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Comparison of surface and down-core samples from northern Nazca plate sediment cores shows that for most elements the temporal variability over 105 to 106 yr is comparable to the modern spatial variability over 103 to 104 km2. Even mildly reducing conditions in the sediments lead to depletion of Mn down core, however. Systematic enrichments of Fe, Cu, and Zn in surface versus down-core samples west of the crest of the East Pacific Rise and depletion of the same elements in surface versus down-core samples from the Bauer Basin imply a recent change of near-bottom circulation that now tends to sweep hydrothermal debris west from the rise crest.

East-west profiles of the accumulation of the five sediment components, detritus, hydrothermal material, biogenic debris, authigenic precipitates, and solution residue from dissolved opal, show a westerly decrease in detrital input, except for a maximum of presumed volcanic origin on the rise crest. Hydrothermal material accumulates at more than 200 mg-cm-2-I0-3 yr-1 on the East Pacific Rise, but decreases rapidly within a few hundred kilometres from the rise crest, and is essentially zero 2,500 km to the east. The other components accumulate fairly uniformly across the region as expected from their sources in the relatively monotonous surface and bottom waters of the central southeast Pacific Ocean.

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