Seismic data show that glacial unconformities are located within lower Pliocene strata on the Antarctic continental shelves. The glacial unconformities are significant because they provide direct evidence that the Antarctic ice sheets advanced despite the generally warmer climates and elevated sea levels that characterized most of the early Pliocene. The magnitudes of peak eustatic lowstands and (super 18) O enrichments indicate that the ice volume on Antarctica may have exceeded today's ice volume by approximately 18%, which suggests that the ice-sheet grounding events on the shelves probably were associated with larger than present ice volumes on two to three occasions during the early Pliocene.