42 



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

 Table 13 



water column. The nearer the Pole, the weaker is the vernal outburst and the 

 sooner it passes. In the seas adjacent to the Pole this lasts no more than a 

 month (August), but farther south the vegetation period is longer: in the 

 central part of the Kara Sea it lasts nearly three months, while in the south- 

 west of the Barents Sea it continues for about eight months (Fig. 5). 



Although in the circumpolar part of the Arctic basin there is only a 'spring' 

 in the development of phytoplankton, in the Kara and Laptev Seas there is 

 also a ' summer', while in the Barents Sea there is an ' autumn', and the vegeta- 

 tion period lasts from April till November. 



However luxuriant the development of phytoplankton, if its vegetation 

 period is of short duration, its production will be small. The maximum phyto- 

 plankton biomass at any single time in our Arctic seas may sometimes be 

 expressed by very high rates — from 6 to 14 g/m 3 even in the East Siberian and 

 Laptev Seas. Nevertheless this cannot in any way be considered as a measure 

 of the high productive capabilities of these bodies of water. The average values 

 for a layer thirty metres thick are more truly indicative. The true value of 

 annual production is well demonstrated by a conventional index (the product 

 of the average biomass during observations times the length of the vegetation 

 period in months, divided into 12 months — Table 14) introduced by P. 

 Usachev, especially in comparison with similar indices for the southern seas. 



Table 14 



