824 



KOCZY 



[CHAP. 30 



processes near the sediment-sea-water interface will have to be carried out to 

 obtain better understanding of the radium release. 



Radium is also built into carbonate shells (Koczy and Titze, 1958). The 

 radium content varies between 0.014 to 0.136 x 10~i2 g/g. The highest radium 

 content was found in a fresh plankton sample mainly composed of diatoms that 

 contained 0.275 x 10~i2 g/g. It is, therefore, evident that the radium content 

 of sea-water is depleted in the surface layer by incorporation in organisms and 

 may be released by solution of the organisms when they are slowly sinking in 

 the ocean. Further investigation of the effect of this process on radium distri- 

 bution has to be made. 



1/ = 1 X 10~2 cm year ^ 



3 

 Years (x 10^) 



Fig. 6. The distribution of radium with the depth m a sediment layer. The settUng rate of 

 the sediment is assumed to be constant at 1 x 10~3 cm per year. It is further assumed 

 that a constant amount of radivim diffuses out from the sediment into the ocean water 

 and the rate of ionium precipitation is constant during the time and corresponds to 

 the total ionium produced in the water column of average depth containing 3 x 10~6 

 grams uranium per liter. The different curves indicate the distribution assuming 

 different rates of diffusion from D = to D= 10 cm^ per year. The depth in the sedi- 

 ment is given as the time when the respective layer of sediment was settling. 



D. Carbon-14 and Beryllium 



The composition of sea-water with respect to carbon-14 has been rather 

 intensely studied and a summary is given by W. Broecker in Volume 2 of this 

 work (Chapter 4). Carbon-14 enters into carbonate shells formed in the ocean 

 in a certain ratio to carbon- 12 which is determined by isotopic fractionation. 



Beryllium- 10, which is added to the ocean from the atmosphere, follows the 

 geochemistry of beryllium in ocean water. No specific survey has been carried 

 out, but it can certainly be assumed that the main part of beryllium contained 

 in deep sediments has been transported in mineral resistates and only a small 



