well I stated that the stern was heavier, but at the same time it still had a lot of air in it. And what I meant by seperation further under water, was that the bow and stern seperated further down, since they were still attached by a "thread". Not that the ship actually broke under water. Models and articles show the two pieces seperating just under the surface, but I think the stern was dragged under with the bow a short distance before they seperated. Once they did seperated, the bow went away immediately with speed. The stern started decending slowly because air was still exploding out, but as it filled more and more with water, it decended with more speed. To put my theory more simply; The ship broke, the bow went under and pulled the stern down with it, before they seperated further down under the surface. I just find it really hard to believe that the stern could have gone down the way it did all by it's self when it was still almost completely filled with air. Even despite it's weight. I think this theory explains partly why the stern is so severly damaged in comparison to the bow. The air trying to escape and all.

Jessica