Controls on redox-sensitive trace metals in the Mauritanian oxygen minimum zone.

Rapp, Insa, Schlosser, Christian , Menzel Barraqueta, Jan-Lukas , Wenzel, Bernhard, Lüdke, Jan , Scholten, Jan, Gasser, Beat, Reichert, Patrick, Gledhill, Martha, Dengler, Marcus and Achterberg, Eric P. (2018) Controls on redox-sensitive trace metals in the Mauritanian oxygen minimum zone. Open Access Biogeosciences Discussions . pp. 1-49. DOI 10.5194/bg-2018-472.

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Abstract

The availability of the micronutrient iron (Fe) in surface waters determines primary production, N2 fixation and microbial community structure in large parts of the world's ocean, and thus plays an important role in ocean carbon and nitrogen cycles. Eastern boundary upwelling systems and the connected oxygen minimum zones (OMZs) are typically associated with elevated concentrations of redox-sensitive trace metals (e.g. Fe, manganese (Mn) and cobalt (Co)), with shelf sediments typically forming a key source. Over the last five decades, an expansion and intensification of OMZs has been observed and this trend is likely to proceed. However, it is unclear how trace metal (TM) distributions and transport are influenced by decreasing oxygen (O2) concentrations. Here we present dissolved (d; <0.2μm) and leachable particulate (Lp; >0.2μm) TM data collected at 7 stations along a 50km transect in the Mauritanian shelf region. We observed enhanced concentrations of Fe, Co and Mn corresponding with low O2 concentrations (<50μmolkg−1), which were decoupled from major nutrients and nutrient-like and scavenged TMs (cadmium (Cd), lead (Pb), nickel (Ni) and copper (Cu)). Additionally, data from repeated station occupations indicated a direct link between dissolved and leachable particulate Fe, Co, Mn, and O2. An observed dFe decrease from 10 to 5nmolL−1 coincided with an O2 increase from 30 to 50μmolkg−1 and with a concomitant decrease in turbidity. The changes in Fe (Co and Mn) were likely driven by variations in their release from sediment pore water, facilitated by lower O2 concentrations and longer residence time of the water mass on the shelf. Variations in organic matter remineralization and lithogenic inputs (atmospheric deposition or sediment resuspension) only played a minor role in redox-sensitive TM variability. Vertical dFe fluxes from O2-depleted subsurface to surface waters (0.08–13.5μmolm−2d−1) were driven by turbulent mixing and vertical advection, and were an order of magnitude larger than atmospheric deposition fluxes (0.63–1.43μmolm−2d−1). Benthic fluxes are therefore the dominant dFe supply to surface waters on the continental margins of the Mauritanian upwelling region. Overall, our results indicated that the projected future decrease in O2 concentrations in OMZs may result in increases in Fe, Mn and Co concentrations.

Document Type: Article
Keywords: trace metals, iron, Mauritania, OMZ, ETNA
Research affiliation: OceanRep > SFB 754 > B10
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-CH Chemical Oceanography
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-PO Physical Oceanography
OceanRep > SFB 754
Kiel University
Refereed: No
Open Access Journal?: Yes
DOI etc.: 10.5194/bg-2018-472
ISSN: 1810-6285
Projects: SFB754
Expeditions/Models/Experiments:
Date Deposited: 10 Dec 2018 14:38
Last Modified: 11 Dec 2018 07:47
URI: http://oceanrep.geomar.de/id/eprint/44921

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