Abstract. Accurate reconstructions of seawater salinity could provide valuable constraints for studying past ocean circulation, the hydrological cycle and sea level change. Controlled growth experiments and field studies have shown the potential of foraminiferal Na ∕ Ca as a direct salinity proxy. Incorporation of minor and trace elements in foraminiferal shell carbonate varies, however, greatly between species and hence extrapolating calibrations to other species needs validation by additional (culturing) studies. Salinity is also known to impact other foraminiferal carbonate-based proxies, such as Mg ∕ Ca for temperature and Sr ∕ Ca for sea water carbonate chemistry. Better constraints on the role of salinity on these proxies will therefore improve their reliability. Using a controlled growth experiment spanning a salinity range of 20 units and analysis of element composition on single chambers using laser ablation-Q-ICP-MS, we show here that Na ∕ Ca correlates positively with salinity in two benthic foraminiferal species (Ammonia tepida and Amphistegina lessonii). The Na ∕ Ca values differ between the two species, with an approximately 2-fold higher Na ∕ Ca in A. lessonii than in A. tepida, coinciding with an offset in their Mg content (∼ 35 mmol mol−2 versus ∼ 2.5 mmol mol−1 for A. lessonii and A. tepida, respectively). Despite the offset in average Na ∕ Ca values, the slopes of the Na ∕ Ca–salinity regressions are similar between these two species (0.077 versus 0.064 mmol mol−1 change per salinity unit). In addition, Mg ∕ Ca and Sr ∕ Ca are positively correlated with salinity in cultured A. tepida but show no correlation with salinity for A. lessonii. Electron microprobe mapping of incorporated Na and Mg of the cultured specimens shows that within chamber walls of A. lessonii, Na ∕ Ca and Mg ∕ Ca occur in elevated bands in close proximity to the primary organic lining. Between species, Mg banding is relatively similar, even though Mg content is 10 times lower and that variation within the chamber wall is much less pronounced in A. tepida. In addition, Na banding is much less prominent in this species than it is in A. lessonii. Inter-species differences in element banding reported here are hypothesized to be caused by differences in biomineralization controls responsible for element uptake.

Trace and minor elements incorporated in foraminiferal shells are among the most used proxies for reconstructing past environmental conditions. A prominent issue concerning these proxies is that the inter-specimen variability in element composition is often considerably larger than the variability associated with the environmental conditions for which the proxy is used. Within a shell of an individual specimen the trace and minor elements are distributed in the form of bands of higher and lower concentrations. It has been hypothesized that differences in specimen-specific element banding patterns cause the inter-specimen and inter-species variability observed in average element composition, thereby reducing the reliability of proxies. To test this hypothesis, we compared spatial distributions of Mg, Na, Sr, K, S, P and N within chamber walls of two benthic foraminiferal species ( Amphistegina lessonii and Ammonia tepida ) with largely different average Mg content. For both species the selected specimens were grown at different temperatures and salinities to additionally assess how these parameters influence the element concentrations within the shell wall. Our results show that Mg, Na, Sr and K are co-located within shells, and occur in bands that coincide with organic linings but extend further into the calcite lamella. Changes in temperature or salinity modulate the element-banding pattern as a whole, with peak and trough heights co-varying rather than independently affected by these two environmental parameters. This means that independent changes in peak or trough height do not explain differences in average El/Ca between specimens. These results are used to evaluate and synthesize models of underlying mechanisms responsible for trace and minor element partitioning during calcification in foraminifera.

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Abstract. Shell chemistry of foraminiferal carbonate proves to be useful in reconstructing past ocean conditions. A new addition to the proxy toolbox is the ratio of sulfur (S) to calcium (Ca) in foraminiferal shells, reflecting the ratio of SO42- to CO32- in seawater. When comparing species, the amount of SO42- incorporated, and therefore the S∕Ca of the shell, increases with increasing magnesium (Mg) content. The uptake of SO42- in foraminiferal calcite is likely connected to carbon uptake, while the incorporation of Mg is more likely related to Ca uptake since this element substitutes for Ca in the crystal lattice. The relation between S and Mg incorporation in foraminiferal calcite therefore offers the opportunity to investigate the timing of processes involved in Ca and carbon uptake. To understand how foraminiferal S∕Ca is related to Mg∕Ca, we analyzed the concentration and within-shell distribution of S∕Ca of three benthic species with different shell chemistry: Ammonia tepida, Bulimina marginata and Amphistegina lessonii. Furthermore, we investigated the link between Mg∕Ca and S∕Ca across species and the potential influence of temperature on foraminiferal S∕Ca. We observed that S∕Ca is positively correlated with Mg∕Ca on a microscale within specimens, as well as between and within species. In contrast, when shell Mg∕Ca increases with temperature, foraminiferal S∕Ca values remain similar. We evaluate our findings in the light of previously proposed biomineralization models and abiological processes involved during calcite precipitation. Although all kinds of processes, including crystal lattice distortion and element speciation at the site of calcification, may contribute to changes in either the amount of S or Mg that is ultimately incorporated in foraminiferal calcite, these processes do not explain the covariation between Mg∕Ca and S∕Ca values within specimens and between species. We observe that groups of foraminifera with different calcification pathways, e.g., hyaline versus porcelaneous species, show characteristic values for S∕Ca and Mg∕Ca, which might be linked to a different calcium and carbon uptake mechanism in porcelaneous and hyaline foraminifera. Whereas Mg incorporation might be controlled by Ca dilution at the site of calcification due to Ca pumping, S is linked to carbonate ion concentration via proton pumping. The fact that we observe a covariation of S and Mg within specimens and between species suggests that proton pumping and Ca pumping are intrinsically coupled across multiple scales.

Reconstructing millennial‐ to centennial‐scale climate variability for the Eemian—an interval with estimated sea surface temperatures ~0.5 °C warmer than “preindustrial”—requires records with high temporal resolution. Sapropel S5 sediments, deposited under anoxic conditions in the Eastern Mediterranean Sea, offer the rare opportunity to assess multicentennial climate variability during this time. Here we present high‐resolution S5 piston core data from the Nile delta region. Specifically, we focus on Ba/Ti, Br/Ti, and Mo/Ti, as they are proxies for paleo‐productivity, marine organic carbon, and sediment anoxia, respectively. A high correlation between our Ba/Ti values in core 64PE‐406‐E1 and well‐dated Ba records of nearby cores (LC21 and ODP967) was found. We, therefore, tuned our data to these cores obtaining an initial age model. A time‐frequency analyses indicated significant frequency content in the multicentennial band, although the frequency components drifted over time. Assuming spectral simplicity, we corrected for sedimentation rate changes on a multicentennial time scale. This novel approach grants a higher‐resolution age model. The resulting variability in sedimentation rate is similar to records of monsoon variability, indicating a possible link between sedimentation at the core location and low‐latitude monsoon variability, linked via the River Nile. Moreover, the periodicities found in the sapropel time series are similar to the frequency content of total solar irradiance and sunspot records known for the Holocene, at least at high frequencies (~50–150 years). Hence, our data suggest cyclic intrasapropel variability, at least during the deposition of sapropel S5, may be linked to solar cycles.

<p><strong>Abstract.</strong> Accurate reconstructions of seawater salinity could provide valuable constraints for studying past ocean circulation, the hydrological cycle and sea level change. Controlled growth experiments and field studies have shown the potential of foraminiferal Na/Ca as a direct salinity proxy. Incorporation of minor and trace elements in foraminiferal shell carbonate varies, however, greatly between species and hence extrapolating calibrations to other species needs validation by additional (culturing) studies. Salinity is also known to impact other foraminiferal carbonate-based proxies, such as Mg/Ca for temperature and Sr/Ca for seawater carbonate chemistry. Better constraints on the role of salinity on these proxies will improve their reliability. Using a controlled growth experiment spanning a salinity range of 20 units and analysis of single chamber element composition using laser ablation-ICP-MS, we here show that Na/Ca correlates positively with salinity in two benthic foraminiferal species (<i>Ammonia tepida</i> and <i>Amphistegina lessonii</i>). The Na/Ca values differ between the two species, with an approximately 2-fold higher Na/Ca in <i>Amphistegina</i> than in <i>Ammonia</i>, which coincides with an offset in their Mg content (~ 35 mmol/mol versus ~ 2.5 mmol/mol for <i>A. lessonii</i> and <i>A. tepida</i>, respectively). Despite the offset in average Na/Ca values, the slopes of the Na/Ca-salinity regressions are similar between these two species. In addition, Mg/Ca and Sr/Ca are positively correlated with salinity in cultured <i>A. tepida</i>, but do not show a correlation to salinity for <i>A. lessonii</i>. Electron microprobe mapping of incorporated Na and Mg of the cultured specimens shows that within chamber walls of <i>A. lessonii</i>, Na/Ca and Mg/Ca occur in elevated bands in close proximity to the primary organic lining. For specimens of <i>A. tepida</i>, Mg-banding shows a similar pattern to that in <i>A. lessonii</i>, albeit that variation within the chamber wall is much less pronounced. Also Na-banding is much less prominent in this species. The less prominent banding and lower Mg and Sr contents of <i>A. tepida</i> are likely related to the absence of an inter-element correlation within experimental conditions.</p>

<p><strong>Abstract.</strong> Shell chemistry of foraminiferal carbonate proves to be useful in reconstructing past ocean conditions. A new addition to the proxy toolbox is the ratio of sulfur (S) to calcium (Ca) in foraminiferal shells, reflecting the ratio of SO<sub>4</sub><sup>2−</sup> to CO<sub>3</sub><sup>2−</sup> in seawater. When comparing species, the amount of SO<sub>4</sub><sup>2−</sup> incorporated, and therefore the S/Ca of the shell, increases with increasing magnesium (Mg) content. The uptake of SO<sub>4</sub><sup>2−</sup> in foraminiferal calcite is likely coupled to carbon uptake, while the incorporation of Mg is more likely related to Ca uptake since this element substitutes Ca in the crystal lattice. The relation between S and Mg incorporation in foraminiferal calcite therefore offers the opportunity to investigate the timing of processes involved in Ca and carbon uptake. To understand how foraminiferal S/Ca is related to Mg/Ca, we analyzed the concentration and within-shell distribution of S/Ca of three benthic species with different shell chemistry: <i>Ammonia tepida</i>, <i>Bulimina marginata</i> and <i>Amphistegina lessonii</i>. Furthermore, we investigated the link between Mg/Ca and S/Ca across species and the potential influence of temperature on foraminiferal S/Ca. We observed that S/Ca is positively correlated with Mg/Ca on microscale within specimens, as well as between and within species. In contrast, when shell Mg/Ca increases with temperature, foraminiferal S/Ca values remain similar. We evaluate our findings in the light of previously proposed biomineralization models and abiological processes involved during calcite precipitation. Although all kinds of processes, including crystal lattice distortion and element speciation at the site of calcification, may contribute to changes in the amount of S and Mg that is ultimately incorporated in foraminiferal calcite, these processes do not explain the consistent co-variation between Mg/Ca and S/Ca values. We observe that groups of foraminifera with different calcification pathways, e.g. hyaline versus porcelaneous species, show characteristic values for S/Ca and Mg/Ca, which might be linked to a different calcium and carbon uptake mechanism in porcelaneous and hyaline foraminifera. Whereas Mg incorporation is linked to the Ca-pump, S is linked to carbonate ion concentration via proton pumping. The fact that we observe coupled behavior of S and Mg, within specimens and between species suggests that proton pumping and Ca pumping are intrinsically coupled across scales.</p>

Abstract. Over the last decades a suite of inorganic proxies based on foraminiferal calcite have been developed, of which some are now widely used for paleoenvironmental reconstructions. Studies of foraminiferal shell chemistry have largely focused on cations and oxyanions, while much less is known about the incorporation of anions. The halogens fluoride and chloride are conservative in the ocean, which makes them candidates for reconstructing paleoceanographic parameters. However, their potential as a paleoproxy has hardly been explored, and fundamental insight in their incorporation is required. Here we used nano-scale secondary ion mass spectrometry (NanoSIMS) to investigate, for the first time, the distribution of Cl and F within shell walls of four benthic species of foraminifera. In the rotaliid species Ammonia tepida and Amphistegina lessonii Cl and F were highly heterogeneous and correlated within the shell walls, forming bands that were co-located with the banded distribution of phosphorus. In the miliolid species Sorites marginalis and Archaias angulatus the distribution of Cl and F was much more homogeneous without discernible bands. In these species Cl and P were correlated, whereas no correlation was observed between Cl and F or between F and P. Additionally, their F content was about an order of magnitude higher than in the rotaliid species. The high variance in the Cl and F content in the studied foraminifera could not be attributed to environmental parameters. Based on these findings we suggest that in the rotaliid species Cl and F are predominately associated with organic linings. We further propose that in the miliolid species Cl may be incorporated as a solid solution of chlorapatite or associated with organic molecules in the calcite. The high F content together with the lack of correlation between Cl and F or P in the miliolid foraminifera suggests a fundamentally different incorporation mechanism. Overall, our data clearly show that the calcification pathway employed by the studied foraminifera governs the incorporation and distribution of Cl, F, P and other elements in their calcite shells.