Manganese nodules and oceanic radium 



339 



with maxima varying between 85 and 330 units of Ra. The upper surface had much 

 lower values, ranging from 25 to 61 units. The fall-olT in the radium content with 

 depth is more difficult to estimate, owing to the uneven, mamillated lower surface. 

 With due reserve for this uncertainty we find the rate of radial growth in the downward 

 direction comes out at only 0-15 mm in 1,000 years, which is only a fraction of the 

 rate of growth in the upward direction, 0-4 mm in 1,000 years. The content of man- 

 ganese in this nodule is seen to be very high, ranging from 30% to 75% of .MnO,.* 

 On the other hand the content of iron is very low, averaging 1-3% of Fc, with an 

 absolute minimum of only 0-03 %. 



Low values of radium content were found in the nucleus and its vicinity, viz. 5 

 to 6 units of Ra. Still lower values were found in depths of trom 4-5 to 15 mm in a 

 series of samples taken from the back of the nodule, near the lower limit of the domed 



73 mm 



85 mm 

 Fig. 1 



surface, where radium values as low as 2-2 to 2-4 units were measured. The results 

 found with this extraordinary nodule, when summarized, seem to tell of an intense 

 transfer of both manganese and radium from the sediment to the nodule, especially 



to the scoriaceous parts. 



It would have been most interesting to measure the radium, manganese and iron 

 contained in the sediment surrounding this nodule, but unfortunately no sediment 

 from the station was available. I collected instead a sample of the sediment entrapped 

 within the nodule and measured it (last entry in Table HI). The radium content was 

 moderate (24 units), whereas the manganese dioxide was relatively low (9-1 ".,), and 

 the content of iron quite high for this nodule, viz. 41 %. However, too much impori- 

 ance should not be attached to these figures, since an exchange between this entrapped 



* Only in one nodule, taken by the Challenger Expedition in the Pad (ic Ocean lat. 3.V 31' S 

 i^no- 7i^4V W deoth 3 950 was a content of manganese dioxide as high as in this nodule reported 

 ITmu^rIv a^d RenVr'd viz. 77% MnO, in a nodule from blue mud. The .ron content of that 

 nodule was low, 4-5 %. 



