Hi Steve
Yes you it right it is an ice bubbler, powered by an air compressor. I have seen pictures from the 1950s where it was being used, so it has been around a long time.
It would only be used where they don't want the ship frozen in, or if they are going to send divers down to do work on the prop area.
The icebreaker Louis S. St-Laurent has an ice bubbler system mounted in the ship, which is quite impressive when it is running.
Mac