Trace Element Sources and Fluxes in the Zonal Current System of the Western Tropical Pacific Ocean: Evidence From Combined Rare Earth Element, Nd Isotope Distributions and Physical Observations

Melanie K. Behrens1, Katharina Pahnke1, Audrey Delpech2, Sophie E Cravatte2, Frederic Marin2 and Catherine Jeandel2, (1)Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Oldenburg, Germany, (2)LEGOS, Université de Toulouse, (IRD, CNES, CNRS, UPS), Toulouse, France
Dissolved rare earth element concentrations ([REE]) and neodymium (Nd) isotopes (expressed as εNd) in seawater are used to document trace element (TE) input to and transport within the ocean. In combination with physical observations, they are ideal tools to test the potentially important role of the equatorial zonal current system in supplying TEs from the enriched Western Tropical Pacific to the iron-limited Eastern Pacific. Here we present dissolved seawater [REE] and Nd isotope distributions combined with hydrological and velocity data in the surface to mid-depth zonal current system of the Western Tropical Pacific, with a particular focus on alternating eastward and westward mid-depth jets.

Elevated [REE] (e.g., Nd up to 9.51 pmol/kg) and higher εNd values (εNd ~ -2) within the eastward SICC (South Intermediate Countercurrent), located at 2°S, than in surrounding westward flow (e.g., Nd = 7.94-8.36 pmol/kg, εNd ~ -3.4), indicate that this mid-depth jet transports water enriched in the Western Pacific eastward. Similarly, enriched [REE] within the surface to subthermocline equatorial eastward zonal current system (e.g., Nd up to 8.10 pmol/kg) compared to lower [REE] of the westward zonal South Equatorial Current (SEC) (e.g., Nd = 3.24-5.11 pmol/kg) indicate TE input in the Western Pacific. REE patterns characteristic of basaltic rocks suggest Papua New Guinea and New Ireland islands as main sources of TEs. Our results are in line with published total dissolvable iron ([Fe]) concentrations in the study area [1, 2] that show highest [Fe] near Papua New Guinea and New Ireland, and elevated [Fe] within the eastward zonal currents relative to the westward SEC. Overall, our findings highlight the potentially important role of this TE source, together with the subthermocline zonal current system, to feed the Eastern Pacific.

[1] Obata et al. (2008) J. Oceanogr. 64, 233-245.

[2] Slemons et al. (2012) Mar. Chem. 142-144, 54-67.