Stanford University, United States

Drilling of the Antarctic Wilkes Land margin by the Integrated Ocean Drilling Program (IODP) Expedition 323 plans to provide a long-term record of Antarctic glaciation and its relationships with global climatic and oceanographic change. Stratigraphic interpretations indicate that the Wilkes Land sediments contain a record of the critical periods in Earth's climate evolution when the cryosphere formed and evolved to assume its present day configuration. The drilling sites have been selected to obtain: 1) the record of the first arrival of ice at the Wilkes Land margin (earliest Oligocene? Oi-1 isotope event), 2) the significant changes in the geometry of the progradational wedge, likely corresponding with large fluctuations in the extent of the East Antarctic Ice Sheet and possibly coinciding with the transition from a wet-based to a cold-based glacial regime (Late Miocene-Pliocene?), 3) a high-resolution record of Antarctic climate variability during the late Neogene and Quaternary, and 4) an unprecedented, ultra-high resolution (i.e., annual to decadal) Holocene record of climate variability. The age and paleoenvironment of deposition of seismically inferred glacial sequences in the Wilkes Land margin are essential to ground-truth the existing glacial stratigraphic and ice-sheet volume models for this margin. These models suggest that the Wilkes Land became glaciated in the later stages of East Antarctic glaciation, after Prydz Bay and the Weddell Sea, and is presumed to be more sensitive to future temperature changes. Moreover, the East Antarctic Ice Sheet (EAIS) in the Eastern Wilkes Basin is grounded below sea-level and thus may have been more sensitive to climate changes in the late Neogene. The sedimentary sections on the Wilkes Land margin may therefore not only hold the record of the time when the EAIS first reached this margin, but also the record of ice sheet fluctuations during times when the EAIS is thought to be more stable (i.e., after 15 Ma-recent). To understand the Antarctic ice sheet, dynamics and stability is of special societal relevance. State-of-the-art climate models combined with paleoclimatic proxy data suggest that the main triggering mechanism for initial development of Antarctic glaciation was the decreasing levels of atmospheric CO2. Based on IPCC 2007 forecasts, a 2 x CO2 increase, equivalent to a 1.8 degrees to 4 degrees C increase, is expected for the end of this century. Such projected CO2 levels have not existed on Earth for the past 35 m.y., and only since 10-15 Ma has the stable but variable-size Antarctic Ice Sheet existed. The record from drilling the Wilkes Land is thus critical for developing reliable models of future Ice Sheet behavior. IODP Expedition 323, scheduled for January-March 2009, will be a contribution by the IODP and the ACE (Antarctic Climate Evolution) Program of SCAR (Scientific Committee on Antarctic Research) to the International Polar Year.