Dual Nd isotopic archives in fossil teeth reveal bottom-current control of rare-earth element enrichment in deep-sea sediments

Abstract

The global emergence of deep-sea sediments enriched in rare-earth elements and yttrium (REY) after the Late Eocene cooling coincides spatiotemporally with Antarctic bottom water (AABW) expansion, yet the underlying mechanism remains unresolved. Here, we present in situ elemental and neodymium isotopic analyses of apatites extracted from Oligocene-Miocene sediments along the North Pacific AABW pathway. Results show ∼90% of the REY budget resides in inner dentin of fossil teeth. The dentin and coexisting authigenic fluorapatites display similar ε Nd values (∼−5) matching North Pacific seawater, whereas outer dense layer carries a distinct, less-radiogenic ε Nd (∼−10) resembling South Pacific seawater. This isotopic decoupling establishes fossil teeth as dual archives: The outer layer preserves the ε Nd signature of the fish’s living environment, while the inner dentin records its depositional environment. We propose that AABW collects, transports, and sorts fossil teeth along its flow path, ultimately leading to the global occurrence of REY-rich sediments in downstream basins.