80 MIYAKE [CHAP. 3 



the Pacific, the total amount of 90 Sr due to the direct injection and immediate 

 fallout up to 1960 would have been roughly 4-5 megacuries. Miyake and 

 Saruhashi (1960) estimate that the contaminated area in the North Pacific 

 from flowout of radioactivity is about 3 x 10 7 km 2 , which is equal to about 20% 

 of the sea surface of the Northern Hemisphere. 



The average activity in sea-water in the contaminated area would be about 

 1.5-2 (j.(xc/l. including delayed fallout assuming the depth of thermoclire as 

 100 m. Analytical results on 90 Sr in sea- water in the Atlantic obtained by 

 Bowen and Sugihara (1957) ranged from 0.016 to 0.2 u,[i.c/l. during the period 

 from 1956 to 1958. On the other hand, North Pacific waters from 1957 to 1959 

 showed 0.7-2.3 y.[icj\. (Miyake et al., 1960). These latter values are in good 

 agreement with the above estimations. 



Table II 



The Results of Radiochemical Analysis of Sea-Water at 12° 18'N, 161° 03'E, 

 on June, 1954, in the North Pacific (Miyake and Sugiura, 1955). Values for 



December, 1954. 



Miyake and Sugiura (1955) carried out analyses for certain other radioactive 

 nuclides, artificially produced in sea-water collected at 12° 18'N, 161° 03'E, 

 about 450 km northeast of Bikini in June, 1954. The results are shown in 

 Table II. 



The fourth column of the table gives the percentage of the total activity for 

 certain fission products 210 days after the slow neutron fission of 235 U. Note 

 that in sea-water the relative amounts of the rare earths were remarkably 

 enhanced, while those of Zr and Sr were much lower. 



Bowen and Sugihara (1957) also found an excess of 144 Ce in relation to 90 Sr 

 both in the North and South Atlantic. The same tendency was confirmed in 

 the Pacific surface waters by Harley (1956). Based on these findings, Ketchum 

 and Bowen (1958) suggested the possibility of the retention of 144 Ce in surface 

 waters by microplankton. However, Bowen and Sugihara (in lift.) subsequently 

 observed that, in the Atlantic, wherever high 144 Ce: 90 Sr ratios were found, 

 the 144 Ce : 147 Pm (half-life, 2.6 years) ratio showed the mixture to be young. 

 They concluded that the radioactive rare earths are removed from the surface 

 layers of the Atlantic at higher rates than 90 Sr, while in the Pacific the balance 



