Title: “Diagenetic Overprinting of Authigenic Neodymium Records in Marine Sediments”

Time & Location: Tues Nov. 3^rd 12:00 pm & via Zoom

Abstract: 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 εNd and authigenic εNd (correlation coefficient = 0.86, n=871), demonstrating widespread overprinting of authigenic εNd. 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 εNd records to evaluate the relative importance of sediment characteristics and bottom water composition on authigenic εNd 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).

Bio: Dr Abbott is a sediment geochemist currently based at Macquarie University. With over 200 days at sea, Dr Abbott’s main research focus is on understanding how sediments influence element cycling in the modern ocean to better constrain the behavior of these elements in their application as paleoclimate proxies.  Dr. Abbott joined Macquarie as a lecturer in 2016 as she received her PhD from the College of Earth, Ocean, and Atmospheric Sciences at Oregon State. She holds a master’s degree from the University of Minnesota Duluth and a Bachelor of Science from Hobart and William Smith Colleges.