Chromium isotope compositions of sediments from the global oceans

The chromium (Cr) isotope system (δ53Cr) is a promising tool to reconstruct changes in marine redox conditions and biological productivity through geological time, but uncertainties remain regarding the pathway of Cr from the water column to the sediment record (Janssen, 2021; Huang et al., 2021; Bruggmann et al., 2023). While sediment Cr concentration and isotope data are available from continental margin sites and oxygen minimum zones (e.g., Gueguen et al., 2016; Bruggmann et al., 2019), modern sediments from open marine settings are understudied. Such sediments can provide key information to understand how Cr from the water column or across the sediment-water interface accumulates in the sediment.We will investigate the response of Cr concentrations and isotope compositions (i) in the authigenic fraction of different types of pelagic sediments (carbonate-rich versus clay-rich) (ii) from the North Atlantic to the North Pacific to complement published seawater δ53Cr values, and (iii) their changes during well-characterised climate changes in the Quaternary, specifically the Last Glacial Maximum (LGM). The database of Cr isotope compositions in the modern global oceans resulting from this study will significantly enhance the interpretation of Cr isotope changes in sediments from the geological record. ReferencesBruggmann S., Severmann S. and McManus J. (2023) Geochemical conditions regulating chromium preservation in marine sediments. Geochimica et Cosmochimica Acta 348, 239–257.Gueguen B., Reinhard C. T., Algeo T. J., Peterson L. C., Nielsen S. G., Wang X., Rowe H. and Planavsky N. J. (2016) The chromium isotope composition of reducing and oxic marine sediments. Geochimica et Cosmochimica Acta 184, 1–19.Huang T., Moos S. B. and Boyle E. A. (2021) Trivalent chromium isotopes in the eastern tropical North Pacific oxygen-deficient zone. Proc. Natl. Acad. Sci. U.S.A. 118.Janssen D. J. (2021) Release from biogenic particles, benthic fluxes, and deep water circulation control Cr and δ53Cr distributions in the ocean interior. Earth and Planetary Science Letters 574,117163.