Iron Isotope Variations in Coastal Seawater Determined by Multicollector ICP-MS |
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Authors: | Olivier J Rouxel Maureen Auro |
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Institution: | Marine Chemistry and Geochemistry Department, Woods Hole Oceanographic Institution, Woods Hole, MA02543, USA |
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Abstract: | In this paper, we applied a reliable technique for measuring Fe isotope variations in coastal seawater at nanomolar levels. Iron was directly pre-concentrated from acidified seawater samples onto a nitrilotriacetic acid chelating resin and further purified using anion-exchange resin. Sample recovery, determined using a standard addition method, was essentially quantitative. Iron was then determined using a high-resolution multicollector ICP-MS (Neptune) coupled to an ApexQ desolvation introduction system. The external precision for δ56Fe values was 0.11‰ (2s) when using total a Fe quantity between 25 and 100 ng. We initially applied this technique to measure the Fe isotope composition of dissolved Fe from several coastal environments in the north-eastern United States and we observed a range of δ56Fe values between -0.9‰ and 0.1‰ relative to the IRMM-14 reference material. Iron isotope compositions of several reference water materials for inter-laboratory comparisons were also reported. Our results suggest that iron in coastal seawater, derived from benthic diagenesis and/or groundwater has negative Fe isotopic signatures that are distinct from other iron sources such as atmospheric deposition and rivers. |
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Keywords: | iron isotopes water reference materials MC-ICP-MS seawater estuary isotopes du fer eaux de référence MC-ICP-MS eau de mer estuaire |
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