Rock glaciers in Pearse Valley, Antarctica record outlet and alpine glacier advance from MIS 5 through the Holocene

Abstract

Rock glaciers and buried ice are common in the McMurdo Dry Valleys, Antarctica. In central Taylor and Pearse valleys rock glaciers cover at least 10% of the valley walls and occur at elevations of 300–800 m above sea level. We investigate the origin and geomorphology of a ~1.5 km2 rock glacier in northern Pearse Valley, the westernmost extension of Taylor Valley. The rock glacier is cored by sporadic deposits of clean ice that are covered by sand-rich, stratified sediments and dissected by five glacial meltwater streams. Ground-penetrating radar data indicate that the clean buried ice ranges from 1 to 14 m thick and contains dipping sediment-rich bands. Water stable isotopes from five cores extracted from the buried ice support multiple ice sources: (1) recent ice from alpine glaciers and (2) ancient, stagnant ice from East Antarctic outlet Taylor Glacier. The eastern half of the rock glacier lies directly downslope from alpine Fountain Glacier, which is actively feeding ice, sediments and water to the rock glacier via ~1 km-long ice falls. The buried ice in this section of the rock glacier is relatively heavy isotopically and similar to Fountain Glacier (δ18O of −36‰ to −32‰). The ice that cores the western half of the rock glacier is isotopically light and similar to Taylor Glacier (δ18O of −43‰ to −40‰). The last documented advance of Taylor Glacier that was sufficient to reach the rock glacier position occurred during Marine Isotope Stage 5 (70–125 ka), implying long-term preservation of the ice. The age and origin of buried ice in Pearse Valley has implications for rock glaciers throughout the Antarctic. Rock glaciers (1) are potentially long-term archives of glacial ice with complex depositional histories and (2) could be used to map previous advances of both outlet and alpine glaciers.