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

Dissard, Delphine; Reichart, Gert Jan; Menkes, Christophe; Mangeas, Morgan; Frickenhaus, Stephan; Bijma, Jelle

Over the last decades, sea surface temperature (SST) reconstructions based on the inline-formulaMg∕Ca of foraminiferal calcite have frequently been used in combination with the inline-formulaδ18O signal from the same material to provide estimates of the inline-formulaδ18O of water (inline-formulaδ18Oinline-formulaw), 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 inline-formulaMg∕Ca, inline-formulaSr∕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 inline-formulaMg∕Ca and on the combination of inline-formulaMg∕Ca and inline-formulaSr∕Ca. Subsequently, a sensitivity analysis was performed in which one, two or three different equations were considered. Results indicate that foraminiferal inline-formulaMg∕Ca allows for an accurate reconstruction of surface water temperature. Combining equations, inline-formulaδ18Oinline-formulaw can be reconstructed with a precision of about inline-formula± 0.5 ‰. However, the best possible salinity reconstruction based on locally calibrated equations only allowed for a reconstruction with an uncertainty of inline-formula± 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 inline-formulaMg∕Ca and inline-formulaδ18Oinline-formulac preclude salinity reconstructions with a precision better than inline-formula± 1.69 and hardly better than inline-formula± 2.65 due to error propagation. Nevertheless, a direct linear fit to reconstruct salinity based on the same measured variables (inline-formulaMg∕Ca and inline-formulaδ18Oinline-formulac) was established. This direct reconstruction of salinity led to a much better estimation of salinity (inline-formula± 0.26) than the successive reconstructions.



Dissard, Delphine / Reichart, Gert Jan / Menkes, Christophe / et al: Mg∕Ca, Sr∕Ca and stable isotopes from the planktonic foraminifera T. sacculifer: testing a multi-proxy approach for inferring paleotemperature and paleosalinity. 2021. Copernicus Publications.


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