Experimental study of Cu, Fe, and Zn isotopes: Developing tools to understand biogeochemical processes in geologic systems

智力优势。铜、铁和锌是必需的微量金属营养素，它们的稳定同位素特征在地质记录中变化很大，可以提供关键生物和化学相互作用的直接证据。这些同位素工具可能从根本上改变我们探测控制这些金属在自然系统中的分布，丰度和可用性的地球化学机制的能力。此外，这些同位素特征可以在地质记录中的各种空间和时间尺度上进行跟踪，以了解地球化学过程如何响应环境扰动而发生变化。Cu、Fe和Zn同位素地球化学领域还处于起步阶段，我们仍在努力了解许多地球化学反应的同位素系统学。该提案的目标是通过严格的实验量化关键分馏因子，为解释Cu，Fe和Zn同位素特征建立更强大的分析基础。我们将测试的假设，细菌表面吸附和代谢吸收的结果在不同的同位素分馏铜，铁，锌，应考虑解释其同位素签名时，在近地表地质系统。我们认为，吸附和吸收是两个最重要的和最容易被忽视的机制，分形金属同位素。在许多近地表系统中，细菌表面的吸附部分地控制着金属的命运和运输，在此过程中发生的同位素分馏可能与金属与溶解的有机分子络合的情况相似。此外，细菌对金属的代谢吸收可以控制Cu，Fe和Zn在水和岩石环境中的分布和循环，这些金属通常是有限的供应。为了验证这一假设，PI Borrok和CO-PI米勒设计了一系列细菌表面吸附和代谢摄取实验。从完成的实验结果表明，可逆的细菌表面吸附可以fractionalCu和Zn同位素的0.6？0.5？分别与细菌表面结合较重的同位素。考虑到自然界中Cu和Zn的总同位素变化约为8？1.5？分别剩余的实验将集中于定义在有氧[与Fe（III），Cu（II），Zn（II）]和厌氧环境[与Fe（II）]中与其他细菌菌株的吸附和代谢摄取反应的分馏因子。实验将在德克萨斯大学埃尔帕索分校（UTEP）进行，每个实验的金属同位素将由UTEP研究人员在科罗拉多丹佛的美国地质调查局使用MC-ICP-MS进行分析。必要的分析技术以前由PI Borrok与USGS的研究人员开发。该提案侧重于一套定义明确且可实现的实验，这些实验是利用Cu，Fe和Zn同位素解决基本地球化学问题的长期研究计划的关键第一步。例如，PI Borrok正在进行研究，以确定什么样的地球化学机制负责在各种时间尺度上控制溪流和流域中的金属通量和循环，包括天数（即，昼夜周期），月（即，季节变化）和年份（即，地质记录）。这里提出的实验是这项研究的成功和这一新兴技术的进步的基础。更广泛的影响。这项研究具有根本性的影响，为推进我们的地球化学过程的理解，控制的来源，丰度和通量的营养金属在地质系统中。我们的建议还旨在最大限度地发挥UTEP？地质系和生物系。这种安排汇集了关键的科学专业知识，但更重要的是将促进跨学科的设施，培训和教育机会的共享。这项研究将作为一个完整的博士项目，一个地质学研究生谁将利用设备和实验室空间在两个部门和美国地质勘探局，包括？核心？专门为细菌培养、生长和储存而设计的研究设施。在UTEP，西班牙裔服务机构的教育机会，也将通过研究纳入课程和研讨会，并通过提供本科研究的机会得到加强。这些实验适合本科生参与，因为许多程序已经设计和测试，个别实验往往是在几天到几周内管理，而不是几年。研究结果将在顶级科学期刊上传播，并在国家和国际会议上提出。

Intellectual Merit. Copper, Fe, and Zn are essential trace-metal nutrients and their stable isotopic signatures, which vary substantially in the geologic record, may provide direct evidence of key biological and chemical interactions. These isotopic tools may fundamentally change our ability to probe the biogeochemical mechanisms that control the distributions, abundances, and availabilities of these metals in natural systems. Moreover, these isotopic signatures can be tracked on a variety of spatial and temporal scales in the geologic record to understand how biogeochemical processes may have changed in response to environmental perturbations. The field of Cu, Fe, and Zn isotope geochemistry is in its infancy, and we are still working to understand the isotopic systematics for many biogeochemical reactions. The goal of this proposal is to build a stronger analytical foundation for interpreting Cu, Fe, and Zn isotopic signatures by quantifying key fractionation factors through rigorous experimentation. We will test the hypothesis that bacterial surface adsorption and metabolic uptake result in distinct isotopic fractionations for Cu, Fe, and Zn that should be considered when interpreting their isotopic signatures in near-surface geologic systems. We believe that adsorption and uptake are two of the most important and most overlooked mechanisms that fractionate metal isotopes. Adsorption onto bacterial surfaces partly controls the fate and transport of metals in many near-surface systems, and isotopic fractionations that occur during this process are likely similar to those attributable to metal-complexation with dissolved organic molecules. Furthermore, metabolic uptake of metals by bacteria can control the distributions and cycling of Cu, Fe, and Zn in water and rock environments where these metals are often limited in supply. To test this hypothesis, PI Borrok and CO-PI Miller have designed a series of bacterial surface adsorption and metabolic uptake experiments. Results from completed experiments suggest that reversible bacterial surface adsorption can fractionate Cu and Zn isotopes by 0.6 ? and 0.5 ?, respectively, with the bacterial surface incorporating the heavier isotope. The magnitudes of these fractionations are significant considering that the total isotopic variations of Cu and Zn in nature are about 8 ? and 1.5 ?, respectively. Remaining experiments will focus on defining fractionation factors for adsorption and metabolic uptake reactions with additional bacterial strains in aerobic [with Fe(III), Cu(II), Zn(II)] and anaerobic environments [with Fe(II)]. Experiments will be conducted at the University of Texas at El Paso (UTEP), and the metal isotopes from each experiment will be analyzed by UTEP researchers using a MC-ICP-MS at the U.S. Geological Survey in Denver, Colorado. The necessary analytical techniques were previously developed by PI Borrok with researchers at the USGS. This proposal focuses on a suite of well-defined and achievable experiments that are a key first step in a longer-term research plan to utilize Cu, Fe, and Zn isotopes to tackle fundamental geochemical questions. For example, PI Borrok is conducting research to determine what biogeochemical mechanisms are responsible for controlling metal fluxes and cycling in streams and watersheds on a variety of temporal scales, including days (i.e., diel cycles), months (i.e., seasonal variations) and years (i.e., geologic record). The experiments proposed here are fundamental to the success of this research and to the advancement of this emerging technology. Broader Impacts. This research has fundamental implications for advancing our understanding of the biogeochemical processes that control the sources, abundances, and fluxes of nutrient metals in geological systems. Our proposal also aims to maximize the synergy between UTEP?s geology and biology departments. This arrangement brings together key scientific expertise, but more importantly will facilitate the sharing of facilities, training, and educational opportunities across disciplines. This research will serve as a complete PhD project for one geology graduate student who will utilize equipment and laboratory space in both departments and at the USGS, including ?core? research facilities specifically designed for bacteria cultivation, growth, and storage. Educational opportunities at UTEP, a Hispanic serving institution, will also be enhanced through incorporation of research into coursework and seminars, and by providing opportunities for undergraduate research. These experiments lend themselves to undergraduate participation, because many of the procedures have already been designed and tested, and individual experiments are often manageable in days to weeks, not years. Findings will be disseminated in top scientific journals and presented at national and international meetings.