Since it happened I have wondered what kept this plane afloat. I heard this morning about some sort of "water - ___" system that the plane was equipped with. They didn't explain it, other than saying it helped keep the plane from sinking.

I know that the fuel is lighter than water and if not all the tanks were filled with fuel, they are charged with CO2 or some other inert gas. And there were likely some air pockets in the cargo hold, but the plane still apparently still has some bouyancy tied to the pier.
How? WVO or anyone know the systems or principles in play here?