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Friday, April 29, 2011

Neven: Flushing out the Fjord (Jakobshavn Isbræ)

Flushing out the Fjord

by Neven, Arctic Sea Ice Blog, April 13, 2011
I wrote a blog post on Jakobshavn Isbræ last year when a 7-square-kilometer (2.7 square mile) section of the glacier broke up. Here's some basic information from Wikipedia on one of the most important Greenland glaciers, with an image of the glacier on August 5th last year (the glacier is on the bottom right, with the fjord in front of it filled with icebergs):
8-5-2010Jakobshavn Isbræ drains 6.5% of the Greenland ice sheet and produces around 10% of all Greenland icebergs. Some 35 billion tonnes of icebergs calve off and pass out of the fjord every year. Icebergs breaking from the glacier are often so large (up to a kilometer in height) that they are too tall to float down the fjord and lie stuck on the bottom of its shallower areas, sometimes for years, until they are broken up by the force of the glacier and icebergs further up the fjord.
Well, it appears that something convinced those icebergs to get a move on, because in just a few weeks time the Illulisat Isfjord has been flushed clean. On February 26th (day 57), resident Arctic expert Lodger informed us in Open Thread 6 that some of those icebergs had left the fjord. I didn't think much of it at the time (couldn't be bothered really, as images were too cloudy). On March 1st (day 60), everything seemed to be just hunky dory againwith gaps neatly frozen over, but apparently this was just a prelude to the Great Flushing.  I've made a reconstruction with a handful of satellite images that were clear enough to be used from day 52 (Feb. 21st) to day 102 (April 12th). Check out the Royal Flush between days 82 and 83:
The reason I decided to have another look at Jakobshavn was a post from April 10th I read on the NASA Operation IceBridge blog, written by Kathryn Hansen, called Mission Mop up:
After hitting some clouds as expected from the morning's weather brief, we headed back north and reflew the center flow line of Jakobshavn -- always spectacular -- before flying over Illulisat Isfjord, which was surprisingly free of ice. The reason for the ice-free conditions was unknown to scientists onboard. There could have been fewer calving events, warmer water, or wind patterns that pushed ice out of the area.
"Half of the Illulisat Isfjord was open water with several fishing boats in the area, something I have never seen before," said Michael Studinger, the mission's project scientist.
A camera mounted on the belly of the aircraft captured this image of a fishing boat (top) in the Illulisat flord, which was mostly open water with a few visible patches of ice. Credit: NASA/DMS team
Me? I think 'twas the wind.
Here's an animation of the full MODIS images of the region (r02c02). We can clearly see the ice floes in Disko and Baffin Bay retreat northwards full-speed around the time of the Royal Flush:

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