ICE-CORED ROCK GLACIERS IN ANTARCTICA: RECORDING GLACIAL ADVANCES FROM MARINE ISOTOPE STAGE 5 TO THE HOLOCENE

Rock glaciers and buried ice are common throughout the McMurdo Dry Valleys, the largest ice-free region in Antarctica. In some locations these features cover up to 20% of the valley walls, and yet they are poorly understood in terms of age, origin and environmental stability. We investigated two prominent rock glaciers in Pearse and central Taylor valleys, via ground-penetrating radar, stable isotopic analyses of buried ice, major ion chemistry of buried ice and surface ponds, and sedimentology. In both locations, the rock glaciers are cored by clean ice 10+ m thick, with multiple dipping sediment layers. Stable isotopic analyses of buried ice cores from both rock glaciers are consistent with glacial origins for the ice. In the Dry Valleys, cold-based glaciers contain little englacial debris and terminate along ice aprons (a mixture of calved ice blocks, meltwater and sediments). We propose a model for ice-cored rock glaciers in which glacial ice aprons are buried and preserved when covered by sediments. This process occurs at the base of steep bedrock inclines due to increased deposition of fluvial and colluvial sediments. In Pearse Valley, the rock glacier ice is sourced from (1) modern alpine glaciers and (2) a previous advance of East Antarctic outlet Taylor Glacier, possibly during Marine Isotope Stage 5 (70–125 ka). In central Taylor Valley, the rock glacier records multiple advances of a local alpine glacier, including the modern Holocene advance and several pre-LGM advances. Our data indicate that Dry Valley rock glaciers (1) are potentially long-term archives of glacial ice with complex geomorphic histories and (2) can be used to map previous advances of both outlet and alpine glaciers, especially useful in regions that lack dateable moraines and tills.