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

Abstract. In order to better understand the spatial distribution of subglacial environments, ground-based radar profiling data were analyzed for a total distance of ~ 3300 km across Dronning Maud Land, East Antarctica. The relationship between geometrically corrected bed returned power [P^c_bed]_dB in decibels and ice thickness H was examined. When H is smaller than a~critical value that varies according to location, [P^c_bed]_dB tends to decrease relatively smoothly with increasing H, which is explicable primarily by the cumulative effect of dielectric attenuation within the ice. However, at locations where H is larger than the critical H values, anomalous increases and fluctuations in [P^c_bed]_dB were observed, regardless of the choice of radar frequency or radar-pulse width. In addition, the amplitude of the fluctuations often range 10 ~ 20 dB. We argue that the anomalous increases are caused by higher bed reflectivity associated with the existence of subglacial water. We used these features to delineate frozen and temperate beds. Approximately two-thirds of the investigated area was found to have a temperate bed. The beds of the inland part of the ice sheet tend to be temperate, with the exception of subglacial high mountains. In contrast, the beds of coastal areas tend to be frozen, with the exception of fast-flowing ice on the subglacial lowland or troughs. We argue that this new analytical method can be applied to other regions.