594 CYCLES OF ORGANIC AND INORGANIC SUBSTANCES 



higher state than the normal plus three, is enriched in these 

 minerals relative to its periodic table neighbor lanthanum, which 

 exists solely in the trivalent state. In ferromanganese minerals, in 

 which cerium is apparently oxidized in part to the plus four 

 valence state, the cerium/lanthanum ratio normally is of the 

 order of six, although this value was o\'er an order of magnitude 

 higher in the case of a Triassic nodule from Timor. Whereas in 

 crustal rocks on the earth's surface, the cerium/lanthanum ratio 

 is about three. Hence, it is proposed that the oxidation of cerium, 

 which like that of cobalt is not evident from thermodynamic con- 

 siderations, proceeds through the incorporation of eerie oxides 

 into the manganese dioxide lattice with a coupling of the man- 

 ganous and cerous oxidation reactions. The high concentrations 

 of metals susceptible to oxidation offer a dilemma to any bio- 

 logical hypotheses. Are we to have not only manganese oxidizing 

 capabilities in the organisms but also cerium and cobalt oxidizing 

 capacities? 



I do not wish to leave a picture of chemical reactions on the sea 

 fioor not influenced by the large biomass of the oceans. The plants 

 and animals of the seas are responsible for the most dramatic 

 compositional changes in the oceans. In the surface waters where 

 plant production occurs, carbon dioxide and oxygen, the intake 

 and release gases of photosynthesis, respond to this biological 

 activity. Depletion of the former and supersaturation of the latter 

 are often observed in waters near the surface. Also, the plant 

 nutrients, chemical species of phosphorus, nitrogen, and silicon 

 vary over wide ranges of concentrations both in time and space. 



Barium is one non-nutrient element which shows very positive 

 correlations between concentrations in sediments and biological 

 activity. Concentrations of this element are markedly higher in 

 pelagic sediments below productive oceanic areas than in bottom 

 samples below the more barren seas (Goldberg and Arrhcnius, 

 1958; Goldberg, 1958). The high barium contents are associated 

 with both siliceous and calcareous deposits, although the concen- 

 tration of this element is not markedly high in the siliceous or 

 calcareous hard parts of organisms. The barium is probably 

 accumulated in the sediments through chemical reactions involving 

 the organic debris. 



