberg is looming over houses on a promontory in the Innaarsuit village but is grounded and did not move overnight, local media say.

Local officials say they have never seen such a big iceberg before.

Last summer, four people died after waves swamped houses in northwestern Greenland after an earthquake. Those of Inaarsuit's 169 residents living nearest the iceberg have been moved, Danish news agency Ritzau said. "There are cracks and holes that make us fear it can calve anytime," village council member Susanne Eliassen told the local newspaper Sermitsiaq. The village's power station and fuel tanks are close to the shore, she said. Some experts have warned that extreme iceberg events risk becoming more frequent because of climate change. This in turn increases the risk from tsunamis.

Title: Re: What's new in Greenland?
Post by: litesong on July 20, 2018, 03:07:32 AM
A nice reminder that when Greenland's glaciers calve, big stuff falls off.
Here's how such "big stuff" falls off.
https://www.youtube.com/watch?v=hC3VTgIPoGU
Title: Re: What's new in Greenland?
Post by: oren on July 20, 2018, 08:37:18 AM
Thanks litesong. When ASLR posts about ice-cliff failure in the Antractica threads, this is what it looks like in real life. When the leading ice is calved, the remaining ice cliff loses its support and is too tall to stand unsupported.
Title: Re: What's new in Greenland?
Post by: VeliAlbertKallio on July 31, 2018, 11:02:08 PM
Our Changing Climate in Action: the Risk of Global Warming and the Environmental Damage from the Rising Ocean Water Table | Sustainable Seas Enquiry | Written evidence submitted by Veli Albert Kallio, FRGS (SSI0121) | Ordered to be published 23 May 2018 by the House of Commons.

Abstract:

Recently NATURE published a discussion on construction of sills in attempt to prevent or slow melting glaciers that are discharging ice into the ice fjords. Several further papers promptly followed publication of this essentially erroneous article in a respected NATURE magazine. Here it is pointed out that there is a discrepancy of several magnitudes thus excluding a long-term viability to manage the edges of ice fjords or continental ice shelves/sheets due to a phenomenon known as the mega-erratics. These are blocks of hard rocks that are several kilometres in size that have been dislocated by a warmed and wet edges of glacier/ice sheet/ice shelf. This Parliament evidence points out the error that was not apparent to the peer-reviewers at the time and in subsequent papers that followed. The Parliament was shown evidence that large enough obstacles cannot be possibly made to prevent ice discharges due to a progression of melting, that softens and lubricates glaciers, ice caps and ice sheets. The forces unleashed by the ice front exceeds several magnitudes from the conceived objects that sills were proposed. The only, and very only effect is temporary and limited to prevention of warm water incursion where these methods will work for a while in a cold, dry, and relatively stable ice formations.

Long-term projections suggested to prevent warmed and water-infested glaciers from discharging ice into the ocean cannot be made as the forces of ice exceed many magnitudes of the sills and levies that can be made of concrete blocks, aggregates or other materials. Thus the prevention of sea level rise by this method for centuries or millennia is not functional one and thus the mitigation and prevention of rubbish gyros in ocean, the supply of housing, nuclear and food production security must be looked at as solution by the ocean littoral states. Several examples of various types of risk to the sustainability of oceans have been presented in addition to the above exposed misconception. This comes with much regret as it appears that one 'hoped-for-solution' to manage the future climate change impacts has largely foundered on the issue that the sills cannot be made strong enough to contain most important, warmed glaciers or edges of unstable ice shelves. However, for a short-term this may offer small-scale solutions provided that costs remain sufficiently small. Aggressively melting ice formations with darkened surfaces, wide spread melt water ponds, or water filled crevasses it does not offer much, if any, prolonged ice stability. (The document is best viewed as a .pdf file due to the lay-out of graph and legends.)

https://www.academia.edu/37157851/Our_Changing_Climate_in_Action_the_Risk_of_Global_Warming_and_the_Environmental_Damage_from_the_Rising_Ocean_Water_Table_Sustainable_Seas_Enquiry_Written_evidence_submitted_by_Veli_Albert_Kallio_FRGS_SSI0121_Ordered_to_be_published_23_May_2018_by_the_House_of_Commons

Stopping the Flood: Could We Use Targeted Geoengineering to Mitigate Sea Level Rise?
Michael J. Wolovick1 and John C. Moore2,3
1Atmosphere and Ocean Sciences Program, Department of Geosciences, Princeton University, GFDL, 201 Forrestal Road,
Princeton, NJ 08540, USA
2College of Global Change and Earth System Science, Beijing Normal University, Beijing, China
3Arctic Centre, University of Lapland, Finland
Correspondence: M.J. Wolovick (wolovick@princeton.edu)

Abstract. The Marine Ice Sheet Instability (MISI) is a dynamic feedback that can cause an ice sheet to enter a runaway collapse. Thwaites Glacier, West Antarctica, is the largest individual source of future sea level rise and may have already entered the MISI. Here, we use a suite of coupled ice–ocean flowband simulations to explore whether targeted geoengineering using an artificial sill or artificial ice rises could counter a collapse. Successful interventions occur when the floating ice shelf regrounds 5 on the pinning points, increasing buttressing and reducing ice flux across the grounding line. Regrounding is more likely with a continuous sill that is able to block warm water transport to the grounding line. The smallest design we consider is comparable in scale to existing civil engineering projects but has only a 30% success rate, while larger designs are more effective. There are multiple possible routes forward to improve upon the designs that we considered, and with decades or more to research designs it is plausible that the scientific community could come up with a plan that was both effective and achievable. While 10 reducing emissions remains the short-term priority for minimizing the effects of climate change, in the long run humanity may need to develop contingency plans to deal with an ice sheet collapse.

--

http://data.parliament.uk/writtenevidence/committeeevidence.svc/evidencedocument/environmental-audit-committee/sustainable-seas/written/83150.pdf
Title: Re: What's new in Greenland?
Post by: AbruptSLR on August 01, 2018, 09:23:44 PM
From about 50 to 80 million years ago Greenland passed over a hotspot in the Earth's mantle, and consequently it has a band of relatively high geothermal heat flux extending from its northwest corner to its southeast coast.  This unexpected high geothermal heat flux implies that existing ice mass loss projections for Greenland are likely too low:

Title: "How Greenland scorched its underside"

https://www.bbc.com/news/science-environment-45031592

Extract: "From its northwest corner to its southeast coast, the world's biggest island has a band of relatively warm bedrock.

Scientists say this confirms Greenland ran over a hotspot of upwelling molten rock tens of millions of years ago as it shifted towards the Arctic."
Title: Re: What's new in Greenland?
Post by: RoxTheGeologist on August 01, 2018, 10:37:04 PM

Interesting!

It sounds like a stretch to imply heat-flux from magnetism, but sadly I didn't pay enough attention in the geo-magnetism course.  If anyone can slip me a copy I'd like to read it....

Title: Re: What's new in Greenland?
Post by: bluesky on August 03, 2018, 10:48:53 PM

"Large ice loss variability at Nioghalvfjerdsfjorden Glacier, Northeast-Greenland"
(Christoph Mayer et al.) July 2018

https://www.nature.com/articles/s41467-018-05180-x.pdf

Abstract:
"Nioghalvfjerdsfjorden is a major outlet glacier in Northeast-Greenland. Although earlier studies showed that the floating part near the grounding line thinned by 30% between 1999 and 2014, the temporal ice loss evolution, its relation to external forcing and the implications for the grounded ice sheet remain largely unclear. By combining observations of surface features, ice thickness and bedrock data, we find that the ice shelf mass balance has been out of equilibrium since 2001, with large variations of the thinning rates on annual/multiannual time scales. Changes in ice flux and surface ablation are too small to produce this variability. An increased ocean heat flux is the most plausible cause of the observed thinning. For sustained environmental conditions, the ice shelf will lose large parts of its area within a few decades and ice modeling shows a significant, but locally restricted thinning upstream of the grounding line in response."

extract from discussion:
" the reason for the large interannual fluctuations of the thinning rates revealed by this study still need to be found. AW anomalies in Fram Strait take about 1.5 years and longer to reach the 79 North Glacier21, while fjord temperatures may vary greatly on shorter time scales. Also the transient adjustment of the cavity circulation further modulates the response of the glacier to ocean forcing30. Following the method of31 and using the hydrographic profiles to constrain the water mass transformation inside the ice shelf cavity (Supplementary Fig. 2b), it can be shown that the observed 40% increase in basal melting is associated with a 30% stronger cavity overturning circulation. Herein, the temperature difference between ingoing and outgoing waters (using the same definitions as ref.29) changes little between the different years, but the increased meltwater input at the ice base drives a more vigorous sub-ice shelf circulation that accomplishes the additional heat flux of 0.7±1.8×1011 W into the cavity. This results in a reduction of the cavity exchange time scale from about 120±26 days to about 90±35 days, which further increases the sensitivity of the ice shelf to ocean changes30. Thus, while our analysis suggests that the ocean is likely the main driver of the observed changes at 79 North Glacier, the regional dynamics that control the heat transport into the ice shelf cavity and other contributors, such as subglacial discharge induced by surface melt or geothermal heat flux will need further attention to fully understand the observed thickness evolution. Potential consequences for the future ice shelf stability: Despite the fact that 79 North Glacier has a more stable grounding line situation than Zachariæ Isstrøm (rising bedrock inland), the loss of the ice shelf might contribute to destabilize the entire, marinebased ice sheet sector. At the moment the ice shelf is well buttressed in the fjord and even the loss of the outer part would probably not change this. Without the buttressing effect of the floating ice tongue in the fjord, our simplified model approach demonstrates that the ice thickness strongly decreases and the grounding line retreats by about 10km. This is comparable to the results of a recent study32 and poses the question if the disintegration of the ice shelf and its related consequences on the grounded ice are likely to happen in the near future. The ice thickness reduced by about 30% during the period 1998 until 2014. Compared with balanced conditions, implying a mass balance of −12myear−1 in the region of Midgardsormen, the mean ice loss during the observation period results in an almost 1.5 times higher mass balance magnitude. The numerical simulations demonstrate that the thinning will lead to large areas of very thin ice, which are most likely unstable and large parts of the ice shelf will disappear during coming decades. Given that the environmental conditions already enabled ice thickness reductions up to 13m within one year that process could be considerably faster for enhanced oceanic energy fluxes into the ice shelf cavity. Even though the consequences are serious for the neighboring part of the ice sheet, where the ice thins by about 200m after the loss of the ice shelf, it seems that the increased fluxes will not reach far into the ice sheet during the next century, resulting in thickness losses in the order of 30m about 20km upstream. It needs to be considered, however, that our simple model setup is not appropriate to simulate the long-term feedback mechanisms. Therefore a more detailed investigation is required for investigating the long-term stability of the ice sheet in this sector of Greenland."


Title: Re: What's new in Greenland?
Post by: sidd on August 04, 2018, 01:51:37 AM
Thanx for the Mayer reference, very pretty paper. They used the migration of an ice ridge to deduce historical grounding lines, lateral stress and ice thickness. I can see i shall have to spend some hours on it.

sidd
Title: Re: What's new in Greenland?
Post by: johnm33 on August 04, 2018, 01:05:28 PM
Very timely too the fast ice has just about cleared [29th] (http://puu.sh/B8upS/6d9a939f82.jpg) from the front of the ice shelf, and it's now more exposed to tides and Atl. waters. The shelf may only have to retreat a little to have dramatic effects on the overturning circulation.
(https://puu.sh/lmtQR/0379acd0aa.jpg)
Title: Re: What's new in Greenland?
Post by: oren on August 04, 2018, 01:13:51 PM
It would be best to cross-post these interesting posts to the Zachariae/Nioghalvfjerdsfjorden thread.
https://forum.arctic-sea-ice.net/index.php/topic,400.0.html (https://forum.arctic-sea-ice.net/index.php/topic,400.0.html)
Title: Re: What's new in Greenland?
Post by: litesong on August 09, 2018, 02:25:25 AM
A nice reminder that when Greenland's glaciers calve, big stuff falls off.
Here's how such "big stuff" falls off.
https://www.youtube.com/watch?v=hC3VTgIPoGU

 More recent "big stuff" falls off:
https://www.theverge.com/2018/7/9/17550966/greenland-helheim-glacier-calving-icebergs-video
Title: Re: What's new in Greenland?
Post by: sidd on August 11, 2018, 11:09:53 PM
Hard rain falling:

"The extended period of above-normal frequency and intensity of AR events affecting Greenland during 2000–2012 coincided with a well-documented uptick in GrIS mass loss, culminating with the extreme melt season of 2012 which also featured highly anomalous moisture transport by ARs to western and northern Greenland. Subsequent years have seen less extreme GrIS mass loss and a shift of the greatest melt anomalies to northern areas of the GrIS ..."

"Strong AR impacts cause increased melt in all areas of the GrIS and decreased SMB in the ablation zone during summer, and warm seasons with above-average GrIS melt extent are characterized by anomalously strong moisture transport by ARs over Greenland. ARs typically result in SMB gains in the GrIS ablation zone during non-summer seasons and in the accumulation zone during all seasons. However, the intense summer SMB losses in the ablation zone during years of enhanced moisture transport outweigh the positive AR contributions to SMB in other regions and seasons."

AR is Atmospheric river. SMB is surface mass balance.

I notice Fettweis is an author.

DOI: 10.1029/2018JD028714

sidd
Title: Re: What's new in Greenland?
Post by: litesong on August 16, 2018, 01:33:31 AM
A nice reminder that when Greenland's glaciers calve, big stuff falls off.
Here's how such "big stuff" falls off.
https://www.youtube.com/watch?v=hC3VTgIPoGU

 More recent "big stuff" falls off:
https://www.theverge.com/2018/7/9/17550966/greenland-helheim-glacier-calving-icebergs-video
More "big stuff" becoming "big stuff".
https://www.youtube.com/watch?v=6zu-Cl-J8qY
Title: Re: What's new in Greenland?
Post by: Tor Bejnar on August 31, 2018, 07:09:02 PM
GeoTalk: To understand how ice sheets flow, look at the bedrock below
 (https://blogs.egu.eu/geolog/2018/08/17/geotalk-to-understand-how-ice-sheets-flow-look-at-the-bedrock-below/)
  An interview with Mathieu Morlighem, associate professor of Earth System Science at the University of California, Irvine who uses models to better understand ongoing changes in the Cryosphere.  GeoLog (https://blogs.egu.eu/geolog/)  ·  August 17, 2018
Quote
...
Subglacial bed topography is probably the most important input parameter in an ice sheet model and remains challenging to measure. The bed controls the flow of ice and its discharge into the ocean through a set of narrow valleys occupied by outlet glaciers. I am hoping that the new product that I developed, called BedMachine, will help reduce the uncertainty in numerical models, and help explain current trends.
...

[Edit: this is my post #1997 = the year I married my wife, the artist who created the avatar I use here.]
Title: Re: What's new in Greenland?
Post by: Mr.Far on October 11, 2018, 09:01:06 AM
The Arctic has slowly but surely gained visibility as an increasingly important part of the Danish/Greenlandic narrative (in which Greenland’s, in fact, Danish ‘colony’, role has miraculously evolved over time to that of an ‘equal partner’ in the Danish Realm). Denmark submitted the last (fifth) claim in 2014 (it lays claim to the North Pole). But, wait a minute! Its bid for 895,000 sq km of the Arctic Ocean sounds particularly audacious given that this is 20 times the size of Denmark!

They say that the obtaining rights to the North Pole has a symbolic meaning. But… isn’t it too much for the country, which lies on the same latitude as (for example) Britain – more than 2,000 miles from the North Pole?
Title: Re: What's new in Greenland?
Post by: Espen on October 11, 2018, 09:58:33 PM
Greenland is very important to Denmark and the danish political sense of self, without Greenland Denmark would have very little Geo political negotiating power with the US in particular and to some degree other major powers like Russia and China.
The problem now is, Denmark never invested in Greenland in real good faith, and the people of Greenland realized that, but it is an interesting development. The elephant in the room is China.