Session A 



Processes and Mechanisms Governing 

 The Inorganic Composition of Seawater 



Dr. Frank J. Millero, Discussion Leader 



INTRODUCTION 



The ocean is commonly considered a steady state system, at least 

 with regard to the major dissolved constituents over long periods of 

 geological time. Furthermore, it appears that throughout most of the 

 ocean the ratios Na/Cl, K/Cl, SO4/CI, Mg/Cl and Br/Cl are constant 

 within analytical precision (Lyman and Fleming, 1940; Culkin, 1965; 

 Culkin and Cox, 1966; Riley and Tongudai, 1967; Riley and Chester, 

 1971). There is conflicting evidence regarding the variability of Sr/Cl, 

 HCO3/CI, B(OH)3/Cl and F/Cl. The variations of Ca/Cl with depth 

 have been well defined. Fluctuations arising from river runoff and 

 freezing are locally significant, and may, such as in the Arctic, include 

 vast geographical areas (see p. 35). The minor elements are potentially 

 more variable in concentration and reactive in the marine environment; 

 however, in most cases reliable analytical data and physical chemical 

 understanding of these variations are lacking. The present status of our 

 knowledge of the chemical composition of seawater and of chemical 

 speciation, as well as needed research, were reviewed previously by 

 Pytkowicz and Kester (1971). 



The processes that control the major composition of seawater must be 

 removal reactions, because the residence times of these elements are 

 shorter than the age of the ocean. Although the equihbria models of 

 Sillen (1961; 1965a,b; 1967a,b), Holland (1965), and MacKenzie and 

 Garrels (1966a,b) have yielded reasonable suggestions as to how sea- 

 water attained its present major composition and how this composition 

 is maintained, many questions exist concerning the mechanisms and 

 processes that regulate the concentrations of all the major and minor 

 constituents. Many questions pointed out by Broecker (197 1), Chave and 

 Smith (1972), and others concerning the effect of the circulation of 

 the world's oceans and the effect of biochemical processes on the com- 

 position of seawater remain unanswered. For example, Pytkowicz 



