Application of elemental and isotopic proxies to reconstruct Pacific Ocean circulation and productivity during periods of climate change [electronic resource]

Work presented in this dissertation investigates the response of the Pacific Ocean to climate change in the geologic record while evaluating methods to be used for future investigations. A particular focus of this work has been the interplay of ocean productivity, air and water circulation, and the resulting impacts on ocean chemistry. Investigations into ocean productivity in this dissertation have focused on changes in the accumulation rates of marine barite, an established proxy for export production. Across one of the most dramatic climate change intervals in the geologic record, the Eocene-Oligocene Transition, we found that the shift from greenhouse conditions to icehouse conditions corresponds to a sharp decline in export production. This decline in export production was synchronous with changes in the carbonate oxygen and carbon isotope shifts. Additionally, a previous unobserved peak in export production was identified before the onset of glaciation. We postulate that this increase in export production may correlate to an increase in carbon sequestration and should be further explored as a contributing factor to the CO2 drawdown proposed at this time. To understand the impacts of climate change on a more regional scale, ocean sediments from the Oregon shelf were collected. To investigate changes in oxygenation and sediment sources over the previous 1000+ years, this study utilized multiple proxies, including trace metal abundances and carbon and nitrogen isotopes. The results of this study do not show evidence of persistent hypoxia in the geologic record, inconsistent with the modern observations being driven by climate cycles which occurred pre-anthropogenically. The reminder of this dissertation focuses on the expansion of lead (Pb) isotopes for paleoceanographic reconstructions. Measurement of Pb isotopes in detrital fractions from across the Pacific Ocean, presented in Chapter 3, show the differentiation of various dust sources across the Pacific, along with the ability of this fraction to illustrate the location of the intertropical convergence zone. This study provides a more extensive description of Pb isotopes in potential source regions, creating a framework for the interpretation of future down core investigations and highlights some considerations regarding sample processing and analyses. To better understand sources of Pb to seawater, ferromanganese grain coatings were measured across the Pacific Ocean with a particular focus on the eastern equatorial Pacific (EEP). This study shows that dust deposition, particularly Chinese loess in the North Pacific and New Zealand loess in the south Pacific, is the dominant source of Pb to the open ocean. However, additional sources are needed to account for the measured Pb isotopic values, potentially including North Pacific Intermediate water in the North Pacific (Pb in which is sources from local pacific rim volcanism) and a yet unidentified source in the South Pacific (possibly South America or Australia dust). In addition, this investigation illustrates the possible regional impact of hydrothermal fluids in the EEP, with ferromanganese accumulations up to ~3000 km from the probable hydrothermal fluid source showing a measurable influence in the Pb isotopic ratios.

Keywords: Geological and Environmental Sciences.
Advisor: Payne Jonathan L. primary advisor. Thesis advisor
Paytan Adina
Maher Katharine advisor. Thesis advisor