Discussion of the image at the end of the Day After Tomorrow.
 
If North America were shrouded in this much ice, cold air flow off the continent would surely create sea ice in the North Atlantic. In the Labrador Sea, the sea ice edge shown here is similar to the real ice edge today in winter. During the glacial climate, when snow and ice on land might have looked like this, there was sea ice as far south as Newfoundland. Sea ice probably could not advance so far south in a few days (which is about how long it took to reach this state in the movie) because the ocean takes time to cool, but it would certainly advance some!