If there are more molecules in a given volume of air, the density is greater. If there are fewer molecule, the density decreases. Density=Mass/Volume
water density
mixing with sediment.
deep
water density
deep
mixing with sediment
deep
Well because of density anything can sink o float it is caused by density. What i mean is if density is 1 and up it will sink but if density is 1 and down it will float .
density currents and Earth's rotation.
Density Current
I sugest you look up "steam tables". Since convection currents are caused solely by diferences in density ... yes, it is assumed that tempreture diferences CAUSED the density gradiant - but that is not always true.
Optical Density. Which often is caused by normal density.