SECT. 1 1 THE OCEANS AS A CHEMICAL SYSTEM 23 



the temperature of the oceans with time and the composition of fossil skeletal 

 remains of marine organisms. The utilization of the chemical composition of 

 authigenic minerals to enter such investigations has not as yet been realized 

 but clearly is a most promising possibility. 



Determinations of the 18 0/ 16 ratio in the calcium carbonate tests of 

 Foraminifera have enabled Emiliani (1955) to establish fluctuations in oceanic 

 temperatures during the past. Surface sea-water values have shown variations of 

 about 6°C through the Pleistocene as evidenced from the Caribbean Sea and 

 Atlantic samples. Further, this investigator (1954) has also indicated that the 

 bottom-water temperatures have continuously decreased from the Oligocene 

 through the Miocene into the late Pliocene by about 8°C. Also, it appears that 

 the temperatures were more uniform during the Tertiary. 



Such temperature variations would be accompanied by minor changes in 

 the composition of sea-water. The dissolved gases, whose marine concentrations 

 are in part determined by the temperature at which equilibrium took place in 

 the water-atmosphere system, would show decreasing concentrations with 

 increasing temperatures. Further, the calcium contents, whose levels are regu- 

 lated by the precipitation of calcium carbonate, should have decreased during 

 the warmer period. Bramlette (1961) has pointed out that there would have 

 resulted a more uniform areal distribution of the supply of calcium carbonate 

 from surface waters and also the bottom warm waters would greatly reduce in 

 the Tertiary the solution of calcium carbonate in the deeper deposits. 



The composition of the ocean during the past with respect to certain minor 

 elements which substitute in skeletal materials for the major substances can, 

 in principle, be determined by the analyses upon fossils. For example, Lowen- 

 stam (1959), on the basis of 18 0/ 16 ratios, the Sr/Ca ratios and the MgC0 3 

 contents in fossil brachiopods from times as far back as the Mississippian, 

 asserts that strontium and magnesium abundances have remained essentially 

 constant during the last 2.5 x 10 8 years. 



References 



Altschuler, Z. S., R. S. Clarke and E. J. Young, 1958. Geochemistry of uranium in apatite 



and phosphorite. U.S. Geol. Surv. Prof. Paper 314 D, 90 pp. 

 Arrhenius, G. and E. D. Goldberg, 1954. Distribution of radioactivity in pelagic clays. 



Tellus, 7, 226-231. 

 Barth, T. F. W., 1952. Theoretical Petrology. John Wiley and Sons, New York. 

 Barkley, R. A. and T. G. Thompson, 1960. The total iodine and iodate-iodine content of 



sea-water. Deep-Sea Res., 7, 24-34. 

 Bjerrum, J. C, G. Schwarzenbach and L. G. Sillen, 1958. Stability Constants, Part TI 



(Inorganic ligands). Chem. Soc. Spec. Pub. 7. 

 Bramlette, M. \Y.. 1961. "Pelagic sediments". In "Oceanography", Amer. Assoc. Adv. 



Sci., 345-366. 

 Burst, J. F., 1958. Glauconite pellets: their mineral nature and applications to strati- 

 graphic interpretations. Bull. Amer. Assoc. Petrol. Geol., 42, 310-327. 

 Chow, T. J. and E. D. Goldberg, 1960. On the marine geochemistry of barium. Geochim, et 



Cosmochim. Acta, 20, 192-198. 



