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

铜、铁和锌同位素的实验研究：开发了解地质系统中生物地球化学过程的工具

• 批准号: 0745345
• 负责人: David Borrok
• 金额: $ 17.47万
• 依托单位: University of Texas at El Paso
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-01 至 2012-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0745345&HistoricalAwards=false
• 关键词: Experimental; study; Cu; Fe; Zn

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.

智力上的功绩。铜、铁和锌是必需的微量金属营养物质，其稳定的同位素特征在地质记录中变化很大，可能为关键的生物和化学作用提供直接证据。这些同位素工具可能从根本上改变我们探索控制这些金属在自然系统中的分布、丰度和有效性的生物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，以了解生物地球化学过程可能如何因环境扰动而发生变化。铜、铁和锌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生物地球化学反应的同位素体系。这项建议的目标是通过严格的实验量化关键的分馏因素，为解释铜、铁和锌的同位素特征建立更强大的分析基础。我们将检验这样一个假设，即细菌表面吸附和代谢摄取导致铜、铁和锌的不同同位素分馏，在近地表地质系统中解释它们的同位素特征时应考虑这一点。我们认为，吸附和摄取是分离金属同位素的两个最重要和最被忽视的机制。在许多近地表系统中，金属在细菌表面的吸附在一定程度上控制着金属的去向和运输，在这一过程中发生的同位素分馏很可能类似于金属与溶解的有机分子络合造成的分馏。此外，细菌对金属的代谢吸收可以控制水和岩石环境中铜、铁和锌的分布和循环，这些金属的供应往往是有限的。为了验证这一假设，Pi Borrok和Co-Pi Miller设计了一系列细菌表面吸附和代谢摄取实验。已完成的实验结果表明，可逆细菌表面吸附可使铜和锌同位素分馏0.6%？和0.5℃，细菌表面含有较重的同位素。考虑到自然界中铜和锌的总同位素变化约为8？和1.5？其余的实验将集中在确定在好氧环境[与Fe(III)，Cu(II)，Zn(II)]和厌氧环境[与Fe(II)]的吸附和代谢吸收反应的分馏因子。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的研究人员使用位于科罗拉多州丹佛市的美国地质调查局的MC-ICP-MS进行分析。必要的分析技术以前是由皮博罗克与美国地质调查局的研究人员共同开发的。这项建议侧重于一系列定义明确和可实现的实验，这些实验是利用铜、铁和锌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，以确定在各种时间尺度上，包括日(即日循环)、月(即季节变化)和年(即地质记录)，哪些生物地球化学机制负责控制河流和流域中的金属通量和循环。这里提出的实验对于这项研究的成功和这项新兴技术的进步是至关重要的。更广泛的影响。这项研究对于促进我们对控制地质系统中营养金属的来源、丰度和通量的生物地球化学过程的理解具有重要的意义。我们的建议还旨在最大限度地发挥东大？S地质和生物部门之间的协同作用。这一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。这项研究将作为一名地质学研究生的完整博士项目，他将利用两个系和美国地质调查局的设备和实验室空间，包括？CORE？专门为细菌培养、生长和储存而设计的研究设施。西班牙裔服务机构UTEP的教育机会也将通过将研究纳入课程和研讨会以及为本科生提供研究机会来增加。这些实验适合本科生参与，因为许多程序都已经设计和测试过了，个别实验通常可以在几天到几周内完成，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公布。