Is Brook able to drown? It is known that the Yomi Yomi no Mi fruit will only revive its user once, and also that Devil Fruit users can't swim, so I was wondering... What would happen if Brook falls into the ocean? I mean, even if he's alive, as a skeleton he has no lungs, so he should just be unable to go back to the surface, shouldn't he?
He's just a skeleton obviously, so he's not really breathing, however, when his body gets drowned slowly by the sea water, his strength begins to fade away (Chapter 493, page 7): 



And from this scene, I imagine if he falls into the ocean, like all Devil Fruit users, he will be powerless and be unable to resurface unless helped.