2. THE INFLUENCE OF ORGANISMS ON THE COMPOSITION 



OF SEA- WATER 



A. C. Redfield. B. H. Ketchum and F. A. Richards 



1. Introduction 



A number of components of sea-water enter into biochemical processes to 

 such a degree that their concentrations are highly variable when compared to 

 the total salinity. Whereas the distribution of the major constituents of sea- 

 water are to be accounted for on physical and geochemical principles, addi- 

 tional considerations of a biological nature need to be taken into account where 

 the biologically active components are concerned. Since the changes in such 

 components may take place rapidly, relative to the life of a water mass, their 

 study can illuminate the physical description of the sea. 



The object of this chapter is to discuss the special considerations which are 

 required for this purpose. They are of two sorts ; the stoichiometric relations 

 which arise from the specific composition of marine organisms, and the dynamic 

 equilibria between biological and physical processes which determine the 

 concentration of elements present at any point in the sea. 



The influence of organisms on the composition of sea-Avater is determined 

 by physiological influences and consequently exhibits the regularity inherent 

 in organic processes. Elements are withdrawn from sea-water by the growth of 

 marine plants in the proportions required to produce protoplasm of specific 

 composition and are returned to it as excretions and decomposition products 

 of an equally specific nature. While significant differences may occur in the 

 requirements of different individuals and species, the statistical effects pro- 

 duced by the entire population present in any body of water have some regu- 

 larity. Furthermore, ecological principles indicate that certain similarities will 

 occur in populations of any sort when one considers the proportionate activity 

 of the primary producers and of the predators, which occupy later positions in 

 the food chain. 



The dissolved components of sea -water are transported from place to place 

 by advection and move from one parcel of water to another by eddy diffusion. 

 These agencies act equally on all dissolved constituents of the water and their 

 effects may be traced by measuring the concentrations of any one of the con- 

 stituents, such as the chlorides. The biologically active constituents may move 

 from one water layer to another in additional ways : namely, by the sinking of 

 organized matter under the force of gravity and by the active vertical migra- 

 tion of organisms. Such movements of organic matter from one water layer to 

 another provide a fractionating mechanism by means of which the difference 

 in the distribution of conservative and nonconservative properties of sea-water 

 may be explained. 



Because of fractionation the biologically active elements circulate in a 

 different pattern than does the water itself or its inactive solutes. We may 

 speak of a biochemical circulation as distinct from, though dependent on, the 

 physical circulation of the water. Since the elements required for the construc- 

 tion of protoplasm are drawn from the water in proportions which have some 



[MS received August, 1960] 26 



