Preservation of Miocene glacier ice in East Antarctica

ANTARCTIC climate during the Pliocene has been the subject of considerable debate. One view holds that, during part of the Pliocene, East Antarctica was largely free of glacier ice and that vegetation survived on the coastal mountains1a¤-4. An alternative viewpoint argues for the development of a stable polar ice sheet by the middle Miocene, which has persisted since then5a¤-10. Here we report the discovery of buried glacier ice in Beacon valley, East Antarctica, which appears to have survived for at least 8.1 million years. We have dated the ice by 40Ar/39Ar analysis of volcanic ash in the thin, overlying glacial till which, we argue, has undergone little (if any) reworking. Isotope and crystal fabric analyses of the ice show that it was derived from an ice sheet. We suggest that stable polar conditions must have persisted in this region for at least 8.1 million years for this ice to have avoided sublimation.