Selenium biogeochemistry as a deep-time redox proxy and biosignature

硒生物地球化学作为深时氧化还原代理和生物特征

• 批准号: 0921580
• 负责人: Roger Buick
• 金额: $ 30万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-10-01 至 2014-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0921580&HistoricalAwards=false
• 关键词: Selenium; biogeochemistry; deep; time; redox

The history of Earth's environmental oxygenation of the lithosphere, hydrosphere and atmosphere is known in general terms: essentially anoxic in the Archean, passing through two rises during the Proterozoic and maintaining modern highly oxic conditions through the Phanerozoic. This trend of rising oxygenation has influenced the co-evolution of the biosphere by allowing organisms with increasingly high oxygen demands to evolve progressively. However, what is not well known about this history is how high environmental oxygen levels were between the essentially anoxic ancient stage and the highly oxic modern stage, if perturbations in oxygen levels were sudden or gradual, monotonic or step-wise, foreshadowed or uniform, or whether changes in atmospheric oxygen levels were directly reflected in marine oxygenation and by biological metabolism. This proposal seeks to develop a new set of environmental oxygenation tracers to improve our understanding of this history, in the form of selenium isotopic fractionations, selenium abundances relative to sulfur, and selenium redox speciation in marine sedimentary rocks from throughout the geological record. In addition, mass-dependent selenium isotopic fractionations should prove to be a useful new biosignature for investigating the evolution of life during early Earth history. It is also possible that mass-independent fractionations of selenium, analogous to those of sulfur, will be discovered, with the potential to provide novel insights into selenium gas cycling and atmospheric oxygen levels over time.The objective of the project is to refine our knowledge of environmental oxygenation through time and its constraints on selenium biogeochemical cycling through biological metabolic pathways. In order to do this, a recently-devised set of experimental methods will be employed, involving thiol-cotton fiber to quantitatively extract selenium from acid-digested rock samples, continuous-flow hydride generation to selectively volatilize selenium in low concentrations and multi-collector inductively-coupled-plasma mass-spectrometry to simultaneously measure multiple isotopes of selenium with high sensitivity. To provide a theoretical background for interpreting the new isotopic results, investigators will also develop a 4-box model of the selenium biogeochemical cycle and a 1-D photochemical model of selenium gas behavior at different oxygen levels. The broader impacts of the proposed study lie in the advancement of discovery and understanding while promoting teaching, training and learning by involving a graduate student in most of the research activities. It will broaden the participation of underrepresented groups, in this case women in earth science, by the active participation of a female graduate student in the research. It will enhance the infrastructure for research and education, as funding is requested for salary support for a research technician to maintain equipment in ISOLAB, a stable isotope laboratory shared between 3 departments, 2 programs and 4 principal scientists and open to all of the U.W. community and to external users. Funds are also requested so that results can be communicated broadly at interdisciplinary conferences to enhance scientific understanding. The research plan is inherently interdisciplinary, involving scientists affiliated with 3 departments: Earth & Space Sciences, Atmospheric Sciences and Oceanography, thus providing the framework for an environmentally comprehensive investigation of the selenium biogeochemical cycle.

地球的岩石圈、水圈和大气圈的环境氧合历史一般来说是已知的：在太古代基本上是缺氧的，在元古代经历了两次上升，在中生代保持了现代的高氧条件。这种含氧量上升的趋势影响了生物圈的共同进化，使需氧量越来越高的生物得以逐步进化。然而，关于这段历史，人们还不太清楚的是，在基本上缺氧的古代阶段和高氧的现代阶段之间，环境中的氧含量有多高，氧含量的扰动是突然的还是逐渐的，是单调的还是逐步的，是有预兆的还是均匀的，或者大气中氧含量的变化是否直接反映在海洋的氧化作用和生物代谢中。这项建议旨在开发一套新的环境氧化示踪剂，以提高我们对这一历史的理解，在整个地质记录的海洋沉积岩中的硒同位素分馏，硒相对于硫的丰度和硒氧化还原形态的形式。此外，质量依赖的硒同位素分馏应该被证明是一个有用的新的生物标志，调查生命的演化在早期地球历史。这也是可能的，硒的质量独立分馏，类似于硫，将被发现，有可能提供新的见解硒气体循环和大气中的氧气水平随着时间的推移。该项目的目标是完善我们的知识，通过时间和硒生物地球化学循环通过生物代谢途径的限制环境氧化。为了做到这一点，最近设计的一套实验方法，涉及硫醇棉纤维定量提取硒从酸消化的岩石样品，连续流动氢化物发生选择性挥发低浓度的硒和多收集电感耦合等离子体质谱法，同时测量多种同位素的硒与高灵敏度。为了提供解释新的同位素结果的理论背景，研究人员还将开发硒地球化学循环的4箱模型和不同氧水平下硒气体行为的1-D光化学模型。拟议的研究的更广泛的影响在于发现和理解的进步，同时通过让研究生参与大多数研究活动来促进教学，培训和学习。它将通过一名女研究生积极参与研究，扩大代表性不足的群体的参与，在这种情况下是妇女参与地球科学。它将加强研究和教育的基础设施，因为要求为研究技术人员提供工资支持，以维护ISOLAB的设备，ISOLAB是一个稳定的同位素实验室，由3个部门，2个项目和4个主要科学家共享，并向所有U.W.开放。社区和外部用户。还要求提供资金，以便能够在跨学科会议上广泛传播成果，提高科学认识。该研究计划本质上是跨学科的，涉及隶属于3个部门的科学家：地球空间科学，大气科学和海洋学，从而为硒地球化学循环的环境综合调查提供了框架。