Coupled Mg/Ca and clumped isotope analyses of foraminifera provide consistent water temperatures

Sebastian F.M. Breitenbach*, Maryline J. Mleneck-Vautravers, Anna Lena Grauel, Li Lo, Stefano M. Bernasconi, Inigo A. Müller, James Rolfe, Fernando Gázquez, Mervyn Greaves, David A. Hodell

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The reliable determination of past seawater temperature is fundamental to paleoclimate studies. We test the robustness of two paleotemperature proxies by combining Mg/Ca and clumped isotopes (Δ47) on the same specimens of core top planktonic foraminifera. The strength of this approach is that Mg/Ca and Δ47 are measured on the same specimens of foraminifera, thereby providing two independent estimates of temperature. This replication constitutes a rigorous test of individual methods with the advantage that the same approach can be applied to fossil specimens. Aliquots for Mg/Ca and clumped analyses are treated in the same manner following a modified cleaning procedure of foraminifera for trace element and isotopic analyses. We analysed eight species of planktonic foraminifera from coretop samples over a wide range of temperatures from 2 to 29°C. We provide a new clumped isotope temperature calibrations using subaqueous cave carbonates, which is consistent with recent studies. Tandem Mg/Ca–Δ47 results follow an exponential curve as predicted by temperature calibration equations. Observed deviations from the predicted Mg/Ca-Δ47 relationship are attributed to the effects of Fe-Mn oxide coatings, contamination, or dissolution of foraminiferal tests. This coupled approach provides a high degree of confidence in temperature estimates when Mg/Ca and Δ47 yield concordant results, and can be used to infer the past δ18O of seawater (δ18Osw) for paleoclimate studies.

Original languageEnglish
Pages (from-to)283-296
Number of pages14
JournalGeochimica et Cosmochimica Acta
Volume236
DOIs
Publication statusPublished - 1 Sept 2018

Funding

Ian Mather provided invaluable technical support for the clumped isotope measurements. Cedric John and Simon Davis (Imperial College London) helped us with heated gas preparations. We thank Gerald Ganssen (Amsterdam Global Change Institute) for use of his sample collection. Ludvig Löwemark (National Taiwan University) and Richard Gyllenkreutz (Stockholm University) kindly provided some Arctic samples and the Taiwan Ocean Research Institute provided the sample from the Okhotsk Sea. Professors Paolo Forti and Jose Maria Calaforra provided the sample NAICA-01. Julio Lompronti is thanked for his support with SEM imaging. Finally, we thank Norbert Marwan (PIK Potsdam), and Niklas Boers (ENS Paris), for fruitful discussions. Harry Elderfield contributed to this study with his deep insights into the (bio)geochemistry of foraminifera. His enthusiasm for paleoceanographic research is deeply felt as a loss for all authors. We dedicate this publication to the memory of our colleague and friend Prof. Harry Elderfield FRS who sadly passed away prior to the final preparation of the manuscript. This study was predominantly supported by NERC project ID NE/M003752/1 to D.A.H. and H.E.. S.F.M.B., F.G. and D.A.H. also acknowledge support from the European Union’s Horizon 2020 Research and Innovation programme (Marie Sklodowska-Curie grant agreement No. 691037). S.M.B acknowledges support of SNSF project No. 200020_160046 .

Keywords

  • Clumped isotopes
  • Mg/Ca analysis
  • Paleoceanography
  • Paleoclimatology
  • Planktonic foraminifera

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