Why on earth is the ice thickening, apparently from below, despite apparently warm water temps (as well as >0 surface temps)??
I asked the BAS that precise question, but no response as yet.
It might be a "false bottom" caused by melt water, but without further info from the BAS I'm not sure how their IMB buoys work. It looks a bit too "regular" for that though. If the IMB's "floating" in it's hole in a melt pond that might (just about!) explain it.
I'll see if I can dig out some evidence from last summer tomorrow.