SECT. 1 | THK tNFLUENCE OF ORGANISMS ON THE COMPOSITION OF SEA-WATER 27 



uniformity, they are distributed in somewhat similar patterns by the bio- 

 chemical circulation. 



2. The Biochemical Cycle 



The exchange of chemical elements between sea-water and the biomass is a 

 cyclic process. The cycle may be broken down into two phases, synthesis and 

 regeneration. Elements are withdrawal from the water during the synthetic 

 phase by photosynthesis in the proportions required for the grow T th of the 

 primary producers, which are predominantly the phytoplankton. These 

 elements are ultimately returned to the water in the regenerative phase as the 

 decomposition products and excretions of both the primary producers and 

 the subsequent members of the food chain which prey upon them, including 

 the microorganisms which complete the decomposition of organic debris. 



Oxygen occupies a unique position in the biochemical cycle because this 

 element is set free in the course of photosynthesis. The concentration of oxygen 

 consequently increases in the water when synthesis takes place and this oxygen 

 becomes quantitatively available for the subsequent oxidation of the products 

 of this synthesis. 



A . The Elementary Composition of Plankton 



The proportions in which the elements of sea-water enter into the bio- 

 chemical cycle is determined by the elementary composition of the biomass. 

 Since the plankton comprises the bulk of the biomass these proportions are 

 indicated by the analysis of plankton samples. Earlier analyses of net plankton 

 by Redfield (1934) were substantiated by more extensive data assembled by 

 Fleming (1940) who obtained the atomic ratios for the principal elements present 

 in the organic matter given in Table I. The elementary composition of the zoo 

 plankton and phytoplankton is very similar and the average ratios may be 

 taken as representative of the biomass as a whole. 



Table I 

 Atomic Ratios of the Principal Elements Present in Plankton 



X 



Zooplankton 103 16.5 1 



Phytoplankton 108 15.5 1 



Average 106 16 1 



The oxygen set free in the synthesis or consumed in the decomposition of 

 the biomass would be 212 atoms for each atom of phosphorus if the oxidation 

 of carbon alone were considered. If, in addition, four atoms of oxygen are con- 

 sumed in oxidizing each atom of nitrogen, the oxidative ratio for phosphorus, 



