Chromium stable isotope distributions in the southwest Pacific Ocean and constraints on hydrothermal input from the Kermadec Arc

• Published in: Geochimica et cosmochimica acta 2023-02, Vol.342, p.31-44
• Main Authors: Janssen, David J, Gilliard, Delphine, Rickli, Jörg, Nasemann, Philipp, Koschinsky, Andrea, Hassler, Christel S, Bowie, Andrew R, Ellwood, Michael J, Kleint, Charlotte, Jaccard, Samuel L
• Format: Article
• Language: English
• Subjects: Chromium; Chromium isotopes; GEOTRACES; Hydrothermal flux; Paleoproxy
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/j.gca.2022.12.010

Special attention has been given to chromium (Cr) as a paleoproxy tracing redox cycling throughout Earth’s history, due to differences in the solubility of its primary redox species at Earth’s surface (Cr(III) and Cr(VI)) and isotope fractionation associated with their interconversion. In turn, chromium’s paleoproxy potential has motivated studies of the modern ocean to better understand which processes drive its cycling and to constrain their impact on the Cr isotope composition (δ53Cr) of seawater. Here, we present total dissolved seawater Cr concentrations and δ53Cr along the GEOTRACES GP13 section. This section is a zonal transect extending from Australia in the subtropical southwest Pacific Ocean. Surface signals of local biological Cr cycling are minimal, in agreement with distributions of dissolved major nutrients as well as biologically-controlled trace metals in this low productivity, oligotrophic environment. Depth profiles have Cr concentration minima in surface waters and maxima at depth, and are largely shaped by the advection of nutrient- and Cr-rich subsurface waters rather than vertically-driven processes. Samples close to the sediment–water interface indicate important benthic Cr fluxes across the section. The GP13 transect crosses the hydrothermally-active Kermadec Arc. Hydrothermal fluids (consisting of