THE BARENTS SEA 85 



Table 30 



Oxygen 



The Barents Sea, as has already been mentioned, is on the whole well aerated. 

 In summer the oxygen content of the surface layer is usually slightly above 

 100 per cent of saturation, on the average 105 per cent. In summer the 10 to 

 25 m layer contains the maximum amount of oxygen where it sometimes 

 reaches 123 per cent of saturation, which corresponds to the maximum 

 development of phytoplankton. In the autumn when the photosynthesis pro- 

 cess becomes weaker, while the vertical circulation increases, the amount of 

 oxygen in the upper layer is somewhat below 100 per cent of saturation (90 to 

 100 per cent). The average minimum amount of oxygen is rarely below 85 per 

 cent of saturation. Smaller oxygen contents were recorded in the deep trough 

 south of Novaya Zemlya (down to 70 per cent). The amount of oxygen in the 

 bottom layer is usually about 90 per cent. These data, however, do not cover 

 the actual bottom layer, since during the so-called 'bottom' sampling the 

 bathymeter remains at some distance from the sea floor. We shall revert 

 to this problem later in connection with the quantitative distribution of 

 benthos. 



Nutrient salts 



The distribution of nutrient salts, most important for the development of 

 vegetable plankton, is correlated with the system of vertical circulation. A 

 very full picture of the annual cycle of the changes of nutrrient salts in the 

 Barents Sea is given by the excellent research carried out by E. Kreps and 

 N. Verzhbinskaya (1930, 1932). The Arctic waters are slightly richer in nutrient 

 salts than the Atlantic ones. Owing to the vigorous development of phyto- 

 plankton in the photosynthesis layer, the amount of phosphates present 

 gradually decreases in the spring and during the summer. An accumulation 

 of nutrient salts in the abyssal layers proceeds simultaneously and, by August, 

 a definite stratification (Fig. 27) which also coincides with the period of the 

 highest temperature is established. At that time the nitrates are absent from 

 the upper layer, while their amount increases with depth and in the bottom 

 layer reaches 200 mg/m 3 . The summer shortage of phosphates is particularly 

 marked in the upper layer, from which they are absent during that season, but 

 in the bottom layer the quantity reaches 60 mg/m 3 . 



With the arrival of the autumn circulation and during the winter, when the 

 whole water column gets mixed, the nutrient salts are brought up from the 

 lower levels and a uniform distribution of them is established. The most uni- 

 form distribution is observed in March (Fig. 26) — a period of most marked 



