Digital surface models are not always representative of former glacier beds: Palaeoglaciological and geomorphological implications

Quantitative palaeoglaciological studies that use digital surface models (DSMs) may be subject to error because former glacier beds are not always accurately represented. This is because the Earth's surface may have changed significantly since deglaciation. This paper evaluates some of the potential errors caused by postglacial sedimentation, by comparing the results of physical palaeoglaciological reconstructions and bedform morphometric analyses in parts of Scotland, using both the modern land surface and interpolated former glacier beds derived from borehole data. For a former terrestrial outlet glacier, removal of postglacial sediments increases the modelled ice surface elevation and ice thickness by 0.7% and 5%, respectively, over a 27-km flow line. For a former tidewater glacier, the reconstructed steady state ice flux is increased by 250% when the modern land/seabed surface is replaced with an interpolated former glacier bed. In a classical drumlinised landscape, removal of postglacial sediments affects bedform morphometrics, with an increase in measured drumlin length, width, relief, and volume. The cases presented in this paper are from environments known to have experienced postglacial sedimentation. They provide situational examples of the degree of error that can be introduced when the modern land surface is used to represent former glacier beds in these environments. In some regions, sufficient subsurface data exists over large areas to create improved topographic representations of former glacier beds; these could form important inputs to the next generation of palaeo-ice-sheet and palaeo-glacier simulations.