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

Abstract

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.

Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core

“…The study by Fujita et al (2012) shows that in many areas of the high plateau regions of Dronning Maud Land between Dome F and the EDML drill site, the ice sheet is water based. In the inland regions, this is mainly due to the high ice thickness, and only sites where the ice thickness is lower than approximately 2400 m appear not to be affected by basal melting in keeping with our model exercise.…”

“…Indirect evidence of basal melting exists from the imprint of subglacial lakes in the surface topography of the ice sheet and from recent progress in the evaluation of ice penetrating radar measurements (Fujita et al, 2012) that allow the identification of liquid water at the base using the higher backscatter signal where liquid water is present. The study by Fujita et al (2012) shows that in many areas of the high plateau regions of Dronning Maud Land between Dome F and the EDML drill site, the ice sheet is water based.…”

Regional modeling of the Shirase drainage basin, East Antarctica: full Stokes vs. shallow ice dynamics

“…(6)-(9) for the SIA case with the finite element method. Since radar data indicate that the basal temperature in the area is at the melting point everywhere except for the highest peaks of the bed topography (Fujita et al, 2012), for simplicity we assumed a temperate base for the entire domain (Eq. 19).…”

Adaptively constraining radar attenuation and temperature across the Thwaites Glacier catchment using bed echoes

“…Therefore, correction for englacial attenuation is required in order to make inferences about the material and geometric properties of the bed from basal reflectivity. Variations in radar-sounding bed-echo strength have long been used to constrain and correct for englacial attenuation in areas where the depth-averaged attenuation rate could be assumed to be constant ( Robin and others, 1969;Winebrenner and others, 2003;Jacobel and others, 2009;Matsuoka and others, 2010;Barrella and others, 2011;Fujita and others, 2012;MacGregor and others, 2012) or to vary linearly with distance along flow (Schroeder and others, 2016). However, these assumptions can limit the utility of such approaches to areas far below the scale of a glacier catchment (Jacobel and others, 2010), making them unsuitable for observationally constraining larger-scale englacial temperature structure.…”