Lead isotope tracing of terrigenous, hydrothermal and anthropogenic lead sources in the ocean
File(s)
Author(s)
Leung, Yee
Type
Thesis
Abstract
The anthropogenic perturbation of the oceanic lead (Pb) budget during the last 200 years has generated a unique Pb tracer that offers numerous applications for research in marine geochemistry. This thesis improves understanding of the marine sources and the internal cycling of Pb in the modern ocean. To this end, Pb concentrations and isotope compositions are presented for seawater and hemipelagic sediments, which are employed to study the terrigenous and hydrothermal fluxes of Pb to the oceans and the mechanisms responsible for the observed distribution of anthropogenic Pb in the ocean interior. Lead and additional neodymium (Nd) isotope results are presented for two hemipelagic sediment core-tops from the Eastern Equatorial Pacific Ocean. The results suggest that proximal Mexican and Northern Andean sources dominate the detrital sedimentary component, with local weathering inputs impacting the dissolved deep water budgets of both elements. The data also indicate that Pb of hydrothermal origin is dispersed much more efficiently compared to Nd. Dissolved Pb concentration and isotope data were obtained for five seawater depth profiles collected at and near the TAG Hydrothermal Field in the North Atlantic Ocean. Dissolved Pb deficits in the buoyant TAG plume demonstrate that hydrothermal activity can act as a net sink for dissolved seawater Pb, due to intense scavenging by hydrothermal particles. The results also reveal unexpected anthropogenic Pb isotope signatures in some seawater samples from the hydrothermal plume, which most likely reflect enhanced Pb exchange between sinking aerosol particles and ambient seawater. Finally, dissolved Pb concentration and isotope data were obtained for two seawater depth profiles from the Southern Ocean. Together with previous data, the results provide a full meridional transect between Tasmania and Antarctica, which enables investigations of the sources of dissolved Pb, water mass origins and vertical flux dynamics in this poorly explored ocean region.
Version
Open Access
Date Issued
2023-06-23
Date Awarded
2024-05-01
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Rehkämper, Mark
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)