62 



Atomic Radiation and Oceanography and Fisheries 



reduces the settling rate, and the shape may 

 vary considerably from the smooth sphere as- 

 sumed for Stokes' Law. 



The particle-size distribution of solids sus- 

 pended in the ocean as shown by sediments is 

 broad, varying from over a millimeter in di- 

 ameter for sands found near shore, to 0.1 micron 

 or less for sediments taken from the open ocean. 

 The median diameter of open-ocean particles is 

 in the range 1 to 8 microns. 



The accumulation of solids on the ocean floor 

 is a relatively slow process. Table 2 (Holland 

 and Kulp, 1952) indicates the rate of sedimen- 

 tation on the several parts of the ocean floor. 



TABLE 2 Sedimentation Rates 



Fraction of sea Sedimentation 



Type of sediment water rate x 10'* 



gm/cm^ per year 



Shelf 0.08 40 



Hemipelagic 0.18 1.3 



Pelagic 0.74 



globigerina\ 



pteropod I ^-^^ 0-5 



red clay 0.28 0.2 



diatom "I ^ , ^ „ , , 



J. , . \ 0.10 0.15 



radiolarian J 



A weighted average gives approximately 0.75 

 mg/cm2 per year for the oceans. If the area of 

 the ocean floor is 3.6 x 10^^ cm^, the total depo- 

 sition will be 2.7 x 10^^ grams or 2.7 x 10^ tons 

 per year. 



Retention 



Prior to actual deposition on the bottom, 

 radioactive solids that have been formed above 

 the bottom may encounter changes in environ- 

 ment that will tend to return them to solution 

 and prevent or hinder deposition. For example, 

 resolution of precipitates with increasing pres- 

 sure (calcium carbonate), releases of radioac- 

 tivity from solids as they fall through uncon- 

 taminated water, vertical migration of organ- 

 isms, and vertical components of circulation are 

 all possible mechanisms that will tend to pre- 

 vent the deposition of radioactive material on 

 the bottom and, when coupled with horizontal 

 circulation features, will tend to disperse the 

 radioactivity over large areas. 



The retention of radioactive material on the 

 ocean floor once it has been deposited there will 

 depend upon the stability of the floor relative 

 to erosion, to further deposition, and to tur- 



bidity currents, and upon the chemical features 

 of the bottom relative to those through which 

 the solids have settled. 



The deep ocean basins are the regions of 

 greatest stability in all respects. Regions near 

 shores and shelves are subject to the greatest 

 variations in deposition and erosion; in regions 

 where rivers enter the seas, relatively wide 

 changes in chemical properties take place. 



Discussion of existing data 



Three sources of information give some 

 insight into the probable behavior of fission 

 product elements in sea water. They are: (1) 

 existing information concerning the solution 

 chemistry of the elements in question, (2) the 

 behavior of radioactive debris observed in con- 

 nection with bomb tests in the Pacific, and (3) 

 information concerning the geochemistry of the 

 elements in question. 



In utilizing information from these sources 

 to assess the probable fate of fission product ele- 

 ments in the oceans the chemical properties of 

 the oceans are of major importance. Table 3 

 lists the elementary composition of sea water 

 together with an estimate of the amounts of 

 natural activities present. 



In Table 4 are listed fission product elements, 

 together with their half lives and the equilib- 

 rium quantities that would be in existence after 

 100 days cooling when formed in connection 

 with 10^^ megawatt hours per year of nuclear 

 power production. Also listed are the specific 

 activities that would result were these activities 

 to be mixed throughout the oceans. It will be 

 obvious from a consideration of oceanic prop- 

 erties, presented in other sections of this re- 

 port, that under any practical method of intro- 

 duction of wastes, attainment of uniform specific 

 activity of any given element throughout the 

 oceans will not occur. There will be gradients 

 of radioactivity, decreasing from the region of 

 introduction. The figures for specific activities 

 are, therefore, unrealistic and are included only 

 as a basis for making a better estimate when 

 the effects of circulation and fractionation can 

 be provided. 



In a few cases, knowledge of the fraction of 

 an element, that would be normally removed by 

 geochemical processes will permit an estimate 

 to be made of the fraction of a radioisotope that 

 will be removed for a given loading. Con- 



