SECT. 2J PRODUCTIVITY, DEFINITION AND MEASUREMENT 161 



influence the measurement of primary production very much during the 

 summer. However, an exception exists. If the bulk of the planktonic algae is 

 concentrated near the lower boundary of the photic zone, a situation found 

 under certain hydrographical conditions, photosynthesis will take place at the 

 very low light intensities where, even in the shade-adapted algae, the rate of 

 photosynthesis is directly proportional to the light intensity. Therefore, the 

 rate of photosynthesis (gross production) per surface unit is virtually propor- 

 tional to the radiation penetrating the sea surface. In the winter at higher 

 latitudes the situation is the same. It has been found in Danish waters 

 (Kattegat) that, in years with an exceptional number of bright days during 

 December, a considerable stock of algae remains in the water until the New 

 Year ; they maintain a high rate of photosynthesis on the bright days. During 

 years with relatively few bright days in winter the phytoplankton almost 

 disappears during December (unpublished data). 



In the winter at higher latitudes the light conditions prevailing on the 

 particular days of investigation are always of decisive importance for the rate 

 of production found. Fortunately, in the winter, the rates ordinarily found are 

 so low that even considerable deviations from the average values would only 

 slightly influence the rates of primary production computed for a whole year. 



References 



Anderson, E. C. and W. F. Libby, 1950. World-wide distribution of natural radiocarbon. 



Phys. Rev., 81, 64-69. 

 Atkins, W. R. G., 1922. The hydrogen ion concentration of sea water in its biological 



relations. J. Mar. Biol. Assoc. U.K., 12, 717-753. 

 Atkins, W. R. G., 1923. The hydrogen ion concentration of open sea water and its variation 



with depth and season. J. Mar. Biol. Assoc. U.K., 13, 754-771. 

 Bauer, G., 1957. Die Ausniitzung der Sonnenenergie durch das Phytoplankton eines 



eutrophen Sees. Inaugural Dissertation, Miinchen. 

 Berge, G., 1958. The primary production in the Norwegian Sea in June, 1954, measured 



by an adapted 14 C technique. Rapp. Cons. Explor. Mer, 144, 85-91. 

 Bernard, F., 1958. Donnees recentes sur la fertilite elementaire en Mediterranee. Rapp. 



Cons. Explor. Mer, 144, 103-108. 

 Braarud, T., 1958. Counting methods for determination of the standing crop of phyto- 

 plankton. Rapp. Cons. Explor. Mer, 144, 17-19. 

 Brown, A. H., E. W. Fager and H. Gaffron, 1949. Kinetics of photochemical intermediate 



in photosynthesis. In photosynthesis in plants. Monog. Amer. Soc. Plant Physiol., 



403-422. 

 Cooper, L. H. N., 1933. Chemical constituents of biological importance in the English 



Channel. J. Mar. Biol. Assoc. U.K., 18, 677-753. 

 Cooper, L. H. N., 1958. Consumption of nutrient salts in the English Channel as a means 



of measuring production. Rapp. Cons. Explor. Mer, 144, 35-37. 

 Cushing, D. H., 1959. The seasonal variation in oceanic production as a problem in 



population dynamics. J. Cons. Explor. Mer, 24, 455-464. 

 Doty, M. L., 1958. Current status of carbon- 14 method of assaying productivity of the 



ocean. University of Hawaii. MS. 

 Doty, M. L. and M. Oguri, 1957. Evidence for a photosynthetic daily periodicity. Limnol. 



Oceanog., 2, 37-40. 



