ALBERT

Description: The Recovery Glacier is draining about 8% of the East Antarctic ice sheet and feeds into the Filchner Ice Shelf. There were suggestions that the dynamics of the glacier is driven by large subglacial lakes that initiate the ice stream flow (Bell et al., 2008). As the Recovery Glacier is one of the least surveyed ice streams due to its remote location, this hypothesis could not be tested rigorously so far. In austral summer 2013/14 AWI carried out a survey of the Recovery Glacier including radio echo sounding, gravimetry, magnetics, and laser scanner. In total more than 22000 km survey lines were flown. Here we present an ice thickness map of the main trunk of the Recovery Glacier, as well as its tributaries Blackwall and Ramp glaciers. The ice thickness varies between 70 m in the vicinity of the Shackleton Range and nearly 3800 m close to the Bell lakes. Using different DEMs including one CryoSat-2 DEM (Helm et al., 2014), we determine the basal topography and the hydraulic head. We estimate the basal reflection coefficient and assess by this locations with potentially wet ice base. The distribution shows that few of the formerly proposed lakes show indeed a wet base, while others are missing clear lake like basal reflections.

Description: Basal water presence features crucial significance in ice sheet dynamics and evolution. Lubrication reduces friction at the interface, thus facilitating basal sliding and the restrain of the ice sheet to glacial motion. In-situ observations of ice base conditions bear a scientific challenge, as the bottom interface is hardly to access and yet limited by the availability of borehole investigations. Hence, progressions of indirect measurements are of largest interest in glaciological community and mainly inferred by radar acquisition. Radio-echo sounding has ever since been a proven tool for subsurface ice sheet exploration. The capability of radar investigations that take advantage of the ice sheet’s transparence at certain radio frequencies, is used to determine subglacial environments by means of basal echo returns. This work infers subglacial water extends beneath the East Antarctic Ice Sheet by analyses of the basal reflection coefficient, delineates bedrock characteristics by changes of the dielectric permittivity. Presented assignments retrieve water dominated radar foot prints alongside a distance of 120.000 km that have been established in a study area from tributaries of the Filchner Ice Shelf up to Dronning Maud Land. Basal echo strengths exceeded the signal-to-noise level have been recorded by the AWI RES system, which operates at a carrier frequency of 150 MHz and alternating pulse lengths of 60 and 600 ns. Estimates of the basal reflection coefficient are ascribable to wet ice bedrock properties, since lubrication significantly affects its magnitude. Greatest difficulties are remained by dielectric absorption losses attenuate the signal energy. Englacial absorption rates strongly depend on local temperature regimes and the ice’s acidity which answers changes of dielectric conductivity. Contributions are made by implications of modelled temperatures evaluated at each radar trace by using the Parallel Ice Sheet Model PISM runs on 20 km resolution. The dependence on impurities is considered by attributing dielectric profiles of the EDML and EDC ice core. Basal reflection coefficients though constitute as diagnostic parameter, which quantifies the nature of the ice base on wet scale. Subglacial lakes are moreover traceable. Research results revealed ice stream onset areas of Jutulstraumen and Slessor Glacier by high reflection coefficients that indicate a lubricated bedrock regime. Further assessments of significant high reflectivity suggest a terrain in Coats Land has been identified by former basal roughness studies to be a location of an extremely smooth bed which panders basal water accumulation. Reflection coefficients achievements have been referenced by known lake boundaries of Vostok that are matching concluded predictions of subglacial water presence.