Constraints on the Age of Million-Year-Old Buried Ice Mass in Ong Valley, Antarctica Obtained from Cosmogenic Nuclide Measurements

We collected two 10-m ice cores from relict glacier ice in Ong Valley, Transantarctic Mountains, Antarctica. The ice mass is buried under a thin layer (< 1 m) of sublimation till. Cosmogenic-nuclide measurements from the overlying till show that it is > 1.1 Ma old, therefore making this one of the oldest ice bodies found on Earth. If indeed the buried ice is found to be old, it can potentially yield direct information on climate history of the vast interior of Antarctica, past atmospheric chemistry, ancient life forms, and geology of greater antiquity than most currently known ice bodies.

To obtain additional constraints on the age, origin, and sublimation rate of the ice, we measured concentrations of the cosmic-ray produced nuclides ¹⁰Be, ²⁶Al, and ²¹Ne in englacial sediment in one core. These nuclides are produced by cosmic-ray interactions with minerals near the Earth's surface. As the production rate decreases rapidly with depth below the Earth's surface, nuclide concentrations can yield information about the sediment source (e.g., subglacial or supraglacial), the age of the ice, and the rate at which the till is forming due to ice sublimation.

Large downcore variations in nuclide concentrations and ratios show that englacial sediment includes both subglacially derived sediment and sediment that was previously exposed at the surface and most likely incorporated into the ice during glacier advance into Ong Valley. Nuclide ratios in this recycled surface sediment are well below production ratios but vary among different sediment packages, indicating that englacial sediment has a complex origin involving multiple episodes of recycling and mixing. We will discuss constraints on the age, origin, and sublimation rate of the buried ice derived from these observations.