Bottom melting is running wild now. I think it is not because of the recent effect of storm since it already started earlier. It is because a generous number of days passed with temperatures around 0C.
If this buoy, in this relatively protected area, is seeing this bottom melt at this 83N of latitude, imagine what to expect south of 80N. Caveat, it is just one location.
What about bottom melt in all these low concentration areas within in CAB after all? mmm We'll see.
This sudden melt rate is really surprising to me.
Edit: could it be that the buoy is located very close to a recent fracture? Otherwise I don't see how bottom melting rate can go off suddenly like that
Thanks for bringing up this issue of bottom melt on buoy 2015F, seaicesailor.
For reference, this is the profile you presented :
I mentioned before that 2015F is an excellent source to investigate the less common forms of bottom-melt : heat conduction and sunlight shining through the ice.
For many such issues, I like to get a ballpark estimate by using basic physics.
For that, let us make a rough estimate about how much heat is causing bottom-melt on that buoy right now. The thickness data on the buoy is a bit erratic, but I would say that over the past 14 days, 20 cm of bottom-melt happened (please correct me if you think otherwise).
20cm bottom-melt over 14 days is 1.4 cm/day which suggests that somehow some 50 W/m^2 of heat reached the bottom (50 W/m^2 *3600*24/330000 = 13 kg/m^2/day = 1.3 cm/day).
Heat conduction through the ice (with surface at 0C and bottom at -1.8C) is negligible : with ice heat conduction of 2 W/m/K, through 1 meter ice gives 4 W/m^2. Less for this 1.8 m thick floe. So that's not it.
What is more likely is that the sunlight is shining THROUGH the ice, and causing bottom-melt that way. At this time, insolation is still high (some 400 W/m^2 for open skies, 200 W/m^2 average) and thus if 25% of the sunlight goes through the ice, we could explain 2015F's bottom melt.
Note that this bottom melt rate started to occur only after the snow melted. That suggests this effect of sunlight through the ice is indeed contributing to the bottom melt rate observed, but I must admit that the melt rate is still a bit steep. After all, sunlight that goes through the ice (even if it is 25 % of incident insolation) will also warm the water well below the ice, and thus not all of that light energy immediately goes to bottom melt, but instead some of that will cause bottom-melt much later (all the way into fall).
So even though "light shining through the ice" appears to be a serious candidate in explaining 2015F's bottom-melt, there may be a third mechanism at play. Maybe there are some leads around this floe. Or some upwelling that just started happening recently.
Let me know your thoughts, and either way, let us keep a close eye on this buoy and the bottom melt it is recording.
[edit] On second thought, since the snow on this floe melted, it will have an albedo of about 0.4 or 0.5 at best, so it will absorb half of insolation (which will be about 100 W/m^2 for average weather). If half of that goes to top-melt and half to bottom-melt it would explain the melt rate of this buoy quite nicely.