"A cosmic feature of our planet lies in its riches of salt water. The world Ocean contains about 1413 x 10¹⁸ kg of aqueous solution of electrolyte of medium concentration. Salt water occupies about 71% of planet Earth's surface. The substances contained in such a huge amount of water can be subdivided into two categories. The first category includes dissolved substances such as salts, organic compounds and dissolved gases; the second category includes substances forming an independent phase, such as bubbles of gas and solid particles of both inorganic and organic origin. In addition, electrolytes and non-electrolytes are sometimes distinguished among dissolved substances. When dissolved in water, electrolytes form the particles which are able to transfer the electric charge (the ions) and, thereby, to decrease the electric resistance of  the system.

 The substances dissolved in seawater  are represented primarily by salts. The chemical composition of seawater is rather complicated in detail. Here it is sufficient to mention that a 'typical" specimen of seawater weighting 1 kg contains about 19 g of chlorine in the form of chloride ions, 11 g of sodium ions, 1.3 g of magnesium ions and 0.9 g of sulfur (mainly in the form of sulfate-ions). In orther words, seawater represents an aqueous 0.5 M solution of NaCl and 0.05 M solution of MgS0₄.

 

In addition, sea water contains small admixtures or traces of almost all elements of Mendeleyev's table.

 

The well-known physical fact that the water possesses a considerable heat capacity suggests that the oceans represent an excellent thermostat for the entire climatic system of the Earth. This simple and, at the same time, fundamental fact involves some unusual consequences - it provides one of the necessary conditions (the 'greenhouse' effect) for the origin and development of biological life on Earth. In addition, the existence of moderate (and, moreover, comfortable for a human being) climatic conditions where there is a moderatiung influence from neighbouring seas has played an important part in the history and development of human civilization.

 

The oceans of the Earth represent an actively functioning system, which is regulated, first of all, by thermohaline processes. Therefore, the knowledge and monitoring of spatial-temporal fields of the ocean's surface salinity and of the surface field of temperature are most important problems of remote sensing."

 

from "Passive Microwave Remote Sensing of the Earth Physical Foundations", Series: Springer Praxis Books , Subseries: Geophysical Sciences, Sharkov, Eugene A,2003.