ABSTRACT Severmann, Anbar, McManus (0551716, 0551732, 0551605) Intellectual merit: The biogeochemical cycles of iron and sulfur are closely coupled, and their combined influence impacts the evolution of the global carbon and oxygen cycles as well as the ocean's proton balance over geologic time. Our preliminary data show that Fe isotope compositions of dissolved and particulate species unambiguously reflect their depositional conditions in modern aqueous environments. This research determines the isotopic expressions of these cycles as specifically linked to the primary sources and sinks of Fe and S in oxygen-deficient aqueous settings. Specific questions to be addressed are: (1) how does the relative availability of Fe and S influence the isotopic expression of their cycling and (2) does benthic Fe recycling on oxic continental shelves influence the Fe isotope composition within anoxic basin sediments. Samples from two modern anoxic lake environments with contrasting sulfate levels will be analyzed (the Black Sea sulfate enriched, and Lake Tanganyika sulfate poor). This work leverages off on-going NSF-funded studies and all samples come with rich ancillary data sets, providing essential information regarding S isotope compositions, Fe speciation and general sediment diagenetic parameters. The proposed work will provide information essential to our interpretation of the Fe cycle in both the modern and ancient ocean as well as the evolution of the Earth's atmosphere and the redox balance of the modern atmosphere-ocean system. Fe and S will be extracted from sediment samples by sequential leaching. Fe and S isotopes will be measured using a multi-collector ICP-MS or isotope ratio mass spectrometry. Standard wet chemistry will be used to determine Fe and S speciation in the associated pore waters and mineral leachates.
Broader impacts: This work funds investigators at institutions in three states: California, Oregon, and Arizona and involved international collaborations with scientists in Germany and Turkey. The research supports a young, female principal investigator and a graduate student, the latter who will spend time learning analytical techniques in the collaborating institutions. It will also allow participation of the lead PI and her student to participate in the field program in Africa. US, as well as African undergraduates will be involved and mentored in paleoclimate research.
