Collaborative Research: Iron and Molybdenum Isotope Fractionation During Mineral Weathering

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This proposal seeks funding for research into the fractionation of iron and molybdenum isotopes during one of the most fundamental biogeochemical processes: Mineral weathering. We intend to investigate the effects of organic ligands and bacterial on the isotopic composition of Fe and Mo leached from oxides and silicates in a series of controlled laboratory experiments that mimic weathering processes in nature. Recent analytical advances have revealed, for the first time, significant natural variations in the isotopic compositions of both these elements. In the case of Fe in particular, complementary laboratory studies have provided information on fractionation mechanisms, including fractionation during microbially-mediated reduction of FE (111). These studies suggest that the FE isotope system could provide a powerful tool for studying biological activity in ancient sediments, and/or research into the Fe biogeochemical cycle. The Mo isotope system offers similar possibilities. Because of the unique biological importance of both these metals, and their extreme sensitivity to environmental conditions, the insights gained from Fe and Mo isotope studies are likely to be of broad utility in the geosciences. The fractionation of neither metal has been studied during weathering, despite the obvious importance of weathering in the environmental geochemistry of these metals. Preliminary data indicate that this could be a particularly important process for Fe isotope fractionation when biological mediation is involved. In addition, while some processes capable of fractionating metal isotopes have been identified, the chemical mechanisms of such fractionation remain poorly understood. This research will be conducted collaboratively between Susan Brantley's group at Pennsylvania State University, and Ariel Anbar's group at the University of Rochester. Brantley has a demonstrated track record studying the effects of organic ligands and bacteria on mineral weathering; Anbar has a demonstrated track record with high-precision isotopic measurements of the type required for this research.