Constraining Ages of Glacial Deposits Recorded in a Victoria Valley Permafrost Core

The past stability of the East Antarctic Ice Sheet (EAIS) remains an important, yet unsettled question. Efforts to address this question focus on EAIS stability during the Pliocene (5.33-2.58 Mya), a period characterized by CO₂ levels comparable to today's levels and global mean temperature comparable to those predicted for the end of the century. While the marine record from the Antarctic Drilling Project (ANDRILL) and recent ice-sheet models suggest a dynamic EAIS during the Pliocene, there is not yet strong corresponding terrestrial evidence of a dynamic Pliocene EAIS. Stratigraphic and geomorphic evidence of glacial deposits from EAIS outlet glaciers in the Antarctic Dry Valleys may provide the much-needed terrestrial record of EAIS stability. Here, a 15-meter ice-cemented permafrost core collected in Victoria Valley is analyzed using cosmogenic nuclides to provide quantitative constraints on the timing of the EAIS glacial history in the Dry Valleys. Based on the presence of oxidized layers from apparent paleosols, the core appears to have recorded four depositional events that are believed to represent different periods of glaciation. Each depositional unit was deposited and exposed to cosmic rays at the surface until subsequently buried during the next glacial event that then shielded the sediment from further cosmic ray exposure. Sediment was subsampled in the core at the upper, middle, and lower limits of each depositional unit and analyzed for ¹⁰Be and ²⁶Al, as well as texture, soluble salts, and other parameters. Several possible models of the burial history, accounting for exposure time, burial time, and inherited nuclides, are tested using inverse modeling techniques to provide a timeline for EAIS history in Victoria Valley. Preliminary results of the four units show ages of 30 Ka, 1.05 Ma, 2.4 Ma, and 3.9 Ma, suggesting the earliest expansion of the EAIS coincides with the warmer and wetter conditions during the Pliocene and corroborates the ANDRILL findings.