Impact of seawater [Ca<sup>2+</sup>] on the calcification and calciteMg / Ca of <i>Amphistegina lessonii</i>

Abstract

Abstract. Mg / Ca ratios in foraminiferal tests are routinely used as paleotemperature proxies, but on long timescales, they also hold the potential to reconstruct past seawater Mg / Ca. The impact of both temperature and seawater Mg / Ca on Mg incorporation in Foraminifera has been quantified by a number of studies. The underlying mechanism responsible for Mg incorporation in foraminiferal calcite and its sensitivity to environmental conditions, however, has not been fully identified. A recently published biomineralization model (Nehrke et al., 2013) Nehrke et al. (2013). Here, however, we suggest transmembrane transport fractionation that is not as strong as suggested by Nehrke et al. (2013).

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

“…This trend is seen clearly at the high salinity experiment, where the growth rate of G. siphonifera strongly decreased at Ca sw ≥ 26 mmol/kg and might reflect toxicity effects of Ca at high concentration. This effect has previously been suggested for other foraminifera species cultured under changing Ca sw (Hauzer et al, 2018;Mewes et al, 2015;Raitzsch et al, 2010) as well as for non-calcifying unicellular algae that differ from coccolithophores (that do not show this decrease, Müller et al, 2015). However, the Ca sw threshold seems to differ among the species; for O. ammonoides (Hauzer et al, 2018) and A. tepida (Raitzsch et al, 2010) a Ca sw >18 mmol/kg inhibited the growth rate whereas in A. lessonii, the growth still increased at this concentration and started to decrease at Ca sw = 34 mmol/kg (Mewes et al, 2015).…”

Li Partitioning Into Coccoliths of Emiliania huxleyi: Evaluating the General Role of “Vital Effects” in Explaining Element Partitioning in Biogenic Carbonates

“…However, transmembrane transport of Li and Ca in A. lessonii does not exclude additional fractionation steps such as a precursor phase (Jacob et al, 2017), which would introduce a constant offset of the curves but not change their shapes. The need to combine physiological and mineralogical fractionation steps in a description of the minor element incorporation behavior of A. lessonii was previously highlighted for the divalent cation Mg (Langer et al, 2016;Mewes, Langer, Thoms, et al, 2015). The discovery of a metastable precursor phase for shell calcite in foraminifera (Jacob et al, 2017) could perhaps explain why D Li in A. lessonii is different from that of E. huxleyi, because there is currently no evidence for a precursor phase in coccolithophores.…”

Coupled calcium and inorganic carbon uptake suggested by magnesium and sulfur incorporation in foraminiferal calcite

“…For both sets of measurements, samples were measured against six ratio calibration standards with a matching matrix, i.e., 40 ppm Ca for the temperature set and 100 ppm Ca for the Burgers' Zoo set. In addition to the foraminiferal samples, we measured several standards, including NFHS-1 (NIOZ Foraminifera House Standard; for details see Mezger et al, 2016), JCt-1 (Giant Clam, Tridacna gigas) and JCp-1 (coral, Porites sp. ; Okai et al, 2002) to monitor drift and the quality of the analyses.…”

“…Based on the transmembrane transport mixing model (TMT; Nehrke et al, 2013;Mewes et al, 2015), Mg 2+ might be accidentally transported to the site of calcification by Ca channels or pumps, as well as by passive transport (e.g., leakage, initial seawater enclosed at the site of calcification or seawater endocytosis), while SO 2− 4 would not be transported by the Ca channels or pumps. Only prior to or at the first stages of chamber formation, when the membrane is perhaps not fully closed (Nagai et al, 2018) and the fluid in the site of calcification (SOC) resembles seawater, SO 2− 4 is incorporated due to the relatively high [SO 2− 4 ] in seawater.…”

“…Just prior to formation of a new chamber, the sulfate concentration at the SOC is probably similar to that in seawater, assuming the calcification fluid is composed of either a small volume of seawater enclosed by the protective envelope separating the SOC from seawater or Figure 9. Average values of S/Ca, expressed as SO 2− 4 /CO 2− 3 , versus Mg/Ca of different hyaline (circles) and porcelaneous (diamonds) species of foraminifera of this study (open symbols) and other studies (grey symbols), including values obtained for the NFHS (for a description see Mezger et al, 2016). Culture experiments with varying salinity (c), temperature (1) and pCO 2 (d, e), min and maximum ranges are indicated by grey bars but in most cases fall within the symbol.…”