WIDESPREAD OVERPRINTING OF AUTHIGENIC NEODYMIUM ISOTOPE RECORDS: IMPLICATIONS FOR PALEOCEANOGRAPHIC RECONSTRUCTIONS

Sediment-water interactions during early diagenesis have a significant potential to influence authigenic paleoclimate records. The recently proposed sedimentary source of rare earth elements to the ocean suggests that the paleocirculation signal reconstructed from authigenic neodymium isotope records may be compromised by sediment-water exchange processes during early diagenesis. Here, we compile paired authigenic and detrital neodymium records from every major ocean basin and from 80 Ma to present. Our compilation reveals a strong linear relationship between detrital ε_Nd and authigenic ε_Nd (correlation coefficient = 0.86, n=871), demonstrating widespread overprinting of authigenic ε_Nd. To further understand this relationship, we present new authigenic and bulk sediment neodymium isotope data for International Ocean Drilling Program sites 1063 and 1308 paired with high resolution SEM images. We demonstrate that changes in the authigenic neodymium isotope signature are concurrent with changes in sediment provenance and sediment composition over this time period. These findings support a diagenetic overprinting of the seawater signature in the authigenic phases by the pore water but do not entirely preclude the use of neodymium proxy records. Instead, we propose that the authigenic neodymium isotope record can reveal information about changes in circulation and changes in sedimentation when coupled with total sediment composition and provenance. Using the detail of our new records and the breadth of the compilation of existing records, we propose a novel interpretive framework for authigenic ε_Nd records to evaluate the relative importance of sediment characteristics and bottom water composition on authigenic ε_Nd records. This framework is likely widely applicable to understanding the fluxes of trace elements and their isotopes at the sediment-water boundary (e.g. Zn, Fe).