Table 2 



Chemical Reactions Controlling the Concentration 



of Major Constituents in Seawater 



only 10'^ moles of calcium are deHvered to the ocean each year by 

 rivers. Thus, more than 90% of the carbonate precipitated each year 

 must redissolve if the ocean is to maintain a constant composition 

 (Chave and Smith, 1972). It is not at all clear where this resolution 

 occurs. 



Reaction 2. Seawater is about one-fifth saturated with respect to 

 gypsum. Thus, for this reaction effectively to remove SOj- from sea- 

 water, significant evaporation must occur. There appear to be too few 

 marginal hypersaUne seas in the modern oceans to affect significantly 

 the SOr^ concentration in the ocean. Perhaps in the past this mechanism 

 was more effective. 



Reactions 3 and 4. Anoxic conditions are necessary for the reduction 

 of sulfate to sulfide and for the precipitation of metal sulfides. Although 

 Bemer (1971) presents some thermodynamic data on the metastable 

 ferrous sulfides, there is still much to be learned. Precipitation of hydrous 



9 



