Thanks Laurent.
I found a converter here:
http://epsg.io/3413/map . It's hard to say accurately from the graphs on the Obuoy site, but the position appears to be at:
~ 156 to 158 W / 77.0 to 77.2 N , which by the EPSG:3413 system is
~ -1320000 to -1280000 / 553000 to 544000 .
This puts the buoy somewhere here (see attached images; the close-up view from same date as photo, Aug. 17; the far-away view is from the day before, which was clearer so gives a better idea where the buoy is relative to the "bite").
I also checked the sun direction (
http://suncalc.net/), which seems actually more east than north. But regardless, there is indeed very little or no open water within a few km to the north-east, if the numbers are correct. (The horizon is ~5 km when viewed from ~2 m elevation.) However, a few km to the south there is actually quite a bit of open water.
But it's hard to say how accurate the above numbers are. I still guess that it is water, because what else explains the reflection in the picture? It seems to me very unlikely that it could be a pressure ridge, given the fragmentation in the area. Or perhaps it is the edge of another large floe, but if so, why is the sun reflecting at the same angle as off the melt pond in the foreground.
(Note: Oddly, the Obuoy10 picture hasn't updated since the one we are discussing.)