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Climate of the Past An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  10 Mar 2020

10 Mar 2020

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This preprint is currently under review for the journal CP.

Evaluation of isotopes and elements in planktonic foraminifera from the Mediterranean Sea as recorders of seawater oxygen isotopes and salinity

Linda K. Dämmer1, Lennart de Nooijer1, Erik van Sebille2, Jan Haak1, and Gert-Jan Reichart1,3 Linda K. Dämmer et al.
  • 1Department of Ocean Systems, NIOZ Royal Netherlands Institute for Sea Research, and Utrecht University, Texel, The Netherlands
  • 2Department of Physics, Institute for Marine and Atmospheric research Utrecht (IMAU), Utrecht University, Utrecht, The Netherlands
  • 3Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Utrecht, The Netherlands

Abstract. The Mediterranean Sea is characterized by a relatively strong west to east salinity gradient, which makes it an area suitable to test the effect of salinity on foraminiferal shell geochemistry. We collected living specimens of the planktonic foraminifer Globigerinoides ruber (white) to analyse the relation between element/Ca ratios, stable oxygen isotopes of their shells and surface seawater salinity, isotopic composition and temperature. The oxygen isotopes of sea surface water correlate with salinity in the Mediterranean also during winter, when sampled for this study. Sea water oxygen and hydrogen isotopes are positively correlated in both the eastern and western Mediterranean Sea, though especially in the eastern part the relationship differs from values reported previously for that area. The slope between salinity and seawater oxygen isotopes is lower than previously published. Still, despite the rather modest slope, seawater and foraminiferal carbonate oxygen isotopes are correlated in our dataset although with large residuals and high residual variability. This scatter can be due to either biological variability in vital effects or environmental variability. Numerical models backtracking particles show ocean current driven mixing of particles of different origin might dampen sensitivity and could result in an offset caused by horizontal transport. Results show that Na/Ca is positively correlated to salinity and independent of temperature. Foraminiferal Mg/Ca increases with temperature, as expected, and in line with earlier calibrations, also in the high salinity environment. By using living foraminifera during winter, the previously established Mg/Ca-temperature calibration is extended to temperatures below 18 °C, which is a fundamental prerequisite of using single foraminifera for reconstructing past seasonality.

Linda K. Dämmer et al.

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Linda K. Dämmer et al.

Linda K. Dämmer et al.


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Publications Copernicus
Short summary
The composition of foraminifera shells often varies with environmental parameters such as temperature or salinity, and can thus be used as proxies. Often a single proxy is being influenced by more than one parameter. Here we show that while salinity impacts shell Na/Ca, temperature has no effect. We also show that the combination of different proxies (Mg/Ca and d18O) to reconstruct salinity does not seem to work as previously thought.
The composition of foraminifera shells often varies with environmental parameters such as...