Physical and Chemical Properties

The diverse Ocean environment is a system of complex unions and interactions between the atmosphere, water, bottom and their inhabitants. As a whole, they form the unique character of the Ocean, in which many features are still insufficiently investigated. The influence of the Ocean has an effect in the most remote corners of the Earth. The lack of knowledge of the Ocean environment therefore presents a real problem for modern science.

Chemical Composition/Salinity

Oceanic water is a complex solution, but overall there is an amazing uniformity of its chemical composition throughout the oceans of the earth. It differs from fresh water both in its higher concentration of dissolved components and by physical properties dependent on these dissolved components. The total mass (in grams) of all solid substances dissolved in sea water (one kilogram) was the original measure of salt content, named "salinity" by early scientists. The global average salinity of ocean waters is about 35 grams per kilogram. In practice, it was difficult to measure salinity this way, due to the volatility of some components and the poorly defined nature of some others. When it was found that the ratio of chloride ion to all other components is relatively constant, salinity was routinely measured by the chemical determination of total chloride ion (using a well-known precipitation reaction). All of these early measurements were reported using units of either "per mille" or the symbol 0/00, referring to grams per kilogram. Today, based on the knowledge that electrical conductivity of seawater is directly proportional to the salinity, it is measured with special conductivity meters (at sea or in the laboratory). Conductivity measurements are reported as being derived from the "Practical Salinity Scale (PSS)" or as using "Practical Salinity Units (PSU)." However, because PSU measurements of salinity are actually made by calculating ratios of conductivity, the resulting numbers are without dimensions, and the term PSU is not really a unit of measurement.

Main Physical Properties

Because sea water contains dissolved substances, as well as minute suspended particles, and because it is subject to a wide range of temperatures and depth-induced pressures over the surface of the earth, the principal physical properties vary widely. The properties include DENSITY, SPEED of SOUND, LIGHT PENETRATION, and FREEZING POINT TEMPERATURE.

Text and images are modified from Man and the Ocean, a CD-ROM produced by the Russian Head Department of Navigation and Oceanography (HDNO).