SECT. 1] 



THE OCEANS AS A CHEMICAL SYSTEM 



11 



For such elements, one can expect varying degrees of accumulation in solu- 

 tion going from ocean to ocean or water-mass to water-mass. Goldberg and 

 Koide (1962) have pointed out that the thorium contents of authigenic minerals, 

 presumably reflecting the thorium input to the overlying waters, vary as a 

 function of geographic location. The thorium concentrations were normalized 

 to ionium, 230 Th, whose rate of production in sea-water is essentially constant 

 owing to the uniform distribution of its radioactive predecessor, 238 U. Hence, 

 variations in the 23oxh/ 232 Th ratio can be attributed to differences in the in- 

 puts of 232 Th to different water-masses. A measure of the thorium introduced 

 into oceanic areas may be found in considerations of the relative amounts of 

 continental run-off waters. Lyman (1959), using the data of L'Vovich, gives the 

 areas of the oceans and the respective values of the areas draining into them 

 (Table III). The Pacific Ocean receives but one-sixth of the drainage accepted 

 by the Atlantic on an areal basis. Thus, the amount of thorium entering the 

 Atlantic per unit area per unit time can be assumed to be greater than that 

 going into the Pacific. 



Table III 



Surface Values of the Ionium/Thorium Ratio and Thorium Concentrations in 

 Marine Sediments Compared with Oceanic Areas and the Land Areas Draining 



into Them (Lyman, 1959) 



It is quite clear from the data of Goldberg and Koide in Table III that the 

 relative rate of thorium introduction (normalized to ionium production) into 

 the Atlantic exceeds that of the Pacific. 23oxh/ 232 Th ratios for surface authi- 

 genic minerals vary in the Pacific between 16 and 158 while the Atlantic values 

 span a range of 1.5-19 (in units of disintegrations per unit time of 230 Th/ 

 disintegrations per unit time of 232 Th). The well known observation that more 

 and larger rivers drain into Northern Hemispheric areas is reflected in the 



