I can't believe that aviation fuel is light enough to provide buoyancy for an entire aircraft. Air in the fuel tanks maybe... but it would need a lot...
Maybe the aircraft ran out of fuel? Would help to explain why it floated so well.
Well, I can tell you that icebergs float (on water) and their density is bigger than that of the jet fuel.
Also, I have to agree with you with big "bubbles" of air in different parts of the aircraft, and my complete ignorancy if the cargo compartments were not broken and remained sealed as an "air bubble".
In a previous intervention I mentioned that I didn't see in the newsreels and photos any evident fuel leak. So, if the fuel tanks remained undamaged, and considering that aviation fuel may have a density of about 0.72 kg/l, that will give you a lift (floating) power of about 0.28 kg/l of fuel. Add that to the air pockets and: you have the capability of holding 50 or more people on your wings that will only wet their feet!
From this page:
http://www.airbus.com/en/aircraftfamili ... tions.html
Airbus A320 fuel capacity: 23,860 l
Times 0.28 = 6680 (around 6,7 tons of lift if the tanks are full), or about 15 tons with tanks half full an perfectly sealed (3.4 from fuel and 11.930 from air).
From the same page, we can see that the minimum weight is 42,4 tons and the maximum 73,5. Remove the passengers, keep the holes above the "flotation line" and: you have a nice winged boat!
If we only knew the volume of the aircraft...I would give you a better answer.
Just another cast away from AD.com that reached AD.info island.