Establishing a Baseline for Kinetic and Thermodynamic Origins of Vital Effects: The Interplay of Factors that Control Mg and Sr Signatures in Calcite

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ABSTRACTOCE-0526670The ratios of Mg/Ca and Sr/Ca in carbonate biominerals have emerged as paleotemperature proxies due to their reduced susceptibility to changes in salinity and polar ice volume relative to isotopic indicators. The organisms that produce these biominerals employ complex controlled biomineralization strategies to create spatial and chemical microenvironments that directly influence the nucleation, growth, and shape of biominerals. The collective influences of these microenvironments can significantly mask external environmental signatures through what is called 'vital effects'. Many new studies report extensive vital effects for a variety of signatures and taxa; however, the interplay of factors that give observed signatures is poorly understood. This is an enormous obstacle to building reliable and calibrated paleoenvironmental proxy models. For this reason, a researcher at Virginia Polytechnic Institute and State University will establish the interplays between physical and microenvironmental factors in governing magnesium and strontium signatures in calcites. Using a mechanistic approach, rooted in thermodynamic and kinetic principles of mineralization, the researcher will examine the following: (1) how carbonate ion speciation affects magnesium and strontium content; (2) how coupled non-equilibrium interactions between these elements and other constituents in seawater affect signatures; and (3) how transport conditions affect signatures. By understanding compositional signatures rooted in a mechanism-based approach, paleoenvironmental proxy models will have a fundamental basis that can be reliably calibrated to the appropriate chemical and physical parameters. As regards broader impacts, the PI in collaboration with a Geosciences Outreach Coordinator will develop a hands-on activity (Biominerals-Earth to Life) that integrates minerals, organisms, results from this study, and other resources from the Virginia Tech Geosciences Museum. This activity is targeted for middle school students. Two graduate students and one undergraduate student will be trained as part of this project.