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海洋、生物圈和大气在地质时期的化学变化。尽管这样的重建是基于健全的理论和实验原则，但许多重要的细节仍有待解决，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，碳酸盐在极其受控的条件下生长，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。这一结果将提高我们从碳酸盐岩中提取古环境信息的能力，并可能使我们更好地预测地球将如何应对不断向地球大气输入二氧化碳的人为因素。这项研究将与向K-12学生和地质学专业本科生介绍晶体生长和古气候概念的教学和动手推广活动相结合。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生长缓慢，还是在远离平衡的条件下快速生长。当晶体快速生长或晶体生长是生物调节的时候，氧和碳的同位素分配会受到生长的晶体与溶解的无机碳(DIC)之间的反应动力学以及DIC物种与溶液中的H2O之间的反应动力学的影响。在他们最近成功地解卷这些动力学效应的基础上，研究小组为该项目制定了四个目标：(1)确定不同的盐度如何影响氧和碳同位素行为，(2)确定可变平衡的DIC池如何在碳酸盐的氧和碳同位素组成中表达，(3)比较两种不同的碳酸盐-方解石和文石的行为，以及(4)应用所获得的见解来解释碳酸盐沼泽、凝灰岩、珊瑚、脉状、结核和沉积物中的自然稳定同位素变化。该方法使用最先进的实验设备在固定的pH和生长速度下生长晶体。然后使用质谱学对晶体和溶液进行分析。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.