Postgraduate Profiles

Rebecca O'Donnell

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Thesis: Last Interglacial sea level and Leeuwin Current events: a dual stratigraphic and geochemical approach

The overall purpose of my research project is to combine detailed stratigraphic interpretation and high-precision U-series dating in order to establish an understanding of the timing and behavior of sea level events along Western Australia during the Last Interglacial (MIS 5e) and use this to lead into a reconstruction of Leeuwin Current activity at that time. This study will provide an important opportunity to resolve outstanding uncertainties and advance our understanding of sea level events globally and resolve questions of Leeuwin Current activity during a ‘warmer’ global state.

Why my research is important

The coastal geomorphology of Western Australia presents an extensive stratigraphic record of preserved Quaternary sea level events. At present, only incomplete records of these events are available and few dates older than the Last Interglacial have been obtained. Hermatypic reef-building corals, such as those found along the coast of Western Australia, provide an excellent means in which to constrain the timing of sea level events. This is because former sea level is reflected within the narrow depth range that coral growth occurs, and their incorporation of uranium from seawater into their skeletons is ideal for uranium-series dating methods.

Present knowledge of Last Interglacial sea level events and associated Leeuwin Current behaviors, is largely based on the dating of fossil reef sequences. However, the stratigraphic interpretation underpinning the obtained dates is incomplete and there are inconsistencies in the chronologies developed that restrict any attempt at a wider evaluation of the coastal events at that time. Foremost among these are questions associated with the ‘state’ of the Leeuwin Current during the Last Interglacial. The Leeuwin Current is an anomalous eastern boundary current that facilitates the southward transportation of warm water from tropically sourced currents and is an important control on the biogeography along coastal Western Australia. The distribution of warm water from the Leeuwin Current extends as far south as Cape Leeuwin along southern Western Australia, with the strength and latitudinal scope varying seasonally. Understanding how the Leeuwin Current changed in response to a warmer-than-present Last Interglacial is fundamental when considering how the climate system may behave as the Earth progressively moves into an enhanced greenhouse climate.

Funding

Jan 2014

Jan 2017

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