Depends. The general consensus seems to be that, like lightning, ice is a use of various elements. Fire can be used to remove heat from an area, so that's one possibility. Water certainly should also be able to do ice, and freezing winds are obviously the domain of Air. But you only need one of them to do it.
Bear in mind that the most important thing is how your character visualizes the Elements and what HE thinks Ice would be part of. After all, people with other mystical frameworks wind up not even using the same Elements, much less specific usages.
