22 GOLDBEKG [CHAP. 1 



the profiles show a clear surface depletion which is explained by an incorpora- 

 tion of radium into organisms and a subsequent release at depth during the 

 oxidative decomposition of the biomass. Koczy and Titze (1958) found the 

 highest radium contents (0.275 x lO" 12 g of Ra/g of sample) in fresh plankton 

 composed primarily of diatoms. This number is several orders of magnitude 

 higher than normal sea-water concentrations (10 -16 g of Ra/ml). 



The diffusion of radium from the sediments is supported by a number of 

 examples indirectly indicating the migration of radium within the sediments 

 (Arrhenius and Goldberg, 1954; Kroll, 1953). But more definitive evidence 

 arises from studies of radioactive equilibrium in the 238 U series in deep-sea 

 cores. Table VII gives the 2 30Th and 210 Pb activities as a function of depth in 

 Core Monsoon 49G (14° 27'S, 78° 03'E ; 5214 m depth). It is evident that 

 210 Pb is not in radioactive equilibrium with ionium down to depths of 15 cm. 

 The only nuclide between these two series members whose half-life is long 

 enough to allow diffusion is radium. 



Table VII 



Ionium ( 230 Th) and 210 Pb Activities in the Leachates from Core Monsoon 49G 

 (14° 27'S, 78° 03'E ; 5214 m depth) 



11 Disintegrations per minute per gram. 



Attempts to calculate the rate of diffusion of radium in sediments were made 

 by Koczy and Bourret (1958) on the assumption of constant rates of sediment 

 precipitation, radium accumulation and radium diffusion. In a single core they 

 obtained a value of radium diffusion of 10" 10 g of Ra/m 2 /yeai\ a value nearly 

 identical with the results of the eddy diffusivity calculations. 



Although a definitive knowledge of the composition of the oceans in past 

 times is lacking, all evidence derived from chemical, geological and biological 

 reasoning suggests that at best only modest deviations from the make-up of to- 

 day's water have taken place (Rubey, 1951). Recent experimental approaches 

 to delimiting such changes have centered about two bases : the variations in 



