Mg/Ca analyses of the planktic foraminifera Acarinina soldadoensis from ODP Hole 113-690B

Acarininid shells were cast in epoxy, ground to midsection and imaged by SEM to identify suitable domains for analysis. Fully quantitative Mg/Ca analyses by a CAMECA SX-51 Electron Probe Microanalyzer (mineral standards, background subtracted, and matrix corrected) were performed using Probe for EPMA© software. An accelerating voltage of 15 kV with 10 nA Faraday current and a tightly focused beam were used, with a counting time of 20s on the peak and 10s on each of the two background positions. These analyses were performed using the “Time Dependent Intensity” feature of the Probe for EPMA software, where Ca and Mg were measured in 4 s increments and counts were plotted against time, with extrapolation to time = 0s as the true count rate. The natural carbonate standards Delight Dolomite, Callender Calcite, and UWC-3 were used for Mg and Ca; Mg-KαX-rays were measured on two spectrometers and aggregated. Carbon was calculated within the matrix correction on an atomic basis as C = (Ca + Mg + Sr). Whenever possible, multiple Mg/Ca measurements were placed in each acarininid shell, and the average value was calculated. Data Quality Information: Only EPMA analytical totals of 98.5 – 100.5 wt.% were considered acceptable