Milestones in antarctic ice sheet history-preliminary results from leg 188 drilling in Prydz Bay Antarctica

ODP Leg 188 started as one of a series of drilling proposals by the Antarctic Offshore Stratigraphy project (ANTOSTRAT) sponsored by the Scientific Committee for Antarctic Research (SCAR). ANTOSTRAT aims to understand stand major events in the development of the Antarctic Ice Sheet by synthesising seismic data and then drilling. Major events targeted are the earliest Paleogene ice sheet development, the expansion of ice onto the continental shelf, variously thought to be Oligocene to mid-Miocene and the development of the cold, polar ice sheet of today through the Pliocene and Pleistocene. Prydz Bay was chosen because it lies at the downstream end of the Lambert Glacier-Amery Ice Shelf drainage system, the largest single ice stream flowing from the interior of East Antarctica (Fig. 1). The glacier flows within a major graben that has been active since the Permian. Part of the ice originates from the subglacial Gamburtsev Mountains, the area where some models of ice sheet growth suggest that the Antarctic Ice Sheet first developed. Thus, Prydz Bay was thought likely to contain the earliest evidence of Cenozoic glaciation in Antarctica. The large size of the drainage basin (20% of East Antarctica) and the focussing of the ice into one massive ice stream means that major changes in the East Antarctic Ice Sheet should be seen as fluctuations of the Lambert-Amery system. Three holes were drilled, each one aimed at providing insights into different aspects of Antarctic glacial history.