I've caught up with my manga reading, and I must say I did notice something that I was not expecting:
The "Gates of Justice", those enormous doors behind Enies Lobby, were completely and utterly destroyed by Buster Call! Now, Oda has a tendancy at the end of "major" arcs to put some sort of god-like/supernatural event occur at each arcs' climax; for Arabasta, the defeat of Crocodile brought down rain. In Skypiea, Eneru's total defeat was heralded by the sound of the Golden Bell.
So, since the obvious "supernatural" closure to Enies Lobby has been ruled out as a possibility, what do you lot think it could be?