The speciation and behavior of sulfur gases in biogeochemical processes

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。该奖项支持一个项目，以确定和解决无机和有机硫物种的形态，包括气体，将地质和地球化学过程与生物过程联系起来。我们对硫气体的性质和行为的有限理解阻碍了我们重建过去硫循环的能力，主要是因为很难测量气体进入、流出或穿过沉积系统的运动。为了克服这个问题，我们最近制作了第一个硫k边x射线吸收近边缘结构（XANES）光谱，用于从简单含硫固体中抽离并逐渐加热到~400℃的气体。XANES是研究生物地球化学系统中硫形态的最有效工具之一。以前，很少有硫气体XANES光谱的例子；化合物是室温下的气体或高蒸气压下的液体。因此，这种新的气相XANES技术的应用扩展了我们评估所有相硫形态的能力，以解决三个主要的研究问题：(1)当含硫无机和有机固体被加热时，硫形态会发生什么变化？(2)前驱体硫相的组成（如矿物学、有机质含硫量）是否影响系统中凝聚硫相的类型？(3)微生物过程（如同位素）的特征能否与低温地质（如成岩）过程区分开来？在加热至200℃的过程中，不同实验中硫种类的变化和反应副产物的分类将通过XANES进行研究。使用四极杆质谱法同时收集气相XANES光谱和质量（即同位素组成）将识别新的气体。该研究有望揭示与成岩反应相关的硫物种类型的独特描述，以及生物地球化学系统中挥发性和凝聚性硫物种之间的联系。这项工作将增加我们对地球历史上与硫循环有关的地球化学和代谢过程是如何被记录甚至改变的理解。更广泛的影响：这项工作正在路易斯安那州立大学同步加速器辐射源，巴吞鲁日高级微结构和器件中心（CAMD） J. Bennett Johnston, Sr.进行。这是美国南部唯一的同步加速器，也是唯一一个由国家资助的设施。我们的团队包括来自德国柏林工业大学和荷兰海牙壳牌国际公司的学术和工业地球化学家。这些合作将向参与该项目的学生展示在当今全球政治和经济气候下国际合作的回报和挑战。目前，研究技术人员、研究生和本科生代表了未被充分代表的少数民族和妇女。该项目将继续提供独特的教育机会，通过参与CAMD正在进行的REU项目和路易斯安那州立大学地质与地球物理学的马拉松地球科学多样性丰富项目（GeoDE），提高STEM学生在各个层次和背景下的参与和成功。除了接受媒体采访和维护网站外，项目负责人还通过“发现日”等活动，积极向科学界和公众传播研究成果。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This award supports a project to identify and resolve the speciation of inorganic and organic sulfur species, including gases, which link geological and geochemical processes to biological processes. Our ability to reconstruct the past sulfur cycle is hampered by our limited understanding of the nature and behavior of sulfur gases, primarily because it is difficult to measure gas movement into, out of, or through sedimentary systems. To overcome this problem, we recently produced the first sulfur K-edge X-ray Absorption Near-Edge Structure (XANES) spectra for gases that were evacuated and evolved from simple sulfur-bearing solids that were incrementally heated to ~400 oC. XANES is one of the most efficient tools to study sulfur speciation in biogeochemical systems. Previously, there were few examples of sulfur gas XANES spectra; compounds were gases at room temperature or liquids under high vapor pressure. Therefore, the application of this new gas-phase XANES technique expands our ability to evaluate sulfur speciation in all phases in order to address three main research questions: (1) What sulfur speciation changes occur when sulfur-bearing inorganic and organic solids are heated? (2) Does the composition of the precursor sulfur-phase (e.g., mineralogy, organic matter sulfur content) influence the type of condensed sulfur phase(s) in a system? (3) Can the signature of microbial processes (e.g., isotopic) be differentiated from low-temperature geological (e.g., diagenetic) processes? Changes in sulfur species and the classification of reaction byproducts from different experiments, during heating to temperatures 200 oC, will be examined by using XANES. Simultaneous collection of gas-phase XANES spectra and masses (i.e. isotopic compositions) using quadrupole mass spectrometry will identify novel gases. The research promises to reveal a unique depiction of the types of sulfur species associated with diagenetic reactions and of the connection between volatile and condensed sulfur species in biogeochemical systems. The work will increase our understanding of how possible geochemical and metabolic processes related to the sulfur cycle have been recorded, and even altered, throughout Earth's history. Broader Impacts:The work is being done at the Louisiana State University synchrotron radiation source, the J. Bennett Johnston, Sr., Center for Advanced Microstructures and Devices (CAMD) in Baton Rouge. This is the only synchrotron in the southern US, and the only state-funded facility. Our team includes academic and industry geochemists at the Technical University in Berlin, Germany, and Shell International in Hague, The Netherlands. These collaborations will demonstrate to the students engaged on the project the rewards and challenges of international collaboration in today's global political and economic climate. Currently, the research technicians and graduate and undergraduate students represent underrepresented minorities and women. The project will continue to provide unique educational opportunities to increase participation and success of STEM students, at all levels and backgrounds, through involvement in the ongoing REU program at CAMD and the Marathon Geoscience Diversity Enrichment Program (GeoDE) program in LSU Geology & Geophysics. In addition to interviews with media and website maintenance, the PIs actively disseminate results to the scientific community and to the public through events at CAMD like "Day of Discovery".