Spectral roughness of subglacial topography and implications for former ice-sheet dynamics in East Antarctica

摘要

Ice-sheet basal erosion is controlled by ice dynamics (including the basal thermal regime) and the lithology of the substrate. Spatial variation in subglacial roughness is therefore likely to be a function of these controls. In Antarctica, very little is known about former ice dynamics and sub-ice geology. Here, we calculate the spectral roughness of subglacial East Antarctica from an analysis of radio-echo sounding data. As the modern glaciological setting is understood reasonably well in East Antarctica from numerical ice-sheet modelling, we are able to compare the roughness calculations with contemporary ice-sheet dynamics. We show that ice divides at Ridge B and Dome A are underlain by rough terrain and a cold thermal regime. At the Dome C ice divide, however, the bed is noticeably smooth at the shorter wavelengths (～5—10 km) but rougher at longer wavelengths. One interpretation is that subglacial morphology has been eroded, leaving a smoothed landscape that contains valleys and hills. Regardless of the origin of the valleys, their erosion is only possible if the ice sheet were more dynamic than at present. Hence, whereas Dome A and Ridge B have a bed morphology consistent with the present ice sheet, the morphology at Dome C is likely to predate the present ice-sheet configuration.