I therefore cannot help wondering whether the extra thickness on the poleward sides of these islands is at least partly caused by extensive ice ridging in these areas thickening the ice rather than by MYI somehow occurring in relative isolation in these three areas.
that's exactly how it is and if partly then big partly no doubt IMO
I agree. What we end up with and where, is almost all due to winds and currents, rather than old thick ice. It looks like the reason that the ice even gets old, is because it was piled up, allowing it to survive the next summer.
At least, that is how it is now. I think in the past some ice survived through the summer to increase thickness the next winter, but after this year I think almost all of the multiyear ice will be gone.
Also, the final pattern that we end up with doesn't have that much to do with melt patterns per se, but winds. For example, if you look at 2012 around the end of June, the area between the pole and Greenland was looking pretty ragged, and yet that's exactly where the thickest ice ended up at the minimum.
If you look at all the minimums, the thickest ice ends up on the Canadian/Greenland side, usually in the notch at Nares Strait, or if not there, further west along the CAA.