Radar diagnosis of the subglacial conditions in Dronning Maud Land, East Antarctica

In order to better understand the spatial distribution of subglacial environments, ground-based radar sounding data for a total distance of ~3300 km across Dronning Maud Land, East Antarctica, were analyzed. The relationship between geometrically corrected bed returned power [Pcbed]dB in decibels and ice thickness H was examined. When H is smaller, [Pcbed]dB was found to decrease simply with increasing H, which is explicable by the thickness variation of dielectric attenuation. However, an anomalous increase in [Pcbed]dB at larger H occurred, which was independent of the choice of radar frequencies or radar-pulse widths. We suggest that the existence of water at the ice/substrate interfaces at larger H caused this anomalous increase. We herein propose a new analytical method using these features to delineate frozen and temperate bed areas. Approximately two-thirds of the investigated area was found to have a temperate bed. Basal melting tends to occur when H is larger and the surface elevation is lower. In other words, beds inland of the ice sheet tend to be temperate, with the exception of subglacial high mountains. In contrast, beds of coastal areas tend to be frozen, with the exception of fast-flowing ice at subglacial lowland or troughs. These observations suggest that subglacial water is dominantly produced at the bed of wide inland plateau and that the water is discharged to the sea dominantly through a bed of fast-flowing ice. We also found that a 20-km-wide bed in the subglacial high mountains of an inland plateau near Dome Fuji is frozen, suggesting the existence of very old ice above the bed.