"South Pacific Paleogene Climate" IODP Expedition 378: Stratigraphy, Chronology and Provenance of late Eocene-early Oligocene South Pacific sediments

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Over the last 66 million years, Earth's climate has changed from a near ice-free "Greenhouse" world to an "Icehouse" world, where large ice sheets cover huge areas of land in both the northern and southern hemispheres. Although some of this change has been gradual, the first time Antarctica was covered with a large ice sheet occurred approximately 33.9 Million years ago. This transition is referred to as the Eocene-Oligocene Transition. A large drop in atmospheric carbon dioxide concentrations has been proposed as the main cause of the first major Antarctic glaciation. However, another key condition for ice sheets forming on Antarctica is that this continent needed to be thermally isolated from warm waters that spread from the Earth's equator. In the present day, a large, cold deep-water current circles Antarctica, thereby providing a temperature barrier. This current is called the Antarctic Circumpolar Current, and some research suggests that the first Antarctic glaciation occurred when this deep-water current first started. However, this claim is debated. It is currently difficult to solve this debate as there are insufficient records that can trace the start of the Antarctic Circumpolar Current accurately. Scientific ocean drilling programmes like the International Ocean Discovery Program (IODP) and its predecessors are the only way to recover the archives of past climate change locked away in deep-sea sediments stored on our ocean floor. The south Pacific Ocean is a key area that is dominated by the Antarctic Circumpolar Current, however, it remains entirely unexplored by scientific ocean drilling. This will change with IODP Expedition 378, which will go to the South Pacific and recover key sediments and enable us to look back at climate dynamics when large ice sheets first formed on Antarctica. Here, we propose to use these sediments to investigate when the Antarctic Circumpolar Current first appeared in the South Pacific by looking at the chemistry and mineralogy of the past sediments across the Eocene-Oligocene Transition. We will also make an initial assessment of how the ice volume changed over longer timescales during the same time interval, using the chemistry of microscopic fossils that live on the ocean floor, called benthic foraminifera. Combining these preliminary ice volume records with the chemistry and mineralogy records should improve our understanding of the role of the Antarctic Circumpolar Current in the first major glaciation of Antarctica.