EAR-PF: First evidence for low temperature oxygen isotope exchange and fractionation between crystalline iron oxides and water: Role of biogeochemical iron cycling

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Dr. Andrew J. Frierdich has been awarded an NSF Earth Sciences Postdoctoral Fellowship to carry out a research and education plan at the University of Iowa and the University of Wisconsin-Madison. He will investigate oxygen isotope exchange and fractionation between iron oxides and water. Iron oxides are ubiquitous minerals whose intimacy with local meteoric precipitation makes their oxygen isotope composition a potential proxy for paleoclimate. However, the use of oxygen isotope signatures in iron oxides is stymied by the inability to accurately determine mineral-water oxygen isotope equilibrium fractionation factors and a limited understanding of the temporal processes that alter their isotopic composition. Dr. Frierdich will address these challenges by investigating oxygen isotope exchange and fractionation between iron oxide minerals and water that is initiated by aqueous Fe(II), a product of microbial Fe(III) reduction, which has recently been shown to catalyze such reactions at low temperature. The main premise of the experiments is to utilize a novel "double three-isotope approach" (57Fe-56Fe-54Fe and 18O-17O-16O) whereby mineral-water isotopic exchange is assessed by measuring enriched 57Fe and 17O tracers, and natural mass-dependent isotope fractionation for iron and oxygen is determined by monitoring the 56Fe/54Fe and 18O/16O ratios, respectively. These measurements will contribute to the fundamental understanding of iron and oxygen bonding, reactivity, and isotopic fractionations in iron oxides, an important mineral group in environmental science and geology.This proposal will generate an innovative research and education outreach experience by establishing mentoring opportunities for undergraduate student researchers in geology and engineering, provide broadening participation activities to increase diversity in the geosciences, and create scientific knowledge that impacts numerous disciplines. The interdisciplinary and multi-institutional work plan provides a unique opportunity to perform collaborative research. This fellowship will also allow Dr. Frierdich to develop his mentoring skills and community outreach experiences. The inquiry-based broadening participation activities will guide undergraduate researchers, engage grade school students and parents at Iowa City local schools, and educate local Girl Scout troops about the importance of geosciences to societal problems. The proposed research will also offer societal benefits by identifying the fundamental processes controlling iron oxide reactivity which affects water quality, nutrient availability, and contaminant fate.