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Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 652508 times)

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1850 on: May 04, 2017, 08:17:13 PM »
I do not follow Jakobshavn so much as previously, but I have noticed a surge/expansion in both the southern branch as others in the Forum have reported, but what I have not seen is any reports of is the surge in the northern branch, I wonder what is the reason behind this new behaviour of the glacier?
Is the ice coming from the ice sheet getting warmer and smother resulting in a faster flux?

Below you will find images from 2016 and 2017 retrived from Sentinel 1 and 2.
Have a ice day!

iwantatr8

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1851 on: May 05, 2017, 10:28:24 AM »
Espen,
The expansion in the north branch occurred sometime over the winter, I'm not sure it's a surge or if the melange caused enough back pressure on the northern calving face to inhibit actual calving (which seems possible given the southern branch behavior) resulting in the advancing that we see to early April.

Sentinel 2 Animation of April @ JI below (this will probably need a click to animate)


johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1852 on: May 05, 2017, 02:57:13 PM »
Espen, if you look at the new bed topography image the northern branch is quite shallow, so I suspect if was previously entirely grounded, as it's retreated the tides wash it's base, and the base now consists of broken ice resting in seawater. Further retreat looks unlikely on it's eastern side.

Even if things weren't changing all the time I suspect it would take a few years for the ice fall thereabouts to reach equilibrium.

TenneyNaumer

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1853 on: May 17, 2017, 06:25:03 AM »
That's such a great map.

You know where you have the -200 on the north edge of the south branch?

Looks like something might be going on there, perhaps, judging by today's NASA Worldview.

It would be the most vulnerable spot right now, wouldn't it?

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1854 on: May 17, 2017, 11:13:56 AM »
Yes we have sidd to thank for that, there's been an increase in fresh water escaping into Disko bay and most of the blockages stalling the flow of the melange have been short lived so somethings got to give.
Nukefix I was looking back over last year for signs of basal ice breaking up from the troughs and the best candidate was that wave form you noticed, what do you think?

TenneyNaumer

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1855 on: May 17, 2017, 07:39:40 PM »
Sidd's the best!

Tealight

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1856 on: May 21, 2017, 08:59:59 PM »
Because of the popularity I made a close-up comparison of the northern branch between the record low conditions in 2015(August or September) and May 2017.

Despite the recent advancement on all sides Jakobshavn is still thinning. I spotted new exposed bedrock 2.5 km upstream. It is clearly distinguishable from the blue melt/rain water. Let's see if the glacier can retreat all the way to previous years in just one melting season.

1st image needs a click to start the animation

AbruptSLR

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1857 on: May 25, 2017, 11:42:15 PM »
Surface meltwater is increasing ice flux from Jakobshavn:

Joseph, C. A. and Lampkin, D. J.: Spatial and temporal variability of water-filled crevasse hydrologic states along the shear margins of Jakobshavn Isbrae, Greenland, The Cryosphere Discuss., doi:10.5194/tc-2017-86, in review, 2017.

http://www.the-cryosphere-discuss.net/tc-2017-86/

Abstract. The impact of melt water injection into ice streams over the Greenland Ice Sheet is not well understood. Water-filled crevasses along the shear margins of Jakobshavn Isbræ are known to fill and drain, resulting in weakening of the shear margins due to reduced basal friction. Seasonal variability in the hydrologic dynamics of these features has not been quantified. In this work, we characterize the spatial and temporal variability in the hydrological state (filled or drained) of these water-filled crevasse systems. A fusion of multi-sensor optical satellite imagery was used to examine hydrologic states from 2000 to 2015. The monthly distribution of crevasse systems observed as water filled is unimodal with peak number of filled days during the month of July at 329 days, while May has the least at 15. Over the study period the occurrence of drainage within a given season increases. Inter-seasonal drain frequencies over these systems ranged from 0 to 5. The frequency of multi-drainage events are correlated with warmer seasons and large strain rates. Over the study period, summer temperatures averaged from −1 and 2 °C and tensile strain rates have increased to as high as ~ 1.2 s. Intermittent melt water input during hydrofracture drainage responsible for transporting surface water to the bed is largely facilitated by high local tensile stresses. Drainage due to fracture propagation may be increasingly modulated by ocean-induced calving dynamics for the lower elevation ponds. Water-filled crevasses could expand in extent and volume as temperatures increase resulting in regional amplification of ice mass flux into the ice stream system.
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sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1858 on: May 26, 2017, 12:58:42 AM »
I lookes at that paper at cryo discuss, and the  positioning of the crevasse groups in fig 1 struck me as possibly significant in comparison to bed topo. i attach part of fig 1

sidd

Dave55

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1859 on: June 06, 2017, 06:18:09 AM »
Looks like there was a big calving in the southern arm between the 3rd and 5th June (partly concealed by low cloud on the 4th in Worldview).

There was also some movement on the northern arm around the 1st.  There is a dark splotch (calved berg) that seems to move down the Fjord over the first few days of the June but was stationary before that.  I can't see where it calved from though - need higher res imagery than provided by Worldview.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1860 on: June 06, 2017, 11:10:17 AM »
Curious outflow switched to more saline
https://www7320.nrlssc.navy.mil/GLBhycomcice1-12/navo/arcticsss_nowcast_anim30d.gif
https://www7320.nrlssc.navy.mil/hycomARC/navo/arcticsss_nowcast_anim30d.gif
The first animation also has a burst of bottom melt north of greenland on the 90w meridion.

solartim27

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1861 on: June 14, 2017, 07:58:56 PM »
Another good sized calving visible on worldview from Jun 13 - 14
Edit:  Added a gif
« Last Edit: June 14, 2017, 08:58:37 PM by solartim27 »
FNORD

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1862 on: June 14, 2017, 09:29:54 PM »
This is from the 13th, sentinal hub, just before showing a breakout of the dammed ice.

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1863 on: June 14, 2017, 10:04:44 PM »
Yes Jakobshavn is back to "normal" retreat mode:
Have a ice day!

iwantatr8

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1864 on: June 15, 2017, 01:49:27 PM »
Yes it's an astonishing image from the 13 showing a huge amount of surface water all over the ice sheet some is even very close to the calving face, though what this means is unclear for now.

It's worth reviewing your gain settings in the sentinel app i find that a gain of 0.4 is the best for viewing ice areas with. it really brings out a lot of detail in this area.
 :o


johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1865 on: June 17, 2017, 11:59:09 AM »
I had to take a closer look at the northern fronts 9-16


from http://apps.sentinel-hub.com/sentinel-playground/?lat=69.18135720547525&lng=-49.493408203125&zoom=10&preset=CUSTOM&layers=B04,B03,B02&maxcc=27&gain=0.4&gamma=1&time=2015-01-01|2017-06-16&cloudCorrection=none&atmFilter=&showDates=false&evalscript=&showImage
showing melt is widespread.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1866 on: June 21, 2017, 09:44:43 PM »
I was looking generally at the amount of melt in the area, and was struck by the the openess of the 2 tributaries N/S of the fjord 20thN  13nthS


It seems the northern tributary could easily retreat to it's apparent bend this season.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1867 on: June 27, 2017, 10:08:06 AM »
Wonderful clear skies on the 26th Jakobshavn retreats on all fronts if you have the time take a look round. http://apps.sentinel-hub.com/sentinel-playground/?lat=69.34540320218453&lng=-50.39634704589844&zoom=12&preset=CUSTOM&layers=B8A,B03,B02&maxcc=100&gain=0.4&gamma=1.0&time=2015-01-01|2017-06-26&cloudCorrection=none&atmFilter=ATMCOR&showDates=false&evalscript=&showImage northern tributary /main fronts /meltwater finding it's way into the southern embayment.



nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1868 on: June 27, 2017, 10:37:32 AM »
Wonderful clear skies on the 26th Jakobshavn retreats on all fronts if you have the time take a look round.
Wonderful image...the shadow of the main branch looks like it will allow the estimation of the calving front height via using incidence angle & sun elevation angle at the time of imaging...

A-Team

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1869 on: June 27, 2017, 05:10:18 PM »
Nice image, indeed. The north branch calved quite a large piece (0.6 km in length) between 23-26 Jun 17 that stayed upright. This ice has come off the floating ice shelf that forms seasonally in wither, not from grounded glacier.

With considerable difficulty, it could be moved from the 26th location to overlay on the glacier on the 23rd.

There is no particular significance to the north branch or this event  as the ice is thin and the glacier segment short and disconnected to the interior. Looking now at the same date last year, it appears that the frontal ice shelf has not yet retreated to edge of the grounded glacier, ie 2017 lags 2016 in this respect.
« Last Edit: June 28, 2017, 11:18:23 PM by A-Team »

Espen

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1870 on: June 27, 2017, 07:46:09 PM »
As noted above (Nice to see you back good old friend A-Team) large calvings seen between June 23 and June 26 2017:
Have a ice day!

A-Team

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1871 on: June 28, 2017, 04:41:32 PM »
Quote
Nice to see you back good old friend
I've been obsoleted by new Sentinel playground interfaces that make it so easy to toggle dates, channel combinations and contrast without downloading. The animation below combines the two dates to show area calved (prior to adjustment for 3 days of advancement @ 40m/d) which could be combined with improved depth at the calving front from the Rignot group to get volume.

My impression is that the position of the calving front is not unusual for this date (which is still fairly early in the season). The 2nd animation shows lags both north and south relative to 2016. Difference to mid-Sept 2016 show the maximal retreat attained last year.

http://apps.sentinel-hub.com/sentinel-playground/?lat=69.16133661381689&lng=-49.606618881225586&zoom=13&preset=8_BATHYMETRIC&layers=B04,B03,B02&maxcc=20&gain=0.4&gamma=1.1&time=2015-01-01|2017-06-28&cloudCorrection=none&atmFilter=&showDates=false&evalscript=&showImage
« Last Edit: June 29, 2017, 12:07:09 AM by A-Team »

FredBear

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1872 on: July 08, 2017, 11:40:36 PM »
More calving July 5-7? (8 cloudy on arctic io)
http://www.arctic.io/explorer/4Xa5A//4-N90-E0

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1873 on: July 20, 2017, 10:12:15 AM »
Another clear day on the 18th well worth zooming in and looking around, huge backlog of calved ice to clear, melt ponds/water on and at the periphery of the ice.
http://apps.sentinel-hub.com/sentinel-playground/?lat=69.21598354214609&lng=-49.472808837890625&zoom=10&preset=CUSTOM&layers=B04,B03,B02&maxcc=97&gain=0.5&gamma=1.0&time=2015-01-01|2017-07-19&cloudCorrection=none&atmFilter=ATMCOR&showDates=false

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1874 on: July 30, 2017, 11:07:16 AM »
Just a couple of images north first, with the calving front bottom right, then south, both illustrating the melt surrounding the fjord

edit images redone.
« Last Edit: September 20, 2017, 09:54:04 PM by johnm33 »

Sigmetnow

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1875 on: September 20, 2017, 09:29:49 PM »
"If you really want to see ice in motion go where it moves faster than anywhere else. Jakobshavn Isbrae, #Greenland.#RemoteSensing #Sentinel2 "
https://twitter.com/IceOlly_/status/910076184129675264
Nice GIF at the link, from 4/2016 to 9/2017
People who say it cannot be done should not interrupt those who are doing it.

Neven

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1876 on: September 25, 2017, 10:50:29 PM »
This one popped up in my mailbox this afternoon. Looks interesting. From The Cryosphere:

Quote
Non-linear retreat of Jakobshavn Isbræ since the Little Ice Age controlled by geometry

Abstract. Rapid acceleration and retreat of Greenland's marine-terminating glaciers during the last two decades have initiated questions on the trigger and processes governing observed changes. Destabilization of these glaciers coincides with atmosphere and ocean warming, which broadly has been used to explain the rapid changes. To assess the relative role of external forcing versus fjord geometry, we investigate the retreat of Jakobshavn Isbræ in West Greenland, where margin positions exist since the Little Ice Age maximum in 1850. We use a one-dimensional ice flow model and isolate geometric effects on the retreat using a linear increase in external forcing.

We find that the observed retreat of 43 km from 1850 until 2014 can only be simulated when multiple forcing parameters – such as hydrofracturing, submarine melt and frontal buttressing by sea ice – are changed simultaneously. Surface mass balance, in contrast, has a negligible effect. While changing external forcing initiates retreat, fjord geometry controls the retreat pattern. Basal and lateral topography govern shifts from temporary stabilization to rapid retreat, resulting in a highly non-linear glacier response. For example, we simulate a disintegration of a 15 km long floating tongue within one model year, which dislodges the grounding line onto the next pinning point. The retreat pattern loses complexity and becomes linear when we artificially straighten the glacier walls and bed, confirming the topographic controls.

For real complex fjord systems such as Jakobshavn Isbræ, geometric pinning points predetermine grounding line stabilization and may therefore be used as a proxy for moraine build-up. Also, we find that after decades of stability and with constant external forcing, grounding lines may retreat rapidly without any trigger. This means that past changes may precondition marine-terminating glaciers to reach tipping-points, and that retreat can occur without additional climate warming. Present-day changes and future projections can therefore not be viewed in isolation of historic retreat.
Compare, compare, compare

TenneyNaumer

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1877 on: October 01, 2017, 05:17:48 PM »
Did Jakobshavn Isbrae undergo a wave from upstream, or what is going on?


johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1878 on: October 02, 2017, 11:01:16 AM »
It looks to me pretty much as in Nevens post above, every ice stream is mobile, some more than others, and the exit remains jammed. With things as they are i expect a big surge sometime during the winter, when the fjord has emptied somewhat and tidal waters can reach the calving front, meanwhile until the surrounding meltwater freezes just more of the same.

nukefix

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1879 on: October 04, 2017, 12:38:10 PM »
Hint: Now that winter is coming start using S-1 SAR, it's great for glacier monitoring... ;)

Shared Humanity

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1880 on: October 04, 2017, 02:43:35 PM »
Did Jakobshavn Isbrae undergo a wave from upstream, or what is going on?

I am thinking those waves are more a result of the underlying topography.

solartim27

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1881 on: October 12, 2017, 05:09:00 PM »
FNORD

TenneyNaumer

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1882 on: October 15, 2017, 12:50:19 AM »
Yeah, I think so, now, too. Must be visible now due to a further decrease in elevation in that area -- at least their persistence in the same shape and position would seem to indicate that.

Did Jakobshavn Isbrae undergo a wave from upstream, or what is going on?

I am thinking those waves are more a result of the underlying topography.

sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1883 on: November 30, 2017, 12:21:31 AM »
In another thread there was a call for prediction of grounding line in 2028. For what it's worth, i think the grounding line will be just inland of the deep trough behind the current grounding line.

That is i mean the grounding line will be close the the position A45 on the image at


https://forum.arctic-sea-ice.net/index.php/topic,2205.msg135092.html#msg135092


sidd
« Last Edit: November 30, 2017, 05:12:17 AM by sidd »

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1884 on: January 08, 2018, 12:02:42 AM »
There's been a very small calving, but more interesting is that the tides have been very active and have begun to clear the lower fjord. Then look inland to see a circular feature developing whether that's just a surface phenomenon or something deeper ?
http://bslmagb.nerc-bas.ac.uk/iwsviewer/?image=DataPolarview/111_S1jpeg2000_201801/S1A_IW_GRDH_1SDH_20180107T100008_2DDD_N_1.8bit.jp2

Martin Gisser

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1885 on: January 08, 2018, 07:43:01 AM »
What circular feature?
Amazing how visible the melt lakes are. Looks like a picture from summer (but isn't). Seems it hasn't snowed there yet.
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johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1886 on: January 08, 2018, 11:09:38 AM »
"What circular feature?"


Martin Gisser

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AbruptSLR

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1888 on: January 08, 2018, 04:40:47 PM »
The linked reference verifies that Jakobshavn ice velocities are largely modulated by ocean tides:

Xie, S., Dixon, T. H., Voytenko, D., Deng, F., and Holland, D. M.: Grounding line migration through the calving season of Jakobshavn Isbræ, Greenland, observed with terrestrial radar interferometry, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-231, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2017-231/

Abstract. Ice velocity variations near the terminus of Jakobshavn Isbræ, Greenland were observed with a terrestrial radar interferometer (TRI) during three summer campaigns in 2012, 2015, and 2016. Ice velocity variations appear to be largely modulated by ocean tides. We estimate a ∼ 1 km wide floating zone near the calving front in early summer of 2015 and 2016, where ice moves in phase with ocean tides. Digital Elevation Models (DEMs) generated by the TRI show that the glacier front here is thin (ice surface is < 125 m above local water level). However, in late summer 2012, there is no evidence of a floating ice tongue in the TRI observations. Ice surface elevation near the glacier front was also higher, > 140 m above local sea level within a very short distance (< 1 km) from the ice cliff. We hypothesize that during Jakobshavn Isbræ's recent calving seasons, the ice front advances ∼ 3 km from winter to spring, forming a > 1 km floating ice tongue. During the subsequent calving season in mid- and late-summer, the glacier retreats by losing its floating portion through a sequence of iceberg calving events. By late summer, the entire glacier is likely grounded. In addition to ice velocity variations driven by tide rise and fall, we also observed a transverse velocity variation in the mélange and floating ice front. This across flow-line signal is in phase with the first time derivative of tidal height, and is likely associated with tidal currents or bed topography.
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johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1889 on: January 08, 2018, 10:35:29 PM »
Martin "I guess it's the first major branch of the flow channel system:" made me think, so i compared the image linked above to this

posted by Sidd upthread, looks more like the second to me, not in that image unfortunately, because this image shows it's connected to the sea by a deep channel, so the light area central on your a image.
 

Martin Gisser

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1890 on: January 08, 2018, 11:19:23 PM »
Time to get the Gimp on my new box, to do some image overlay, and not just pure eyeballing. But not today  8)
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johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1891 on: February 07, 2018, 07:12:48 PM »
Looks like the western part of the northern calving front has been active, and the north side of the southern front is beggining to move. We're still having big tides [cornwall] so if it's similar up there the action could carry on through the new moon too. zoomable

Iceismylife

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1892 on: February 12, 2018, 12:06:26 AM »
https://go.nasa.gov/2EXz4uT
The fjord is clear no clouds.

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1893 on: February 12, 2018, 10:55:30 AM »
A little more detail here

AbruptSLR

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1894 on: February 12, 2018, 10:40:37 PM »
One possible contributing reason that the ice velocity for the Jakobshavn Glacier has decelerated of the past five years is that its grounding line has be retreating up a local rise in the bed topology; and it may well accelerate after the grounding line retreats past the local crest:

Lemos, A., Shepherd, A., McMillan, M., Hogg, A. E., Hatton, E., and Joughin, I.: Ice velocity of Jakobshavn Isbræ, Petermann Glacier, Nioghalvfjerdsfjorden and Zachariæ Isstrøm, 2015–2017, from Sentinel 1-a/b SAR imagery, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-251, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2017-251/

Abstract. Systematically monitoring Greenland’s outlet glaciers is central to understanding the timescales over which their flow and sea level contributions evolve. In this study we use data from the new Sentinel-1a/b satellite constellation to generate 187 velocity maps, covering 4 key outlet glaciers in Greenland; Jakobshavn Isbræ, Petermann Glacier, Nioghalvfjerdsfjorden and Zachariæ Isstrøm. These data provide a new high temporal resolution record of each glacier’s evolution since 2014, and resolve recent seasonal and inter-annual changes in Greenland outlet glacier speed with an estimated certainty of 10 %. We find that since 2012, Jakobshavn Isbræ has been decelerating, and now flows approximately 1250 m yr−1 (10 %) slower than 5 years previously, thus reversing an increasing trend in ice velocity that has persisted during the last decade. Despite this, we show that seasonal variability in ice velocity remains significant; up to 750 m yr−1 (14 %) at a distance of 12 km inland of the terminus. We also use our new dataset to demonstrate a strong relationship between ice front position and ice flow at Jakobshavn Isbræ, with increases in speed of ~ 1800 m yr−1 in response to 1 km of retreat. Elsewhere, we record significant seasonal changes in flow of up to 25 % and 18 % at Petermann Glacier and Zachariæ Isstrøm, respectively. This study provides a first demonstration of the capacity of a new era of operational radar satellites to provide frequent, and timely, monitoring of ice sheet flow, and to better resolve the timescales over which glacier dynamics evolve.
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Adam Ash

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1895 on: February 19, 2018, 07:49:16 AM »
Does lower ice stream velocity indicate lower discharge volume of combined ice and melt water? i.e. is the mass balance of the Jk catchment showing a similar trend in reduced rate of loss, or ...?

johnm33

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1896 on: March 10, 2018, 02:03:56 AM »
Another zoomable from polar view. The glacier's advanced a little and there appears to be some movement at the first bend, but mainly linked for future reference.
and another
« Last Edit: March 16, 2018, 01:01:04 AM by johnm33 »

sidd

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1897 on: March 10, 2018, 05:33:24 AM »
ice discharge is a product if ice depth at grounding, ice velocity at grounding and width (modulo some ice shelf melt delay.) As such it is not coupled to melt directly except in so far as bed lubrication and uplift causes seasonal acceleration.

As far as catchment precip goes, i don't think there is a trend, but a lot more of the preacip is coming as rain rather than snow, especially in the ablation zone. I susect it runs away to sea quickly as opposed to the past when it was snow and stuck around.

sidd
 

Bernard

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1898 on: March 10, 2018, 02:52:38 PM »
Hotel Arctic at Ilulissat has set up a new (don't know since when, just stumbled on it) webcam with panoramic view on Disko Bay and mouth of the Isfjord. Nice weather/visibility today  :)
 
http://hotelarctic.com/files/webcam/webcamshot.jpg

Disclaimer : I'm not a stakeholder of Hotel Arctic business  8)

Bernard

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Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1899 on: April 03, 2018, 11:44:38 AM »
Clear skies above Jakobshavn those days. MODIS yesterday shows the sea ice beginning to crack in the fjord. No big bergs in the fjord as far I can see, the calving front seems to have been quite calm during the winter.
https://lance.modaps.eosdis.nasa.gov/imagery/subsets/?subset=Arctic_r01c03.2018092.terra.250m