>>I suppose that the cold temperature of the ice would also affect the way the weapon worked, maybe even stopping it from working. <<
Well maybe, but then the catch here is that icebergs...even the smallest ones...tend to be pretty massive. There's just so much sheer mass there to absorb the energy. The Navy and Coast Gaurd has tried a lot of schemes from black coatings to speed up melting, to charges of thermite being placed. At best, the thermite burns some small holes in the monster and black coatings tend to melt or wash off in short order. When you get down to it, during any season, you have so much ice in the water that even if you could blast them to bits, you still couldn't hope to get them all.
Since you can't really beat 'em, the best way to deal with icebergs is to be aware of where they are, and to make a point of not being where they are.