NSF Award
2421816
All chemical elements are present dissolved in the ocean. Differences in their concentrations and in the relative amounts of their isotopes at various locations and depths are used to understand the workings of the ocean and the geochemical cycles of the planet as a whole. In this project, investigators from three institutions will conduct the first study of the marine chemistry of zirconium isotopes. Pilot data from the team have indicated differences in isotopic composition between seawater and sediments. The proposed work will build on these pilot data by characterizing the zirconium isotopic composition of a comprehensive array of seawater, particle, and sediment samples already collected from the Pacific Ocean. One aim of the work will be to test the idea of whether zirconium isotopes in sediments provide a record of past ocean conditions. The project will support one PhD student and provide research experience for one undergraduate student. The results of this research will be incorporated into class material taught by the PIs and reported in plain language summaries on their research websites and through university press releases. This work will support a diverse, interdisciplinary team of three early career faculty. The team will promote broadening participation in science through targeted educational outreach including the development of educational modules for high school students to spur interest in chemical oceanography and isotope geochemistry among students at an early career stage. <br/><br/>Previous work on high field strength elements including zirconium (Zr) and hafnium (Hf) indicated that the ratio of dissolved Zr/Hf varies extensively and systematically with latitude and depth in the ocean. Pilot data obtained by this team on the stable Zr isotopic composition of marine authigenic sediments and seawater has revealed systematic fractionations, but further investigation of this proxy in seawater profiles and marine particulates that intersect major currents is crucial for: i) providing insight into the mechanisms responsible for the isotopic fractionations observed in the ocean; and ii) further developing their application as a potential tracer of paleo-oceanographic processes. The proposed work aims to build upon the pilot observations by characterizing the Zr isotopic composition of seawater, marine particulates, sediments, and leaches in an array of well-characterized samples collected during a previous cruise. This project will apply high-precision, novel non-traditional stable isotope techniques to marine samples to: (1) determine the stable Zr isotopic composition of various endmembers in the ocean (dissolved, particulate, authigenic sediments), (2) probe whether these isotopic compositions correlate with water mass age, (3) test whether the Zr isotopic composition of authigenic sediments faithfully record the water composition they originated from, and (4) test whether adsorption of dissolved Zr onto sinking particulates is the driver of the observed Zr isotopic fractionation in the ocean.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
