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

碳酸盐生物矿物中的Mg/Ca和Sr/Ca比值由于其相对于同位素指示剂对盐度和极地冰体积变化的敏感性降低而成为古温度代用指标。 产生这些生物矿物的生物体采用复杂的受控生物矿化策略来创建直接影响生物矿物的成核、生长和形状的空间和化学微环境。 这些微环境的集体影响可以通过所谓的“生命效应”显著掩盖外部环境特征。 许多新的研究报告了广泛的重要影响的各种签名和类群，但是，相互作用的因素，观察到的签名是知之甚少。这是建立可靠和校准的古环境代理模型的巨大障碍。出于这个原因，弗吉尼亚理工学院和州立大学的一名研究人员将建立物理和微环境因素之间的相互作用，以控制方解石中的镁和锶特征。 使用机械方法，植根于矿化的热力学和动力学原理，研究人员将研究以下内容：（1）碳酸根离子形态如何影响镁和锶含量;（2）这些元素与海水中其他成分之间的耦合非平衡相互作用如何影响签名;以及（3）运输条件如何影响签名。 通过理解植根于基于机制的方法的成分特征，古环境代理模型将有一个基本的基础，可以可靠地校准到适当的化学和物理参数。 至于更广泛的影响，PI与地球科学外展协调员合作，将开发一项实践活动（生物矿物-地球生命），整合矿物，生物，本研究的结果以及弗吉尼亚理工大学地球科学博物馆的其他资源。 这项活动的对象是中学生。 两名研究生和一名本科生将作为该项目的一部分接受培训。

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.