GENERAL CHARACTERISTICS OF THE NORTHERN SEAS 



45 



cus there are large amounts of Metridia longa (II). These two species together 

 form 90 per cent of the total plankton biomass. The total biomass is about 

 90 mg/m 3 . 



In the upper layers of the northern part of the Kara and Laptev Seas 

 Calanus finmarchicus (not exceeding 60 per cent of the total biomass) is still the 

 main constituent of the plankton, but С hyperboreus (III) is mixed with it to a 

 considerable extent and, what is of special interest, in the deeper layers there 

 is a considerable admixture of forms penetrating from the north along the 

 troughs from the warm intermediate layer of the Arctic basin, such as 



Fig. 6. Distribution of main types of zooplankton in northern seas (Jashnov, with 



certain alterations). 

 /, // Pronounced predominance of Calanus finmarchicus (90 per cent of biomass ; 

 many boreal forms present) ; /// Predominance of Calanus finmarchicus (not more than 

 60 per cent of total biomass) and C. hyperboreus ; a considerable admixture of Atlan- 

 tic forms from intermediate layer; /^Predominance of Pseudocalanus elongatus and 

 a selection of brackish- water forms ; V Same as IV but with an admixture of Pacific 



Ocean forms. 



Pareuchaeta norvegica and P. glacialis, Conchoecia elegans, Themisto abys- 

 sorum, Eukrohnia hamata, Diphyes arctica and others. The plankton of the less 

 saline littoral waters of the bordering seas is characterized by the great pre- 

 dominance of brackish forms. The sea form of Pseudocalanus and brackish- 

 water Limnocalanus ghmaldi, Drepanopus bungei and Derjuginia tolli (IV) are 

 predominant here. All these copepoda crustaceans comprise 60 per cent of 

 the plankton biomass. About 20 per cent of the plankton consists of Sagitta 

 elegans, mixed with a considerable quantity of fresh- water forms. 



Finally in the southern part of the Chukotsk Sea, as a result of an increase 

 of salinity, the brackish-water forms are becoming rare. Pacific Ocean forms 

 are found here but, as has been noted by V. Jashnov (1940), they do not play 

 any substantial role in the biomass (V). 



