Planktonic foraminiferal spine versus shell carbonate Na incorporation in relation to salinity

Abstract

<p><strong>Abstract.</strong> 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.</p>

Salinity Effect on Trace Element Incorporation in Cultured Shells of the Large Benthic Foraminifer Operculinaammonoides

“…However, further work by Mezger et al. (2019) demonstrated a significant difference in Na concentrations between shell and spine of spinose planktonic foraminifera and concluded that coretop specimens lacking spines were characterized by a low sensitivity of Na/Ca shell to salinity. In addition to the Na/Ca shell , previous studies have shown that Mg/Ca shell and Sr/Ca shell also correlate with salinity (e.g., Allen et al., 2016; Dissard et al., 2010; Geerken et al., 2018; Kısakürek et al., 2008; Lea et al., 1999; Nürnberg et al., 1996; Wit et al., 2013).…”

“…While Hauzer et al (2018) focused on the calibration of the Na/Ca shell as a proxy for Ca sw , other studies have shown that Na/Ca shell may also change as a function of salinity, and hence may also be used as a salinity proxy (Land & Hoops, 1973;Mezger et al, 2018;Wit et al, 2013). However, further work by Mezger et al (2019) demonstrated a significant difference in Na concentrations between shell and spine of spinose planktonic foraminifera and concluded that coretop specimens lacking spines were characterized by a low sensitivity of Na/Ca shell to salinity. In addition to the Na/Ca shell , previous studies have shown that Mg/Ca shell and Sr/Ca shell also correlate with salinity (e.g., Allen et al, 2016;Dissard et al, 2010;Geerken et al, 2018;Kısakürek et al, 2008;Lea et al, 1999;Nürnberg et al, 1996;Wit et al, 2013).…”

Distribution of chlorine and fluorine in benthic foraminifera

“…Similarly, spine and the spine attachment zone of planktic foraminifera are enriched in Na while depleted in Mg, and vice verca, respectively (Branson et al, 2016;Mezger et al, 2019;Bonnin et al, 2019).…”

Testing the Influence of Changing Seawater Ca Concentration on Elements/Ca Ratios in Planktic Foraminifera: A Culture Experiment

“…The control groups were sampled at the same time as the cultured foraminifera and represent the natural population of the Gulf of Eilat. From this natural population, we picked only G. siphonifera specimens without spines (i.e., spines were shed during the sampling and picking) because it was shown that spines have different chemical composition than the shell especially higher Na (Bonnin et al., 2019; Branson et al., 2016; Mezger, de Nooijer, Bertlich, et al., 2018; Mezger et al., 2016). Control specimens were grouped by size, cleaned, and analyzed by the same methods as the cultured specimens and their ICP‐MS values were used as R ini (i.e., the initial calcite).…”