Please support this Forum and Neven's Blog

Author Topic: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland  (Read 517286 times)

Espen

  • ASIF Governor
  • Posts: 2976
    • View Profile
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

  • ASIF Lurker
  • Posts: 38
    • View Profile
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

  • ASIF Middle Class
  • Posts: 714
    • View Profile
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

  • ASIF Lurker
  • Posts: 66
    • View Profile
    • Climate Change: The Next Generation
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

  • ASIF Middle Class
  • Posts: 714
    • View Profile
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

  • ASIF Lurker
  • Posts: 66
    • View Profile
    • Climate Change: The Next Generation
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1855 on: May 17, 2017, 07:39:40 PM »
Sidd's the best!

Tealight

  • ASIF Citizen
  • Posts: 251
    • View Profile
    • CryosphereComputing
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

  • ASIF Emperor
  • Posts: 12040
    • View Profile
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.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

  • ASIF Upper Class
  • Posts: 1257
    • View Profile
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

  • ASIF Lurker
  • Posts: 2
    • View Profile
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

  • ASIF Middle Class
  • Posts: 714
    • View Profile
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

  • ASIF Citizen
  • Posts: 406
    • View Profile
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

  • ASIF Middle Class
  • Posts: 714
    • View Profile
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

  • ASIF Governor
  • Posts: 2976
    • View Profile
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

  • ASIF Lurker
  • Posts: 38
    • View Profile
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

  • ASIF Middle Class
  • Posts: 714
    • View Profile
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

  • ASIF Middle Class
  • Posts: 714
    • View Profile
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

  • ASIF Middle Class
  • Posts: 714
    • View Profile
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

  • ASIF Citizen
  • Posts: 371
    • View Profile
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

  • ASIF Upper Class
  • Posts: 1698
    • View Profile
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

  • ASIF Governor
  • Posts: 2976
    • View Profile
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

  • ASIF Upper Class
  • Posts: 1698
    • View Profile
Re: Jakobshavn Isbræ / Ilulissat Isfjord / West Greenland
« Reply #1871 on: June 28, 2017, 04:41:32 PM »
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

  • ASIF Lurker
  • Posts: 37
    • View Profile
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

  • ASIF Middle Class
  • Posts: 714
    • View Profile
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