THE KARA SEA 



235 



The following biogeographic groups are commonly distinguished in the 

 Kara Sea plankton : 



(7) forms widely distributed throughout the Arctic 



(2) forms of western origin (Atlantic-Barents Sea forms) 



(3) forms belonging to the cold Arctic waters, which have come from the 

 north 



(4) forms of the warm Atlantic intermediate layer of the central part of the 

 Arctic basin 



(5) brackish-water forms 



(6) fresh-water forms. 



Khmisnikova distinguishes four main regions in the Kara Sea according to 

 the distribution of these groups (Fig. 100). 



J X'/'WA 



Fig. 100. Areas of the Kara Sea according to plankton distribution (Khmisnikova). 

 1 Area of penetration of Atlantic and Arctic forms from the north ; 2 Area of pene- 

 tration of Barents Sea forms from the south ; 3 Area of predominance of brackish- 

 water forms ; 4 Area of predominance of fresh-water forms. 



