A long-standing debate concerning Neogene Antarctic climate in the McMurdo Dry Valleys relies largely on evidence from landscape evolution, glacial modeling and stratigraphy. We provide new evidence from meteoric Be for the onset of frozen, hyper-arid conditions on a high elevation (1840m) interfluve at Table Mountain. A simple decay model for the co-occurrence of meteoric Be and illuviated clay in cores of ice-cemented glacial sediments indicates that the clays were actively migrating down from the surface in a warm climate until the system froze between 6 and 9Ma. Although this age range may be sensitive to possible interference by in situ produced Be, the implied minimum age of 6Ma for the Sirius Group indicates that the Dry Valleys were permanently frozen down to this elevation at this time. The model also suggests denudation rates of 1-6cmMyr since freezing. These data provide an independent test of glacial-stratigraphic evidence used to determine Antarctic paleoclimate.