3.6 Summary of Section 3

• The constancy of composition means that the ratio of many different dissolved salt ions in seawater is constant.
• Water has very unusual physical and chemical properties and the polar molecular structure means that in fresh water maximum density is not the freezing point. However, in seawater this is different and density is a non-linear function of temperature and salinity.
• Seawater is heated at the surface by solar radiation and the salinity of seawater is controlled by the balance between evaporation and precipitation, E-P.