The process of plate tectonics tends to amplify this distinction. This diagram shows average temperature, density, and salinity of seawater as a function of latitude on earth. The density is given in unconventional units. This diagram allows one to look up density, temperature, or salinity of ocean water if you only have two out of the three quantities available. Temperature is given in Celsius degrees, and salinity in parts per thousand.
Density is in units as above.