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The Center for Oldest Ice Exploration (COLDEX) is a US initiative funded to search for climate records over the last 5 million years, including locating sites for an accessible continuous ice core going back 1.5 million years. As part of this effort, COLDEX has mapped the southern flank of Dome A, East Antarctica using an instrumented Basler, including dual frequency radar observations of the ice sheet and ice bed, as well as potential fields measurements (see presentation by Kerr in EGU session G4.3) across two field seasons from Amundsen-Scott South Pole Station. The aerogeophysical system included both the UTIG VHF MARFA radar system operating at 52.5-67.5 MHz, as well as a new large high resolution UHF array from CReSIS operating at 670-750 MHz operating simultaneously. A goal of this project was to obtain airborne repeat interferometry for segments of the survey, as well as directly feed ice sheet models using englacial isochrons (see Singh presentation in EGU session CR5.6). These goals lead to a survey explicitly designed around ice sheet flow lines. While prior work had sampled the region at lithospheric scales, the COLDEX survey had two components - the first was to map the region at crustal scales (line spacing of 15 km), and the second was to map subareas at ice sheet scales (line spacing of 3 km). Immediate observations include an extensive basal unit and strong discontinuity in englacial stratigraphy that runs across the survey area and appears correlated with changes in bed interface properties. The airborne campaign will be used to inform follow up ground campaigns to understand processes relevant for old ice preservation. 

Abstract The deep interior of the East Antarctic Ice sheet likely contains important records of climate and ice sheet evolution. Here we report on a recent aerogeophysical survey of the southern flank of Dome A, over South Pole Basin. We find an extensive radioglaciologically defined basal unit under Dome A that abruptly truncates within South Pole Basin. This truncation aligns with a change of subglacial bed properties and distinct subglacial landforms. We infer that this basal unit may be slowly transporting and depositing material through local basal melting in South Pole Basin into an extensive, subglacially forming, sedimentary basin. In turn, this sedimentary basin may induce locally enhanced melting by hosting local groundwater.