Coupled Isotope Ratio Mass Spectrometer and Inductively Coupled Plasma Mass Spectrometer Analysis of Single and Partial Orbulina universa Shells
Abstract
Foraminifera stable oxygen and stable carbon isotopes are widely applied in paleoceanographic reconstructions. Oxygen and carbon isotopes are typically measured either using bulk sample analysis or single shell analysis (for larger shells). When analyzing foraminifera in bulk, many shells are combined which precludes exploration of population variability. Single shell analysis is commonly performed on samples that exceed 20 micrograms but is difficult or impossible with small shells (typically less than 10 micrograms).The ability to couple stable isotope analyses to laser-ablation ICP-MS analyses of trace metals is desirable, but this puts further demands on shell size. We recently customized a Thermo 253Plus IRMS for the analysis of calcite samples as small as 5 micrograms. Our goal is to improve methods for precisely and accurately measuring stable isotopes on extremely small samples, and, ultimately, single chambers or shell fragments. We conducted reproducibility tests with the species Orbulina universa because their trace-metal chemistry is relatively uniform within their final spherical chamber, and they are large enough to split into several fragments. We split each shell in half and analyzed them for stable isotopes. Shell fragments that weighed near 5 micrograms in initial experiments have acceptable reproducibility (+/- 0.2 for 18O, and 13C), with no systematic changes in accuracy near 5 micrograms. Further improvements are in progress. We will analyze additional O. universa fragments after analyzing them for their trace element (TE) composition. Analysis of TEs via laser ablation prior to isotopic analysis via IRMS will facilitate comparison of trace elemental data and isotopic ratios. This will expand our ability to conduct paired TE and isotope analyses of species found in high latitude regions that often weigh less than 10 micrograms. It will also allow for the analysis of single chambers, which will be transformative in the study of chamber to chamber isotope variability and single chambers grown in the laboratory setting.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMPP25C0938M