SECT. 2 J 



PRODUCTIVITY, DEFINITION AND MEASUREMENT 



157 



is not found during the unproductive parts of the year. Although during the 

 height of summer the rate of primary production is relatively low in certain 

 areas of the north-eastern part of the North Atlantic (about 100 mg C/m 2 per 

 day), the depth of the photic layer does not exceed 60 m. The transparency in 

 the ocean far from the coast reflects not only the actual primary production at 

 the time but also to some extent the production which has previously taken 

 place in the water-mass. 



LEGEND 



__|0% deep blue 

 "" 0-2% blue . 

 '////^ 2-5%blue-^reen 

 > 5 %qreen 



Fijz. 18. Distribution of the colour of the sea. South Atlantic. (After Schott.) 



Fig. 18 (Schott in Hentschel, 1933-1936), showing the distribution of the 

 colour of the sea in the South Atlantic, represents at the same time the rate 

 of primary production. At present it is not possible to publish a much better 

 relative chart for this area (see Steemann Nielsen and Aabye Jensen, 1957). It 

 agrees even in detail with the measurements of primary production — and 

 standing stock of phytoplankton — made in the South Atlantic. 



6. The Significance of Single Individual Measurements of Primary Production 



The significance of single individual measurements of primary production 

 must necessarily vary depending on the area from which the measurements 

 originate. Both variations due to the sequence of seasons and to horizontal 

 displacements of the water-masses must be considered. If a typical seasonal 

 variation is found, as is always the case in the temperate and arctic zones, it is 

 compulsory to make measurements throughout the productive season. 



If a field "station" is situated in the centre of a large and hydrographically 



