Ocean Drilling Program, United States

Information on the Antarctic ice sheets has been increased by drilling on the Antaractic continental margin. The drilling was made to try and recover direct evidence of glacial ice and to investigate the transition from pre-glacial to the current full polar glacial conditions. ODP Leg 188 started as one of a series of drilling proposals by the Antarctic Offshore Stratigraphy Project sponsored by the Scientific Committee for Antarctic Research. ANTOSTRAT attempts to further the understanding of major events in the development of the Antarctic Ice Sheet by synthesizing seismic data and then drilling. Especially of interest are the earliest Paleogene ice sheet development, the expansion of ice onto the continental shelf which is variously thought to be Oligocene to mid-Miocene and the development of the cold, polar ice sheet of today through the Pliocene and Pleistocene. Leg 188 has now extended records back to the late Eocene, showing the presence of floating ice in association with a terrestrial flora stunted by cold temperatures. This drilling project produced more evidence for the existence of a more temperate glacial regime in Antarctica until the middle Miocene, when the ice advanced onto the continental shelf and started eroding it. This was followed by a cooling trend caused by more polar conditions, reducing erosion rates and sediment delivery to the ocean. This trend to cooler, less active ice continued through the Plio-Pleistocene, with evidence that the Lambert Glacier has not advanced to the shelf edge in step with global ice volumes as indicated by oxygen isotope records recorded by other authors.