RADIUM CONTENT OF OCEAN-BOTTOM SEDIMENTS 



187 



76,000 times its weight of sea water. If the uranium in 

 this bulk of water were taken into the shelly limestones, 

 their radioactivity would be much greater than it is 

 found to be. If the concentration is brought about by sea 

 organisms one would expect to find some connection be- 

 tween the radium content and the character of animal 

 remains comprising the sediment. Examination of the 

 tables and the map does not support this reasoning. Al- 

 though a few high figures are associated with Globiger- 

 ina or radiolaria deposits, the red clays, which are 

 predominantly mineral in composition, show more con- 

 sistently higher radium contents. If we confine our av- 

 erages to the more recent analyses, we arrive at the 

 figures given below: 



27 red clays average 12.1 x 10-^2 grams Ra per gram; 

 13 Globigerina oozes, 4.1 x 10-12 grams Ra per gram 



The uranium in the sea water must come ultimately 

 from the igneous rocks. It exists in the water in solu- 

 tion, and some process is operating to remove it from 

 this solution and to cause it to accumulate in the bottom 

 sediments at a concentration considerably greater than 

 in the igneous rocks. 



The fact that the radium concentration falls off near 

 shore and there approaches more or less the concentra- 

 tion found in sedimentary rocks, indicates that the pro- 

 cess is notone of detrital accumulation or sedimentation. 

 Furthermore, the fact that the higher concentration is 

 found in the red clays, which are assumed to accumulate 

 very slowly and the minerals of which are thought to be 

 largely formed in place, indicates that the skeletal re- 



mains of organisms tend to dilute an otherwise higner 

 concentration. 



Pettersson (1930, pp. 41, 44) does not think that the 

 red clays are rich in uranium per se, nor does he be- 

 lieve that a process of extraction or precipitation from 

 the sea water is operating, but that these high concen- 

 trations are the result of submarine volcanism associ- 

 ated with excessive and rather specialized hydrolytic 

 action at that surface where hot rock and sea water 

 meet. This explanation involves a mechanism and se- 

 quence of events which seems rather too specialized to 

 account for the observed conditions. It is true that in 

 the two or three core samples which Pettersson had the 

 good fortune to secure he found a stratified condition 

 with respect to radium content, and the high radium 

 strata were principally volcanic debris; but a differen- 

 tial dilution of a continuing process is quite as likely as 

 a sudden and unusual concentration. These observa- 

 tions serve to emphasize again the great desirability of 

 the development of some technique which will produce 

 core samples for detailed study. 



Chemically, uranium, iron, and manganese are sim- 

 ilar, in so far as their oxides are among their less sol- 

 uble compounds, and it is usually in those parts of the 

 ocean bottom where the oxides of manganese and iron 

 are separated (as revealed by the nodules of these ele- 

 ments) that the uranium concentration (as revealed by 

 the radium content) is the higher. 



If we accept the radium content of sea water to be 

 about 0.02 X 10-12 grams per cc-which is probably 

 high -Qoly, 1908), which corresponds to a uranium con- 



Table 3. Radium in ocean-bottom sediments collected by the Carnegie (Piggot) 



Carnegie 



station 



no. 



Latitude 



Longitude 



Depth, 

 meters 



Type of sediment 



Radium 

 g X 10-12 per g 



