Temperature and density of ocean water are related inversely: warm water means low density, cold water means denser seawater. The salt content of the water also affects Ocean density. Sea Surface Salinity: Sea water is about a 3.49% salt solution, the rest is freshwater. The more saline, the denser the seawater. As the range of salt concentration in the ocean varies from about 3.2 to 3.8%, oceanographers refer to salt content as 'salinity', express salt concentration as parts per thousand; 34.9 ppt is the average salinity.