Rare earth elements and neodymium isotopes in the South Pacific: impact of hydrothermal activity, particle fluxes, and ocean circulation

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Knowledge of the biogeochemical processes affecting trace elements and their isotopes (TEIs) in the ocean and their impact on TEI distributions and budgets is essential for a comprehensive understanding of the roles of TEIs as micronutrients and tracers. Neodymium (Nd) isotopes and rare earth elements (REEs) are highly useful marine tracers and have been widely applied to improve our understanding of both modern and past processes and changes in the ocean. The particle reactivity of REEs and the source information carried by Nd isotopes make them particularly useful for elucidating dissolved TEI sources and modifications in the ocean, scavenging by particles, and lateral transport by water masses. In the study proposed here, I will test the hypotheses that hydrothermal particles lead to intense REE scavenging and characteristic REE and Nd isotope signatures that allow tracing the fate of hydrothermal plumes in the South Pacific and potentially their upwelling to the surface of the Southern Ocean. Moreover, I will test whether the extremely low particle fluxes in the oligotrophic subtropical South Pacific gyre lead to a dominant control of lateral advection on the distribution of dissolved REEs in this area. The project will further assess the potential modification of the original dissolved Nd isotope signatures of newly formed Southern Ocean water masses through input from New Zealand and/or contact with the New Zealand margin and the Kermadec hydrothermal system. The study will therefore provide insight into the impact of the highly active hydrothermal system of the southern East Pacific Rise, as well as the shallow and with respect to TEIs so far largely unstudied hydrothermal system of the Kermadec Arc on dissolved REEs and Nd isotopes in the Pacific. The expected results will have far-reaching implications for the global REE budget in the ocean, the use of REEs and Nd isotopes as tracers, as well as for the impact of the studied processes on other dissolved TEIs.