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



of salinity, especially near the river mouths. Only one period of phytoplankton 

 bloom is observed in the spring ; the autumn one is absent. 



The circumpolar zone with its numerically rich fauna and its considerably 

 increased productivity forms a belt round this pre-polar zone of the northern 

 hemisphere which has an impoverished fauna and a lowered productivity; 

 this belt passes through the northern Atlantic and the northern Pacific. Hydro- 

 logically this zone has the following characteristics : (/) the most favourable 

 conditions for vertical circulation, approaching uniformity of temperature 

 and salinity, (2) a temperature of more than 0°, and (3) a normal sea salinity. 

 The main meeting place of the warm waters moving from the south with the 

 local cold ones is situated in this zone, hence the phenomenon of the 'polar 

 front' develops here with all its consequences. To this given combination of 

 hydrological factors which determine the best conditions for feeding and life 

 processes, there corresponds an increased biomass (for benthos more than 

 100 to 200 g/cm 2 ), a considerable productivity and polymixed communities. 

 Zooplankton biomass, consisting mainly of Calanus finmarchicus, is subject 

 to great fluctuations (from 1-5 to 3,843 mg/m 3 ) and for the southwestern part 

 of the Barents Sea it is, on the average, about 230 mg/m 3 in August. Two 

 maxima of bloom — the spring and autumn ones — are observed in the develop- 

 ment of phytoplankton. 



Moving farther south, beyond the influence of the polar front, we reach a 

 zone with different hydrological and biological characteristics. The hydro- 

 logical conditions of this zone are : (/) a considerably higher temperature of 

 the upper layer of water which creates a thermal stratification in the warm 

 parts of the ocean in such marked degree that the whole nature of the biolo- 

 gical processes is determined by it, and (2) restricted vertical circulation. These 

 regions are characterized by the rich qualitative composition of their popu- 

 lation and their decreased biomass. Conditions for increased biomass and 

 productivity are created only in places with favourable circulation and in the 

 shallows. 



Table 27 gives a typological scheme for the zonation of the northern 

 Atlantic and the polar basin, for the upper layer of the sea (200 to 300 m) due 

 to M. J. Dunbar (1951, 1953). It is drawn up according to particular char- 

 acteristics, both biological (the composition of the population and the pecu- 

 liarities of biological productivity) and hydrological (temperature, mixing). 

 The northern boundary of Dunbar's boreal region coincides with that given 

 by most of the biologists, except that Finmark and the western part of the 

 Murman coast are usually included in the boreal region. Dunbar divides the 

 region to the north of this boundary into Arctic and sub- Arctic zones of life. 

 These two zones on the whole correspond to the division generally accepted 

 in the u.s.s.r. for the Arctic region: the high Arctic sub-region (Dunbar's 

 Arctic) and lower Arctic one (Dunbar's sub-Arctic). We think that there is 

 not sufficient ground to call these two sub-regions independent ecological 

 zones of life on the regional scale. Their population does not possess sufficiently 

 sharp distinctive characteristics allowing them to be separated into categories 

 of a higher order. 



The boundary between the Arctic and sub-Arctic of Dunbar differs in some 



