radiation (below 10 kcal/cni2/month) extends at 60°S from February through 

 the end of November, at 40°S--only from March to early October, two and 

 one half months shorter. 



As the illumination increases, the rate of photosynthesis increases 

 up to a certain limit--to the point of light saturation. This point is not 

 the same at different latitudes (Steemann Nielsen. 1963) or for different 

 groups of algae (Ryther, 1956). Strickland (1958) reached the conclusion 

 that the maximum growth of mixed populations of algae occurs with an 

 intensity of incident radiation of over 0.15 cal/cm2/min, while severe 

 suppression of growth occurs at over 0.5 cal/cm2/min. Using data on the 

 mean monthly radiation (Braginskaya et al . , 1966) and the duration of the 

 light time (Dubovskiy, 1966) to calculate the mean daily radiation, then 

 comparing it with the conclusions of Strickland, we can see that the light 

 factor limits the development of algae at the surface at 60°S from May 

 through August, at 70°C--from April through July. However, in the extreme 

 south, some areas are freed of ice rather late (Fig. 1?), when the 

 illumination is beginning to subside, and as a result of this, the period 

 of optimum light is briefer there. 



A mean daily level of radiation sufficient to suppress photosynthesis 

 is reached at 40°S only in December; further south--it is never reached. 

 Thus, in the first approximation (ignoring daily changes in radiation), we can 



1 xj in I a 



^ r ii a- 



Fig, 12. Variation in position of northern limit of icepack during the 

 course of the year at various meridians (after Eskin, 1966). 



81 



