Arsenic in sediments of the North Atlantic Ocean and the Eastern Mediterranean Sea |
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Authors: | Colin Neal Henry Elderfield Roy Chester |
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Institution: | 1. Institute of Hydrology, Crowmarsh Gifford, Wallingford Great Britain;2. Department of Earth Sciences, University of Leeds, Leeds Great Britain;3. Department of Oceanography, University of Liverpool, Liverpool Great Britain |
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Abstract: | Chemical extraction techniques show that the majority of the arsenic in North Atlantic deep-sea sediments is associated with an iron phase compositionally similar to that found in deep-sea ferromanganese nodules (As/Fe ~ 11 · 10?4) and is probably of seawater origin. Some sediments also contain As associated with Fe oxides produced by continental weathering. A minority (~8%) of the arsenic is of detrital origin but is not associated with Fe or Mn oxides; it has a content (1.7 ppm) similar to the average crustal abundance. In the Eastern Mediterranean Sea, near-shore sediments contain As associated with land-derived Fe oxides (As/Fe ~ 2 · 10?4), but As/Fe ratios increase to ~ 13 · 10?4 in deep-sea sediments as the contribution of seawater derived arsenic becomes dominant. Arsenic is enriched in metalliferous sediments (As/Fe ~ 20?50 · 10?4) but As/P ratios of metalliferous sediments, deep-sea ferromanganese nodules and deep-ocean water are all similar. Although a hydrothermal contribution cannot be discounted, it is likely that the arsenic is also of seawater origin, suggesting that hydrothermal iron oxyhydroxides remove As more efficiently from seawater than do iron phases (goethite) in deep-sea sediments and nodules. Arsenic accumulates in deep-sea sediments (~ 6 μg cm?2 10?3 yr?1) at sediments (~ 120 μg cm?2 10?3 yr?1) at rate sufficient to balance river input input (~3 · 1010 g yr?1). These estimates give an oceanic residence time for arsenic of 1–2 · 105 yr. |
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