Paleoglaciological study of the Ahlmannryggen, Borgmassivet and Kirwanveggen nunatak ranges, Dronning Maud Land, East Antarctica, using WorldView imagery

Abstract: Paleoglaciological reconstructions based on glacial geological and geomorphological traces are used to test and constrain numerical models of ice sheet extent and dynamics. MAGIC-DML (“Mapping, Measuring and Modelling Antarctic Geomorphology and Ice Change in Dronning Maud Land”) project is trying to reconstruct the timing and pattern of ice surface elevation changes since the mid-Pliocene across western Dronning Maud Land, East Antarctica. The study area has sparse pre-existing field data and considerable ice sheet model uncertainties. A remote sensing-based mapping of glacial geomorphology on nunataks and structures on the ice sheet surface is presented for a coastal-inland transect including Ahlmannryggen, Borgmassivet, and Kirwanveggen using high-resolution WorldView imagery. The primary aim of the study is to map traces of a thicker ice sheet on nunatak slopes that were formerly partly or entirely covered during ice surface highstands. Panchromatic and multispectral images were analysed in a multi-step procedure using ArcGIS, including image processing and mosaicking, visual feature recognition, and mapping. The identification of key landforms (such as till veneers and erratic boulders) required the adoption of some assumptions to differentiate, for example, till from regolith. Where patterned ground was mapped, we infer a presence of till rather than regolith because subglacial erosion is more likely to produce finer material than subaerial weathering. Very large boulders on plateau surfaces are mapped as erratics because they could not have been delivered by slope processes to local highpoints. However, the reliability of derived paleo-ice sheet reconstructions is limited by both the necessary assumptions and the absence of crosscutting relationships between landforms. At face value, the presence of till cover and erratics above the present ice surface on some nunataks indicate thicker ice in the past. According to the geomorphological mapping of the transect, in Kirwanveggen the former ice elevation was at least 100 m higher, in Borgmassivet the ice lowered more than 600 m and in Ahlmannryggen the ice was at least 300 m thicker. Additional mapping of structures on the ice sheet surface is used to yield target field routes for upcoming field season(s) to potential cosmogenic nuclide (CN) sampling locations. The chronology derived from CN dating will permit the delineation of ice sheet surface elevations as targets for ice sheet modeling.