[. CHEMISTRY 



1. THE OCEANS AS A CHEMICAL SYSTEM 



E. D. Goldberg 



One hundred years ago Forchhammer (1865) elegantly posed the theme of 

 marine chemistry : "Thus the quantity of the different elements in sea water is 

 not proportional to the quantity of elements which river water pours into the 

 sea, but inversely proportional to the facility with which the elements in sea 

 water are made insoluble by general chemical or organo -chemical actions in 

 the sea." Since this time the many complex chemistries involved in giving sea- 

 water its rather curious composition have been investigated by workers from 

 the varied branches of marine science. Inroads have been made through a 

 number of complementary attacks which may be systematized into four groups : 

 (1) the speciation and isotopic compositions of elements in sea- water; (2) the 

 relative reactivities of the elements ; (3) the chemical reactions in the oceans 

 and the compositions of the end-products ; and (4) the spatial and temporal 

 distributions of the reactants and products. It is the purpose of this presenta- 

 tion to elaborate upon the hypothesis of Forchhammer by consideration of 

 examples and problems from these four types of studies. 



1. The Composition of Sea-Water 



Table I purports to give the average composition of ocean water, although 

 such a tabulation suffers from a number of deficiencies (Goldberg, 1957). First 

 of all, many of the values are from a single set of analyses of surface waters, 

 samples possibly quite uncharacteristic of the marine hydrosphere as a whole. 

 The upper 100 m or so, containing only a few per cent of the volume of the 

 oceans, form an environment for intense biological activity which can cause 

 large-scale fractionations of certain materials (see Chapter 2 by Redfield, 

 Ketchum and Richards). Elements involved in the biochemical cycles, such as 

 iron and silicon, can differ from one water-mass to another by a factor of 10 3 or 

 even higher. Finally, some of the analyses failed to assay all of the various 

 forms, dissolved and/or particulate, of the element in question. Since chemical 

 reactions in the oceans take place at phase discontinuities, namely the 

 atmosphere-hydrosphere, biosphere-hydrosphere or sediment-hydrosphere, a 

 knowledge of the chemical make-up of the water at the reaction site is critical 

 for significant studies. 



In spite of these limitations such a listing is important for initial considera- 

 tions of the speciation of elements in sea-water. To consider equilibrium 

 reactions in the oceans, as well as to gain an insight into the stability of various 

 dissolved species, a knowledge of the forms in which the reacting elements 



[MS received October, 1961] 3 



