This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). This proposal requests funds to support research by a Ph.D. student, who is working to establish a record of sulfur isotope ratios (involving all four sulfur isotopes) using carbonate associated sulfate as a proxy of seawater sulfate and using this record to test a developing hypothesis about the evolution of the sulfur cycle. Specifically, we hypothesize that there was a change in the magnitude of the fractionation between sulfate and buried pyrite that occurred in the middle Phanerozoic, and that points to a change in the biological pathways involved in sulfur cycling. We aim to test this hypothesis and to explore its implications for and connections with the sulfur cycle as well as to elucidate the mechanisms behind the change if such change is confirmed. Preliminary results of analyses and of model calculations form the basis for the hypotheses that are to be tested and are described in more detail in the body of this proposal. This proposal requests funds to support the second two years of research and includes a request for a graduate stipend, standard benefits, tuition, analytical costs and travel to two meetings where results will be presented. No funds are requested to support the PI, but funds are requested to support an undergraduate researcher. This is done as part of a laboratory policy to involve undergraduates, which we believe carries benefits for them by integrating them in high-level research projects, and for the postdoctoral student's professional development by placing him in the role of mentor as well as researcher. In the past these projects have resulted in new ideas being developed and independent projects that may form the basis for University of Maryland senior thesis projects. Other broader impacts include the ncorporation of research results and the research model in public presentations and other professional activities by the PI.
