CAREER: Deconvolving organic substrates as the critical link between changes in organic matter and global biogeochemical sulfur, carbon, and oxygen cycling

The sedimentary sulfur isotope record has been used to reconstruct variations in atmospheric carbon dioxide and oxygen levels and their impact on life and the environment. The main process that impacts sulfur isotope signatures is microbial sulfate reduction, which is responsible for up to 50% of organic matter degradation in marine sediments and therefore plays a major role in determining how much carbon dioxide is removed from the atmosphere via organic carbon burial. This project will determine how the production of simple organic substrates by fermenting microorganisms impacts rates of microbial sulfate reduction and sulfur isotope signatures when sediment is dominated by organic matter from plants versus microorganisms. The results will be used to evaluate how the rise of seed plants lead to the establishment of the “modern” style of biogeochemical sulfur cycling and how mixing of different types of organic matter impacts the modern carbon cycle. The project will include educational activities that will build enthusiasm for geoscience in science-motivated high school students and offer them opportunities to get involved with geoscience research. The project will document how rates of organic substrate accumulation affect average cell specific reduction rates and their impact on sulfur isotope fractionations. The project will determine what are the dominant organic substrates available for sulfate reduction in seed plant-rich versus microbially-dominated sediment, document the relationship between average cell specific reduction rates and sulfur isotope fractionations in these settings, and model Phanerozoic sulfur cycle evolution using a box model of the marine sulfur cycle constrained by the time-distribution of sedimentary packages. A one-week Geoscience camp will enhance knowledge of how geoscientists contribute to solving environmental problems that affect local communities. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.