In situ measurements on benthic foraminifera: a comparison between Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and Wavelength-Dispersive X-Ray Spectroscopy (WDS).

Mg/Ca ratios of foraminiferal calcite are one of the most commonly used geochemical proxies for past temperature reconstructions. Classical measurement techniques, such as Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), used to gather these data, require full or partial destruction/consumption of the foraminifera shells. Thus, it is important to test if different measurement techniques that allow the preservation of the samples/tests, provide accurate and precise Mg/Ca data.

In this research, we present preliminary comparisons of two different techniques LA-ICP-MS (Teledyne Photon Machines Analyte Excite laser (193 nm) and Thermo X Series II ICP-MS at the University of California, Santa Cruz) and Wavelength-Dispersive X-Ray Spectroscopy (WDS; JEOL 8530F Electron Probe Microanalyzer in the Department of Mineral Sciences, Smithsonian Institution) using the benthic foraminifer Uvigerina spp. The test samples are from Site ODP 1015 in the California Margin. Preliminary results show a positive correlation between the two methodologies (r=0.590). Statistically robust assessment of the agreement between methodologies, however, requires techniques specifically designed for this purpose. We therefore create Bland-Altman (mean-difference) plots and calculate the mean bias and 'Limits of Agreement (LoA)' between methodologies. The latter expresses agreement in terms of measurement units, so it is more directly applicable than a unitless correlation coefficient.

Analyzing the chemical composition of individual foraminifer using different techniques is necessary for ensuring consistency in data and enabling comparison so we better understand linked paleoceanographic and paleoclimate events.