Mg/Ca ratios measured by Electron Probe Microanalyzer in shells of the planktic foraminifer Morozovella velascoensis from ODP Site 865 (Central Pacific) across the PETM (~56 Ma)

Foraminiferal shells of the species M. velascoensis from sediments spanning ~650 ka across the PETM section of ODP Site 865, Central Pacific, were embedded in epoxy and polished to midsection. Suitable, well-preserved domains for in-situ analysis were identified by scanning electron microscopy. In-situ measurements of the Mg/Ca ratios were performed using a CAMECA SX-51 electron microprobe housed in the Cameron and Wilcox Microbeam Laboratory at the UW-Madison Department of Geoscience. Depending on the number of suitable targets for analysis, between one and seven Mg/Ca measurements were performed for each shell. Fully quantitative microanalyses (mineral standards, background subtracted, and matrix corrected) were performed using Probe for EPMA software (Probe Software, Inc.). The natural carbonate standards Delight Dolomite and Callender Calcite were used for Mg and Ca, respectively. Mg-K alpha X-rays were measured on two spectrometers and aggregated. Carbon was calculated within the matrix correction, being allocated as one atom of carbon to 3 atoms of oxygen, and oxygen by stoichiometry to the cations measured, thus analytical totals of 98 – 100.5 wt. % are a measure of accuracy. Analyses featuring analytical totals below 98 wt. % or above 100.5 wt. % were excluded from the data set.