CLASSIFICATION OF THE OCEANS AND SEAS 9 



Estimates of the volume show even greater differences. The 

 volume of the Arctic Ocean is one-twentieth that of the Atlantic 

 and one-forty-second that of the Pacific. 



3. Classification according to Form or Configuration. 



Three main types : Oceans ; seas narrowly connected there- 

 with ; seas widely connected therewith. 



4. Salinity. 



The great volume of the open oceans consists of water of 

 salinity 35 per mille, and except in a narrow band round the 

 coasts the extreme variation may be said to be between 34 and 

 37J per mille. 



There is a marked difference between the open ocean and 

 the seas, since the latter are usually below or above the normal, 

 the chief exception being the Caribbean Sea Gulf of Mexico, 

 which stand in close connection by means of strong currents 

 with the open Atlantic. 



Subtropical seas usually have water above normal salinity 

 e.g., the Mediterranean, the Red Sea, and the Persian Gulf. 

 These lie in regions of relatively dry climate, so there is strong 

 evaporation due to high temperature and low rainfall. The 

 Gulf of California is also possessed of water of higher salinity 

 than the neighbouring Pacific. 



Salinity below the normal is met with in tropical waters 

 with excessive rainfall, or in temperate waters where, owing to 

 large rivers and excessive land drainage, the dilution is con- 

 siderable. 



Example of the former, sea between North Australia and 

 South-East Asia e.g., Banda Sea. 



Example of the latter sea, the Baltic Sea and Hudson 

 Bay. 



The variation of the salinity from the oceanic type depends 

 naturally to some extent on the size (e.g., breadth and depth) 

 of the connecting passage between the sea and the ocean . With 

 a narrow entrance we get extreme variation e.g., on the one 



