CHEMISTRY IN THE OCEANS 593 



on the nodules by previous investigators, possibly with not enough 

 elegance, and not found, the enthusiasm of the adherents of 

 biochemical theories has not been dampened. 



The alternate hypothesis that the organic matter in the nodules 

 was adsorbed from sea water appears plausible. The ferroman- 

 ganese minerals possess rather high specific surface areas, ranging 

 from 6 to 190 mVg (Buser and Griitter, 1956), reactive sites 

 capable of the uptake and retention of organic phases. Further, it 

 is conceivable that bacterial activity does take place at such 

 surfaces and that benthic organisms might not be attracted to 

 such material. But an extension of such thought to a direct 

 biological deposition at the present time seems unwarranted. 



On a biochemical basis, it is very difficult to account for the 

 relative proportions of certain metals in these minerals, two in 

 particular, cobalt and cerium. Cobalt exists in sea water at a 

 concentration of about one-seventh that of nickel (Taivo Laevestu, 

 personal communication) on the basis of recent, refined analyses. 

 Although cobalt and nickel show a strong geochemical coherence 

 in behavior during the major sedimentary cycle, the ferroman- 

 ganese phases contain nearly as much cobalt as nickel on the 

 av^erage (Table IV). Cobalt shows a wider spectrum of concen- 

 trations in nodules than does nickel. 



An explanation for these abundances may well be found in the 

 greater ease of oxidation of cobalt from the divalent to the tri- 

 valent state. The oxidation potential of cobalt for such a reaction 

 is slightly higher than that for manganese and the free energy of 

 the reaction, using typical marine concentrations, appears to be 

 positive, i.e., the reaction should not proceed. However, a com- 

 bination of the cobalt and manganese oxidation reactions to form 

 a solid solution of the cobalt oxides in the manganese dioxides 

 gives a thermodynamically possible reaction, which could result 

 in a fractionation of cobalt over nickel. Where the redox potential 

 of the environment is relatively low, the cobalt/nickel ratios of 

 sea water would be expected in the nodules, as only the divalent 

 ions are involved. Thus, the cobalt/nickel ratios may well be a 

 sensitive indicator of the oxidation environment in the vicinity 

 of ferromanganese mineral formation. 



Cerium, one of the rare earths susceptible to oxidation to a 



