Sources and transport of dissolved iron and manganese along the continental margin of the Bay of Biscay

Laes, A., Blain, S., Laan, P., Ussher, S.J., Achterberg, E.P., Treguer, P. and de Baar, H.J.W. (2007) Sources and transport of dissolved iron and manganese along the continental margin of the Bay of Biscay. Biogeosciences, 4 (2), 181-194.

Abstract

Dissolved iron (DFe; <0.2µm) and dissolved
manganese (DMn; <0.2µm) 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 (2.39nM 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, 1.58nM and 2.12nM, 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. At stations off the continental
slope, the vertical distribution of both metals were typical of
open ocean conditions, indicating that inputs from the continental
margin did not impact the metal distributions in the
offshore waters.

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