Collaborative Research: US GEOTRACES GP17-OCE: Understanding neodymium isotopes and rare earth element systematics in the South Pacific

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The goal of the international GEOTRACES program is to understand the distributions of multiple chemical elements and their isotopes in the oceans. The National Science Foundation is supporting a U.S. GEOTRACES sampling expedition in the South Pacific and Southern Ocean, one of the most remote and poorly sampled ocean regions on Earth. Neodymium (Nd) isotopes and rare earth elements (REE) are important tools used to track water masses along global circulation pathways, trace the sources of continental inputs into the oceans, and constrain biogeochemical processes in the water column. The investigators will analyze Nd isotopes and REE in seawater, suspended particles, and core top sediments on this expedition. The project will support an early career lead investigator, two postdoctoral researchers, and several undergraduate students. Outreach to local high schools and paid undergraduate research positions are designed to broaden participation in geosciences.The GP17-OCE cruise track is well-designed for illuminating the processes that govern the marine cycling of REE and Nd isotopes, as it (i) covers the oligotrophic South Pacific Gyre, (ii) crosses the sub-tropical, sub-Antarctic and polar fronts, capturing transitions between different productivity regimes, (iii) traverses through the high latitude South Pacific, which hosts areas with extensive deep water upwelling and new water mass formation. It offers a unique opportunity to study biogeochemically important yet largely unsampled regions in the South Pacific at unprecedented detail. The investigators plan to (1) generate seawater Nd isotope and REE data to characterize the intermediate and deep water masses that form in the high latitude South Pacific, (2) decipher the evolution of dissolved Nd isotope and REE abundances across oceanic fronts and atmospheric dust flux gradients, (3) identify the roles of particle abundance, composition, and size in modulating dissolved Nd isotopes and REE, (4) evaluate the effect of REE contributions from the Antarctic and Chilean margins on water column Nd isotopes and REE inventory, (5) evaluate the impacts of the benthic flux of REE, (6) understand the process of signal transfer between the deep water and sedimentary archives (fossil fish teeth, Fe-Mn oxide coatings). This information is important for our understanding of Nd cycling in the global ocean and will also facilitate a thorough evaluation of the use of Nd isotopes as a past water circulation proxy.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.