Global Biogeochemical Cycles

Fluxes and distribution of dissolved iron in the eastern (sub-) tropical North Atlantic Ocean

Authors

  • Micha J. A. Rijkenberg,

    Corresponding author
    1. School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, UK
    2. Royal Netherlands Institute for Sea Research, Den Burg, Netherlands
      Corresponding author: M. J. A. Rijkenberg, Royal Netherlands Institute for Sea Research, Den Burg NL-1790 AB, Netherlands. (micha.rijkenberg@nioz.nl)
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  • Sebastian Steigenberger,

    1. School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, UK
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  • Claire F. Powell,

    1. Laboratory for Global Marine and Atmospheric Chemistry, School of Environmental Sciences, University of East Anglia, Norwich, UK
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  • Hans van Haren,

    1. Royal Netherlands Institute for Sea Research, Den Burg, Netherlands
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  • Matthew D. Patey,

    1. School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, UK
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  • Alex R. Baker,

    1. Laboratory for Global Marine and Atmospheric Chemistry, School of Environmental Sciences, University of East Anglia, Norwich, UK
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  • Eric P. Achterberg

    1. School of Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, UK
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Corresponding author: M. J. A. Rijkenberg, Royal Netherlands Institute for Sea Research, Den Burg NL-1790 AB, Netherlands. (micha.rijkenberg@nioz.nl)

Abstract

[1] Aeolian dust transport from the Saharan/Sahel desert regions is considered the dominant external input of iron (Fe) to the surface waters of the eastern (sub-) tropical North Atlantic Ocean. To test this hypothesis, we investigated the sources of dissolved Fe (DFe) and quantified DFe fluxes to the surface ocean in this region. In winter 2008, surface water DFe concentrations varied between <0.1 nM and 0.37 nM, with an average of 0.13 ± 0.07 nM DFe (n = 194). A strong correlation between mixed layer averaged concentrations of dissolved aluminum (DAl), a proxy for dust input, and DFe indicated dust as a source of DFe to the surface ocean. The importance of Aeolian nutrient input was further confirmed by an increase of 0.1 nM DFe and 0.05 μM phosphate during a repeat transect before and after a dust event. An exponential decrease of DFe with increasing distance from the African continent, suggested that continental shelf waters were a source of DFe to the northern part of our study area. Relatively high Fe:C ratios of up to 3 × 10−5 (C derived from apparent oxygen utilization (AOU)) indicated an external source of Fe to these African continental shelf waters. Below the wind mixed layer along 12°N, enhanced DFe concentrations (>1.5 nM) correlated positively with apparent oxygen utilization (AOU) and showed the importance of organic matter remineralization as an DFe source. As a consequence, vertical diffusive mixing formed an important Fe flux to the surface ocean in this region, even surpassing that of a major dust event.

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