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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-208
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-208
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 18 Jun 2020

Submitted as: research article | 18 Jun 2020

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This preprint is currently under review for the journal BG.

Mg/Ca, Sr/Ca and stable isotope from planktonic foraminifera T. sacculifer: testing a multi-proxy approach for inferring paleo-temperature and paleo-salinity

Delphine Dissard1,2, Gert Jan Reichart3,4, Christophe Menkes5, Morgan Mangeas5, Stephan Frickenhaus2, and Jelle Bijma2 Delphine Dissard et al.
  • 1IRD/UMR LOCEAN (IRD-CNRS-MNHN-Sorbonne Université), Centre IRD de Nouméa 101 Promenade Roger Laroque, Nouméa 98848, New Caledonia
  • 2Alfred-Wegener-Institute, Helmholtz-Zentrum für Polar- und Meeres Forschung, Am Handelshafen 12, 27570 Bremerhaven, Germany
  • 3NIOZ Royal Natherlands Inst. Sea Res, Den Burg, Texel, the Netherlands
  • 4Univ. Utrecht, Fac Geosci. Dept Earth Sci. Utrecht, the Netherlands
  • 5IRD/UMR ENTROPIE (IRD, Univ. de la Réunion, CNRS, IFREMER, UNC), Centre IRD de Nouméa 101 Promenade Roger Laroque, Nouméa 98848, New Caledonia

Abstract. Over the last decades, sea surface temperature (SST) reconstructions based on the Mg/Ca of foraminiferal calcite have frequently been used in combination with the δ18O signal from the same material, to provide estimates of δ18O of the water (δ18Ow), a proxy for global ice volume and sea surface salinity (SSS). However, because of error propagation from one step to the next, better calibrations are required to increase accuracy and robustness of existing isotope and element to temperature proxy-relationships. Towards that goal, we determined Mg/Ca, Sr/Ca and the oxygen isotopic composition of Trilobatus sacculifer (previously referenced as Globigerinoides sacculifer), collected from surface waters (0–10 m), along a North-South transect in the eastern basin of the tropical/subtropical Atlantic Ocean. We established a new paleo-temperature calibration based on Mg/Ca, and on the combination of Mg/Ca and Sr/Ca. Subsequently, a sensitivity analysis was performed in which, one, two, or three different equations were considered. Results indicate that foraminiferal Mg/Ca allow for an accurate reconstruction of surface water temperature. Combining equations, δ18Ow can be reconstructed with a precision of about ± 0.5 ‰. However, the best possible salinity reconstruction based on locally calibrated equations, only allowed reconstruction with an uncertainty of ± 2.49. This was confirmed by a Monte Carlo simulation, applied to test successive reconstructions in an ideal case, where explanatory variables are known. This simulation shows that from a pure statistical point of view, successive reconstructions involving Mg/Ca and δ18Oc preclude salinity reconstruction with a precision better than ± 1.69 and hardly better than ± 2.65, due to error propagation. Nevertheless, a direct linear fit to reconstruct salinity based on the same measured variables (Mg/Ca and δ18Oc) was established. This direct reconstruction of salinity lead to a much better estimation of salinity (± 0.26) than the successive reconstructions.

Delphine Dissard et al.

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Delphine Dissard et al.

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Latest update: 07 Jul 2020
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Short summary
Results from an invaluable data set acquired on living foraminifera T. sacculifer collected from surface waters of the Atlantic Ocean are presented, showing that foraminiferal Mg/Ca allow for an accurate reconstruction of SST. When combining equations, δ18Ow can be reconstructed with a precision of ± 0.5 ‰, while successive reconstructions involving Mg/Ca and δ18Oc preclude salinity reconstruction with a precision better than ± 1.69. A direct linear fit to reconstruct salinity could be established.
Results from an invaluable data set acquired on living foraminifera T. sacculifer collected from...
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