Mg∕Ca, Sr∕Ca and stable isotopes from the planktonic foraminifera T. sacculifer: testing a multi-proxy approach for inferring paleotemperature and paleosalinity

Type Article
Date 2021-01
Language English
Author(s) Dissard DelphineORCID1, 2, Reichart Gert Jan3, 4, Menkes Christophe5, Mangeas Morgan5, Frickenhaus StephanORCID2, Bijma JelleORCID2
Affiliation(s) 1 : UMR LOCEAN (IRD-CNRS-MNHN-Sorbonne Université), Centre IRD de Nouméa, 101 Promenade Roger Laroque, Noumea 98848, New Caledonia
2 : Alfred-Wegener-Institute, Helmholtz-Zentrum für Polar- und Meeresforschung, Am Handelshafen 12, 27570 Bremerhaven, Germany
3 : Royal Netherlands Institute for Sea Research (NIOZ), Den Burg, Texel, the Netherlands
4 : Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, the Netherlands
5 : UMR ENTROPIE (IRD, Université de la Réunion, CNRS, IFREMER, UNC), Centre IRD de Nouméa, 101 Promenade Roger Laroque, Noumea 98848, New Caledonia
Source Biogeosciences (1726-4170) (Copernicus GmbH), 2021-01 , Vol. 18 , N. 2 , P. 423-439
DOI 10.5194/bg-18-423-2021
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 the δ18O of 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 the 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 and subtropical Atlantic Ocean. We established a new paleotemperature 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 allows 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 for a reconstruction with an uncertainty of ± 2.49. This was confirmed by a Monte Carlo simulation, applied to test successive reconstructions in an “ideal case” in which explanatory variables are known. This simulation shows that from a purely statistical point of view, successive reconstructions involving Mg∕Ca and δ18Oc preclude salinity reconstructions 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 led to a much better estimation of salinity (± 0.26) than the successive reconstructions.

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Dissard Delphine, Reichart Gert Jan, Menkes Christophe, Mangeas Morgan, Frickenhaus Stephan, Bijma Jelle (2021). Mg∕Ca, Sr∕Ca and stable isotopes from the planktonic foraminifera T. sacculifer: testing a multi-proxy approach for inferring paleotemperature and paleosalinity. Biogeosciences, 18(2), 423-439. Publisher's official version : https://doi.org/10.5194/bg-18-423-2021 , Open Access version : https://archimer.ifremer.fr/doc/00677/78884/