title: A solvent extraction technique for the isotopic measurement of dissolved copper in seawater.
abstract: Stable copper (Cu) isotope geochemistry provides a new perspective for investigating and understanding Cu speciation and biogeochemical Cu cycling in seawater. In this work, sample preparation for isotopic analysis employed solvent-extraction with amino pyrollidine dithiocarbamate/diethyl dithiocarbamate (APDC/DDC), coupled with a nitric acid back-extraction, to concentrate Cu from seawater. This was followed by Cu-purification using anion-exchange. This straightforward technique is high yielding and fractionation free for Cu and allows precise measurement of the seawater Cu isotopic composition using multi-collector inductively coupled plasma mass-spectrometry. A deep-sea profile measured in the oligotrophic north Tasman Sea shows fractionation in the Cu isotopic signature in the photic zone but is relatively homogenised at depth. A minima in the Cu isotopic profile correlates with the chlorophyll a maximum at the site. These results indicate that a range of processes are likely to fractionate stable Cu isotopes in seawater.
authors.affiliation: Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia. claire.thompson@anu.edu.au
authors.forename: Claire M
authors.initials: CM
authors.lastname: Thompson
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ellwood
authors.forename: Martin
authors.initials: M
authors.lastname: Wille