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Distribution, Morphology, and Geochemistry of Manganese Nodules from the Valivia 13/2 Area, Equatorial North Pacific
|Title:||Distribution, Morphology, and Geochemistry of Manganese Nodules from the Valivia 13/2 Area, Equatorial North Pacific|
show 2 moreGhosh, A.K.
|Issue Date:||Apr 1982|
|Publisher:||University of Hawai'i Press|
|Citation:||Glasby GP, Friedrich G, Thijssen T, Pluger WL, Kunzendorf H, Ghosh AK. Roonwal GS. 1982. Distribution, morphology, and geochemistry of manganese nodules from the Valdivia 13/2 area, equatorial North Pacific. Pac Sci 36(2): 241-263.|
|Abstract:||Manganese nodules were collected during cruise 13/2 of R.V.
Valdivia in 1976 in a small area of the equatorial north Pacific characterized by
abyssal hill topography. The sediments are dominantly siliceous oozes in which
extensive dissolution ofsiliceous material has taken place. Three principal nodule
morphologies were recovered: polynucleate nodules, mononucleate nodules, and
manganese crusts. Polynucleate nodules occur throughout the entire depth range
studied whereas mononucleate nodules are found principally below 5000 m;
manganese crusts are restricted to the abyssal hill environments. Nodule density
remains on average roughly constant (> 7 kg/m2) with water depth (although
varying considerably, 0-27 kg/m2, throughout the area), but the form in which
the nodules occur changes with water depth. Nodule composition was investigated
as a function of water depth, nodule size, and nodule morphology and
shown to be related principally to nodule morphology. Mononucleate nodules
have higher contents of Mn, Ni, Cu, and Zn and lower contents of Fe and Co
than polynucleate nodules. The lithogenous fraction in the nodules is similar in
both morphologies, although it varies considerably with nodule size. Both
morphologies contain todorokite andJ-Mn02as the principal manganese oxide
phases, but todorokite is relatively more abundant in the mononucleate nodules.
The data are best interpreted in terms of the diagenetic supply of the transition
elements Mn, Ni, Cu, and Zn to the nodules resulting from the in situ dissolution
of siliceous tests in the sediment column. This process is more pronounced in the
abyssal regions than on the flanks of the abyssal hills and leads to the enrichment
of these elements in the larger mononucleate nodules embedded at the sediment
-water interface there. This enhanced supply of transition elements also leads to
the stabilization of todorokite in these nodules. Polynucleate nodules appear to
be preferentially formed under conditions of higher sedimentation rate on the
flanks of abyssal hills in an environment where abundant seeds are available.
Mononucleate nodules are formed in abyssal environments characterized by
lower sedimentation rate where enhanced rates of supply of biogenically derived
elements can take place.
|Appears in Collections:||Pacific Science Volume 36, Number 2, 1982|