Hawaiian imprint on dissolved Nd and Ra isotopes and rare earth elements in the central North Pacific: Local survey and seasonal variability
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© 2016 Elsevier Ltd. Dissolved neodymium isotopes ( 143 Nd/ 144 Nd, expressed as ε Nd ) and rare earth elements (REEs) have the potential to trace the provenance of lithogenic material as well as water masses. The central North Pacific is poorly investigated with respect to its Nd isotope signature and REE cycling, and little is known about the contributions of volcanic islands, such as Hawaii, relative to dust input from Asian deserts to the surface water REE budgets. Here we present dissolved Nd isotope and REE data along with long-lived radium isotope activities from Hawaii Ocean Time-Series Station ALOHA and coastal waters from Oahu, sampled for a GEOTRACES process study in February 2011. The data are supplemented with seasonal samples from ALOHA. Our results show a clear influence of the Hawaiian Islands on the coastal ocean and surface waters at ALOHA during February, expressed by higher surface water Ra activities, radiogenic surface ε Nd (ε Nd = +1.4 to -1.0), and elevated Eu anomalies (Eu/Eu * ≥ 1.3). Seasonal cycles of Asian dust deposition most likely contribute to the seasonal ε Nd variability of surface waters at ALOHA, as suggested by more negative ε Nd and the lack of Eu anomalies in summer. Neodymium isotopes in the intermediate and deep water column at ALOHA trace typical North Pacific water masses, such as North Pacific Intermediate Water and North Pacific Deep Water. We suggest that a radiogenic ε Nd excursion in 1000-2000 m water depth, observed in various North Pacific profiles, is controlled by advection of a modified Upper Circumpolar Deep Water or North Equatorial Pacific Intermediate Water. We further present an updated average ε Nd signature of -3.5 ± 0.5 for North Pacific Deep Water and show that REE patterns of deep waters at ALOHA are dominantly controlled by vertical processes.
author list (cited authors)
Fröllje, H., Pahnke, K., Schnetger, B., Brumsack, H., Dulai, H., & Fitzsimmons, J. N.