Assumng that the tanks are open to atnosphere at sea level and are pure water:
Scotty is right. The water in the lower tank would be frozen!
Here is a headache inducing one:
If you drop two identicle dimension spheres, with the same surface finish and dropped from the same height. One shhere is of a heavy material (say iron) the other of a light material (say wood).
Experement has shown that the wooden one will hit the ground first.
Why??
You attached the iron one to a bungee cord? :-/
100 Japanese horses now unmuzzled! Derestricted hooliganism has commenced...