98 A TEXTBOOK OF OCEANOGRAPHY 



VARIATIONS OF CARBONIC ACID AND SALINITY. 



At higher températures tlie amount of carbonic acid in solution is 

 lessened 



Sea-Water as a Food Solution for Plants. 



Since phytoplankton is found in the open océan remote 

 from any land, it foUows that sea-water contains ail the 

 éléments necessary for plant life. Generally speaking, the 

 open océans are less rich in plankton than coastal waters ; 

 again, tropical seas are poorer than colder waters, and this is 

 directly dépendent on the amount of vegetable food in the 

 océan. Incidentally marine animais, such as fish, are directly 

 dépendent ultimately on the plants in the sea, since this is their 

 only source of organic nutriment. The colder seas of temperate 

 régions contain not only fish in extraordinary shoals, such as 

 the herring and cod, but also marine animais of the largest 

 size, such as the right or true whales. Tropical seas fail in 

 this respect. 



Brandt has summarised the conditions under which plant 

 and animal life flourish in the sea. Certain éléments are 

 absolutely indispensable for marine plants : thèse are carbon, 

 oxygen, hydrogen, nitrogen, sulphur, phosphorus, calcium, 

 potassium, magnésium, iron, and silicon. If one of thèse 

 éléments be absent plant life is impossible. 



The amount of growth of the vegetable plankton is 

 determined by the minimum quantity présent of any one of 



