CHEMISTRY OF THE SEA 173 



Ocean Nitrogen in Nitrates Nitrogen in Ammonia 



Atlantic 102 mg. (88 mg.) 47 mg. (46 mg.) 



Indian 119 mg. (77 mg.) 52 mg. (43 mg.) 



Pacific 69 mg. (66 mg.) 46 mg. (50 mg.) 



This part of the ocean is probably poorest in life, the only exceptions 

 being in places where there is extensive upwelling of the bottom waters. 

 Alexander Agassiz 16 refers to the middle Pacific as "barren grounds," 

 in sharp contrast with the abundance of life in the Gulf of Mexico or 

 in the main current of the Gulf Stream along the Florida Reef. The 

 western Pacific, into which the great Asiatic rivers flow, with its wide 

 shallow areas and good development of coastal formations, is much 

 richer in life. Mitsukuri 17 speaks of the plankton of the Japanese sea 

 between Nipon and Shikoku as quantitatively the richest known to 

 him. The fisheries of the Japanese coast and of part of the Chinese 

 coast are among the most productive in the world. 



The rivers of southern Asia and the great extent of the coast lines 

 in the East Indies are favorable to a rich marine life. In contrast. 

 Chun 18 finds the crystal-clear surface waters between the Seychelles 

 and the east African coast poor in animal life. 



The general conclusion that the tropical seas are poor and the 

 cooler and cold seas rich in plankton, although relatively true, requires 

 some modification. The distribution of life in the sea depends on the 

 fertility of the water, and this depends in turn on a variety of factors 

 varying from place to place and sometimes from season to season. 



Even at its best, sea water is a very dilute solution of many of the 

 mineral nutrients essential for plant growth; the concentration, even 

 of essential substances, may be many times less than in good soil. This 

 means that planktonic plants must secure many of their essential salts 

 from an extremely dilute solution, and this necessitates that they be 

 of small size in order to have a high ratio between area of surface and 

 bulk. In contrast to the trees, shrubs, and grasses of the land, the 

 marine plants which form the base of the food chain, even for fishes 

 and whales, consist of minute diatoms and other, even smaller, algae. 



Oxygen. — Of the substances dissolved in sea water, oxygen is one 

 of the most important for marine life. The amount of gas absorbed by 

 water is larger at low than at high temperatures, and the amount dis- 

 solved in sea water is accordingly greater at the poles than at the 

 equator. A liter of sea water of 35% salinity can contain 8.03 cc. of 

 oxygen at 0°, and only 4.93 cc. at 25°; on account of the presence of 

 salts, oxygen is about 20% less soluble in sea than in fresh water. The 

 most superficial layers replace used oxygen from the air, and it is 

 distributed to moderate depths by wave action. Within the lighted 



