Changes in Chemical Composition of Some Pacific Manganese Nodules During their Growth
Manganese nodules were sampled from 133 stations in the Central Pacific during a cruise of the German research vessel Valdivia in 1976. The abundance of nodules on the sea floor of the area was calculated. A change in the abundance of nodules with water depth was found: on the slopes of the seamounts the population density varies from 0 to 7.3 kg/m2, in the abyssal plains from 7.3 to 32 kg/m2.
Si, Al, Mn, Fe, Ni, Cu, Co, Zn, Pb, Mg, and Ca were analysed for 76 nodules from 21 abyssal plain stations. Besides bulk analyses, analyses of different zones from the nodules were made.
The centers of the nodules are formed by the fragments of disintegrated older nodules or crusts which were recemented in dislocated positions together with some stone fragments.
There are differences in the chemical composition within the laminated layer around the center.The water side and the sediment side have similar chemical compositions.The equatorial zone,however,has elevated Ni and Cu contents and relatively low Fe and Co contents.We suggest that the reason for this enrichment is the growth of this part of the nodule layer within the sediment-water interface layer.
The loose outer layer of nodules has elevated Mn,Cu,Ni- and Zn contens.The comparison of this layer with micronodules from the surrounding sediment indicates recent deposition of diagenetically mobilized metals.
KeywordsAbyssal Plain Manganese Nodule Laminate Layer Stone Fragment Equatorial Part
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