The gas National Geographic was talking about was Methane. The Methane gets dislodged from it's frozen confines down at the bottom of the sea and
causes bubbles on the surface. Since surface tension on the water is displaced by the bubbles, there is no buoyancy - hence, the boat sinks. The
same is true for aircraft. Methane will displace the thicker air and those aircraft will drop like rocks. That episode of National Geo also had the
videos from the Bermuda to prove that the missing aircraft and ships - most of them - were caused by the Methane rising to the surface. As far as
screwy compasses are concerned, I can't remember what they attributed that to. It could just be stronger than normal electromagnetism in that area.
The Earth, is after all, a giant powerplant.



