From Greenhouse to Icehouse: Past changes in southern hemisphere vegetation and the evolution of the Antarctic ice sheet

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The polar regions play a key role in our understanding of environmental change in a future warmer-than-present world. The past vegetation and climate of Antarctica and the evolution of its highly sensitive and dynamic ice sheet are poorly constrained by geological data. The few existing far-field data, and even fewer proximal records, indicate a major ice-sheet build-up in Antarctica from the Oligocene to the Miocene, with partial or even complete ice-sheet collapses during warm Late Cenozoic intervals with near-modern atmospheric CO2-concentrations. The onset of the Antarctic Circumpolar Current (ACC) about 30 million years ago coincided with major changes in global ocean circulation and a significant decline in atmospheric carbon dioxide concentration during which Antarctica transformed from a "greenhouse environment" into an ice desert. Today the ACC regulates the exchange of heat and carbon between the ocean and the atmosphere, and although this large ocean current is a key component of Earth's climate system, many controversies exist about its origin, evolution and impact on the global environment. The PhD project will use fossil pollen, spores and dinoflagellates from selected marine and terrestrial records to reconstruct Cenozoic vegetation and terrestrial climate. The project will focus on key regions in South America, Antarctica and Australasia, which are closely located to the Drake Passage and Tasman Gateway. Tectonic changes in both ocean gateways were a major control for the development of the ACC since the late Eocene. In order to improve our understanding about the timing of the main events and processes controlling the evolution of the ACC, the project will focus on selected geological time intervals that include critical threshold in Earth's climate evolution, such as the Eocene-Oligocene and Oligocene-Miocene transitions.