158 



[cHAr. 7 



more or less uniform area, single individual measurements reflect the im- 

 mediate situation found in this big mass of water. Berge (1958) has presented a 

 considerable series of measurements from the Norwegian Sea made during a 

 relatively short time. He showed that the rate of primary production may be 

 treated in a way similar to that used for chemical and physical properties (see 

 Fig. 19). Horizontal displacements of the water are of little importance near the 

 centre of a big water-mass. It is only necessary to make enough measurements 



Production 

 g C /m'/d*jf 



Fig. 19. Primary production in g C/day below 1 m 2 of the surface. Norwegian Sea, June, 

 1954. (After Paasche, 1960.) 



throughout the year in order to be able to follow the seasonal fluctuations. 

 Measurements made twice a month — as on the Danish light-vessels — must 

 ordinarily be considered sufficient. Even measurements made once a month 

 give at least a general idea of the situation. 



If, on the other hand, the station is situated near the border of two different 

 water-masses, variations from day to day may be very pronounced depending 

 on which water-mass predominates. During experiments at the northern 

 entrance to the sound off Elsinore (see Steemann Nielsen, 1937), the rate of 



