Two Buried And Stacked Ice Masses Dated To Early And Late Pliocene; Ong Valley, Antarctica

• Main Author: Bergelin, Marie
• Format: Text
• Language: unknown
• Published: UND Scholarly Commons 2022
• Subjects: Antarctica; Cosmogenic Nuclides; Geochronology; Glacial geology; Antarctic; Ong Valley; The Antarctic; Transantarctic Mountains; Antarc*; ice core; Ice Sheet
• Online Access: https://commons.und.edu/theses/4252; https://commons.und.edu/cgi/viewcontent.cgi?article=5253&context=theses

A debris rich ice core was collected from a buried ice mass in Ong Valley, located in Transantarctic Mountains in Antarctica. Measured cosmogenic nuclide concentrations in quartz obtained from the ice core were used 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. In order to further constrain the age, this research focuses on a novel forward model that predicts the accumulation of the cosmic-ray produced nuclides 10Be, 21Ne, and 26Al in quartz in the Ong Valley englacial and supraglacial debris. Large observed downcore variation in measured cosmogenic nuclide concentrations suggests that the englacial debris is sourced both from subglacially-derived material and recycled surface debris that has experienced surface exposure to cosmic rays prior to entrainment. Modeled results show 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 is estimated to be 4.3-5.1 Myrs old. The ages of these two stacked, but temporally 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 information on past climates.