98 A TEXTBOOK OF OCEANOGRAPHY 



VARIATIONS OF CARBONIC ACID AND SALINITY. 



At higher temperatures the amount of carbonic acid in solution is 

 lessened. 



SEA-WATER AS A FOOD SOLUTION FOR PLANTS. 



Since phytoplankton is found in the open ocean remote 

 from any land, it follows that sea-water contains all the 

 elements necessary for plant life. Generally speaking, the 

 open oceans are less rich in plankton than coastal waters; 

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

 directly dependent on the amount of vegetable food in the 

 ocean. Incidentally marine animals, such as fish, are directly 

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

 only source of organic nutriment. The colder seas of temperate 

 regions contain not only fish in extraordinary shoals, such as 

 the herring and cod, but also marine animals 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 elements are 

 absolutely indispensable for marine plants : these are carbon, 

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

 potassium, magnesium, iron, and silicon. If one of these 

 elements be absent plant life is impossible. 



The amount of growth of the vegetable plankton is 

 determined by the minimum quantity present of any one of 



