Using radar-derived measurements of basal reflectivity to locate Antarctic subglacial lakes

Mapping basal water distribution is a primary goal in exploring ice sheet dynamics due to the major influence of water on ice velocity. We report results of a study of basal conditions from a ground-based, ice-penetrating radar survey that was part of the 2006-08 US-ITASE traverse from Taylor Dome to South Pole. The 1700 km traverse provided the opportunity to collect continuous high resolution radar records of the bed and internal stratigraphy across the major catchments draining the East Antarctic Ice Sheet (EAIS) to the Ross Ice Shelf. The radar power returned from the basal interface is determined primarily by the phase state of water after corrections for losses due to geometric spreading and dielectric attenuation. Brighter bed echoes correspond to thawed conditions and vice versa. These results depict the distribution of water in key areas draining the EAIS and contribute to understanding the role played by basal conditions in ice sheet processes. Dielectric attenuation of radar signals within the ice is primarily a function of temperature and impurities. First-order estimations of attenuation can be made from an exponential model based on the decrease in bed reflected power with depth for large statistical samples, however these methods ignore variations in attenuation along the traverse as temperature and chemistry profiles change. Instead, in this study we use the decrease in power with depth of the echoes returned from englacial reflectors as a proxy for dielectric attenuation. Results show areas of high basal reflectivity in the northern portion of the traverse that correlate well with zones of increased ice velocity. They also indicate generally more thawed basal conditions approaching South Pole where ice speed is low. The traverse route crossed above two locations identified as subglacial lakes in an inventory based on satellite-detected changes in ice surface elevation but found no indication of basal water at either site. We report two previously unidentified lakes, both at a distance of ~200 km from South Pole, outside the range of IceSAT coverage, and we present new results for another lake previously studied by radar and seismic surveys just 15 km from South Pole Station.