I’ve read the part about the Polar sink in the Arrakis source book but I don’t feel like it gave enough Information about this region. From the map it looks like the area could have snow or ice but is this possible for how hot the planet is? But if there is snow or ice, is there any mention that there is any mining operation for collecting water?
If you go with the Novels then they talk about there being small polar ice caps. The map at the front of the book shows them and the Barons globe of Arrakis is described with “The Polar Caps were insets of finest cloud-milk diamonds”
There is also a ‘water shipper’ in the banquet scene whose “summer mansion was near his polar-cap factory” which definitely sounds like they are mining the polar caps for water.
I would say that there is ice on Arrakis in the very northern latitudes. After all as far as we can tell there is ice on Mercury & the moon in our solar system. All you need is somewhere that the sun can’t effectively heat, which the angle of the planet may give far enough North & South.
Plus if the ice is frozen that would stop the sandtrout from sealing it.