Sr partitioning in the benthic foraminifera <i>Ammonia aomoriensis</i> and <i>Amphistegina lessonii</i>

The shallow water benthic foraminifera Ammonia aomoriensis and Amphistegina lessonii were grown at differentseawater Sr/Ca and the test Sr/Ca ratio was determined by Laser Ablation - Inductively Coupled Plasma - MassSpectrometry. A. aomoriensis test Sr/Ca is positively correlated with seawater Sr/Ca. The linear regression has aslope of 0.17, representing the overall Sr partitioning coefficient KDSr. The slope remains unchanged, if seawaterCa concentration is changed in order to change the seawater Sr/Ca. In the case of A. lessonii, the slopes of the linearregressions representing KDSr differ fromone another i.e., 0.16 if the Sr concentration is changed and 0.32 if the Calevel is changed. This difference in KDSr can be explained by the, relative to A. aomoriensis, highMg content of A.lessonii (ca. 40mmol/mol), distorting the calcite lattice andweakening the discrimination against Sr. TheMg contentof A. aomoriensis is too low (ca. 4 mmol/mol) to observe the influence on Sr partitioning. All data are compatiblewith a recently developed model for minor element partitioning in foraminifera (Nehrke et al., 2013;Mewes et al., 2015a). On thewhole, our data confirm themodel (applicability of themodel to Sr and dependenceof the calcite Sr/Ca on seawater Sr/Ca, as opposed to seawater Sr concentration), and improve our understandingof the model (influence of calcite Mg/Ca on Sr partitioning)