herring. 



Annual Fluctuations in the Envelopment of Plankton 



During a number of years while observing the production of plankton in the Norwegian cind 

 Barents Seas, many researchers noticed considerable fluctuations in the time of the development 

 of various complexes of plankton as well as in the composition and amount of planktonlc organisms. 



Most scientists link these phenomena directly with the changes in the flow of Atlantic waters 

 into these seas /Linko (16); Eteryugin (9); Virketis (7, 8); Boldovskiy (5)7- 



B. P. Manteyfel' (19) is of the opinion that a number of factors influences the composition of 

 plankton and the time of its development: The annual "pulsations" of the North Cape branch, solar 

 radiation within the confines of the Barents Sea, the times of the atmospheric spring, the water 

 run-off from the land, consumption of the plankton, etc. 



Observing the composition of plankton for many years made it possible to establish that the 

 years of the greatest influx of warm Atlantic waters into the Barents and Norwegian Seas are char- 

 acterized by the appearance of large numbers of thermophilic representatives of plankton such as 

 CoUozoum , Physophora hydrostatica , Meganyctiphanes norvegica , Nematoscellis megalops , 

 Tomopteris . 



In connection with this the thermophilic organisms are carried by the current far to the 

 north and to the east. It is known that the North Cape and the Norwegian currents are not mono- 

 lithic currents; but, following the bottom contour, they divide into a number of branches or arms. 

 The intensity of the flow of Atlantic waters along the various branches or arms of the currents in 

 the Barents Sea as well as in the Norwegian Sea changes or varies from year to year. Helland- 

 Hansen and Nansen (37), on the basis of oceanographic observations in 1900-1904, have already 

 written about the existence of annual fluctuations in the temperature conditions of the waters in the 

 Norwegian Sea. 



Their hypothesis, as mentioned above, about more favorable conditions for plankton devel- 

 opment in cold years is confirmed also by our observations . It seems that a larger influx of waters 

 from the polar region, which contain a large amount of nutritive substances, creates conditions in 

 the Norwegian Sea in cold years that are conducive to an abundant production of plankton and, sub- 

 sequently, to a rapid fattening of the fish. 



Figure 7 shows how great the fluctuations can be in the amount of plankton for the same 

 month in different years. For a comparison, we took cross sections that cut across the two main 

 branches of the Norwegian current: The eastern (at the latitude of Bear Island) and the North Cape 

 branch (following the Kola meridian). Plankton was collected from these cross sections or profiles 

 every year during the second half of June (the period of the maximum production of plankton in those 

 regions). 



Comparing the curves shows that their general character is retained from year to year . 

 Their peaks correspond to the increase in the amount of plankton in the branches of the current. 

 The position of the separate branches of the Norwegian current remains unchanged. But the amount 

 of plankton in them for the same period in different years can change considerably. It is character- 

 istic that in years of a maximum production of plankton in the waters of the eastern branch of the 

 Norwegian current, the amount of plankton often becomes less in the waters of the North Cape cur- 

 rent (1948) and, on the other hand, when the biomass of plankton becomes larger in the Barents Sea, 

 then the biomass of plankton becomes smaller in the Bear Island- Spitsbergen region (1950). There 



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