This idea began forming from my annoyance at the timing of the addition of the ice bears. I'm extremely likely to quit 16.1 before the next winter, so I won't see them until the next world. During the previous two winters, I've stumbled upon multiple patches of ice in the deep ocean (it seemed like none of them formed in the very deep). While these mostly served as obstacles for my knarrs' queued movement, they provided me with some inspiration.
Basically, icebergs would function similarly but exist all year round, serving as mini biomes for ice bears, grey seals, walruses, and garefowl. They could have mineable walls and elevation (not just flat ice like we have now), but the surface itself should probably be indestructible. Lastly, they should exist exclusively in the very deep ocean (access locked behind at least a snekkja) and if possible, they should change locations.
Alternatively, it can just be a big ice biome (not a pole, we don't do that here) with icebergs spawning around it.