The Nd isotopic compositions of hydrogenous ferromanganese encrustations and nodules largely reflect those of the overlying seawater, integrated over the few millions of years over which they grow. Available Nd isotope data on ocean-floor hydrogenous deposits suggest control by Nd from particulates blown from the continents and released by volcanic activity associated with subduction zones and midocean ridges. The regional Nd isotope variations display a marked similarity to the broad patterns of present-day deep-ocean circulation, suggesting that the particulates that are the sources of oceanic Nd travel along with water masses. Despite rapid (10-100 ka) perturbations during glacial periods, the long-term patterns of water-mass movements and oceanic fluxes of particulates have remained essentially stable over the last few million years.

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