January 17, 2016
@TenneyNaumer contacted Alun Hubbard, Jason Box and I with an astute observation last evening. “But what I am getting at is that in general the temperature anomalies over the region of Jakobshavn have been high in the last few days, and I spotted weird temperatures off the coast via Climate Reanalyzer (which is seriously low resolution). I just checked with the manati satellite (also seriously low resolution), and it seems some sort of event has taken place.”
Following up on what are typically good observations from Tenney I looked at the Radarsat-2 and Sentinel-1 imagery posted by the Danish Meteorological Institute. Weather records from automatic weather stations in the region from PROMICE and the surface mass balance model results for the week from Polar Portal.
It is evident from the PROMICE weather records on the ice sheet just south of the Disko Bay region that temperatures have been exceptionally high since January 5th and atmospheric pressures have been high since January 9th. The Polar Portal mass balance model indicates some actual declines/ablation in the last week. This is more likely sublimation from föehn conditions than actual melt. The real changes are in the sea ice fronts and ice in the coastal inlets illustrated by MODIS. Below are images from January 9, 11, 13 and 16 for Disko Bay and January 9, 13 and 16 from Uummannaq Bay.
The arrow at location 1# is an area of sea ice across the fjord in front of Jakobshavn Glacier on January 9, that disappears by January 13. Location #2 is at the fjord mouth and location #3 is at the sea front south of Disko Island on January 9. There is no real cloud cover evident in any of images. Maybe low level fog in places. By January 11th a plume is sweeping from Point 2 towards Point 3. Notice the sea ice in the fjord disappears by January 13th and the ice front is pushed back in a concave fashion at Point #3. This indicates a clear push of water driving sea ice offshore. The Ilulissat Fjord mouth lack of ice is also evident in Webcam images from 1-16-16 and 1-17-16 at the Hotel Arctic, last images below with two boats plying the open water. on the 16th and icebergs clogging the fjord mouth on the 17th. The Sentinel-1 image from January 16th shows a significant flushing of icebergs from Ilulissat Fjord, pointed out by black arrows. This image has better clarity and with the icebergs scattered through the plume, indicate more clearly the plume is a water source change event, even if wind driven. The iceberg plume in the fjord has a brighter aspect due to the varied surface aspect-reflectance and has expanded down fjord. The event must be due to or enhanced by strong offshore winds and Ruth Mottram (@ruth_mottram) indicates there was at least one föehn event this week. The plume includes bergs from the ice melange in front of Jakobshavn has been largely removed, which can have implications for calving and frontal velocity. Moon et al, (2015). indicate the role that a rigid ice melange has on the calving and frontal velocity of tidewater outlet glaciers in Greenland.
In Uummannaq Bay a very similar sequence plays out, note on January 9 the sea ice connecting islands near #4. By January 13th the ice at location #4 is gone. The ice front is now at location #3, which on January 9th was well into the ice pack. Again we have a clear push of water leading to a concave sea ice front that is pushed well offshore. Icebergs can be seen amidst plume on January 16th, the plume opacity and size has diminished since January 13th.
In both of the January 13th images there is a plume leading to the concave sea ice front, the question being is this sediment laden water, with the resultant higher reflectivity or is it a combination of a surface water change from wind or a combination. We had questioned if the plume had any sediment origin initially. Its widespread nature and persistence suggested not. Aeration was another suggestion. Jason Box suggests that the opaque water plume leading to the developing polyna is driven by the strong offshore winds and the opaque whitening is capillary waves on the sea surface. Examples of identification of observed high backscatter from offshore winds are from Monaldo and Beal (1998) and Li et al, (2007) The ice must in part be driven back by a surface water push. You can see icebergs in sections of the plumes closer to shore suggesting this is a surface near surface phenomenon. This is a short term event. However, it could have broader implications, in this case the ice melange in front of Jakobshavn has been removed, and probably from in front of other glaciers, which will impact near term calving rates. I have incorporated many insights from the community and welcome more.
RADARSAT-2 IMAGE FROM Disko Bay 1/09/2016
RADARSAT-2 IMAGE FROM Disko Bay 1/11/2016
RADARSAT-2 IMAGE FROM Disko Bay 1/13/2016
Sentinel-1 imagery from 1-16-16 of Disko Bay-notice expanded brightness area in the fjord by #1.
Sentinel 1 imagery of Uummannaq Bay 1/09/2016
RADARSAT-2 IMAGE FROM Uummannaq Bay MODIS 1/13/2016
Sentinel 1 imagery of Uummannaq Bay 1/13/2016 plume size and opacity diminishing.
Ilulissat Fjord mouth webcam view 1-16-16.
Ilulissat Fjord mouth webcam view 1-17-16.