Ice usually makes the polar regions impassible, restricting movement. Many times they form a solid barrier which connects with land and makes it impossible to circumnavigate continents. However, sometimes icebergs are distributed among the solid ice in such a way as to form canals and allow naval and embarked units to pass through. So, don't give up completely on trying to find a path until you hit a solid wall! You may need to wait until you've researched Cartography before trying, though, because many times the canals are formed by both Coastal and Ocean waters.
Ice is impassable to ships (more than a few have come to grief, just ask the crew of the Titanic), and not much fun for other travelers. Except maybe the polar bears.