Basal Unit Radar Characteristics at the Southern Flank of Dome A, East Antarctica

Abstract. The basal unit near the base of the Antarctic Ice Sheet (AIS) plays a critical role in AIS dynamics and the preservation of old ice, yet its structure and origin remain poorly understood. Using a new airborne ice-penetrating radar dataset collected by the NSF Center for Oldest Ice Exploration (NSF COLDEX), we investigate the radar characteristics of the basal unit at the southern flank of Dome A, East Antarctica. We combine manual mapping with Delay-Doppler analysis to characterize the spatial distribution of incoherent scattering and to distinguish between two types of radar-apparent basal unit top boundaries: a sharp transition from specular to scattering reflections (type I) and a gradual disappearance of specular reflections due to radar signal attenuation (type II). We find that incoherent scattering is widespread upstream and decreases downstream, correlating with both subglacial topographic roughness and a shift from type I to type II boundaries. These patterns are interpreted as resulting from spatial variability in englacial temperature, with warmer ice downstream enhancing signal attenuation and obscuring radar features. Although incoherent scattering is not visible in the downstream region, its absence may reflect radar detection limits rather than true absence of scattering reflectors in the basal unit. Moreover, the observed correlation between scattering and subglacial roughness suggests deeper geological controls in which subglacial lithology influences both basal temperature and subglacial geomorphology.