The cause of buoyancy in terms of the molecules

[TheLil'Turkey]

I think that buoyancy is caused by the increase of density with depth (the deeper you go, the more molecules there are per unit volume). Therefore an object in a fluid will be hit by more of the fluid molecules from below than from above (even if the difference is only a tiny fraction of 1%). Is this correct?

 

[Spinnor]

Right, but the object is likely compressed more then water so the buoyancy of the object is decreased?

 

[TheLil'Turkey]

It depends what the object is made out of. I just looked up water and copper and water is an order of magnitude more compressible.

I still don't feel 100% convinced that my hypothesis in the OP is correct.