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Particulate aluminium, iron and manganese chemistry at the deep Atlantic boundary layer |
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| Authors: | CE Lambert JKB Bishop PE Biscaye R Chesselet |
| Institution: | aCentre des Faibles Radioactivités, Laboratoire Mixte CNRS-CEA, Avenue de la Terrasse, F 91190 Gif-sur-Yvette France bLamont Doherty Geological Observatory of Columbia University, Palisades, NY 10964 U.S.A. |
| Abstract: | Scanning electron microscopy and instrumental neutron activation analyses of filtered suspended matter from the Atlantic Ocean show that particulate aluminium (Alp) is a sensitive measure of bottom derived or resuspended material. The proportion of Alp in suspended particulate matter (SPM) increases slightly between surface and intermediate depths but shows large and steady increases in deep waters with approach to the bottom. Fep/Alp andMnp/Alp ratios are always higher than the crustal ratios throughout the water column. We show that the processes which can explain such enrichments are different for particulate matter in surface waters (scavenging, incorporation in biogenic particles) than for resuspended material (precipitation from interstitial waters on surficial sediments). Close to the Mid-Atlantic Ridge, the bottom suspended matter exhibits higher Fep/Alp andMnp/Alp ratios than in abyssal plains. A ridge crest source must be invoked to explain the striking enrichment of Mnp. This source could also explain the enrichment of Fep, although primarily because the resuspended flux is small in that region, one cannot exclude the contribution of particles from the mid-water column. |
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