Reactive-transport modeling of neodymium and its radiogenic isotope in deep-sea sediments: The roles of authigenesis, marine silicate weathering and reverse weathering

Dissolved Rare Earth Elements (REE) and radiogenic neodymium (Nd) isotope composition (?Nd) of seawater are widely used geochemical tools in studying marine processes, but their modern ocean budgets poorly understood. Recent discoveries large benthic fluxes REE with unique ?Nd signatures from sediments, particularly the deep-sea, have led to a “bottom-up” hypothesis, which suggests that early diagenesis below sediment-water interface (SWI) controls ocean's budgets. To investigate such sedimentary we created reactive-transport model for biogeochemical cycling Nd sediments. Here, attempt quantify roles authigenesis, silicate weathering reverse diagenetic at deep-sea (3000 m) site on Oregon margin. Our predicts that, this site, carried by Fe/Mn oxides into sediments eventually transforms authigenic Nd-phosphate, during ?9% incoming solid flux is released as dissolved back overlying bottom water. We also find classic reversible scavenging formulation applied co-cycling inconsistent data. Rather, co-precipitation formulation, assuming structurally incorporated oxides, successfully simulates The shows authigenesis alone cannot explain pore water ?Nd, both more than site. However, volcanic silicates sourced local subduction zone can ?Nd. suggest because clay formation maintains under-saturation primary water, proceed. processes likely affect many other trace elements isotopes, much broader implications understanding biogeochemistry.