Ancient Ice Buried Below a Meter of Regolith; Ong Valley, Antarctica

We have discovered and cored a massive ice mass buried underneath a meter of glacial debris in Ong Valley, Antarctica, which we report here to consist of two stacked ice bodies dated at >2 Ma. Glacial ice is known to be a great archive of atmospheric gasses, chemical compounds, and airborne particles. An ice mass of such antiquity, as reported here, may reveal information about our past which is otherwise unknown.

We determine the age of the ice directly by dating the dirt suspended within the ice and by dating the till layer covering the ice using cosmogenic nuclide: ¹⁰Be, ²⁶Al, and ²¹Ne. These cosmogenic nuclides are produced by cosmic-ray interactions with minerals near the Earth’s surface, and in this case in suspended dirt embedded in the ice. As the production rate of cosmogenic nuclides decreases rapidly with increasing depth below the Earth’s surface, the cosmogenic nuclide concentration profile yields information about the exposure history and further aid to constrain geological processes such as sublimation rates, and surface erosion rates. We further compare the cosmogenic nuclide model results with mapped glacial moraines adjacent to the current ice, and stable water isotope analysis throughout the core in order to explore the unique history that these two stacked ice masses have.

We find the uppermost section of this buried ice mass to be >2 Ma old. Large variation of cosmogenic nuclide concentrations downcore and stable water isotopes, suggests that the deepest section of the ice core may belong to a separate, older ice mass that has previously been exposed at the surface. Lateral moraines and measurements of cosmogenic nuclides in glacial debris further up valley suggest that this deeper, older ice may be >2.6 Ma old, and was most likely buried during glacial advancement into Ong Valley < 4 Ma ago.