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



Table 22 



direct contact with the Atlantic waters. Thus owing to a more or less complete 

 ice cover pelagic life of the central parts of the Arctic basin is very poor ; 

 V. Jashnov thinks that its average biomass does not exceed 10 to 30 mg/m 3 . 

 It is richer in coastal waters, but here too it grows poorer gradually as one 

 moves eastward. 



According to V. Jashnov the sum total of the plankton biomass of the 

 central part of the Arctic basin is equal to 50 to 70 million tons, in the seas 

 bordering Siberia together with the Barents and White Seas also approxi- 

 mately 50 million tons, while the whole Arctic Ocean including the Green- 

 land Sea contains about 150 million tons. 



Exceedingly interesting observations on the seasonal changes in the com- 

 position of biomass and of the plankton of our Polar seas were carried out by 

 V. Bogorov during the remarkable cruise of the icebreaker Litke in 1934, when 

 all the Siberian seas beginning with the Chukotsk Sea and ending with the 

 Barents Sea were traversed in a single voyage (3 July to 18 September). 



Biological seasons of plankton 



As V. Bogorov has shown (1938, 1939) it is difficult to establish a direct con- 

 nection between the distribution of the plankton biomass in the seas on the 

 edge of the Arctic basin and the variations of temperature and salinity ob- 

 served in them. On the other hand at the ice fringe there can be observed 

 everywhere a very rich development of plankton and a huge preponderance 

 of phytoplankton (bloom) over zooplankton (Fig. 5). But in the region of 

 solid ice zooplankton always preponderates over phytoplankton. In open 

 water, sufficiently far from the ice fringe and from the mouths of rivers, the 

 animal and vegetable parts of the plankton biomasses are almost equal. At 

 the mouths of rivers where fresh and saline waters meet, a huge development 

 of plankton, with a preponderance of its vegetable part, is observed. 



Leaving aside this last increase of plankton at the mouths of rivers, caused 

 by the outflow of a mass of plant food and detritus in the river waters, the 

 regularity of the quantitative development of plankton and its two main 

 parts in the Arctic seas is determined, according to V. Bogorov, by the change 

 of the three main seasonal phases in the annual cycle of plankton. During the 

 period of ' biological winter' plankton is poor (less than 200 mg/m 3 ) and the 



