THE BARENTS SEA 87 



most investigators to be an intermediate phase of the process of ammonia 

 and amino-acid oxidation to nitrates. On the other hand, V. Butkevitch 

 considers that the nitrites accumulate under the photosynthesis layer as a 

 result of the reduction of nitrates, since no nitrifying bacteria have been found 

 in the surface layers of sea water. 



Quantitative correlation between the nitrates and nitrites is evident from 

 Fig. 27, drawn by Verzhbinskaya (1932) for the Barents Sea. Ammonia is 

 formed during the decomposition of organic substances. Nitrogen content in 

 the form of ammonia is low in the upper layer of the Barents Sea — no more 

 than 10 to 20 mg/m 3 . Below the photosynthesis layer (50 m) the amount of 

 ammonia decreases with depth and at the bottom it is 3 to 5 mg/m 3 . Similar 

 results were obtained for the Danish Strait by the Meteor expedition. 



There is no shortage of silica in the Barents Sea even in the period of the 

 highest increase of photosynthesis, and therefore it is not a limiting factor in 

 the development of phytoplankton. The silica content in the waters of the 

 western part of the Barents Sea reaches 1 ,000 mg/m 3 . Within the region of the 

 Kola meridian the amount of silica in the winter varies between 400 and 800 

 mg/m 3 . By the end of summer, as a result of phytoplankton development, 

 the silica content in the upper layers of water falls to 200 mg/m 3 , and in the 

 bottom layer rises to 600 to 800 mg/m 3 . 



Sea soils 



M. Klenova (1940, 1961), who has for many years investigated the sea-bed of 

 the Barents Sea, points out that its sediments consist of grains of greatly vary- 

 ing sizes, mostly of mineral origin, from a thin silt to large boulders (Fig. 28). 

 Sandy silt (10 to 30 per cent; about 21 per cent of the fine fraction*) is the 

 preponderant soil of the Barents Sea, occupying about 4 per cent of its bottom 

 area. Fifteen per cent of the bottom area is covered with sand or sandy silt, 

 the remaining 25 per cent with silts. Clayey mud forms only 1 per cent of the 

 bottom area. There is a great predominance of silica and alumina in the 

 chemical composition of typical Barents Sea soils (Table 31). 



Table 31. Typical percentage compositions of floor of Barents Sea 



* Bottom sediments formed of grains less than 001 mm in diameter are called the fine 

 fraction. 



