Growth rates of manganese-rich nodules at MANOP Site H (Eastern North Pacific) |
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| Authors: | Bruce Finney GRoss Heath Mitchell Lyle |
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| Institution: | College of Oceanography, Oregon State University, Corvallis, Oregon 97331, USA |
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| Abstract: | Estimates of the growth rates of ferromanganese nodules at MANOP Site H (6°33′N, 92°49′W) lie between 7 and 1200 mm/my. The most probable range (estimated from nodule size distributions, nodule chemistry, accumulation rates of authigenic elements and U-series modeling) is 30–300 mm/my. Such rates are much faster than measured values for most pelagic nodules. The distributions of U-series and stable elements suggest that a typical nodule consists of two compositionally distinct non-detrital components, one rich in Mn, U and Sb, and the other in Fe, Co, REE, Ni, Cu and Th. When the uncorrected U-series data, which do not show simple decay patterns with depth, are normalized to the relative proportion of the Fe-rich component, the data yield well-constrained growth rates of 55 mm/my for a nodule top and 200 mm/my for its bottom. The component enriched in Mn, which is most abundant on nodule bottoms, appears to accrete much faster than the component enriched in Fe. |
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