Late Miocene onset of hyper-aridity in East Antarctica indicated by meteoric beryllium-10 in permafrost

Continental-scale ice sheets have covered Antarctica since an interval of global cooling near the Eocene–Oligocene boundary around 33.9 million years ago (Ma). However, the sequence of events that led to the emergence of the persistent ice sheet in modern East Antarctica remains disputed. The transition to permanent polar aridity in high elevations of East Antarctica is critical to our understanding of the threshold response of glacial systems in Antarctica to changes in surface temperature at lower elevations. Here we constrain the onset of the polar aridity—which was probably necessary for regional ice-sheet stability—by assessing meteoric beryllium-10 profiles in mid-Miocene and late Quaternary soils at three sites situated 1,200–1,800 metres above sea level in the McMurdo Dry Valleys. Interpreting these profiles as indicators of water infiltration, we find that meteoric beryllium-10 entered mid-Miocene soils as late as the late Miocene. Reconstructions based on palaeo-active-layer thickness and known thresholds of meteoric beryllium-10 mobility suggest late Miocene summer temperatures of 7–10 °C with annual precipitation >10 mm. Therefore, the high elevations have probably been under a hyper-arid polar climate since the late Miocene (~6 Ma) and not the middle Miocene (13.8–12.5 Ma) as indicated by some previous reconstructions. Together, our findings indicate that high elevations of the McMurdo Dry Valleys probably experienced warm and wet climatic intervals from ~14.0 to 6.0 Ma, which reconciles observations of coastal warmth and reduced ice in the Ross Embayment. This finding also suggests that the McMurdo Dry Valleys may be more susceptible to climate change than anticipated.