672 ARRHENIUS [CHAP. 25 



Picciotto (1955) (Goldberg and Arrhenius, 1958, p. 198). Similar values are 

 obtained for manganese micronodules in pelagic clays and zeolitites by inte- 

 grating the manganese content in a column of known interval of time. 



Several hypotheses have been advanced regarding the ultimate source of the 

 manganese. ^Murray, in contrast to Renard (Murray and Renard, 1884) and 

 lately Pettersson (1945, 1955, 1959), suggested that the manganese is derived 

 from pjTOclastics decomposing on the ocean floor; so far, no decomposition 

 residue correspondingly deflcient in manganese has been observed. Further, by 

 order of magnitude, the manganese found on the ocean floor is accounted for by 

 the amount of this element known to be continually lost from the continents 

 (Kuenen, 1950, p. 390; Goldberg and Arrhenius, ojp. cit.; Wedepohl, 1960). 

 Consequently many authors assume that the manganese on the ocean floor, 

 other than the relatively small part which can be accounted for by decomposi- 

 tion in situ of basaltic pyroclastics, originates from dissolution of this element 

 from continental rocks and from volcanic exhalates. Recent geochemical 

 balance computations by Wedepohl {op. cit.) indicate that the volcanic ex- 

 halates are quantitatively important sources of manganese, iron, and other 

 heavy metals with high halide vapor pressures. World-wide or large regional 

 changes in the absolute rate of deposition of manganese in pelagic sediments 

 could accordingly be due to variations in the rate of weathering on the conti- 

 nents, or in volcanic activity. Local or regional differences in the concentration 

 of manganese in pelagic sediments, such as between the North and South 

 Pacific at the present time or between Atlantic and Pacific sediments, can be 

 accounted for by differences in dilution of the sediments with terrigenous 

 material. Strata with a markedly increased manganese concentration, fre- 

 quently found in pelagic sediments (see, for example, Arrhenius, 1952, pis. 

 2.51, 2.56; Revelle et al., 1955, fig. 7; Pettersson, 1959), appear to corres- 

 pond to periods of a lowered rate of total deposition, resulting in a decreased 

 dilution of the halmeic oxide minerals with terrigenous silicates. 



Whatever the ultimate source and mode of transportation of manganese 

 and associated elements, several processes have been suggested to explain the 

 mode of subsequent accretion of the manganese oxide minerals. One group 

 involves various inorganic reactions (a review of these is given in Goldberg and 

 Arrhenius, 1958); another group assumes organic (bacterial) mechanisms 

 (Dieulafait, 1883; Butkevich, 1928; Dorff", 1935; Kalinenko, 1949; Ljunggren, 

 1953; Graham, 1959; Kriss, 1959). Goldberg and Arrhenius suggest specifically 

 that manganese is removed from the bottom water by catalytic oxidation of 

 manganous ion by colloidal ferric hydroxide at the sediment- water interface. 

 In support of the biotic transfer (Jraham has demonstrated the presence of 

 organic matter in the nodules. Although investigations in process (Galen Jones, 

 unpublished) have demonstrated that the nodules contain bacteria capable 

 of reducing manganese, it is difficult at the present time to evaluate the biotic 

 hypothesis against an inorganic one. 



Under the oxidizing conditions on the ocean floor, the only elemental 

 mineral observed, besides carbon from burning forests and grasslands, is 



