Purely speculating, but, they may have thought that the thickness varied even deep into the interior of the ice caps for some reason, hence why the guy doing the modifications to the sub wanted that light sensor to gauge thickness.
Good share. I hadn’t even heard of the Nautilus expedition. Totally seems like a Wikipedia rabbit hole I would have already gone down.
The biggest takeaway for me was learning the North Pole isn’t actually on land but rather sea ice. I had always assumed it was on a continental landmass.