Meteoric Be-10 from Sirius Group suggests high elevation McMurdo Dry Valleys permanently frozen since 6 Ma

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-10 for the onset of frozen, hyper-arid conditions on a high elevation (1840 m) interfluve at Table Mountain. A simple decay model for the co-occurrence of meteoric Be-10 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 9 Ma. Although this age range may be sensitive to possible interference by in situ produced Be-10, the implied minimum age of 6 Ma 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 1-6 cm Myr(-1) since freezing. These data provide an independent test of glacial-stratigraphic evidence used to determine Antarctic paleoclimate. (C) 2012 Elsevier B.V. All rights reserved.