Rare earth elements and neodymium isotopes in the South Pacific: impact of hydrothermal activity, particle fluxes, and ocean circulation
Final Report Abstract
Dissolved trace elements that exist in the ocean only in extremely low concentrations, play important roles in the marine environment as micronutrients, contaminants, or tracers of biogeochemical processes and element transport. Knowledge of their behaviour, sources and sinks in the ocean is therefore crucial for a comprehensive understanding of the ocean and its physical, biological and chemical functioning. Rare earth elements (REE) are of particular interest, because they have a relatively long residence time in the ocean and are not biologically active, i.e. they are not removed from the ocean by biological activity. Moreover, they show relative concentration patterns within their series that are indicative of input and removal processes. The radiogenic isotope of one of the REE, neodymium (Nd), traces the provenance of material and water masses. In this project we analysed dissolved REE concentrations and neodymium isotopes along a zonal transect across the oligotrophic South Pacific gyre and a meridional transect west of New Zealand to study the influence of hydrothermal activity and ocean circulation on the characteristics and distributions of REE concentrations and Nd isotopes. Intermediate to deep waters along both transects are marked by a deficit of light REE. This indicates intense REE scavenging in the interior of the ocean that can only be explained by hydrothermal activity and preferential scavenging of the light REE on ferromanganese oxide particles that form as metal-rich hydrothermal fluids get in contact with oxic seawater. Detailed water mass analysis along the zonal transect using hydrographic parameters and coupling with dissolved Nd concentration and isotope data support the non-conservative removal of seawater Nd in the hydrothermal plumes of the East Pacific along the circulation pathway of Pacific Deep Water. In contrast, Nd isotopes are unaffected by hydrothermal activity and instead trace the provenance of the different water masses and their mixing.
Publications
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Behaviour of dissolved Neodymium Concentrations and Isotopes in the deep South Pacific Ocean. Goldschmidt2022 abstracts. European Association of Geochemistry.
Waltemathe, Henning; Struve, Torben; Ferdelman, Timothy & Pahnke, Katharina
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Dissolved neodymium concentrations and neodymium isotope compositions for deep water (≥1500 m) samples of R/V SONNE cruise SO245 - UltraPac in the South Pacific [dataset]. PANGAEA
Waltemathe, H., Struve, T., Rehbein, M. & Pahnke, K.
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Influence of water mass mixing and hydrothermal processes on the distribution of dissolved Nd isotopes and concentrations in the South Pacific. Earth and Planetary Science Letters, 642, 118846.
Waltemathe, Henning; Struve, Torben; Rehbein, Matthias & Pahnke, Katharina
