Experimental calibration of stable isotope and REE partitioning in bioapatite

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Technical description:The geochemistry of biogenic calcium phosphate (bioapatite) is widely used in studies of paleoclimatology, paleoecology, paleoceanography, anthropology/archeology, fossil forensics, geochronology, and tooth caries. Many such endeavors are compromised by poor understanding of the fractionation of stable isotopes of oxygen and carbon in structural carbonate (CO3), and partitioning of rare-earth elements (REE) between bioapatite and aqueous solutions. Stable isotope fractionations and REE partition coefficients will be measured by synthesizing bioapatite in isotopically- and chemically- characterized solutions at temperatures ranging from 10 to 60 °C. Particular emphasis will be placed on identifying the crystallographic site of CO3 substitution as a control on isotope fractionations, calibrating spectroscopic measurements of tooth chemistry, and characterizing particle sizes and surface areas to distinguish intracrystalline vs. adsorption partition coefficients for REE. Time-series experiments will be conducted to ensure close approach to equilibrium, and past experimental methods will be reproduced for improved particle size characterization and comparison to new chemical and isotopic data. Non-technical/Broader impacts:This grant funds a comprehensive calibration of the geochemical behavior of bioapatite - the mineral that constitutes bones and teeth. This work is important for validating past research and improving quantitative interpretations in numerous fields ranging from paleoclimate and paleoceanography to anthropology, forensic discrimination of fossils, geochronology and possibly dental stability. Specifically, we will calibrate methods to determine the carbonate (CO3) content of bioapatite, which strongly controls tooth enamel solubility, and synthesize bioapatites with different CO3 contents. The tendency for bioapatite to accumulate lanthanide-group elements and the heavy isotopes of oxygen and carbon will be calibrated and compared with sparse previous measurements. These data will inform past interpretations of modern tooth and fossil geochemistry and improve targeting of future studies involving modern and fossil teeth. Educational outreach includes research training for a graduate student, and development of undergraduate research for underrepresented groups. Additional training includes development of mentorship skills for a young female research scientist. Boise State serves a large proportion of returning and part-time students with an average undergraduate age of 27. Thus, research and education activities impact a different demographic than at most other universities.