The Association of Cobalt with Iron and Manganese (Oxyhydr)oxides in Marine Sediment |
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Authors: | Anthony Stockdale William Davison Hao Zhang John Hamilton-Taylor |
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Institution: | (1) Department of Environmental Science, Lancaster Environment Centre (LEC), Lancaster University, Lancaster, LA1 4YQ, UK;(2) Present address: Centre for Ecology and Hydrology, Lancaster Environment Centre, Lancaster, LA1 4AP, UK |
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Abstract: | Formation and dissolution of authigenic Fe and Mn (oxyhydr)oxides influence cycling of trace metals in oxic/suboxic surface
sediments. We used the diffusive gradients in thin films technique (DGT) to estimate the association of cobalt with iron and
manganese oxides. We compared Co, Fe and Mn maxima measured by DGT in the pore waters of fresh and aged marine sediment cores
and estimated the Co/Fe and Co/Mn ratios in the metal oxides. A Mn maximum was not visible in DGT concentration profiles of
freshly collected sediment cores, but after ageing the sediment, we observed a distinct Mn peak, presumably due to broadening
of the depth range over which the various electron acceptors occur. Estimated Co/Mn ratios from both experiments are within
the range of literature values for marine sediments, but the value from the aged experiment is at the lower end of the range.
This is attributed to stimulation of sulphate reduction and precipitation of cobalt sulphides. The good correlation between
Co and Fe maxima in the fresh sediments is attributed to the similarity of their reactions with sulphide rather than Co being
released during authigenic Fe oxide reduction. |
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