I understand that the density of the oceans on Earth in on average constant regardless of the depth. It is 1020 kg/m^3 at the surface and 1050 kg/m^3 at deep waters.
I understand too that this is not the case with the atmosphere. The density of the atmosphere decreases with height.
Though, I could not find any description in QM, that would describe the difference between the two media, and how they react differently to gravity, and the distance from the center of mass does or does not change their density.
Is there an explanation why the density of the oceans is (mostly) independent of depth, but the atmospheric density changes with height (is this just because of one is liquid and one is gas)?
Is there a QM explanation to this (different material) or is this just because of the distance from the center of mass (GR)?