This kind of calculation is less meaningful than one which could be 

 made considering each constituent individually, because seawater is 

 different from river water in the ratios of its various components. The 

 calculation, nevertheless, illustrates the point that the total salt content 

 of the sea can be added in a very short time. It thus raises such questions 

 as. What regulates seawater composition? and. Have such regulatory 

 mechanisms been constant over geologic time periods? 



Careful study of ancient marine sediments, their pore waters and 

 fossils contained in these sediments, give little indication of any changes 

 in seawater composition. Thus, a considerable effort has gone into ex- 

 planations of mechanisms for maintaining a constant composition in 

 seawater. The best known of these are the equilibrium models first 

 proposed by Sillen (1961), and expanded by Holland (1965), Siever 

 (1968), Garrels and MacKenzie (1971), and others. All of these models 

 are somewhat vague in detailing the exact reactions occurring in the 

 ocean, and little evidence has been found to indicate that the suggested 

 reactions are occurring. At the same time, the models have been criticized 

 on theoretical grounds (e.g., Pytkowicz, 1972) and seem not to be 

 consistent with the actual solid phases found at the sea floor. Further 

 work is needed on the interaction of minerals with seawater, as deter- 

 mined from their solubilities and rates of solution and precipitation. 

 The available literature on this topic, including the effects of pressure 

 which are vital for our understanding of the deep oceans, has been 

 summarized in part by Pytkowicz and Kester (1971). 



Broecker (1971) has proposed a kinetic model for the chemical 

 composition of seawater, but he gives few specific examples of either 

 supply or removal mechanisms for the major constituents of seawater, 

 concentrating rather on the biologically active elements carbon, nitrogen, 

 phosphorus and silicon. If we are to extend this approach, we need 

 better data on the rate of supply and removal of various constituents 

 from seawater. As mentioned above, the rate of supply of the major 

 components by river water is not as well known as we would hke. 



The rate of supply of minor constituents dissolved in river water is 

 even more poorly known, and the rates of supply of both major and 

 minor elements as particulate matter and their subsequent release to 

 the water are almost completely unknown. In the same way, the amounts 

 of materials added to the oceans from undersea volcanic exhalations, 

 springs, weathering of solid volcanic material, and the like, can only 

 be grossly estimated at the present time. 



Our knowledge of how dissolved materials are removed from the sea 

 is little better than that of how they are added. The factors involved have 

 been commented on elsewhere in this document (e.g. see Session C), 

 and it is sufficient to note here that well-defined removal mechanisms 

 exist for bicarbonate and calcium but for none of the other major con- 



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