Radio-frequency probes of Antarctic ice birefringence at South Pole vs. East Antarctica; evidence for a changing ice fabric

Following pioneering efforts in East Antarctica, we herein report on the amplitude and temporal characteristics of polarized surface radar echo data collected in South Polar ice using radio sounding equipment with 0.5-ns echo-time precision. We observe strong echoes at 6, 9.6, 13.9, 17, and 19 μs following vertical pulse emission from the surface, in the upper half of the ice sheet. The synchronicity of those echoes for all broadcast azimuthal polarizations affirms the lack of observable birefringence over the upper half of the ice sheet, in contrast to East Antarctica measurements in the vicinity of Dome Fuji, and signifies a dramatic difference in the character of the ice sheet in the intervening 1400 km. Of the five strongest echoes, three exhibit an evident correlation with the local surface ice flow direction, qualitatively consistent with measurements in East Antarctica. Our radio sounding measurements also permit the most precise determination to date of the ice thickness at South Pole.