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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 574992 times)

AbruptSLR

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #400 on: August 01, 2014, 02:35:19 AM »
A-Team,

Thank you for the link to the British Survey repository.  Your posts on Jakobshavn has inspired me to open a new thread in the Antarctic folder on the internal structure of the Antarctic Ice Sheet (see the link below):

http://forum.arctic-sea-ice.net/index.php/topic,939.0.html

I will stop intruding on the Greenland folder (which has fascinating discussions, but for which I do not have the time, expertise, or energy to participate appropriately), and I will try expand the information on the new AIS internal structure thread (which I think will become increasingly critical in the Amundsen Sea Embayment marine glaciers in the next few decades).

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #401 on: August 01, 2014, 06:49:21 AM »
A-Team yes the Danish involvement in Greenland on all levels, is pathetic! >:(
Have a ice day!

Shared Humanity

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #402 on: August 01, 2014, 04:33:34 PM »
A-Team yes the Danish involvement in Greenland on all levels, is pathetic! >:(

They are focusing on lining up multinationals for exploiting the emerging natural resources.

(I wish this wasn't actually true.)

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #403 on: August 01, 2014, 07:46:44 PM »
A-Team yes the Danish involvement in Greenland on all levels, is pathetic! >:(

They are focusing on lining up multinationals for exploiting the emerging natural resources.

(I wish this wasn't actually true.)

To be fair, that is a Homerule Authoritys (Greenland "Government") project!
Have a ice day!

nukefix

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #404 on: August 02, 2014, 02:08:09 PM »
Here's a Sentinel-1 SAR-image of Jakobshaven taken on 19.7.2014

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #405 on: August 02, 2014, 02:11:49 PM »
Here's a Sentinel-1 SAR-image of Jakobshaven taken on 19.7.2014

Hope they will come up with better resolution?
Have a ice day!

nukefix

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #406 on: August 02, 2014, 02:55:01 PM »
Here's a Sentinel-1 SAR-image of Jakobshaven taken on 19.7.2014
Hope they will come up with better resolution?
Here's a zoom showing individual pixels, the pixel-size is 10m in both range and azimuth. Note that this zoom shows a tiny corner of a 480 megapixel (per polarization) datatake. In other words, S-1 will provide huge area coverage while other SARs should be used when very high resolution is desired.

edit: the cool thing is that starting very soon S-1 will image Jakobshaven twice (ascending and descensing datatakes) every 12 days throughout the year.
« Last Edit: August 02, 2014, 04:17:52 PM by nukefix »

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #407 on: August 02, 2014, 06:24:35 PM »
Nukefix, that is fantastic news. Can you share the link to these Sentinel images ... or does one have to go through a klutzy map search interface?

Here is an awesome image posted by a graduate student ('Spaz') who doesn't even work on Greenland. He used the surf command in MatLab to visualize a 2012 Cresis transect across north central Greenland. The color tinting reflects diminishing return echo power of the radar. The surface is shaded by illumination from above to draw out the layers. The original track data can be found as the file sets 20120507_03, 20120507_04, 20120507_05, and 20120507_06 at the Cresis ftp site.

Greenland is really, really flat. We almost always see it with huge (and unspecified) vertical scale exaggeration. While it does reach a height of  10,551' at Summit (~ GISP2) that takes several hundred km at low gradient to attain. Standing on the surface, it is all but impossible even to see downhill flow lines; other methods had to be used at Foxx/Gull drill sites.

His image has 75x vertical resolution. From it, I made versions with 1x, 5x, and 10x vertical exaggerations. The original  is at <url>http://i.imgur.com/J5oAtH0.jpg</url>. The vertical gray pipes are not explained but are possibly NEEM and NEGIS bore holes; I narrowed them and suppressed annoying overlaid text with the cloning tool.

It would make a great deal of sense for Cresis to process every transect flight line in the same manner as Spaz did here and provide the whole collection centrally. And of course the hypersurface story should be updated in real time or at least seasonally with the additional data.

The bottom line here is many isochron striations are easily traced across the entirety of Greenland. This image also refutes published 2014 rubbish to the effect that nothing much has been preserved below the Wisconsin-Holocene Transition at  1.42 kyr.

It's fair to say though, especially in north Greenland, spectacular deformations occur. We know today that many of these are freeze-ups from the bottom at least upstream of Petermann.

Researchers are audibly grumbling about the long-standing obsession with Eemian ice and getting a climate record comparable to the 400 kyr Vostok record in Antarctica. That was never destined to happen because really deep ice is extremely deformed in Greenland -- as we already knew years before NEEM was even drilled. That focus has come at the expense of the mission-critical overall history of the late Pleistocene and Holocene on the Greenland ice sheet.

My question: with hundreds of academic researchers on the Greenland payroll, why do I have to prowl internet blogs for proper workup of the (very expensive) data? These radar overflights began in earnest in 1993.

Click on the image to see full size. It is a beauty.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #408 on: August 02, 2014, 06:38:22 PM »
My question: with hundreds of academic researchers on the Greenland payroll, why do I have to prowl internet blogs for proper workup of the (very expensive) data? These radar overflights began in earnest in 1993.

The answer is within your question, I am afraid! ;)

But very nice work again, not sure how many of those mentioned above it is worth, but quite a few!!!
Have a ice day!

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #409 on: August 02, 2014, 07:03:23 PM »
Do we know what this is? (red encircled):
Have a ice day!

nukefix

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #410 on: August 02, 2014, 08:01:48 PM »
Nukefix, that is fantastic news. Can you share the link to these Sentinel images ... or does one have to go through a klutzy map search interface?
It is necessary to go to https://senthub.esa.int/ to do the download. Just draw a rectangle over Greenland and press search. The product in question is:

S1A_IW_GRDH_1SDH_20140719T205102_20140719T205131_001562_001821_F94C

..and the quicklook is here: https://senthub.esa.int/odata/product(239)/Quicklook
« Last Edit: August 02, 2014, 08:08:13 PM by nukefix »

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #411 on: August 02, 2014, 10:03:38 PM »
Espen, that is a very good question. First thing to do is try to box the features in with nearby tracks to bring their 3D dimensional structure with interpolative range (radar sections being 2D can never fully get to 3D).

That's not impossibly hard with Cresis search though it would be a heck of a lot easier if they replaced what they have with the search code from EarthExplorer. Did I mention that Cresis is totally built around MatLab file format so there is a certain irony to scraping fantastic MatLab scenes off some kid's reddit page.

Second thing to try is look at earlier Bell 2014 posts, see if what you've circled was covered. They verified that at least some of these features are not side-scan radar artifacts (bounces off submerged land forms that confuse the record) but are instead directly nadir, massive freeze-ups of water under the ice sheet. Rocks have much higher density than ice but gravity says they're not there.

A big deal especially for Petermann but I'm recalling these features going all the way south to Epiq. This is a huge interpretive breakthrough if it holds up. They knew to do this from their earlier work in Antarctica!

Abrupt -- thanks for the new for  forum on internal ice structure in Antarctica. I have that open as a browser tab (along with 38 others I can't bear to close).

Nukefix, thanks for those directions. We can do a lot with this Sentinel imagery of JI.

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #412 on: August 02, 2014, 10:22:08 PM »
Scientists are ever so fond of saying, 'oh yes, my last paper was so incredible but hey I was standing on the shoulders of giants.'  That might even be true, but it doesn't speak to the midgets who kick away the ladder so no one can stand on theirs.

Let's just say that people who publish blurry old unsourced radar scans, rescaled differently in horizontal and vertical dimensions all so it fits on the *print version* of a heavily paywalled 2014 journal page, then flip it horizontally and delete the lat,long data it came with, and mark it up illegibly with off-centered crucial insider knowledge they have on a drill hole (chronological dates correlated to radar horizons) are not furthering climate science research by design.

I did eventually manage to transfer this piece of junk onto a professionally prepared and fully documented image of Pellon discussed earlier. It does seem that a fair proportion of the radar stratifications will have climate-related explanations, rather than rubbish of dielectric echoes arising by haphazard convergences of contributing factors.

The image halves do align over the NGRIP borehole if you slide one over. It is incredibly important to get dates assigned correctly to a high quality recent fiducial stratigraphic track running through the 5 main boreholes before pushing the date lines out to the coasts.

Meanwhile thanks to greatdying2, my time is being well-spent a set of 3 really well done new pdfs on the only deep interior ice stream of Greenland,  NEGIS. People are always trying to blow off the firn but they have very decent results are a bore hole back to 1617. Also an explanation as to why the NEGIS ice stream so high up and located where it is (geothermal heat anomaly and shear margin, resp.) Espen has a NEGIS forum going so better to post on this over there.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #413 on: August 04, 2014, 02:24:30 AM »
Phase I, collect all the climate change events that could conceivably have been responsible for radar echo striations in Greenland's glaciers. Here the earlier start-stop dates will be based on GICC05 and later ones (out to the Eemian) on  AICC2012, both in terms of years before 2000 (b2k has supplanted 1950).

And to that, add the depths of these features in the NEEM, NGRIP, GISP, NEGIS, DYE2, and Camp Century drill cores (not forgetting FOXX, GULL nd DUCK for Jakobshavn). And a citation to whatever articles these numbers were lifted from (with the help again of greatdying2).

I'm posting below a simple database of where this project is at. If you see events that have been omitted, dates that are not the best, know of a better published compilation, or have links to articles that can furnish missing drill core depths, please add a comment or PM me.

Phase II, make a catalog of radar striations. That is, the ones that are reproducibly observed with multiple radar setups and traceable over hundreds of km. The trick here is to develop a flexible numbering system that allows for intercalated additions as radar resolution improves. The most representative striation seed area is probably the NGRIP to NEEM ridge line but there is a pressing need to be able to objectively identify the 'same' striation wherever it occurs.

As a second database, a row consists of a name, a depth on one or more of the cores, and an arrow pointing to it in a multi-striation Cresis image.

Phase III is merger ... these are relational databases but (given the holes) lack an overall indexing field. However with enough zigzagging, it will be possible to arrive at a universal date field. Simply sorting on that sandwiches radar striations between the climate events that we know of, and so generates hypotheses as to what might have caused each radar horizon.

There still may be reflections that just do not correspond to any of the couple dozen things they measure on ice cores. So here we are looking for something that was there but didn't get measured.

94 rows, 8 tabbed columns, I hope it retains its pastability into excel in passing through the blogware: I added some new events, filled in the NEEM depth column, and made myriad other small fixes on 04 Aug 14. Will likely move this over to a new forum topic on the interior of the Greenland Ice Sheet to mirror what AbruptASL is doing for Antarctica.

Order   Event   acronym   Start   End   NEEM   NGRIP   GRIP
1   Little Ice Age   LIA   450   150   122   107   ---
2   Medieval Warm Period   MWP   1050   750   245   217   ---
3   Bond   B1   1545   1385   341   304   ---
4   Vesuvius ash layer   ---   1921   ---   410   368   ---
5   Bond   B2   2974   2784   592   539   ---
6   Bond   B3   4329   4155   796   742   ---
7   Bond   B4   5802   5612   981   940   ---
8   Bond   B5   8207   8032   1228   1219   1325
9   ash inside Bond 8.2   ---   8236   8237   1230   1229   1334
10   Holocene Climactic Optimum   HCO   9000   6000   1287   1302   ---
11   Bond   B6   9271   9096   1304   1323   1432
12   Saksunarvatn tholeiitic ash   ---   10347   ---   1364   1410   ---
13   Bond   B7   10413   10253   1367   1414   ---
14   Bond   B8   11180   11020   1399   1463   ---
15   Start of Holocene   end Wisconsin D0   11703   ---   1419   1492   1624
16   Vedde alkali ash   NAAZ I   12171   ---   1429   1506   ---
17   Younger Dryas   GS-1 or H0   12800   11500   1442   1524   ---
18   stadial 1   GS-1   12896   ---   1444   1527   1662
19   interstadial la   GI-la   13099   ---   1450   1535   1672
20   interstadial 1b   GI-1b   13311   ---   1454   1542   1681
21   interstadial lc   GI-lc   13954   ---   1471   1571   1714
22   alkali ash   ---   ---   ---   1472   1573   ---
23   Older Dryas   OD   14000   13500   1472   1572   ---
24   interstadial Id   GI-Id   14075   ---   1473   1575   1719
25   Bølling–Allerød   BA   14100   12900   1474   1576   ---
26   Dansgaard-Oeschger   GI-le DO1   14680   ---   1489   1605   1753
27   Heinrich   H1   18146   15535   1533   1682   ---
28   stadial 2b   GS-2b   20900   ---   1568   1745   1900
29   stadial 2c   GS-2c   22900   ---   1593   1784   1940
30   Dansgaard-Oeschger   GI-2 DO2   23238   ---   1597   1793   1950
31   Last Glacial Maximum   LGM   26500   19500   1627   1844   ---
32   Heinrich   H2   26501   24282   1627   1844   ---
33   Fugloyarbanki tephra   FMAZII   26690   ---   1629   1848   ---
34   stadial 3   GS-3   27540   ---   1638   1862   2018
35   Dansgaard-Oeschger   GI-3 DO3   27780   ---   1641   1869   2025
36   alkali ash   ---   ---   ---   1649   1882   ---
37   stadial 4   GS-4   28600   ---   1650   1883   2038
38   Dansgaard-Oeschger   GI-4 DO4   28900   ---   1654   1892   2046
39   alkali ash   ---   ---   ---   1656   1895   ---
40   tholeiitic ash   ---   ---   ---   1665   1909   ---
41   alkali ash   ---   ---   ---   1669   1915   ---
42   alkali ash   ---   ---   ---   1678   1930   ---
43   stadial 5   GS-5   32000   ---   1683   1939   2087
44   Dansgaard-Oeschger   GI-5 DO5   32500   ---   1690   1952   2099
45   tholeiitic ash   ---   ---   ---   1689   1950   ---
46   Heinrich   H3   32637   31201   1691   1953   ---
47   alkali ash   ---   ---   ---   1690   1952   ---
48   stadial 6   GS-6   33360   ---   1698   1964   2110
49   interstadial 6   GI-6   33716   ---   1703   1975   2119
50   Dansgaard-Oeschger   DO6   33740   ---   1703   1974   ---
51   Mono Lake geomagnetic   Mono   34100   35200   1706   1983   ---
52   stadial 7   GS-7   34740   ---   1712   1990   2132
53   Dansgaard-Oeschger   GI-7 DO7   35480   ---   1722   2009   2149
54   stadial 8   GS-8   36580   ---   1734   2027   2163
55   Dansgaard-Oeschger   GI-8 DO8   38120   ---   1756   2070   2200
56   tholeiitic ash   ---   ---   ---   1756   2064   ---
57   Faroe Marine Ash Zone III   FMAZIII   38070   ---   1757   2067   ---
58   tholeiitic ash   ---   ---   ---   1760   2071   ---
59   tholeiitic ash   ---   ---   ---   1764   2078   ---
60   stadial 9   GS-9   40121   39372   1777   2095   2220
61   Dansgaard-Oeschger   GI-9 DO9   40160   ---   1777   2100   2224
62   Heinrich   H4   40209   38120   1778   2100   ---
63   tholeiitic ash   ---   ---   ---   1780   2104   ---
64   stadial 10   GS-10   40800   ---   1783   2110   2232
65   Laschamp geomagnetic   Las   41520   45600   1792   2119   ---
66   Dansgaard-Oeschger   GI-10 DO10   41460   ---   1791   2124   2243
67   stadial 11   GS-11   42240   ---   1798   2135   2252
68   Dansgaard-Oeschger   GI-11 DO11   43340   ---   1810   2157   2271
69   stadial 12   GS-12   44280   ---   1818   2170   2280
70   Dansgaard-Oeschger   GI-12 DO12   46867   ---   1846   2222   2324
71   Dansgaard-Oeschger   GI-13 DO13   49280   ---   1865   2257   ---
72   Heinrich   H5   49869   46997   1870   2266   ---
73   Dansgaard-Oeschger   GI 14 DO14   54220   ---   1912   2346   ---
74   Heinrich   H5a   55352   54178   1920   2360   ---
75   North Atlantic Ash Zone II   Z2   55400   ---   1920   2359   ---
76   Dansgaard-Oeschger   GI 15 DO15   55800   ---   1923   2366   ---
77   Dansgaard-Oeschger   GI 16 DO16   58280   ---   1942   2403   ---
78   Dansgaard-Oeschger   GI 17 DO17   59440   ---   1951   2420   ---
79   Heinrich   H6   63185   60052   1971   2456   ---
80   Dansgaard-Oeschger   GI 18 DO18   64039   ---   ---   ---   ---
81   Dansgaard-Oeschger   GI 19 DO19   70523   ---   ---   ---   ---
82   Heinrich   H7a   73107   72063   2011   2539   ---
83   Toba ash layer   ---   74000   ---   2015   2547   ---
84   Heinrich   H7b   77023   75849   2031   2583   ---
85   Dansgaard-Oeschger   GI 20 DO20   78286   ---   ---   ---   ---
86   Dansgaard-Oeschger   GI 21 DO21   83692   ---   ---   ---   ---
87   Heinrich   H8   87076   84465   2103   2712   ---
88   Dansgaard-Oeschger   GI 22 DO22   89436   ---   ---   ---   ---
89   Heinrich   H9   93342   89556   2148   2778   ---
90   Dansgaard-Oeschger   GI 23 DO23   102154   ---   ---   ---   ---
91   Heinrich   H10   102872   101958   2184   2879   ---
92   Dansgaard-Oeschger   GI 24 DO24   106769   ---   ---   ---   ---
93   Dansgaard-Oeschger   GI 25 DO25   112615   ---   ---   ---   ---
94   Eemian MIS 5e termination   Eem   125000   ---   ---   ---   ---
« Last Edit: August 05, 2014, 03:02:09 AM by A-Team »

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #414 on: August 05, 2014, 02:41:43 AM »
Espen may have slept in today, missing a new record. Here is the quickie EarthExplorer for today:

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #415 on: August 05, 2014, 04:02:10 AM »
Here are separate north and south branch images from today, 10 m resolution derived from the Landsat panchromatic. The database shows the cloud-free Landsats for this year, along with the best case scenario for the rest of August.

LC80080122014241LGN00   Aug   29   241
LC80080112014241LGN00   Aug   29   241
LC80832332014239LGN00   Aug   27   239
LC80100112014239LGN00   Aug   27   239
LC80090112014232LGN00   Aug   20   232
LC80080122014225LGN00   Aug   13   225
LC80080112014225LGN00   Aug   13   225
LC80832332014223LGN00   Aug   11   223
LC80100112014223LGN00   Aug   11   223

LC80090112014216LGN00   Aug   4   216
LC80080122014209LGN00   Jul   28   209
LC80080112014209LGN00   Jul   28   209
LC80812332014208LGN00   Jul   27   208
LC80100112014207LGN00   Jul   26   207
LC80090112014200LGN00   Jul   19   200
LC80822332014200LGN00   Jul   19   200
LC80080122014193LGN01   Jul   12   193
LC80080112014193LGN01   Jul   12   193
 LC80812332014192LGN00   Jul   11   192
LC80100112014191LGN00   Jul   10   191
LC80090112014184LGN00   Jul   3   184
LC80832332014175LGN00   Jun   24   175
LC80080122014161LGN00   Jun   10   161
LC80080112014161LGN00   Jun   10   161
LC80100112014159LGN00   Jun   08   159
LC80090112014152LGN00   Jun   01   152
LC80080122014129LGN00   May   09   129
LC80080112014129LGN00   May   09   129
LC80100112014127LGN00   May   07   127
LC80100112014111LGN00   Apr   21   111
LC80090112014104LGN00   Apr   14   104
LC80080122014097LGN00   Apr   07   097
LC80080112014097LGN00   Apr   07   097
LC80080122014081LGN00   Mar   22   081
LC80080112014081LGN00   Mar   22   081
LC80090112014056LGN01   Feb   25   056
LC80090112014040LGN00   Feb   09   040

sidd

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #416 on: August 05, 2014, 08:11:40 AM »
Do we know what this is? (red encircled):

Let me venture a conjecture: Those are NEGIS and Peterman/Humboldt flows
I am on the road, so i cannot justify this further. Treat as an ansatz, if you will, and consider that deeper ice is warmer and more plastic.

sidd

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #417 on: August 05, 2014, 06:17:33 PM »
Sidd, good suggestions -- this is why the whole set of flight transects needs be brought into a single interactive image. The track is a long ways from Petermann glacier per se (see upper right inset on full image) but could represent bottom freeze-up or shear margins of the newly discovered canyon that runs two thirds the length of Greenland, exiting at Petermann.

Some very decent 2014 publications on NEGIS:

Basal conditions and ice dynamics inferred from radar-derived internal stratigraphy of the northeast Greenland ice stream
http://www.igsoc.org/annals/55/67/t67A090.pdf

Initial results from geophysical surveys and shallow coring of the Northeast Greenland Ice Stream (NEGIS)
http://www.the-cryosphere.net/8/1275/2014/

Dilatant till facilitates ice-stream flow in northeast Greenland
DOI: 10.1016/j.epsl.2014.05.060 paywalled: $39.95

Here is brief slide show of different combinations of yesterday Landsat Bands 2,4,5 made into color composites. The area shown is the upstream region of Jakobshavn Isbrae, where the ice stream character blurs into generic ice sheet movement. The last one seems quite effective in drawing out melt features of the 'Lake District' that aren't so apparent in grayscale.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #418 on: August 06, 2014, 01:36:47 AM »
Espen, sidd: I pulled out the track graphics in the Bamber 2013 Greenland canyon paper in Science. It does look like some of the dipsydoodling in radar horizons is an effect arising in ice sitting over the canyon.

They did not provide track ids nor indicate half of the scales so I could not co-register it with the spectacular colored track above (the new normal). I added a light blue line for sea level -- only the upper right came with a depth scale however. I could not fully remove the gratuitous text that should have been off to the side. I also added arrows from the canyon DEM transects over to the respective radar tracks.

Note all the east-west tracks in light black in upper left; it would not be difficult to krige this feature all the way to where Petermann meets the sea. Three transects is just a start. It is better to extract horizon lines from the radar traces and just display them in see-thru mode (a la Antarctica 2008).

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #419 on: August 06, 2014, 04:33:49 PM »
Here is a follow-up on the growth of the dynamic influence area of Jakobshavn Isbrae. It is poaching ice sheet input from neighboring ice sheds, as well as implicating more ice sheet east towards the summit. I did not include the color key because the map maker didn't embed it during the map process (considered a class C felony in cartography), causing it to lose all connection with colors in the final map product.

The second map graphs this loss. It is a little confusing because the losses are not shown cumulatively relative to fixed sea level. Note ice losses (thinning + ablation - accumulation) run to about a meter per year even 100 km inland. Joachin 2014 has added 2011-13 but in a different format.

nukefix

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #420 on: August 06, 2014, 11:20:39 PM »
Here is a follow-up on the growth of the dynamic influence area of Jakobshavn Isbrae. It is poaching ice sheet input from neighboring ice sheds, as well as implicating more ice sheet east towards the summit.
What altimeter is that based on?

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #421 on: August 07, 2014, 03:10:32 AM »
So appreciative of google's reverse image search -- I am awash in documents and had tossed this one.

It appears to be a pdf made from a power point presented at a recent but undated NASA conference. The author is Ian Howat of Byrd Polar with five others. This is page 12, details are sketchy but the figure label indicates it comes from an Airborne Topographic Mapper (ATM). Various instruments, not a unique descriptor associated with a particular satellite.

The elevation depletion map series look very similar to velocity map series ... not a coincidence.

http://etienne.berthier.free.fr/SPIRIT/Talk/Howat_Greenland.pdf

Later (?) Howat reports similar work using "data from ICESat and ATM as well as SPOT 5 DEMs from 2007 and 2008 ... stereoscopic Digital Elevation Models (DEM) from both airborne and satellite..." with article header
Journal of Glaciology, Vol. 00, No. 000, 0000 which does not make a whole lot of sense.

http://bprc.osu.edu/GDG/JFL_JGLAC.pdf
 
The Joughin 2014 paper added some more recent along-channel surface elevation annual data to this in Fig3 which is cut down to that below.

http://www.the-cryosphere.net/8/209/2014/

There is yet another paper predicting lots of sub-surface lakes in Greenland (a la Antarctica) which claims to reconstruct a time series of drainage patterns since the Last Glacial Maximum, in which in Fig.6 the northern limb of the Jakobshavn drainage network is captured by the Uummannaq system 16,000 yr ago, the opposite of what is trending now.

http://www.the-cryosphere.net/7/1721/2013/

Two subglacial lakes have been in fact just been discovered just north of Qaanaaq (not confirmed by drilling yet) but they were not among the thousands predicted by the above paper (making me wonder about how much water the above authors were able to squeeze out of a turnip, the Shreve hydraulic potential equation).

http://www.sci-news.com/othersciences/geography/science-subglacial-lakes-greenland-01581.html
http://onlinelibrary.wiley.com/doi/10.1002/2013GL058383/abstract

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #422 on: August 07, 2014, 07:25:18 AM »
Update: here are 3 very recent papers on the Greenland ice surface DEM changes (change in height per unit time, dh/dt with dt taken as the year 2012-13. Jacobshavn and NEGIS are given special attention in subsections.

The first paper gives a very thorough technical discussion of what CryoSat-2 actually sees and gets for overall accuracy for anyone here thinking of using this data. For Greenland though, pg 1680, the authors conclude the Greenland Ice Mapping Project (GIMP, second paper) produces a better product.

"Prominent in Greenland is the strong thinning of the entire western ice sheet, as well as the south-east and north-west ice sheet margins, as shown in Fig. 8. The dynamic thinning of Jakobshavn Isbræ in particular has penetrated deep into the ice sheet.... Thinning rates observed in 2011–12 exceeded 4 m per year. This thinning is most pronounced in the
lower part of both tributaries, but extends 250km upstream."

"Thinning of the Zacharias Isstrømen, an outlet glacier of the North East Greenland Ice Stream (NEGIS), show rates of 1.0 m per yr  at the glacier terminus. This thinning extends 250km upstream of the NEGIS, where values of 0.2–0.3 m per yr have been reported... This pattern of pronounced thinning is a new development (third paper).

I've attached their DEM which is well done technically except for the lat,lon line overlay which could have been done as a side thumbnail. The slope map, new for us is, unfortunately provided in postage stamp resolution, ~150 pixels wide or 1/3 that of the DEM. The Greenland dh/dt map is rather pixellated but gives the overall idea; when localized to Jakobshavn, it does a lot better.

Helm 2014 Elevation and elevation change of Greenland and Antarctica derived from CryoSat-2,The Cryosphere Discuss., 8, 1673–1721, 2014 www.the-cryosphere-discuss.net/8/1673/2014/ doi:10.5194/tcd-8-1673-2014

Howat, I.M., A. Negrete, B.E. Smith, 2014, The Greenland Ice Mapping Project (GIMP) land classification and surface elevation datasets, The Cryosphere, 8, 1509-1518, doi:10.5194/tc-8-1509-2014. Final version 19 Aug 14: http://www.the-cryosphere.net/8/1509/2014/

Khan 2014: Sustained mass loss of the Northeast Greenland ice sheet triggered by regional warming, Nature Climate Change, doi:10.1038/nclimate2161, 2014.
« Last Edit: October 04, 2014, 01:17:48 PM by A-Team »

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #423 on: August 07, 2014, 06:46:02 PM »
Here is the ultimate Greenland DEM by Howat et al, just clearing open peer review at The Cryosphere. The reviews and responses are well worth reading in their own right for the intricacies involved in processing years of satellite data of diverse origins. While that aspect is far more sophisticated than what we do here (include myself in that), we can still benefit from and perhaps add value to the products.

It's all available for download. While that is fast enough, the file sizes are landsat-huge 16,600 x 30,000 = 489,600,000 pixels on the big guy. So think twice before clicking on a command in ImageJ (even crop) or your desktop will get tied up for 15 minutes. Better to look at the tlle map in the pdf and order only what you need. Conveniently, they provide both plain grayscale DEM and hillside shaded. I've attached an overview plus a couple of zooms into the Jakobshavn calving front.

<url>http://www.the-cryosphere-discuss.net/8/453/2014/tcd-8-453-2014.pdf</url>
<url>Index of ftp://ftp-bprc.mps.ohio-state.edu/downloads/gdg/gimpdem/</url>

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #424 on: August 08, 2014, 06:11:45 PM »
The land-terminating glaciers don't get much attention on Greenland but are significant because impacts of overall melting can be disentangled from the effects of warming ocean water (eg Irminger Current) on the bases of marine-terminating glaciers.

The paper below studied an area just to the south of Jakobshavn, hauling radar behind snowmobiles to get a higher resolution sense of bedrock. As a referee noted, the authors did not do a whole lot with interpretation of their data. Indeed, only one radar trace was provided and the rest of the graphics were of 'presentation' quality, ie so-so.

The slides provide the ice stratigraphy, elevation contours, ice thickness and bedrock elevations (all above sea level here). The second graphic, enlarged way beyond resolution provided, fits the radar stratigraphy track to the bedrock surface.

The authors write that the surface topography provides few clues to that of bedrock. Indeed fresh snow and firn form a rather featureless incline. However look how the isochron surfaces drape over bedrock topography while maintaining their spacing. The ice is moving from east to west here.

Here I had to adjust the fit of radar slice hills and valleys to the mounds and drainages of the DEM. The red dots show the literal fit after adjusting the various scales and low res imagery provided. No doubt that closely spaced radar lines would show a fully conformal fit --  a thousand meters of ice with 20 internal reflectors -- to the bottom topography.

http://www.earth-syst-sci-data-discuss.net/7/129/2014/

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #425 on: August 08, 2014, 10:21:43 PM »
The land-terminating glaciers don't get much attention on Greenland but are significant because impacts of overall melting can be disentangled from the effects of warming ocean water (eg Irminger Current) on the bases of marine-terminating glaciers.



Yes A-Team, I am aware of the importance of land terminating glaciers, firns and ice caps, at least in my mind they are important, but far less impressive (no calvings), they are are in the same discipline as  "studying paint dry" ;)
Have a ice day!

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #426 on: August 09, 2014, 12:54:24 AM »
Could be completely unreliable (Modis), but still?:

Indications of collapse of side wall (northern) at the southern branch

And that could eventually result in a faster flow?
« Last Edit: August 09, 2014, 01:32:31 AM by Espen »
Have a ice day!

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #427 on: August 09, 2014, 01:34:36 AM »
Espen, did you mean 08 Aug above rather than 3rd? Next Landsats arrive Monday -- maybe bringing your spot in the guinness book of records.

Yes, that is jaw-dropping to see so much of the landscape (2nd slide above) moving at merely 8 meters per year, or rather that nearby Jakobshavn ice stream is moving 2,000 times faster. Considering the deepest radar horizons of the ice at the land-terminating site are >10,000 years old, it hasn't come that far down the hill during the Holocene.

There is another new paper out mapping ice "frozen to the bed" across the entire Greenland Ice Sheet; these are 0 meters per year sites, in Antarctica, called 'stagnant'.

I wonder if not moving really corresponds to frozen to the bed, does that also mean a hockey puck is frozen to the ice rink when the players go on break? van der Waal forces are about all that is left between hexagonal ice and rock, not much to talk about. However an ice cube is certainly not frozen to its inert teflon tray yet the tray has to be flexed to get it out, so I suppose there is friction from geometrical constraint.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #428 on: August 09, 2014, 01:50:11 AM »
A-Team I prefer the dark Guinness, the one you drink ;)
Have a ice day!

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #429 on: August 09, 2014, 04:20:08 AM »
Could be completely unreliable (Modis), but still?:

Indications of collapse of side wall (northern) at the southern branch

And that could eventually result in a faster flow?

MODIS false-color suggests cloud effect. 
http://lance-modis.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r02c02.2014220.terra.367.500m

I made a similar error recently, which is how I learned to check the false-color images.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #430 on: August 09, 2014, 09:33:35 AM »
Yes Steve, that could be, but ASAR also show some changes:
Have a ice day!

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #431 on: August 09, 2014, 01:24:18 PM »
A place in forum history? Still 6 weeks left in the calving season.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #432 on: August 09, 2014, 02:16:20 PM »
A place in forum history? Still 6 weeks left in the calving season.

Cheers mate!
Have a ice day!

SteveMDFP

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #433 on: August 09, 2014, 03:20:32 PM »
Yes Steve, that could be, but ASAR also show some changes:

Wow, that is impressive.  Odd that there should suddenly be a small, dense cloud on the false-color modis at the same spot.  Makes you wonder if a huge calving/collapse could cause its own cloud of snow being thrown up in the air.  We'll know more very soon.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #434 on: August 10, 2014, 05:15:33 PM »
I came across this peculiar photo of the late great Willi Dansgaard handling a precious, unprotected DYE3 ice core with ordinary work gloves while smoking a pipe. DYE3 is an old radar station in south central Greenland drilled in 1979. Dansgaard also drilled at Camp Century and on 18 other expeditions.

The odd part is Dansgaard's main lab analytic specialty was mass spectroscopy (16O, 18O, 2H, methane, ammonia, sulfuric acid) and so he would have been acutely aware of the contamination issue. In 1949 this might have been cutting edge knowledge, not 1979.

And he wasn't the only one to contaminate ice cores -- I've seen pictures right up and through NEEM of people not taking even the most elementary precautions (face masks, sterile gloves, clean suits, laminar flow hoods) -- yet later the papers flow on parts per trillion beryllium 10 in 'soil' at the bottom of GISP2, pine needles at the bottom of NGRIP (never pursued) and ancient dna used to date the Greenland Forest and determine whether even the northernmost ice sheet melted out during the Eemian (didn't, putting the onus of sea level rise on Antarctica).

The drilling fluids alone give me the creeps: brown kerosine, n-butyl acetate, lamp oil, halogenated-hydrocarbon densifier, etc. Documented contamination on the outer but not inner surfaces of ice cores includes lead, 1000 times higher bacterial density and 100 times higher dissolved organic carbon.

The cost of deeper cores must run into the tens of millions at these remote expedition sites. Contamination is a very expensive proposition, not just the drilling but for erroneous downstream interpretations that could affect climate policy recommendations.

Steam boring at Jakobshavn raises different issues as a different technology -- a lot of well logging techniques but to date no cores or melt retrieved.

http://meetingorganizer.copernicus.org/EGU2014/EGU2014-10721.pdf
http://www.ncbi.nlm.nih.gov/pubmed/17615355
 

Shared Humanity

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #435 on: August 10, 2014, 07:31:15 PM »
I believe the calving on the north face of the south branch began at least 1  month ago and you captured it on this animation above.

http://forum.arctic-sea-ice.net/index.php?action=dlattach;topic=154.0;attach=8751;image

Shared Humanity

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #436 on: August 10, 2014, 07:36:51 PM »
In fact, the deep crevasing that we see on the north wall of the south branch, I believe is evidence of bottom melt on this portion of the ice sheet due to it be grounded below sea level. (See image below.) As more of this north wall is exposed by the retreat of the glacier up the fjord, it should be the source of some spectacular calving. The ice sheet is very tall at this point.
« Last Edit: August 10, 2014, 07:59:32 PM by Shared Humanity »

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #437 on: August 10, 2014, 07:40:13 PM »
This new calving front that is opening up should behave much like the northern calving front, fairly rapid retreat unless the ice sheet begins to move much more rapidly here. I don't think this will happen as the water is shallow, much like the northern calving front. The significant difference from the northern front is the grounding below sea level goes much further into Greenland.

If you look at the speed of the ice sheet, it is clear that the ice is already moving faster over this shallow sea. (See image below.) You can see the faster ice following the outlines of the ice that is grounded below sea level. As the main calving face retreats, unpinning this ice, it should speed up considerably.

I am definitely going to keep watching this area closely. (Or I would if I had a clue how  Espen does his magic.)

It is actually amazing how ice that is grounded below sea level moves so much more rapidly than ice grounded above sea level. If you follow Jacobshavn up the fjord, you see ice on the north of the fjord, well inland from the calving face, that is moving more rapidly towards the fjord. This ice is also grounded below sea level.
« Last Edit: August 10, 2014, 07:57:33 PM by Shared Humanity »

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #438 on: August 11, 2014, 10:39:49 PM »
The Landsats due today have not been posted yet and may not be -- tomorrow is a scheduled server dink day.

The animation below compares the melt lakes, day 214 vs day 200. Some have drained, others have filled. The still image shows the features that have changed.

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #439 on: August 12, 2014, 01:24:32 AM »
I've been looking to date the oldest ice being flushed out via the Jakobshavn Isbrae. Ice-penetrating radar is by far the easiest way to 'drill' a core -- in fact, a flight track amounts to thousands of virtual cores.

Since radar horizons have been dated with reference to annual ice layer counting at all of the conventional ice cores (NEEM, NGRIP, GRIP and GISP2), simply follow the lowest continuous radar horizon up the hill until it ties in. That gives the age of the ice at JI at that horizon.

Note an annual ice layer at NGRIP is ~13 millimeters thick at a depth of 2500 m which exceeds the resolution of the radar (~ 3.9 meters,  number of vertical pixels representing a 1000 m section of a Cresis jpeg) by a factor of 300. In addition, the striations appear several pixels thick even though they do in fact correspond in some cases to an event wholly confined to one year (eg volcanic ashfall).

But there's more. Deformations to the radar horizons almost always come from below (ignoring firn). If the horizon being followed is not deformed, then neither are the ones above. That implies all the other horizons are present, possibly thinned and not distinctly visible, meaning all the properties logged on the fiducial tie-in core are transferable all along the track, even properties like beryllium-10, temperature, or methane that don't have anything directly to do with bumping dielectric above that of pure ice.

Because the thinning is known from surface to horizon depth, this can actually be verified via radar track synthesis, a 'dry lab' computation that takes properties giving rise to radar reflectors (ie conductance, dust, sulfate) measured along the core and figures out what the radar return from them should look like when thinned.
 
Looking at the Panton and Spuz radar horizon graphics above, the last easily traceable striations are a triple whose top unit hits the NGRIP core at about 2558 meters (resp 2000 m for NEEM). Those depths correspond to calendar dates of ~ 74,000 as determined by annual ice layer counting. There are still older striations but those are intermittant and tracing them soon becomes problematic.

So the issue is, does this get down to where the ice sheet feeds into Jakobshavn Isbrae or even to the coast by Swiss Camp? The lower ice stream itself has undergone a lot of turmoil in conforming to sills and troughs of overdeepenings. There may be one identifiable radar striation but I suspect this is just the Bølling–Allerød at 14100-12900 B2K at a depth of 1576 m up at NGRIP.

I'm interested in the ~ 74,000 triple though because it may correspond to the enormous erruption of Toba, the largest event by far in the Pleistocene. That left its mark all over the world in form of tephra and sulfuric acid depostion. Better yet, that event  was very carefully studied by Svensson and 26 colleagues on multiple Greenland and Antarctic cores.

<url>http://www.clim-past.net/9/749/2013/</url>

The table below describes 9 closely spaced sub-events spanning 1,980 calendar years (25.39 m of NGRIP core) observed isochronically at both poles. (I've added the NEEM dates using the correspondence with NGRIP depths provided by the latest GICC05 timeline.)

Event      Acronym   Year B2K   NEEM   NGRIP  GRIP   GISP2
Toba tephra 1   T1   74057      2015   2547   2565   2591
Toba tephra 2   T2   74156      2016   2548   2565   2592
Toba tephra 3   T3   74358      2016   2550   2567   2593
Toba tephra 4   T4   74484      2017   2551   2567   2594
Toba tephra 5   T5   75039      2020   2558   2572   2599
Toba tephra 6   T6   75064      2020   2559   ---   ---
Toba tephra 7   T7   75479      2023   2564   ---   ---
Toba tephra 8   T8   75505      2023   2565   ---   ---
Toba tephra 9   T9   76037      2026   2573   2581   2608


The accompanying graphic shows annual core values for delta 18O (~temperature), ECM (direct current electrical conductivity measurement of acidity), DEP (dielectric profile), sulfate, and conductivity. There is no mention of radar horizons in the article even though the items that peaked are key players in generating those.

The overall timing corresponds closely to certain Greenland stadials (cold) and Dansgaard-Oeschger interstadials (warm), GS-21, GI-20, GS-20 and GI-19 though Toba is not put forth as an explanation for any of them. For reasons unknown, these AMOC cycles are in a separate graphic on a longer time scale, which I've adjusted below. The radar track running over NGRIP at this depth was enhanced by Panton as discussed above.

Toba was a supervolcano, two orders of magnitude more extreme than Mount Tambora, with a volume of some 2800 cubic km. Its ashfall has a diagnostic horizon called the Youngest Toba Tuff (YTT) that has not yet been identified in polar ice cores. The huge crater is located in Indonesia a couple of degrees north of the equator. There are pros and cons to various theories of nuclear winters and human genetic bottlenecks associated with it.

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #440 on: August 12, 2014, 03:20:43 AM »
A nice clear ascending orbit Landsat just got posted, LC80100112014223LGN00 path 10, row 11 with the usual azimuths and sun elevations. A very impressive flotilla of icebergs has exited the fjord and is heading north (not shown). The images are made from Bands 3,4,5 composited as CMY which is displayed however as RGB.

Very noticeable calving along much of the north branch though no dramatic change in location.

The south branch is quite curious. The upper two slower feeder streams are developing quite distinct character from the lower two faster feeder streams at the calving front (the ones developing an extensive crevasse network for a km or so upstream. The image looked better to me as flipped north to south.

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #441 on: August 12, 2014, 04:40:48 AM »
Jakobshavn up date:

No big changes from August 4 2014. Some calving and retreat at the northern branch, gains but changes of direction at the northern side wall in southern branch, it looks like it wants to expand the operation area in southern branch.
It must have been the changes of surface structure in southern branch northern side wall, that made it look like calving in the Modis and ASAR images?
Have a ice day!

nukefix

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #442 on: August 12, 2014, 11:04:17 AM »
Yes Steve, that could be, but ASAR also show some changes:
What is ASAR? Certainly not the Envisat ASAR as that satellite is dead and tumbling..

diablobanquisa

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #443 on: August 12, 2014, 02:31:05 PM »
Yes Steve, that could be, but ASAR also show some changes:
What is ASAR? Certainly not the Envisat ASAR as that satellite is dead and tumbling..

Now DMI uses RADARSAT instead of ASAR. Both of them are SAR (Synthetic Aperture Radar).

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #444 on: August 12, 2014, 03:10:02 PM »
I marked up weekly positions of ice that will move to the current position of the calving front under the assumption of a 16 km/yr icestream velocity, which translates to 41 pixels per week on the scale of this 7.5 m image of 11 Aug 14. I slowed this by 1 pixel for each successive week to represent the onset of backpressure from the freezing fjord.

The final position of the calving front amounts to the eastward velocity of calving minus the westward motion of the ice stream. That difference vacillates but was slightly negative for the week of Aug 4-11 (as shown above by Espen): forward motion exceeded backward calving.

This calving proceeds by fits and starts especially at the start of the season so our occasional snapshots in time are not necessarily representative. I suspect the deeply crevassed regions in the center (up to Sep 02 line) will be the next to go.

While retreat of the calving front per se is significant in unleashing future retreat, in terms of sea level rise it is only the volume of ice moving through the flux gate that matters (as it will calve sooner or later). That volume is not so easy to calculate because a faster moving icestream thins which won't show up in nadir-only Landsat view.

A-Team

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #445 on: August 15, 2014, 06:17:38 PM »
Espen writes, 'land terminating glaciers, firns and ice caps in the same discipline as "studying paint dry".

Exceptions might include the regions just to the north and south of Jakobshavn; only there are we getting long-term meteorological data on an interior transect (21 years for K-line), direct experimental evidence about hydrological conditions at the bottom of the ice sheet, and convenient access to horizontal ancient ice at ice margins like Pakitsoq.

Mind you, the blogosphere has settled on surface temperature re-analysis from a warm office afar and the melt lake moulin acceleration meme. While rapid draining isn't disputed, what happens at the bedrock is: drainage to the sea via innocuous tunnel or catastrophic sheet. The reality is more nuanced.

Classical summit ridge cores involve multi-year expeditions that cost millions and take a decade to analyze; another one seems not even in the works. Meanwhile steam rigs can drill local clusters to known basal topography and elevation transects at 120 meters/day and get two dozen to bedrock in a summer season. Neither method really yields significant access to older ice.

However studying land-terminating glaciers may be the glaciology equivalent of looking for lost car keys under a street lamp because the light is better there. Results may not be applicable to the Big Three in Greenland, each a special case in its own way: Jakobshavn (fast, narrow, deep ice stream), Petermann (ice shelf, interior connection), and NEGIS (headwall geothermal anomaly, broad discharge).

The images below tell the Pakitsoq story. Ice from the summit below GISP2 has made it way out to the coast above Jakobshavn where, after ablation of ice above, it lies exposed but still nicely layered a few hundred meters east of the rocks. The age of this ice spans the Last Glacial, Bølling–Allerød, Younger Dryas and pre-boreal time frame. I chased down a 2011 ice-penetrating radar overflight a bit further to east as well as what this corresponds to at NGRIP depth scales.

Ice stratigraphy at the Pakitsoq ice margin, West Greenland
V.V. Petrenko et al. Quaternary Science Reviews 25 (2006) 865–875
http://tinyurl.com/q28kxku
http://icebubbles.ucsd.edu/Publications/petrenko_pakitsoq_qsr_2006.pdf

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #446 on: August 17, 2014, 06:28:48 PM »
The rocky margin in west-central Greenland is also critical to dating past advances and retreats of both the ice stream per se and position of the overall Greenland ice sheet, in particular responses to previous warming and cooling events. This is done on terminal moraines (10 Be is only formed during surface exposure) and marine sediments (14C in Pluto Lake layers).

At the Last Glacial Maximum, sea level was much lower than today; skid marks on the bottom show the Greenland ice sheet extended way out onto the continental shelf. At Jakobshavn Isfjord, the big ice sheet had not retreated from Disko Bugt and made landfall until well into the early Holocene (~10.2 ka).

The main moraines around the fjord today (map below) are Marrait, Tasiussaq and a historical remnant from the Little Ice Age. These are sometimes lumped as Fjord Stade moraines (stade is french for stage). All three represent glacial advances rather than stillstands. The two older ones extend for hundreds of km, down to land-terminating glaciers inland from Kangerlussuaq, so are not attributable to just a fast-moving ice stream.

Isostatic rebound since deglaciation in the Disko Bugt region is surprisingly high: 15.6 m outboard of the final moraine Marrait, 5.0 m between moraines and 4.6 m inboard of Tasiussaq. These elevation changes have a slight but measurable impact on rate of formation of 10 Be in quartz of moraine boulders. ( 10 Be atoms are counted by mass spectroscopy rather measured from beta decay.)

Melting of the Laurentide Ice Sheet (at its peak, the size of Antarctica) had to have consequences. When moraine ice dams broke, the immense volumes of melt lakes didn't go quietly into the night -- we know that from the flood scours at The Ramparts at Lake Good Hope (which hardly differ from those from Lake Missoula) and erosion in Great Lakes outlets such as the Nadoway drift moraine. Instead, that fresh water was abruptly dumped, variously into the Arctic, Hudson Bay, Mississippi and the North Atlantic.

The larger events had to have had chilling consequences for AMOC thermohaline circulation (Gulf Stream) and indeed sharp cooling is seen in Greenland ice cores and speleotherms. However geologists are still fighting a 19th century war (biblical catastrophism) and can hardly bring themselves to acknowledge the obvious in the scientific literature.

Flood routes matter because they determined the site of freshwater injection; only in recent years have these been definitively identified and dated. (Geographic drainage options changed over time because isostatic rebound altered the topography.)

While temporal correlation supports but does not prove causation, the Younger Dryas event in all likelihood was caused by a massive discharge in late summer of Lake Agassiz out the MacKenzie River into the Arctic Ocean.

In the Late Pleistocene/Early Holocene chronology provided above, the Marrait moraine corresponds to Bond event B6 at 9.3 ka with peak cooling ~3ºC and duration 170 years, attributed to the collapse of an ice dam of the Laurentide Ice Sheet below today's Lake Superior and huge surge of freshwater into the North Atlantic Ocean disrupting the AMOC thermohaline circulation (Gulf Stream).

The Tasiussaq moraine formed around 8.2 ka with peak cooling 3.3ºC, and duration 175 years and corresponded to the larger Bond event B5: Lakes Ojibway and Agassiz suddenly drained into the North Atlantic Ocean via Hudson Bay.

The abrupt coolings at 9.3 and 8.2 ka interrupted a period warmer than today when the western Greenland ice sheet was rapidly retreating. The evidence shows that the region around Jakobshavn can fluctuated more or less in lockstep with temperature variation (ie these changes were not a delayed response to warming at the last glacial termination). However, conditions today have not resulted from a sudden influx of fresh water so the past may not be a wholly reliable guide.

Age of the Fjord Stade moraines in the Disko Bugt region
NE Green et al http://tinyurl.com/pd62eht

Freshwater Outburst from Lake Superior as a Trigger for the Cold. Event 9300 Years Ago
Yu et al. http://d.umn.edu/llo/docs/YuetalScience2010.pdf

Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean
JB Murton et al http://www.ualberta.ca/~eec/Murtonetal2010.pdf

Forcing of the cold event 8,200 years ago by catastrophic drainage of Laurentide Lakes
C Morrill et al http://www.clim-past.net/9/423/2013/cp-9-423-2013.pdf
DC Barber et al 1999 http://tinyurl.com/oxc3lfv

Espen

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #447 on: August 17, 2014, 07:04:50 PM »
A-Team,

Interesting to know there was a separate ice sheet in the Jan Mayen area, I was not aware of that, and all together interesting stuff ;)
Have a ice day!

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #448 on: August 18, 2014, 01:50:09 AM »
As part of the never-ending quest to pull more rabbits out of the Landsat hat by magical adjustment dof imagery bands, I took a look at Dstretch, a fancy but free plugin for ImageJ. (I'm actually running it packaged in a .jar or Java Archive bundle.)

The idea with Dstretch: the satellite might very well offer lots of bands at different wavelengths but due to the bland properties of the ice below, pixel values are exceedingly cross-correlated across channels. That means, up to some conventional contrast rescaling, the bands look very much the same. Know one, predict the others.

If so, image enhancement experiments should begin with channel decorrelation. Dstretch does this by cycling the initial RGB through many other possible color spaces based on certain properties of the initial histograms. This amounts to multiplication by a channel mixing matrix that is further subject to all manner of user fine-tuning.

Dstretch's main claim to fame has been enhancement of all but invisible rock petroglyphs and indeed some astonishing results have been attained there. http://www.dstretch.com/

These operations can mostly be done in Gimp though the same level of exploration there would take hours vs minutes here. On Landsat, I found it worked better to have pre-selected an area I was curious about rather than hope to get an entire scene usefully enhanced.

On the Jakobshavn icestream, below, the emphasis is on the wavelike appearance of the region to the north. It's not at all clear to me whether this is within the range of dynamic influence of the ice stream and if so why this particular periodic response results.

The second image shows Zachariae icestream in northeast Greenland. Here I began with one of Wipneus's very sharp images where the 15 m has been stubbed in for the 30 in an HSV decomposition. I'm not familiar enough with the issues there to know is Dstretch is doing anything useful there.

My sense is we should really be working a whole lot more in ImageJ than in Gimp or Photoshop. ImageJ, while it has a learning curve for sure, is much more geared to scientific research, not so much towards graphic arts. The community writing plugins and fixing bugs is very active and almost entirely academic scientists.

In a sense it is mostly a GUI wrapper for whatever operations have been picked up, with some common image manipulations in the core menus. It is very well suited to quantification and 3D representation of Greenland ice-penetrating radar layers. I'll put further thoughts on this in the ImageJ forum someone started a while back as time permits.

oren

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Re: Jakobshavn Isbræ / Sermeq Kujalleq / Ilulissat Icefjord
« Reply #449 on: August 18, 2014, 11:41:07 PM »
A-Team, thank you for your most enlightening post (#447) I learned a lot, very interesting.