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

S Fujita,P Holmlund,F Nakazawa,K Fukui,S Sugiyama,K Matsuoka,S Surdyk,H Enomoto

doi:10.5194/tc-6-1203-2012

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 [Pcbed]dB in decibels and ice thickness H was examined. When H is smaller than a~critical value that varies according to location, [Pcbed]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 [Pcbed]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.

Highlights

Subglacial environments of polar ice sheets are characterized by mass and energy transfers between the ice and its substrate of bedrock, sediment or water
A recent numerical modelling experiment of the icesheet thermodynamics showed that 55 % of the grounded part of the Antarctic ice sheet is at pressure melting point, though this estimate is hampered by insufficient knowledge of geothermal heat flow (Pattyn, 2010)
Following Matsuoka et al (2011), we modelled depth profiles of ice temperature and the attenuation coefficient α for ice thicknesses ranging between 1700 and 3500 m (Table 2), surface accumulation ranging between 20 mm yr−1 and 60 mm yr−1 (Table 2), geothermal fluxes of 40, 50, and 60 mW m−2, and a surface temperature of −50 ◦ C

Summary

Introduction

Subglacial environments of polar ice sheets are characterized by mass and energy transfers between the ice and its substrate of bedrock, sediment or water. Bamber et al, 2000, 2006; Bell, 2008; Bennett, 2003; Pattyn et al, 2005; Rignot et al, 2011), the possible contribution of subglacial melting to the mass balance of the ice sheet Several studies have analyzed the reflectivity of radio waves at the ice base. This reflectivity approach has been applied to several areas of Antarctica

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