Biosiliceous marine floras responses to climatic and environmental changes during late Eocene-oligocene- early Miocene transitions in Antarctica

The Cenozoic Era is one of the most intriguing periods in Earth’s geological, climatic and biological history (major transition from greenhouse to icehouse conditions across the Eocene-Oligocene Transition and the onset of major glaciations). Its major geological events are: 1) tectonic continents onset with the opening of oceanic gateways (like the Drake Passage) 2) the formation of the Antarctic Circumpolar Current with the establishment of the Polar Front and the rapid evolution of the marine phytoplankton floras. Diatoms are the dominant primary producer group in the modern oceans, they account for a major proportion of total oceanic primary productivity and of organic carbon burial in marine sediments. Directly involved in the biological pump, diatoms are commonly used to infer past oceanographic and climatic changes in polar regions. Understanding how ecosystems have evolved in the oceanic area between the continent and the polar front (before, during and after its formation) and comparing with high resolution stratigraphic and geochemical data around Antarctica, is basic to understand relationship among cryosphere /atmosphere /ocean realms and then better define the history of the polar ice cap. A qualitative and quantitative analyses on diatom microflora across the late Eocene-Oligocene-early Miocene interval at ODP Site 744 in Prydz Bay (Indian sector of the Southern Antarctic Ocean) provides a compared biostratigraphy and new informations about the timing and characteristic of climate events linked with ice sheet dynamics. The results include a diatom biostratigraphy, compared with that from other organisms sensitive to water temperature and composition changes. The poster will show the oceanic diatoms response to Antarctic ice sheet evolution from the Eocene (E/O transition) to the late Oligocene/Miocene; during these periods the Earth cooled significantly from a greenhouse to an icehouse