Published September 20, 2021 | Published + Supplemental Material
Journal Article Open

Cold-water corals as archives of seawater Zn and Cu isotopes

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Abstract

Traditional carbonate sedimentary archives have proven challenging to exploit for Zn and Cu isotopes, due to the high concentrations of trace metals in potential contaminants (e.g., Fe Mn coatings) and their low concentrations in carbonate. Here, we present the first dataset of δ⁶⁶Zn_(JMC-Lyon) and δ⁶⁵Cu_(SRM 976) values for cold-water corals and address their potential as a seawater archive. Extensive cleaning experiments carried out on two corals with well-developed Fe Mn rich coatings demonstrate that thorough physical and chemical cleaning can effectively remove detrital and authigenic contaminants. Next, we present metal/Ca ratios and δ⁶⁶Zn and δ⁶⁵Cu values for a geographically diverse sample set of Holocene age cold-water corals. Comparing cold-water coral δ⁶⁶Zn values to estimated ambient seawater δ⁶⁶Zn values (where Δ⁶⁶Zn_(coral-sw) = δ⁶⁶Zn_(coral) – δ⁶⁶Zn_(seawater), we find Δ⁶⁶Zn_(coral-sw) = +0.03 ± 0.17‰ (1SD, n = 20). Hence, to a first order, cold-water corals record seawater Zn isotope compositions without fractionation. The average Holocene coral Cu isotope composition is +0.59 ± 0.23‰ (1SD, n = 15), similar to the mean of published deep seawater δ⁶⁵Cu values at +0.66 ± 0.09‰, but with considerable variability. Finally, δ⁶⁶Zn and δ⁶⁵Cu data are presented for a small subset of four glacial-age corals. These values overlap with the respective Holocene coral datasets, hinting at limited glacial-interglacial changes in oceanic Zn and Cu cycling.

Additional Information

© 2021 The Authors. Published by Elsevier B.V. Under an Attribution 4.0 International (CC BY 4.0). Received 30 November 2020, Revised 23 April 2021, Accepted 2 May 2021, Available online 5 May 2021. We would like to acknowledge Matthew Clarkson and an anonymous reviewer for thoughtful comments on a previous version of this manuscript. Many thanks to Katharina Kreissig and Barry Coles for maintaining the smooth running of the MAGIC labs at Imperial, and to Derek Vance for the use of the Neptune at ETH. Thanks also to Sophie Hines, who sub-sampled New England Seamount corals from the Adkins collection. Finally, thanks to Tristan Horner, who provided valuable insights early on in the development of this project. This research was supported by a Leverhulme Trust early career fellowship to SHL (ECF-2014-615). DJW and TvdF acknowledge support from the Natural Environment Research Council (NE/N001141/1) and a NERC independent research fellowship (NE/T011440/1). SHL is currently supported by a NERC independent research fellowship (NE/P018181/2). The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Additional details

Created:
August 22, 2023
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October 23, 2023