While I do agree that the ship buckled and "broke" at the surface, I also believe that the stern and bow section did not completely seperate at the surface. Instead, that they actually seperated just under the surface. I made a post some time ago about my idea and it was this:

After it breaks (at the surface), the bow section sinks, pulling the stern upright. The stern bobs (up and then down) a small bob, but only once. The bow section is still attached by hull plates and such under water so it bobs too. The bob would have been quite slow, so to on lookers (those that saw it, in utter darkness mind you), it looked like it was just standing there for a minute or so. The stern section still has a lot of air in it. Since the stern is still attached to the bow, when the bow descends (down) again, it has enough inertia this time (for both it and the stern section) to continue down, the stern section still attached. Now since the stern section is still mostly full of air, once it is completely submerged at a certain depth, the two pieces are met with enough opposing force to tear them apart. The stern still wants to float, but the bow wants to keep going down. So they're being pulled in opposite directions (which had been occuring during the entire time, or at the surface too; it's just that they were met with enough force now to seperate them). They seperate and the bow continues on it's way down. The stern may "float" a bit under the surface. Since air was exploding out of it while the bow was pulling on it, it had a chance to "equalize", so it's not going to return to the surface, but it won't sink immediately either. It quickly becomes unstabilized again (since air has been escaping the whole time), enough air has been forced out for it begin a descend (which starts out rather slow) now. There is still a lot of air trapped in the stern as it descends, so a length of it's trip down would have been slower then that of the bow section. It's also being destroyed by the air that's being forced out of it as it goes. Also, since the stern section wasn't as hydrodynamic as the bow section, there would have experienced more parasitic drag , so that would have also managed the speed (making it more difficult for the stern's speed to increase) of the descend. So with the stern section, a lot of the damage was done by the air being forced out. In conjuction with the turbulant flows around it during the descend, it ends up on the ocean floor unrecognizable. I'm sorry this seems like jumble of words, it's much easier to demonstrate. I could draw something if need be.

This is the basic idea, but the two pieces could have seperated while the stern was still visible at the surface. I just believe that there had to have been some inertial forces involved here (the bob), more than what has been shown, that the stern wasn't just "sitting" there, and then all of a sudden descended at a fairly constant, and rapid rate. This is more what I'm emphysizing, even if it didn't happen exactly as I put it above.
I've actually seen a model video of the break up that demonstrates this view exactly, at a Titanic exhibit.

The reason I came up with this is after watching Cameron's movie (although the break up wasn't completely accurate, but for a good reason), and reading some testimony, I just couldn't believe that the stern would just sit up there like that, and then all of a sudden (at the rate that it did) descend. Just unnatural to me. The way it looked in Cameron's movie, it looked as if it were being PULLED down. I mean think about it, why would the bow descend naturally, and then all of a sudden the stern just disappears, with all that air still in it. The reason the stern would have stood upright like that in the first place is because its till had so much air in it.


Jessica