Chapter 3.3 - From Greenhouse to Icehouse at the Wilkes Land Antarctic Margin: IODP Expedition 318 Synthesis of Results

Abstract

Abstract IODP (Integrated Ocean Drilling Program) Expedition 318 drilled a transect of sites across the Wilkes Land margin of Antarctica to provide a long-term record of the sedimentary archives of Cenozoic Antarctic glaciation and its intimate relationships with global climatic and oceanographic change. The Wilkes Land drilling program was undertaken to constrain the age, nature, and paleo-environment of the previously only seismically inferred glacial sequences. The expedition (January–March, 2010) recovered ∼2000 m of high-quality middle Eocene–Holocene sediments from water depths between 400 and 4000 m at four sites on the Wilkes Land rise (U1355, U1356, U1359, and U1361) and three sites on the Wilkes Land shelf (U1357, U1358, and U1360). These records span ∼54 million years of Antarctic history at the Wilkes Land margin. Sediment cores provide an insight into an ice-free subtropical east Antarctica during the early Eocene, and the first cooling during the middle Eocene, coeval with the first incursion of cold westward flowing waters across the southern Tasman Gateway. The cores also reveal the erosional consequences of the onset of the continent-wide glaciation during the Eocene–Oligocene transition, and the counterintuitive of this to cause regional sea level rise along Antarctic coastlines. Starting in the earliest Oligocene (Oi-1 event), the icehouse sediments provide records of the subsequent waxing and waning of the ice sheets, sea ice, and ecosystems. These include times of past elevated temperatures and atmospheric CO2 (i.e., the early Pliocene), and unprecedented records of seasonal to annual resolution records of the last deglaciation that began ∼10,000 years ago. The cores also reveal details of the tectonic history of the Australo-Antarctic Gulf from 54 Ma portraying the onset of the second phase of rifting between Australia and Antarctica, basin and ocean deepening, associated subsidence of the margins, and to the present day isolation of the Antarctic continent surrounded by deep ocean basins.