Intellectual Merit: Oceanic anoxic events (OAE) record significant increases in organic carbon burial and are marked by positive excursions in both marine carbonate and organic carbon (C). While it is widely held that these events were driven by enhanced primary production within surface waters, the details underpinning the initiation, maintenance and termination of OAEs remain equivocal. This work will reveal the potential of sulfur (S) isotope studies to illuminate the role of changing sulfate concentrations on phosphate (PO4) regeneration in marine sediments and will have far-reaching implications for understanding the behavior of the C cycle, and therefore climate, especially in the deep time record. This is because marine sulfate levels have been low for much of Earth history. The objective of this proposal is to investigate the role sulfur plays in regulating the marine carbon cycle in low sulfate oceans. The following hypothesis will be tested: given an average background of low marine sulfate concentrations, an increase in seawater sulfate levels may trigger widespread oceanic anoxia by facilitating enhanced phosphorus (P) recycling and thus higher primary production within marine surface waters. Because seawater sulfate concentrations have been low for most of Earth?s history, substantial fluctuations in sulfate levels in the past may have played a key role in regulating C cycling in ancient oceans. In order to test this hypothesis, this proposal details a study with three fundamental themes, each of which will be integrated with an educational outreach effort developed through the Office of STEM Education Partnerships (OSEP) in the School of Education and Social Policy at Northwestern University. The themes include: (1) S isotope systematics and the link between fluctuating sulfate levels and P recycling in a low sulfate, permanently anoxic lake (Lake McCarrons, MN), (2) the S isotope composition of seawater sulfate, sedimentary pyrite and difference between the two phases (Ä34S) before, during and after two oceanic anoxic events?OAE1a in the Early Cretaceous and the Frasnian-Famennian event in the Late Devonian, and (3) reservoir dependent mass balance modeling using S isotopes. The results from this project will improve the community?s understanding of S and P cycling in low sulfate systems, establish Ä34Ssulfate-pyrite for two time periods marked by widespread anoxia (the Early Cretaceous and the Late Devonian), and help to ascertain the complex set of feedbacks that link ocean redox and the geochemical cycles of C, S, P, and Fe in the low sulfate oceans of Earth?s past.
Broader Impacts: This project will provide training to two graduate students in field research techniques and analytical isotope geochemistry and make contributions to understanding controls on biogeochemical cycles of C, S, P and Fe and their relationship to the redox state of the Earth system. Impacts of this project extend beyond the scientific community via an outreach effort to public high schools. The overall goal of the outreach effort is to bring the excitement and challenge of doing real science to high school students. This proposal requests funds to recruit a local high school science teacher to participate in research each summer. This teacher will collaborate to develop laboratory activities to provide high school students with research experiences through the NSF-funded iLab Network (ilabcentral.org), which allows students and educators to use remote experimental apparatus to carry out experiments via the Web. Once the iLab experiments have been tested, through development with the initial high school and then with OSEP partner schools in the area, they will be made available to any high school teacher with a web browser. To address the problem of underrepresented groups in Earth Science, a partnership has been initiated with Project EXCITE, a program that links Northwestern?s Center for Talent Development with local schools to identify scientifically inclined minority students and support their acquisition of math and science skills through high school. Saturday enrichment sessions with Project EXCITE students and their parents are ongoing, focusing on key Earth science concepts (earthquakes, tsunamis, climate change) and career options in Earth and Planetary Sciences. This proposal seeks funds to support high school students from EXCITE as lab assistants to increase awareness of opportunities in Earth science for local students and their families.
