SCHAUBLE Iron-isotope signatures are a common feature in natural materials that are created or react at low temperatures. These signatures are of great interest in low-temperature geochemistry and geobiology because iron is a vital nutrient, and its oxidation state is a potential indicator of modern and ancient redox conditions. One aspect of iron-isotope geochemistry that is not understood very well is the possibility that large fractionations occur between different species in solution. This proposal describes four sets of experiments and corresponding theoretical calculations to determine equilibrium iron isotope (56Fe/54Fe) fractionations in chloride-bearing solutions. This research will help create a framework for better understanding natural processes that give rise of iron isotope signatures in nature, particularly in distinguishing possible influences of biology and crystallization from solute composition effects. Experiments will exploit the unique solubility of the FeCl4- complex in hydrophobic organic solvents (e.g., diethyl ether), quantifying changes in 56Fe/54Fe partitioning in aqueous solution by measuring variation in the fractionation between aqueous iron and coexisting ether-dissolved FeCl4-. Aqueous speciation modeling and calculation of isotopic partition function ratios of dissolved species will be used to create a theoretical prediction of fractionations in each solution, providing context for understanding experimental result. Each experiment is reversible, so that isotopic exchange equilibrium can be demonstrated. Intellectual Merit: Establishment of iron-isotope geochemistry as a potent, robust tool for understanding modern and ancient environments on the Earth and other bodies requires accurate knowledge of equilibrium isotopic fractionations in iron-bearing solutions. Chloride, among the most ubiquitous dissolved species, is ideally suited for carefully controlled experiments. Use of immiscible liquids will enable rapid equilibration of experimental charges, and relatively easy experimental reversals. Broader Impacts: Proposed research will contribute to the training of a PhD student at UCLA, and support use of MC-ICP-MS analytical facilites in collaboration with Ed Young and spectroscopist Eric Tonui. Development of immiscible-liquid techniques for measuring isotope fractionations in solutions will open up new possibilities for future research in isotopic systems and solution chemistries beyond the scope of the research plan.
