Collaborative Research: Transition Metal Isotope Fractionation during Adsorption to Authigenic Oxides

自生氧化物矿物吸附过程中的同位素分馏是许多金属在古环境中应用的一个重要过程。钼和铁的吸附同位素效应已被证实，Tl的吸附同位素效应被强烈怀疑，至少铬和镉的吸附同位素效应是可能的。这种分馏作用可能影响这些元素的海洋同位素收支，并对根据海洋铁锰结壳等自生氧化物的同位素测量重建金属同位素古记录具有重要意义。为了实现这一潜力，必须定量地了解对同位素分馏的控制，并将重点放在天然样品的实验和理论计算上，而这些实验和理论计算并不是该社区目前工作的重点。在这项研究中，亚利桑那州立大学和普林斯顿大学的研究人员将进行实验室调查和量子化学模拟，以实现以下目标：(1)量化铬、铁、钼、Cd和Tl在各种锰和铁氧化物上的吸附过程中同位素分馏的大小；(2)评估这些影响对温度、pH和盐度等强烈变量的敏感性；以及(3)阐明引起观察到的分馏的反应机理，包括确定它们是来自平衡同位素交换还是动力学效应。需要这些信息来评估这些新的同位素工具是否可以用来了解海洋地球化学循环、重建海洋环境的化学演化或确定海洋的氧化还原历史。就更广泛的影响而言，该项目不仅将支持该项目的早期职业发展，而且还将支持一名研究生、一名本科生和一名博士后在最先进的分析地球化学和理论化学方面的培训。它还将加强研究和教育的基础设施，支持四个不同学术机构的地质学家、地球化学家和化学家之间的伙伴关系，其中包括两个美国以外的机构，他们将整合实验、最先进的分析地球化学和现代理论化学。

ABSTRACTOCE-0526618OCE-0526495Isotope fractionation during adsorption to authigenic oxide minerals is emerging as an important process for paleoproxy applications of many metals. Adsorptive isotope effects have been demonstrated for Mo and Fe, are strongly suspected for Tl, and are at least likely for Cr and Cd. Such fractionation may affect the ocean isotope budgets of these elements and also have important implications for reconstruction of metal isotope paleorecords from isotopic measurements in authigenic oxides such as marine ferromanganese crusts. To realize this potential, it is essential to quantitatively understand the controls on isotopic fractionation and focus on the experiments and theoretical calculations of the natural samples, which have not been the focus of the community's most current work. In this study, researchers at Arizona State University and Princeton University will carry out a laboratory investigation and quantum chemical modeling to attain the following objectives: (1) quantify the magnitude of isotope fractionation of Cr, Fe, Mo, Cd and Tl during adsorption onto various manganese and iron oxides; (2) assess the sensitivity of these effects to intensive variables such as temperature, pH and salinity; and (3) elucidate the reaction mechanisms causing observed fractionations, including definitive determination of whether they arise from equilibrium isotope exchange or kinetics effects. This information is needed to assess whether these new isotopic tools can be used to understand marine geochemical cycles, reconstruct the chemical evolution of the marine environment or determine the ocean redox history. In terms of broader impacts, the project will support not only the early career development of the Co-PI, but also the training of a graduate student, an undergraduate student, and a post-doc in state-of-the-art analytical geochemistry and theoretical chemistry. It will also enhance the infrastructure for research and education by supporting a partnership between geologists, geochemists, and chemists at four different academic institutions, including two outside the United States, who will integrate experiments, state-of-the-art analytical geochemistry and modern theoretical chemistry.