Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 4 2 2007 10.5194/bg-4-181-2007 http://www.biogeosciences.net/4/181/2007/ http://www.biogeosciences.net/4/181/2007/bg-4-181-2007.html http://www.biogeosciences.net/4/181/2007/bg-4-181-2007.pdf 181 194 2007-03-14 Sources and transport of dissolved iron and manganese along the continental margin of the Bay of Biscay A. Laës agathe.laes@ifremer.fr S. Blain P. Laan S. J. Ussher E. P. Achterberg P. Tréguer H. J. W. de Baar Institut Universitaire Européen de la Mer, LEMAR UMR CNRS 6539, Place Nicolas Copernic, 29280 Plouzané, France Centre d'Océanologie de Marseille, LOB UMR CNRS 6535, campus de Luminy, case 901, 13288 Marseille Cedex, France Royal Netherlands Institute for Sea Research (NIOZ), Texel, The Netherlands School of Earth, Ocean and Environmental Science, University of Plymouth, PL4 8AA Plymouth, UK National Oceanography Centre Southampton, University of Southampton, SO14 3ZH Southampton, UK now at: Ifremer, Département TSI, Centre de Brest, BP 70, 29280 Plouzané, France Dissolved iron (DFe; <0.2 µm) and dissolved manganese (DMn; <0.2 µm) concentrations were determined in the water column of the Bay of Biscay (eastern North Atlantic Ocean) in March 2002. The samples were collected along a transect traversing from the European continental shelf over the continental slope. The highest DFe and DMn concentrations (2.39 nM and 6.10 nM, respectively) were observed in the bottom waters on the shelf at stations closest to the coast. The release of trace metal from resuspended particles and the diffusion from pore waters were probably at the origin of elevated DFe and DMn concentrations in the Bottom Boundary Layer (BBL). In the slope region, the highest total dissolvable iron (TDFe), DFe and DMn values (24.6 nM, 1.58 nM and 2.12 nM, respectively) were observed close to the bottom at depth of ca.~600–700 m. Internal wave activity and slope circulation are thought to be at the origin of this phenomenon. These processes were also very likely the cause of elevated concentrations (DFe: 1.27 nM, DMn: 2.34 nM) measured in surface waters of stations located in the same area. 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