Internal and basal ice changes near the grounding line derived from radio-echo sounding

Evidence of changing basal and internal ice properties near the grounding line was derived from airborne radio-echo-sounder observations of the ice sheet around the Sor Rondane Mountains, Antarctica. From the tailing figure of the bottom-echo signal, the roughness of the ice bottom near the grounding line was inferred. Results show that the specular components of scattering begin to appear on the ice-shelf side of the grounding line. Furthermore, double-trip echoes were observed with a strong scattering in the shelf area, and their boundary of occurrence was very close to the grounding line. This is evidence of interaction between ice and sea water at the bottom of the ice shelf. We also examined the occurrence of internal layered echoes. In most of the area around the mountains, internal echoes were observed continuously, but they were not found at or close to the ice shelf. The boundary between the appearance and disappearance of internal-layer echoes is distinct, and occurs 20-30 km inland from the gounding line. These results suggest that some major change may occur in the internal ice on the inland side of the grounding line.