Atmospheric iron deposition and sea-surface dissolved iron concentrations in the eastern Atlantic Ocean |
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| Institution: | 1. Universite de Bretagne Occidentale, LEMAR/UMR 6539/IUEM, Technopole Brest Iroise Place Nicolas Copernic, F-29280 Plouzané, France;2. School of Environmental Sciences, University of East Anglia, Norwich NR4 7TJ, UK;3. Department of Environmental Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK;4. Royal Netherlands Institute for Sea Research (NIOZ), Postbus 59, NL-1790 AB Den Burg Texel, The Netherlands;1. LEGOS (CNRS/CNES/IRD/Université Paul Sabatier), Observatoire Midi-Pyrénées, 14 avenue Edouard Belin, 31400 Toulouse, France;2. Alfred-Wegener Institute for Polar and Marine Research, am Handelshafen 12, D-27570 Bremerhaven, Germany;3. Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA;4. LSCE/IPSL Laboratoire CNRS/CEA/UVSQ, Domaine du CNRS, Bat 12, Avenue de la Terrasse, 91198 Gif-sur-Yvette Cedex, France;5. Institute of Marine and Coastal Sciences, Department of Earth and Planetary Sciences, Rutgers University, 71 Dudley Road, New Brunswick, NJ 08901-8521, USA;6. Vrije Universiteit Brussel, ESSC Research Group, Pleinlaan 2, 1050 Brussels, Belgium;1. Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, USA;2. Florida State University, Tallahassee, FL, USA;3. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA, USA;1. Institute for Isotope Geochemistry and Mineral Resources, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland;2. GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstrasse 1-3, 24148 Kiel, Germany;3. Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany;4. Department of Earth Sciences, University of Oxford, Parks Road, OX1 3PR Oxford, UK;5. Oeschger Centre for Climate Change Research, Institute of Geological Sciences, University of Bern, Switzerland |
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| Abstract: | Atmospheric iron and underway sea-surface dissolved (<0.2 μm) iron (DFe) concentrations were investigated along a north–south transect in the eastern Atlantic Ocean (27°N/16°W–19°S/5°E). Fe concentrations in aerosols and dry deposition fluxes of soluble Fe were at least two orders of magnitude higher in the Saharan dust plume than at the equator or at the extreme south of the transect. A weaker source of atmospheric Fe was also observed in the South Atlantic, possibly originating in southern Africa via the north-easterly outflow of the Angolan plume. Estimations of total atmospheric deposition fluxes (dry plus wet) of soluble Fe suggested that wet deposition dominated in the intertropical convergence zone, due to the very high amount of precipitation and to the fact that a substantial part of Fe was delivered in dissolved form. On the other hand, dry deposition dominated in the other regions of the transect (73–97%), where rainfall rates were much lower. Underway sea-surface DFe concentrations ranged 0.02–1.1 nM. Such low values (0.02 nM) are reported for the first time in the Atlantic Ocean and may be (co)-limiting for primary production. A significant correlation (Spearman's rho=0.862, p<0.01) was observed between mean DFe concentrations and total atmospheric deposition fluxes, confirming the importance of atmospheric deposition on the iron cycle in the Atlantic. Residence time of DFe in the surface waters relative to atmospheric inputs were estimated in the northern part of our study area (17±8 to 28±16 d). These values confirmed the rapid removal of Fe from the surface waters, possibly by colloidal aggregation. |
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