From jungle to ice: the role of changes in weathering and ocean circulation patterns in the onset of Antarctic glaciation

Abstract

The transition from the Greenhouse Eocene climate (55 – 34Ma) to the Icehouse regime of the Oligocene (34 – 23Ma) was marked by a widespread cooling at the Eocene-Oligocene Transition (EOT) (~34Ma), followed by major Antarctic glaciation. The relative contribution of changes in ocean circulation and continental weathering is however not well understood. This thesis takes advantage of new core material recovered during IODP Expedition 318 to Wilkes Land, Antarctica, to study ocean-continent interaction during this critical time interval.

To this end, I have used neodymium (Nd) isotopes in fossil fish teeth to reconstruct water mass composition and ocean circulation. Secondly, I have used Nd isotopes in bulk sediments as a provenance tool to reconstruct erosional patterns on the continent. Additionally, I have used a combination of major and trace element data to evaluated the robustness of Nd isotopes in fossil fish teeth as a water mass tracer in a marine shelf environment, and under changing redox conditions at the seafloor.

My findings are presented in four distinct chapters and yield the following conclusions: i) fossil fish teeth appear to be robust recorders of authigenic Nd in a shelf setting and remain robust under changing redox conditions within the sediments; ii) a multi-site authigenic Nd isotope study in the Tasman region of the Southern Ocean indicates active deep water formation in the Southern Ocean, and excursions recorded are the result of a previously unreported widespread perturbation to the hydrological cycle on Antarctica; iii) the first authigenic Nd record from the North Atlantic EOT is consistent with a change in deep water masses coinciding with the transition to a cooler climate, and iv) changing sediment provenance indicates a dynamic Antarctic ice sheet throughout the Oligocene.