Early to Mid-Miocene East Antarctic Ice Sheet Variability from the Friis Hills Drilling Project

The early to mid-Miocene is characterised by similar atmospheric CO₂ concentrations and associated global temperatures as those projected for the coming decades, with paleogeography, and therefore, atmospheric and oceanic circulation relatively similar to present day configurations. Therefore, examining Antarctic ice sheet behaviour during the early- to mid-Miocene offers insight into future ice sheet response under higher CO₂ scenarios.

At the Mid-Miocene Climatic Transition, 13.9 Ma, ice advanced to a larger than present day ice sheet configuration with sea level falling by up to 60 metres. This transition has are reflected in disparate terrestrial glaci-fluvial/lacustrine deposits across the McMurdo Dry Valleys region, Antarctica, as a shift from temperate wet-based glacial deposits to a polar dry-based deposits (Marchant et al. 1993; Sugden and Denton 2004; Lewis & Ashworth, 2015). Here we present preliminary findings from a series of well-preserved early to mid-Miocene terrestrial glacial deposits in the Friis Hills, an isolated inselberg, protected from subsequent glacial over-riding in the McMurdo Dry Valleys. The Friis Hills drill core reveals fossiliferous glacifluvial/lactustrine deposits, with ten unique sedimentary facies. Repetitive facies successions record regular oscillations in depositional setting, from subglacial to fluvial-deltaic lacustrine environments, bounded by glacial erosional surfaces. These multiple cycles of advance and retreat are representative of variation within a relatively local alpine glacial system connected to the East Antarctic Ice Sheet and provide the first continuous stratigraphic record through this key period in Earth history.

Two dated tephras at 14.5 Ma within the core stratigraphy allow correlation with proximal-marine sedimentary records such as ANDRILL-2A. This sedimentary facies analysis is complemented by paleoenvironmental reconstructions from collaborative work on diatom analyses, palynology, and lipid biomarkers from the Friis Hills drill core. We provide an initial interpretation of East Antarctic Ice Sheet evolution across the Mid Miocene Climate Transition from the terrestrial and marine glacial sediment archives in Transantarctic Mountains and western Ross Sea coastal geological archives.