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".
