Antarctic weathering and hydrologic cycling through the Paleogene greenhouse to icehouse transition (IODP Expedition 318, Wilkes Land)

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Over the past 65 million years of geologic time, Earth's climate has changed dramatically--transitioning from a world with warm oceans and limited polar glaciation to a world with cold polar regions and large continental ice sheets. This long-term change in global climate is known as the 'Greenhouse' to 'Icehouse' transition and primarily occurred during the Eocene and Oligocene geological epochs (between 55 and 23 million years ago). Study of this remarkable episode of ancient climate change can provide valuable information for understanding the mechanisms that precipitated this shift, as well as insight into the operation of different Earth system processes in the past. Further knowledge of these processes, involving the global carbon cycle and different climate feedback mechanisms, can be used to inform future predictions of climate change resulting from anthropogenic greenhouse gas emissions to the atmosphere.In an effort to gain further information on high-latitude climate conditions during the 'Greenhouse' to 'Icehouse' transition, the Integrated Ocean Drilling Program (IODP) recently cored marine sediments on the Antarctic margin off the Wilkes Land coast (directly south of Australia). The drillcores were recovered using a ship-based drilling platform and provide a window into Eocene and Oligocene climate history of the Antarctic coast and marginal seas. The proposed study is focused on clay mineral assemblages preserved in cores obtained from the Wilkes Land coast. Since clay minerals are a primary sedimentary weathering product shed from the terrestrial environment, variation in the types of clay mineral present throughout cores will provide important information on changes in the prevailing weathering regime. Specifically, clay minerals can be used to determine the timing of the switch from a chemical weathering regime (under warm, humid conditions) to physical weathering regime (influenced by glacial activity) during the Eocene-Oligocene time interval. Through collaborative work, the clay mineral records will be integrated with other climate proxy records currently being developed using a variety of approaches. The new Antarctic climate reconstructions that result from this research will provide critical high-latitude climate information that can be used to: (1) determine the nature of Antarctic climate conditions during peak Eocene warmth and during the onset of Oligocene glaciation, and (2) assess links between global climate change and atmospheric pCO2 variability through the 'Greenhouse' to 'Icehouse' transition.