A critical evaluation of the neodymium isotope paleo water mass proxy: insights from the glaciated Antarctic Margin and Southern Ocean
File(s)
Author(s)
Holder, Liam
Type
Thesis
Abstract
Neodymium (Nd) isotopes in modern seawater and sedimentary authigenic archives have been widely utilised to infer changes in water mass mixing and provenance. However, the increase in spatial data coverage has brought into question the fundamental assumptions underlying this paleo water mass proxy. In this thesis, I aim to evaluate the reliability of Nd isotopes to reconstruct changes in past ocean circulation with new data from the understudied region of the Antarctic margin and Southern Ocean.
In chapter 2, new measurements of dissolved Nd isotopes in recently ventilated Ross Sea Bottom Water confirmed an end-member isotopic composition of -7.5 ± 0.3, with prominent areas of boundary exchange along the West Antarctic margin shifting bottom waters to more radiogenic values. In chapter 3, sequential leaching experiments on Ross Sea core-top sediments failed to extract a seawater Nd isotope signature, where all authigenic archives are offset to more radiogenic values than ambient bottom water. This result can be explained if authigenic archives inherit their Nd isotope signatures directly from porewaters. In chapter 4, a new authigenic Nd isotope record at IODP Site U1524, located on the outer Ross Sea, demonstrates that the supply of freshly weathered, reactive volcanogenic material is the primary control on authigenic Nd isotope signals on the Antarctic margin, mediated by changes in sedimentary redox conditions. In chapter 5, an authigenic Nd isotope record constructed at Site TAN1302-97 from the open Southern Ocean exhibits a strong relationship with various lithogenic properties. I demonstrate that a lithogenic control over authigenic Nd isotope records is widespread throughout the Southern Ocean and controlled by dust fluxes.
Overall, this thesis strongly questions the integrity of authigenic Nd isotopes as a paleo water mass tracer where changes in continental weathering fluxes are more likely to exert a dominate control through time.
In chapter 2, new measurements of dissolved Nd isotopes in recently ventilated Ross Sea Bottom Water confirmed an end-member isotopic composition of -7.5 ± 0.3, with prominent areas of boundary exchange along the West Antarctic margin shifting bottom waters to more radiogenic values. In chapter 3, sequential leaching experiments on Ross Sea core-top sediments failed to extract a seawater Nd isotope signature, where all authigenic archives are offset to more radiogenic values than ambient bottom water. This result can be explained if authigenic archives inherit their Nd isotope signatures directly from porewaters. In chapter 4, a new authigenic Nd isotope record at IODP Site U1524, located on the outer Ross Sea, demonstrates that the supply of freshly weathered, reactive volcanogenic material is the primary control on authigenic Nd isotope signals on the Antarctic margin, mediated by changes in sedimentary redox conditions. In chapter 5, an authigenic Nd isotope record constructed at Site TAN1302-97 from the open Southern Ocean exhibits a strong relationship with various lithogenic properties. I demonstrate that a lithogenic control over authigenic Nd isotope records is widespread throughout the Southern Ocean and controlled by dust fluxes.
Overall, this thesis strongly questions the integrity of authigenic Nd isotopes as a paleo water mass tracer where changes in continental weathering fluxes are more likely to exert a dominate control through time.
Version
Open Access
Date Issued
2023-08-25
Date Awarded
01/02/2024
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
van de Flierdt, Tina
Sponsor
Imperial College London
Publisher Department
Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)