CAREER: Toward an inorganic calcite reference frame for interpreting the stable isotope composition of biogenic carbonates

碳酸盐矿物在地球表面或附近的各种环境中从水溶液中生长。随着它们的生长，它们会以对温度、溶液酸碱度和溶液化学敏感的方式吸收环境中的杂质。这种关系使地球科学家能够利用碳酸盐岩重建地质时期海洋、生物圈和大气的化学变化。虽然这种重建是基于合理的理论和实验原理，但许多重要的细节还有待解决，部分原因是不同的环境变量可能会相互干扰。 该项目将进行一系列详细的实验，在实验室中在非常良好的控制条件下生长碳酸盐，使团队能够确定任何一个环境变量如何在碳酸盐晶体中留下印记。这些结果将提高我们从碳酸盐岩中提取古环境信息的能力，并可能导致更好地预测地球将如何应对持续的人类活动向地球大气中输入二氧化碳。这项研究将与教学和实践推广活动相结合，向K-12学生和地质学专业的本科高年级学生介绍晶体生长和古气候概念。 稳定同位素在碳酸盐和水之间的分配取决于晶体是在接近平衡的条件下缓慢生长，还是在远离平衡的条件下快速生长。当晶体快速生长或当晶体生长是生物介导的，如在自然界中经常发生的情况，氧和碳同位素分配可以受到生长晶体和溶解的无机碳（DIC）之间的反应动力学的影响，也可以受到DIC物质和溶液中的H2O之间的反应动力学的影响。 基于他们最近在解卷积这些动力学效应方面的成功，研究团队为该项目制定了四个目标：（1）确定变化的盐度如何影响氧和碳同位素行为，（2）确定可变平衡的DIC池如何以碳酸盐的氧和碳同位素组成表示，（3）比较两种不同碳酸盐，方解石和文石的行为，（4）将所获得的认识应用于解释碳酸盐岩、凝灰岩、珊瑚、矿脉、结核和沉积物中的天然稳定同位素变化。该方法使用最先进的实验装置，在固定的pH值和生长速率下生长晶体。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Carbonate minerals grow from aqueous solutions in a wide variety of settings at or near Earth's surface. As they grow, they incorporate impurities from the environment in ways that are sensitive to temperature, solution acidity or alkalinity, and solution chemistry. Such relationships allow Earth scientists to use carbonate rocks for reconstructing changes in the chemistry of the oceans, biosphere, and atmosphere through geologic time. Although such reconstructions are based on sound theoretical and experimental principles, many important details have yet to be worked out, in part because different environmental variables can interfere with one another. This project will carry out a detailed set of experiments where carbonates are grown in the laboratory under extremely well-controlled conditions, enabling the team to determine how any one environmental variable leaves its imprint in a carbonate crystal. The results will improve our ability to extract paleo-environment information from carbonate rocks and could potentially lead to better forecasts of how the Earth will respond to ongoing anthropogenic inputs of carbon dioxide to Earth's atmosphere. The research will be integrated with teaching and hands-on outreach activities that introduce crystal growth and paleoclimate concepts to K-12 students and undergraduate seniors majoring in geology. The partitioning of stable isotopes between carbonates and water depends on whether the crystals grow slowly, under near-equilibrium conditions, or rapidly, under far-from-equilibrium conditions. When crystals grow rapidly or when crystal growth is biologically mediated, as is often the case in nature, oxygen and carbon isotope partitioning can be affected by reaction kinetics between the growing crystal and dissolved inorganic carbon (DIC), and also by reaction kinetics among the DIC species and H2O in solution. Building on their recent successes towards deconvoluting these kinetic effects, the research team has four objectives for the project: (1) determine how varying salinity influences oxygen and carbon isotope behavior, (2) determine how a variably-equilibrated DIC pool is expressed in the oxygen and carbon isotope composition of carbonates, (3) compare the behavior of two different carbonates, calcite and aragonite, and (4) apply the insights gained to interpreting natural stable isotope variations in carbonate travertines, tufas, corals, veins, nodules, and sediments. The approach uses a state-of-the-art experimental apparatus for growing crystals at fixed pH and growth rate. The crystals and solutions are then analyzed using mass spectrometry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.