Preprints
https://doi.org/10.5194/tc-2022-18
https://doi.org/10.5194/tc-2022-18
 
02 Feb 2022
02 Feb 2022
Status: this preprint is currently under review for the journal TC.

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

Marie Bergelin1, Jaakko Putkonen1, Greg Balco2, Daniel Morgan3, Lee Corbett4, and Paul Bierman4 Marie Bergelin et al.
  • 1Harold Hamm School of Geology and Geological Engineering, University of North Dakota, Grand Forks, ND, 58202
  • 2Berkeley Geochronology Center, Berkeley, CA
  • 3Department of Earth and Environmental Science, Vanderbilt University, Nashville
  • 4Rubenstein School of the Environment and Natural Resources, University of Vermont/National Science Foundation Community Cosmogenic Facility

Abstract. We collected a debris rich ice core from a buried ice mass in Ong Valley, located in 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 kyrs is rare and therefore much effort has been recently focused on finding ice that is older than 1 Ma. 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 10Be, 21Ne, and 26Al 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/−0.22 Myrs. The average ice sublimation rate during this time period is 22.86 +0.10/−0.09 m Myr−1, and the surface erosion rate of the debris is 0.206 +0.013/−0.017 m Myr−1. Burial dating of the recycled paleo surface debris suggests that the lower section of the ice core belongs to a separate, older ice mass which we estimate to be 4.3–5.1 Myrs old. The ages of these two stacked, separate ice masses can be directly related to glacial advances of the Antarctic ice sheet and potentially coincide with two major global glaciations during the early and late Pliocene epoch when global temperatures and CO2 were higher than present. These ancient ice masses represent new opportunities for gathering ancient climate information.

Marie Bergelin et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2022-18', Anonymous Referee #1, 14 Mar 2022
    • AC2: 'Reply on RC1', Marie Bergelin, 05 May 2022
  • RC2: 'Comment on tc-2022-18', Anonymous Referee #2, 28 Mar 2022
    • AC1: 'Reply on RC2', Marie Bergelin, 05 May 2022

Marie Bergelin et al.

Marie Bergelin et al.

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Short summary
Glacier ice contains information on past climate and can help us understand how the world changes through time. We have found and sampled a buried ice mass in Antarctica that is much older than most ice on Earth and difficult to date. Therefore, we developed a new dating application which showed the ice to be 3 million years old. Our new dating solution will potentially help to date other ancient ice masses, since such old glacial ice could yield data on past environmental conditions on Earth.