Date of Award

Fall 2019

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

School

Ocean Science and Engineering

Committee Chair

Christopher Hayes

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Alan Shiller

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Davin Wallace

Committee Member 3 School

Ocean Science and Engineering

Abstract

In the modern Southern Ocean and during the last interglacial period, Marine Isotope Stage 5, there are observations that point to reduced Antarctic Bottom Water (AABW) formation. These reductions are believed to be driven by an increase in the strength of the Southern Ocean density stratification due to surface water freshening. Any reduction in AABW formation has important implications for global climate as AABW plays a vital role in the cycling of carbon in the world’s ocean. The primary question this study seeks to answer is do these AABW reductions occur during any of the other interglacials of the past 500 thousand years? To study AABW changes in the paleoceanographic we look at changes in the redox record. Newly formed AABW is oxygen-rich, so any reduction should lead to a decrease in oxygen concentrations in the deep Southern Ocean. The trace element uranium is useful for studying these redox changes as it is enriched in marine sediments under low-oxygen conditions. When accounting for other factors, such as paleoproductivity, that can also decrease the oxygen concentrations in sedimentary porewater, it is possible to identify changes in AABW using authigenic uranium. The survey conducted by this study found a possible AABW reduction during late Marine Isotope Stage 11 (~395 ka). However, this reduction does not appear to be triggered by a decrease in surface water density. Instead, a change in the strength or position of the southern hemisphere westerly winds is hypothesized to be the driving mechanism behind this reduction.

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