Deposition and fate of reactive Fe, Mn, P, and C in suspended particulate matter in the Bay of Biscay Pierre Anschutz à , Gwe ´ nae ¨ lle Chaillou 1 Universite´ de Bordeaux, CNRS, UMR 5805 Environnements et Pale ´o-environnements OCe ´aniques (EPOC), avenue des faculte ´s, 33405 Talence, France article info Article history: Received 30 May 2008 Received in revised form 29 October 2008 Accepted 11 December 2008 Available online 10 February 2009 Keywords: Suspended particulate matter Early diagenesis Organic carbon Iron oxide Manganese oxide Phosphorus Bay of Biscay abstract Hydrographic structure of the water column, dissolved nutrient concentrations and the distribution of suspended particulate matter were recorded from CDT measurements and Niskin bottles sampling on the continental slope of the Bay of Biscay and on the axis of Capbreton canyon. Ascorbate extraction was applied here for the first time on marine suspended particles to determine the content of reactive Fe- and Mn-oxides, and P associated with Fe-oxides. Hydrographic structure of the south-eastern part of the Bay of Biscay did not change during the last three decades. Particulate organic carbon (POC) contents dropped strongly with depth, showing that organic matter mineralization was efficient in the water column. Organic matter mineralized in the water column had a Redfield N:P ratio. POC percent of particles collected at depth were higher during a bloom period, suggesting that some new organic matter reached the bottom. Contents of Fe and Mn extracted with the ascorbate leaching solution showed that suspended particles originated from the Gironde estuary, one of the major sources of particles in the Bay of Biscay. Intermediate and deeper nepheloid layers occurred in the Capbreton canyon. Particles of nepheloid layers were enriched in Mn- and Fe-oxides because they originated from resuspension of surface sediment. & 2009 Elsevier Ltd. All rights reserved. 1. Introduction Studying the sediments that accumulated on margins is essential to evaluate global biogeochemical cycles (Walsh, 1988; Mantoura et al., 1991; Wollast, 1998). However, continental margins are complex environments, where it is difficult to rely directly on benthic processes to vertical particle fluxes from water column to sediment. In the last decades, several experiments focused on the relationship between sea surface production and flux of particles in deep waters, taking into account the role of mineralization and lateral advection, including hydrodynamics and sedimentary processes. These multi-disciplinary programs intended to quantify carbon cycle on margins. Several programs concluded that resuspended and advected material was particu- larly significant on continental slopes and submarine canyons (e.g., McCave, 1986; Gardner, 1989; Lampitt et al., 1995; Antia et al., 1999; Lapouyade and Durrieu de Madron, 2001). The objective of the present work was to report new data on the hydrographical structure of the south-eastern part of the Bay of Biscay, and to study the spatial distribution and composition of suspended particulate matter (SPM) in samples collected on the Bay of Biscay slope and the canyon of Capbreton. Heussner et al. (1999) reported that the composition of suspended particles in the Bay of Biscay remained steady in traps positioned on the slope close to the bottom because particles originated from permanent resuspension and lateral advection of sediment. Thus, the sampling strategy was conceived so as to obtain a view of the vertical and spatial distribution and composition of SPM, rather than to record the particle flux at a single station with a trap. For that, we decided to sample particles on filtered waters on vertical profiles at selected stations. The study focused on diagenetically reactive compounds, in particular organic C, reactive Fe- and Mn- oxides, and P associated with Fe-oxides. The idea was to examine the origin, the reactivity, and the preservation of these compounds in the water column before their further transformation during sediment diagenesis. 2. Study area and sampling The Bay of Biscay is a semi-enclosed basin at the eastern side of the North Atlantic Ocean. Patterns of surface waters are strongly constrained by seasonal variations of thermocline and mixed layer and river runoff (Puillat et al., 2004). Below surface waters, Northern Atlantic Central Waters (NACW) is present down to 800 m depth. Between 800 and 1200 m, a branch of Mediterranean ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/csr Continental Shelf Research 0278-4343/$ - see front matter & 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.csr.2008.12.022 à Corresponding author. Tel.: +33 540 00 88 73; fax: +33 556 84 08 48. E-mail address: p.anschutz@epoc.u-bordeaux1.fr (P. Anschutz). 1 Present address: De ´ partement de Biologie, Chimie et Ge ´ ographie, Universite ´ du Que ´bec a ` Rimouski, G5L 3A1, Rimouski, Qc, Canada. Continental Shelf Research 29 (2009) 1038–1043