Collaborative Research: Determining Pathways of Diagenetic Sulfurization of Organic Matter Using Compound-Specific Sulfur Isotopic Analysis

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Sulfur is an essential element for all living organisms because it plays a critical role in transferring biochemical energy, enzymatic reactions, and protein synthesis. Thus, the biological and geological chemistry of sulfur is of widespread interest in the Earth science community. Organic sulfur deposited in sedimentary environments is of particular interest due to its impact on petroleum formation and refining and its relationship to microbial sedimentary processes, organic carbon accumulation and the overall interpretation of environmental records. This sedimentary organic matter retains the organic and inorganic history of sulfur initially incorporated into organic tissue (primary) or added during chemical reactions occurring in the sediments (secondary). Despite the importance, little is known about organic sulfur in the natural environment in part because there are a wide variety of organic sulfur compounds and a number of different ways these compounds form. In addition, these compounds can be altered after they are deposited in the sediments. The investigators will use the stable isotope composition of organic sulfur to gain insights into these processes and sources of organic sulfur. Recent technological advances have greatly improved the ability to measure sulfur isotope compositions of individual organic sulfur compounds possible with high precision and at natural abundance. This project will use compound-specific sulfur isotope analysis to study the reaction pathways that form organic sulfur in two anoxic (oxygen free) lakes. The sulfur isotope signature of these compounds will be used to infer reaction pathways to increase understanding of the reactions between sulfur and organic matter that occur in sediments. These new advancements in sulfur isotope analysis have tremendous potential for understanding past changes in elemental cycling, metabolic and ecologic changes, as well as changes in past climatic and environmental conditions.Graduate education will be one broader impact of this project, and we will foster this through extensive collaboration and training in the state of the art sulfur isotope analysis. A second important impact of this project will be to develop educational modules about hypoxic (low oxygen) conditions common to northeast Indiana lakes, and Lake Erie, Pennsylvania, in collaboration with the IUPUI Center for Earth and Environmental Sciences (CEES) Discovering the Science of the Environment (DSE) program. DSE is a public outreach program focused on formal and informal delivery of STEM (Science, Technology, Engineering, and Mathematics) education to fourth through ninth grade students. We will translate knowledge learned from studying sulfur cycling in anoxic lakes into material for teaching modules that inform students about the environmental hazards of human-induced hypoxia.