GC51F-1166
Trace Element Inputs to the Upper West Pacific from Nd Isotopes and Rare Earth Elements

Friday, 18 December 2015
Poster Hall (Moscone South)
Melanie K. Behrens1, Katharina Pahnke1, Bernhard Schnetger2 and Hans-J Brumsack2, (1)Max Planck Research Group for Marine Isotope Geochemistry, Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Oldenburg, Germany, (2)Microbiogeochemistry Research Group, Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Oldenburg, Germany
Abstract:
Neodymium isotopes (143Nd/144Nd, expressed as εNd) and rare earth element (REE) concentrations in the ocean trace water mass transport and margin-seawater exchange processes. The distinct εNd and REE signatures of the lithogenic components of margin sediments of the West Pacific allow characterization of trace element inputs to the Pacific Ocean. We present dissolved εNdand REE concentrations from twelve vertical profiles of a transect from South Korea to Fiji.

Near South Korea, surface waters are marked by unradiogenic εNd (as low as -7.3), high REE concentrations (e.g., Nd = 15.3 pmol/kg) and low salinity. Towards the open ocean, these parameters gradually change towards typical Pacific open ocean values (εNd = -3.3, [Nd] = 5.55 pmol/kg). Subsurface waters show REE depletions, followed by the typical REE increase with increasing water depth. These distributions indicate trace element input near South Korea and enhanced subsurface scavenging, as indicated by strong heavy REE to light REE fractionation.

In the tropical West Pacific (10°N-15°S), high surface and subsurface water εNd values (+0.7) and positive Eu anomalies trace the influence of volcanic islands. Yet, absolute REE concentrations are extremely low at these depths (e.g., Nd = 2.77 pmol/kg). Using shale-normalized Nd/Er and Ho/Dy ratios, that show a much stronger surface to subsurface decrease in coastal waters compared to the open ocean, we suggest enhanced scavenging in this area. Eastward flowing intermediate waters (NPIW, AAIW) have εNd values up to +1.9 (NPIW) and +3.7 (AAIW) higher than those entering the tropical West Pacific from north and south, respectively. Modified εNd at intermediate depths and no change in REE patterns suggest that boundary exchange along volcanic island margins modifies the seawater εNd without changing the REE budget.

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