Particle-seawater interaction of neodymium in the North Atlantic

torben.stichel [ at ]


Dissolved neodymium (Nd) isotopes (expressed as εNd) have been widely used as a water mass tracer in paleoceanography. However, one aspect of the modern biogeochemical cycle of Nd that has been sparsely investigated is the interplay between dissolved and particulate phases in seawater. We here present the first regional data set on particulate Nd isotope compositions (εNdp) and concentrations ([Nd]p) from five stations in the western North Atlantic Ocean along the GEOTRACES GA02 transect, in conjunction with previously published dissolved Nd isotope compositions (εNdd) and concentrations ([Nd]d)1. Key observations and interpretations from our new particulate data set include the following: (1) A low fractional contributions of [Nd]p to the total Nd inventory per volume unit of seawater (~5%), with significant increases of up to 45% in benthic boundary layers. (2) Increasing Nd concentrations in suspended particulate matter ([Nd]SPM) and fractions of lithogenic material with water depth, suggesting the removal of Nd poor phases. (3) Different provenances of particulates in the subpolar and subtropical gyres as evidenced by their Nd isotope fingerprints reaching from εNdp ≈ -20 near the Labrador Basin (old continental crust), over εNdp ≈ -4 between Iceland and Greenland (young mafic provenance), to values of εNdp ≈-13 in the subtropics (similar to African dust signal). (4) Vertical heterogeneity of εNdp, as well as large deviations from ambient seawater values in the subpolar gyre, indicate advection of lithogenic particles in this area. (5) Vertically homogenous εNdp values in the subtropical gyre, indistinguishable from εNdd values, are indicative of predominance of vertical particulate supply. The process of reversible scavenging only seems to influence particulate signatures below 3 km. Overall, we do not find evidence on enhanced particle dissolution, often invoked to explain the observed increase in dissolved Nd in the North Atlantic.

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DOI 10.1021/acsearthspacechem.0c00034

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Stichel, T. , Kretschmer, S. , Geibert, W. , Lambelet, M. , Plancherel, Y. , Rutgers van der Loeff, M. and van de Flierdt, T. (2020): Particle-seawater interaction of neodymium in the North Atlantic , ACS Earth and Space Chemistry . doi: 10.1021/acsearthspacechem.0c00034

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