Papers in Marine Biology and Oceanography. Suppl. to vol. 3 of Deep-Sca Rcscarcn. pp. 335-345. 



Manganese nodules and oceanic radium 



By Hans Pettersson 

 Goteborg 



The manganese nodules found by the Challenger Expedition in great depths have been 

 studied by Sir John Murray and A. F. Renard (1891). They were recognized a.s 

 products of a very slow growth, from manganese dioxide and ferric hydroxide, 

 accumulated round a nucleus, a fragment of waterlogged pumice, or a shark's tooth 

 or some other object lying on the surface of the deposit. Chemical analyses carried 

 out by Brazier et al. proved a considerable number of trace elements like copper, 

 cobalt, nickel, barium and lead to be present in the nodules. Of special interest was 

 their relatively high content of radium first proved through measurements made by 

 J. JOLY (1908). 



As I have been engaged on determinations of the radium present in deep-sea deposits 

 since 1921 (1930; 1939; 1953), and later also of the radioactivity of sea-water, my 

 interest was attracted by the radium contained in the nodules. The close affinity 

 between radium and manganese,* well known from deposits at thermal sources on the 

 continents, is no doubt responsible for the entry of radium into the manganese nodules. 

 Granting this to be the case, I assumed that this radium is " unsupported " by its 

 parent element ionium, in which case it should decay with age and consequently 

 also with the depth below the surface of the nodule, according to the half-value period 

 of radium, about 1,600 years. 



Thanks to the courtesy of the British Museum of Natural History I obtained from 

 their Challenger collections two small nodules, and through a similar courtesy of the 

 Mineralogical Department of the Riksmuseum in Stockholm one half of a much larger 

 nodule, also from the Challenger Expedition. 



The results of my measurements on samples from these nodules, taken from thin 

 layers in the surface and further inwards, confirmed my assumption. The radium 

 content per gram of the samples fell off from a very high value in the uppermost 

 surface, sometimes exceeding 100 units of the 12th decimal place, to a few units 7 to 

 10 mm deeper down. The rate of decline proved to be more rapid on the lower, 

 flattened, side of the nodule, on which it had presumably been lying on the bottom, 

 than on the upper, convex, side which must have been exposed to the settling o\' 

 sediment from above, increasing the rate of growth over the value due only to aggrega- 

 tion into the nodule. The rate of radial growth, calculated from the decrease in 

 radium, proved to be rather less than 1 mm in 1,000 years on the lower side and about 

 50% more on the upper, convex, side (1943). 



The conclusion drawn from these measurements was, thai the radium in ihc nodules 

 is accumulated from the surrounding sediment. These results made it most desirable 

 for me to obtain also other nodules from other parts of the ocean. Through the kind 



* An addition of small quantities of powdered " braunstcin " and a thorough shaking of ihc 

 mixture has been proved through experiments in Goteborg. to be a most elhcient method for extract- 

 ing radium and its isotope ThX from extremely dilute solutions. 



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