Could be centrifugal force due to the earths rotation but more likely has something to do with temperature. Could be a combination of both. I'm just guessing though
It was observed in other planets first: https://en.wikipedia.org/wiki/Planetary_coordinate_system#Eq...
https://en.wikipedia.org/wiki/Post-glacial_rebound
So, it could be quite possible, that even with sea level rise, crust rebound will play bigger role around poles and there might be some new lands in the sea around north pole - as it is quite shallow ocean near Russia and Canada.