Manganese nodules and oceanic radium 34 1 



OCEANIC RADIUM 

 The early hypotheses, put forward by Joly and other early workers m the licld. 

 for the origin of deep-sea radium, have not withstood later criticism. This applies 

 also to other explanations for the surprisingly high radium content in the deepest 

 deposits. 



(A) A precipitation of radium as insoluble sulphate from the water (Joly). 



(B) A production in situ from the uranium present in the sediment (Joly). 



(C) A cosmic origin of the radium, like that of the cosmic spherules (Murray). 



(D) A magmatic origin from submarine volcanoes (Murray). 



(E) A biological extraction from sea water by plankton organisms (Evans, et a/., 

 1938). 



Only the two last alternatives need to be considered seriously. The possibility 

 that some of the deep sea radium is actually derived from volcanoes on the ocean floor 

 cannot be denied. In several instances abnormally high radium values have been 

 found both in the Tyrrhenian Sea and in the equatorial Atlantic, for which a magmatic 

 origin seems probable. That radium to a certain extent becomes adsorbed by marine 

 plankton has been supported by measurements in Goteborg and elsewhere. However, 

 this biological extraction and subsequent transfer to the bottom deposits with 

 siliceous or calcareous tests cannot be a major cause of the high radium content in 

 deep-sea deposit. Such " unsupported " radium must have a highly transient existence 

 in the very uppermost surface layer of the deposit. 



In order to find a better explanation for the high radium content in the Red Clay 

 and in the Radiolarian Ooze, found by Joly and confirmed through my own measure- 

 ments, teamwork on the radioactive elements present in ocean water was started by 

 me over 20 years ago in Goteborg in collaboration with specialists from Vienna and 

 Oslo (1939). By a special technique, extraction of radium from large-volume samples 

 of sea water (20-40 litres), through co-precipitation with radium-free sulphate of 

 barium, dependable values for the radium content were obtained. They turned out to 

 be surprisingly low, in general less than one unit of the 13th decimal place. At the 

 same time, accurate measurements of the content of uranium in sea water were, for 

 the first time, carried out by means of a fluorescence method, developed by Hfrnegger 

 and Karlik (1935) of the Institut fiir Radiumforschung in Vienna. Their results 

 indicated a fairly constant uranium content averaging 1 -3 ■. 10" gr uranium per Hire 

 sea water of normal salinity (357„ J. In a state of radioactive equilibrium this uranium 

 content would correspond to over 0-4 X lO-^^ g Ra per litre of sea water, or to 

 6 times more than the radium actually found. 



In order to explain this partial disappearance of radium from the sea water, I 

 suggested in 1937 (1938), that its parent element, ionium, is being constantly removed 

 from the water through a co-precipitation with ferric hydroxide, which is known to 

 go on in the sea. This transfer of the ionium produced from dissolved uranium to the 

 ocean bottom would explain the high radium content in deep-sea deposits as due to 

 ionium-supported radium. From this ionium-precipitation hypothesis it would 

 necessarily follow that the radium content in the deposit should increase to a near- 

 surface maximum, attained about 9,000 years after precipitation, characterized by a 

 radioactive equilibrium between ionium and radium. From there downwards in the 

 sediment the content of the two elements should decrease together, according to the 

 half-value period of ionium, about 82,000 years. 



