Forchhammer's Principle, also known as the Principle of Constant Proportions, states that the ratio of major salts in samples of sea water from many locations is constant. Though the water may be saltier in one place than another, the percentages of the various salts is the same in each sample. Consequently, the ocean is in a chemical equilibrium because the proportion of dissolved salts per unit volume are nearly constant. Because of the ocean's salinity, many chemical reactions take place between the different salt and water molecules, which modify pure water's properties. Therefore, for an amount of water to rise one degree Celsius, less energy is required than if the water were pure.
Salinity also disrupts the chain of hydrogen bonds in water.
Therefore, as salinity increases, the freezing point of water decreases. Or, as salinity increases, the boiling point of water decreases. Dissolved salts also attract water molecules, so saltwater does not evaporate as quickly as pure water.