Interindividual variability and ontogenetic effects on Mg and Sr incorporation in the planktonic foraminifer Globigerinoides sacculifer

Abstract

In order to investigate the interindividual and ontogenetic effects on Mg and Sr incorporation, magnesium/calcium (Mg/Ca) and strontium/calcium (Sr/Ca) ratios of cultured planktonic foraminifera have been determined. Specimens of Globigerinoides sacculifer were grown under controlled physical and chemical seawater conditions in the laboratory. By using this approach, we minimised the effect of potential environmental variability on Mg/Ca and Sr/Ca ratios. Whereas temperature is the overriding control of Mg/Ca ratios, the interindividual variability observed in the Mg/Ca values contributes 2-3°C to the apparent temperature variance. Interindividual variability in Sr/Ca ratios is much smaller than that observed in Mg/Ca values. The variability due to ontogeny corresponds to À0.43 mmol/mol of Mg/Ca ratio per chamber added. This translates into an apparent decrease of $1°C in Mg/Ca-based temperature per ontogenetic (chamber) stage. No significant ontogenetic effect is observed on Sr incorporation. We conclude that the presence of a significant ontogenetic effect on Mg incorporation can potentially offset Mg/Ca-based temperature reconstructions. We propose two new empirical Mg/Ca-temperature equation based on Mg/Ca measurements of the last four ontogenetic (chamber) stages and whole foraminiferal test: Mg/Ca = (0.55(±0.03) À 0.0002(±4 Â 10 À5 ) MSD) e 0.089T and, Mg/Ca = (0.55(±0.03) À 0.0001(±2 Â 10 À5 ) MSD) e 0.089T , respectively, where MSD corresponds to the maximum shell diameter of the individual.

A reappraisal of the vital effect in cultured benthic foraminifer <I>Bulimina marginata</I> on Mg/Ca values: assessing temperature uncertainty relationships

“…The impact of inter-individual variability on the accuracy of paleo-temperature reconstructions can be calculated by assuming the standard deviation in the Mg/Ca values (measure of variability) from this culture study is applicable to other foraminiferal species as well. The average variability (standard deviation) within one temperature experiment for a population of B. marginata is 16.3 % (Table 2), which is similar to percentages found in other foraminiferal species (Sadekov et al, 2008;Dissard et al, 2010;Wit et al, 2010;Dueñas-Bohórquez et al, 2011a). This percentage can be used to calculate a standard error (σ / √ n) of the average Mg/Ca value at any given temperature for a number of foraminiferal Mg/Catemperature calibrations.…”

“…size effects) may have a relatively large impact on the Mg/Ca-temperature calibration presented here. An effect of ontogeny on planktonic foraminiferal Mg/Ca has been stipulated (Nürnberg et al, 1996;Wit et al, 2010;Dueñas-Bohórquez et al, 2011a study. Intra-test variability for the experiment at 14 • C was, therefore, tested by using an analysis of variance (ANOVA) because the experiment contained enough data for this analysis.…”

Encrustation and trace element composition of <i>Neogloboquadrina dutertrei</i> assessed from single chamber analyses – implications for paleotemperature estimates

“…Calibration was performed against a SRM NIST610 glass standard ablated at a higher energy density (∼ 5 J cm −2 ) between every 12 foraminiferal samples. Simultaneous ablation of a calcite crystal (Iceland spar) at the lower energy density settings allowed for calculation of the analytical uncertainties of the ICP-MS, which are 0.06, 0.04 and 0.07 mmol mol −1 (1σ ) for Mg/Ca, Mn/Ca and Sr/Ca, respectively (Dueñas-Bohorquez et al, 2011).…”

Variability in calcitic Mg/Ca and Sr/Ca ratios in clones of the benthic foraminifer Ammonia tepida

“…Discrepancies between studies could stem from speciesspecific differences in controls on element incorporation, sample size, or both. Field studies of planktonic species show Mg/Ca increases with size in some species and decreases with size in other species (Elderfield et al, 2002;Anand and Elderfield, 2005;Friedrich et al, 2012), while under controlled constant conditions, Mg/Ca of the planktonic Globigerinoides sacculifer decreases with size (Dueñas-Bohórquez et al, 2011a). This implies that part of the relation between planktonic foraminiferal shell size and Mg/Ca is determined by calcification at different water depths (and hence different temperatures), and part of the ontogenetic controls on Mg/Ca are not environment-induced.…”