Determination of the copper isotope composition of seawater revisited: A case study from the Mediterranean Sea

• Published in: Chemical Geology
• Main Authors: Baconnais, Isabelle, Rouxel, Olivier, Dulaquais, Gabriel, Boye, Marie
• Other Authors: University of Saskatchewan Saskatoon (U of S), Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Unité de recherche Géosciences Marines (Ifremer) (GM), Department of Oceanography Honolulu, University of Hawai‘i Mānoa (UHM), Laboratoire des Sciences de l'Environnement Marin (LEMAR) (LEMAR), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique du Globe de Paris (IPGP), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), ANR-10-LABX-0019,LabexMER,LabexMER Marine Excellence Research: a changing ocean(2010), European Project: 247837,EC:FP7:PEOPLE,FP7-PEOPLE-2009-RG,ISOMAR(2009)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: Mediterranean Sea; Seawater; Geotraces; Isotope fractionation; Copper isotope; ACL; envir; geo; North Atlantic
• Online Access: https://doi.org/10.1016/j.chemgeo.2018.09.009; https://hal.archives-ouvertes.fr/hal-02345288/file/Baconnais%20et%20al%202019.pdf; https://hal.archives-ouvertes.fr/hal-02345288

International audience A new technique for the determination of dissolved copper isotope composition (delta Cu-65) of seawater was applied to examine copper sources and internal cycling in the Mediterranean Sea along the GEOTRACES GA04N transect. A succession of chelating resin with nitrilotriacetic acid functional groups and strong base anion exchange resin, together with optimization of the multi-collector inductively coupled plasma mass spectrometry set-up allowed to isolate copper from seawater matrix and to measure the Cu-65/Cu-63 ratios in seawater with an external precision of 0.06% (2 s.d.). This method was first applied for inter-comparison measurements to surface and deep waters sampled at the Bermuda Atlantic Time-Series station (BATS) in the North Atlantic Ocean during the GEOTRACES Intercalibration Cruise 1. Disparities in delta Cu-65 reported here and in the literature over these samples showed a need to investigate whether a new inter-comparison sample should be decided upon, or whether the use of UV-oxidation can also affect the measurement of delta Cu-65. We also measured total dissolved Cu concentration ([dCu](T)) and delta Cu-65 for 12 stations in the Mediterranean Sea. The delta Cu-65 distribution showed significant variations in the euphotic zone, at the Chl a maximum and at bottom depths. Copper isotope ratios ranged from +0.21% to +0.76% (+/- 0.06%, 2 s.d.), yielding an average of + 0.51% (+/- 0.20%, 2 s.d.; n = 96) for the Mediterranean Sea. A strong zonation between natural aerosol deposition to the South and anthropogenic aerosol deposition to the North was seen in the sample set (Dulaquais et al. 2017; Gerringa et al. 2017; Rolison et al. 2015). Natural dust deposits seemed to draw delta Cu-65 toward lower values and deeper in the euphotic zone whereas the impact of anthropogenic aerosols seemed restricted to an increase in [dCu](T). At the Chl a maximum, delta Cu-65 showed significant increase which we attributed to scavenging on and/or uptake by phytoplankton. The isotope signature ...