86 



BIOLOGY OF THE SEAS OF THE U.S.S.R. 



homothermic conditions. At that time the amount of nitrates in the water 

 varies from 1 50 to 250, and of phosphates from 40 to 60 mg/m 3 . The nitrate 

 and phosphate contents increase slightly from south to north and in the 

 northern parts of the Sea the amount of nitrates in bottom layers reaches 450 

 to 460 mg/m 3 . The off-shore waters are, on the contrary, appreciably poorer 

 in nutrient salts. Their nitrate content may fall to 100 mg (and below) and 

 that of phosphates to 14 to 15 mg/m 3 . The Arctic waters are on the whole 

 richer in nutrient salts than the Atlantic ones. Careful all the year round 

 observation has allowed Kreps and Verzhbinskaya not only to draw a full 



picture of the annual cycle of nutrient salts 

 but to come to some interesting conclusions 

 on biological productivity. 



First of all it was found possible to 

 determine the total amount of phosphorus 

 used up during the multiplication period 

 of 1930—31 in the region near the Kola 

 meridian. Knowing the amount of phos- 

 phorus contained in phytoplankton (0-15 

 per cent of the wet weight) it is possible to 

 calculate the amount of phytoplankton 

 which could develop at the expense of a 

 given amount of phosphates. It was estab- 

 lished that 3,000 to 5,000 tons of the wet 

 mass of phytoplankton could be formed 

 for each square kilometre of sea surface 

 at the expense of the phosphates present 

 through the whole depth of the Barents 

 Sea. This amount is about double that of 

 the annual phytoplankton production cal- 

 culated by Atkinson for the English Channel (1,400 tons) and for the Oslo- 

 fjord by Gran (1,600 tons/km 2 ). 



Interesting data on the distribution of nitrites in the Barents Sea are given 

 by S. P. Brujevitch (1931). In summer nitrites are absent from the photo- 

 synthesis layer; the largest amount is accumulated under it, at a depth of 

 50 m or more. 



The amount of nitrites is rarely above 10 mg/m 3 . Usually it is a few milli- 

 grammes. Nitrites are present in such amounts usually only at the end of the 

 summer and in the autumn. They generally disappear after the period of 

 vertical circulation in winter. Hence accumulation of nitrites takes place under 

 the zone of the highest production of plankton by the end of the photo- 

 synthesis period. Brujevitch notes a decrease of oxygen content in the layer 

 of the highest concentration of nitrites. The concentration of nitrites and the 

 decrease of oxygen content are the results of oxidation processes accompany- 

 ing the disintegration of the organic substances of defunct plankton, which 

 decomposes to amino-acids and ammonia. The fact of the rapid summer and 

 autumn accumulation of nitrites followed by their oxidation to nitrates was 

 also noted by Harvey for the Atlantic Ocean. The nitrites are considered by 



MONTHS 

 Fig. 27. Seasonal changes in 

 nitrite and nitrate content in 

 to 100 m layer in Barents Sea 

 in 1930, on the 72° to 72° 30' 

 latitude along the Kola meri- 

 dian (33° 30') (Verzhbinskaya, 

 1932). 



