Behavior of Nd isotopes at the Ocean-Sediment Boundary: Addressing the "Nd Paradox"

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Neodymium isotope ratios (143Nd/144Nd) are increasingly used as tracers of past ocean circulation patterns. However, our understanding of marine Nd dynamics, and thus the reliability of Nd as an oceanic tracer, is currently complicated by an apparent disconnect between the isotopic compositions of Nd (which are distinctive between ocean basins) and the distribution of elemental Nd (which appears to be driven by water column cycling). It is important to resolve this "Nd paradox" in order to refine tracer studies of past ocean behavior. Prior research suggests that the decoupling of isotopic and elemental Nd may occur near the interface between marine sediments and bottom waters. This study, conducted by researchers at Oregon State University, investigates exchange reactions between dissolved and particulate Nd occurring at and around this interface, with a focus on the influence of diagenetic sedimentary processes on Nd isotope ratios. Porewater, sediment, and water column samples will be collected along the Oregon continental margin and analyzed for Nd isotopes and other relevant tracers (including rare earth elements, carbon, and nitrogen). The resulting dataset will not only help to resolve the Nd paradox, but will also be applied to future conceptual and chemical modeling efforts, which in turn will inform the development of paleoceanographic and paleoclimatic models.This project will be incorporated into the COSEE (Center for Ocean Science Education Excellence) Pacific Partnerships ocean literacy effort. A PRIME (Promoting Research Investigations in the Marine Environment) intern, as well as two OSU students (PhD and undergraduate), will be involved in this research. The project includes international collaboration with a geochemist from the University of Bristol, which will strengthen Oregon State University's analytical capabilities. Funding will also help support an early-career researcher at Oregon State University.