Abstract. The quantitative reconstruction of past seawater salinity has yet to be achieved, and the search for a direct and independent salinity proxy is ongoing. Recent culture and field studies show a significant positive correlation of Na∕Ca with salinity in benthic and planktonic foraminiferal calcite. For accurate paleoceanographic reconstructions, consistent and reliable calibrations are necessary, which are still missing. In order to assess the reliability of foraminiferal Na∕Ca as a direct proxy for seawater salinity, this study presents electron microprobe Na∕Ca data measured on cultured specimens of Trilobatus sacculifer. The culture experiments were conducted over a wide salinity range of 26 to 45, while temperature was kept constant. To further understand potential controlling factors of Na incorporation, measurements were also performed on foraminifera cultured at various temperatures in the range of 19.5 to 29.5 ∘C under constant salinity conditions. Foraminiferal Na∕Ca values positively correlate with seawater salinity (Na/CaT. sacculifer=0.97+0.115⋅salinity, R=0.97, p<0.005). Temperature, on the other hand, exhibits no statistically significant relationship with Na∕Ca values, indicating salinity to be one of the dominant factors controlling Na incorporation. The culturing results are corroborated by measurements on T. sacculifer from Caribbean and Gulf of Guinea surface sediments, indicating no dissolution effect on Na∕Ca in foraminiferal calcite with increasing water depth up to >4 km. In conclusion, planktonic foraminiferal Na∕Ca can be applied as a potential proxy for reconstructing sea surface salinities, although species-specific calibrations might be necessary.

No abstract

&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; The quantitative reconstruction of past seawater salinity has yet to be achieved and the search for a direct and independent salinity proxy is ongoing. Recent culture and field studies show a significant positive correlation of Na/Ca with salinity in benthic and planktonic foraminiferal calcite. For accurate paleoceanographic reconstructions, consistent and reliable calibrations are necessary, which are still missing. In order to assess the reliability of foraminiferal Na/Ca as a direct proxy for seawater salinity, this study presents electron microprobe Na/Ca data, measured on cultured specimens of &lt;i&gt;Trilobatus sacculifer&lt;/i&gt;. The culture experiments were conducted over a wide salinity range of 26 to 45, while temperature was kept constant. To further understand potential controlling factors of Na incorporation, measurements were also performed on foraminifera cultured at various temperatures in the range of 19.5&amp;#8201;&amp;#176;C to 29.5&amp;#8201;&amp;#176;C under constant salinity conditions. Foraminiferal Na/Ca ratios positively correlate with seawater salinity (Na/Ca&lt;sub&gt;foram&lt;/sub&gt;&amp;#8201;=&amp;#8201;0.97&amp;#8201;+&amp;#8201;0.115&amp;#8201;&amp;#8901;&amp;#8201;Salinity, R&amp;#8201;=&amp;#8201;0.97, &lt;i&gt;p&lt;/i&gt;&amp;#8201;&lt;&amp;#8201;0.005). Temperature on the other hand exhibits no statistically significant relationship with Na/Ca ratios indicating salinity to be the dominant factor controlling Na incorporation. The culturing results are corroborated by measurements on &lt;i&gt;T. sacculifer&lt;/i&gt; from Caribbean and Gulf of Guinea surface sediments. In conclusion, planktonic foraminiferal Na/Ca can be applied as a reliable proxy for reconstructing sea surface salinities, albeit species-specific calibrations might be necessary.&lt;/p&gt;

Abstract. Sea surface salinity is one of the most important parameters to reconstruct in paleoclimatology, reflecting amongst other things the hydrological cycle, paleodensity, ice volume, and regional and global circulation of water masses. Recent culture studies and a Red Sea field study revealed a significant positive relation between salinity and Na incorporation within benthic and planktonic foraminiferal shells. However, these studies reported varying partitioning of Na between and within the same species. The latter could be associated with ontogenetic variations, most likely spine loss. Varying Na concentrations were observed in different parts of foraminiferal shells, with spines and regions close to the primary organic sheet being especially enriched in Na. In this study, we unravel the Na composition of different components of the planktonic foraminiferal shell wall using electron probe micro-analysis (EPMA) and solution ICP-MS. A model is presented to interpret EPMA data for spines and spine bases to quantitatively assess differences in composition and contribution to whole-shell Na∕Ca signals. The same model can also be applied to other spatial inhomogeneities observed in foraminiferal shell chemistry, like elemental (e.g., Mg, Na, S) banding and/or hotspots. The relative contribution of shell carbonate, organic linings, spines and spine bases to whole-shell Na chemistry is considered quantitatively. This study shows that whereas the high Na areas may be susceptible to taphonomic alterations, the Na chemistry of the shell itself seems relatively robust. Comparing both shell and spine Na∕Ca values with salinity shows that shell chemistry records salinity, albeit with a very modest slope.

&lt;p&gt;&lt;strong&gt;Abstract.&lt;/strong&gt; Sea surface salinity is one of the most important parameters to reconstruct in paleoclimatology, reflecting amongst others the hydrological cycle, paleo-density, ice volume, and regional and global circulation of water masses. Recent culture studies and a Red Sea field study revealed a significant positive relation between salinity and Na incorporation within benthic and planktonic foraminiferal shells. However, these studies reported varying partitioning of Na between and within the same species. The latter could be associated with ontogenetic variations, most likely spine loss. Varying Na concentrations were observed in different parts of foraminiferal shells, with especially spines and regions close to the primary organic sheet being enriched in Na. In this study, we unravel the Na composition of different components of the planktonic foraminiferal shell wall using Electron Probe Micro Analysis (EPMA) and solution-ICP-MS. A model is presented to interpret EPMA data for spines and spine bases to quantitatively assess differences in composition and contribution to whole shell Na/Ca signals. The same model can also be applied to other spatial inhomogeneities observed in foraminiferal shell chemistry, like elemental (e.g. Mg, Na, S) banding and/or hotspots. The relative contribution of shell calcite, organic linings, spines and spine bases to whole shell Na chemistry is considered quantitatively. This study shows that whereas the high Na areas may be susceptible to taphonomy, the Na chemistry of the shell itself seems relatively robust. Comparing both shell and spine Na/Ca values with salinity shows that shell chemistry records salinity, albeit with a very modest slope.&lt;/p&gt;