Cosmogenic nuclide dating of two stacked ice masses: Ong Valley, Antarctica

• Published in: The Cryosphere
• Main Authors: Bergelin, Marie, Putkonen, Jaakko, Balco, Greg, Morgan, Daniel, Corbett, Lee B., Bierman, Paul R.
• Format: Text
• Language: English
• Published: 2022
• Subjects: Ong Valley; Transantarctic Mountains; Antarc*; Antarctica; ice core
• Online Access: https://doi.org/10.5194/tc-16-2793-2022; https://tc.copernicus.org/articles/16/2793/2022/

We collected a debris-rich ice core from a buried ice mass in Ong Valley, located in the Transantarctic Mountains in Antarctica. We measured cosmogenic nuclide concentrations in quartz obtained from the ice core to determine the age of the buried ice mass and infer the processes responsible for the emplacement of the debris currently overlaying the ice. Such ice masses are valuable archives of paleoclimate proxies; however, the preservation of ice beyond 800 kyr is rare, and therefore much effort has been recently focused on finding ice that is older than 1 Myr. In Ong Valley, the large, buried ice mass has been previously dated at > 1.1 Ma. Here we provide a forward model that predicts the accumulation of the cosmic-ray-produced nuclides 10 Be, 21 Ne, and 26 Al in quartz in the englacial and supraglacial debris and compare the model predictions to measured nuclide concentrations in order to further constrain the age. Large downcore variation in measured cosmogenic nuclide concentrations suggests that the englacial debris is sourced both from subglacially derived material and recycled paleo-surface debris that has experienced surface exposure prior to entrainment. We find that the upper section of the ice core is 2.95 + 0.18 <math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="073414a2b77546d8d5847ae97897d626"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="tc-16-2793-2022-ie00001.svg" width="8pt" height="14pt" src="tc-16-2793-2022-ie00001.png"/></svg:svg> − 0.22 Myr old. The average ice sublimation rate during this time period is 22.86 + 0.10 <math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mo>/</mo></math> <svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" ...