Temporal evolution of basal terraces at Ekström Ice Shelf, East Antarctica 

Ekström Ice Shelf is a representative ice shelf for the ice-shelf belt of the Dronning Maud Land Coast in East Antarctica. It has cold ocean-cavity with moderate basal melt rates averaging a few meters per year across the ice shelf. In spite of the comparatively small average basal melt rates, we find basal terraces in a ground-penetrating radar dataset revealing near-vertical walls of more than 30 meters height. Such features have also been observed  elsewhere and linked to large localized basal melt rates which is in parts oriented in the horizontal direction. Here we use a ground-penetrating radar dataset with a profile spacing of <100 m which was revisited in an Eulerian sense in two consecutive field seasons 2021 and 2022. This dataset images the 3D extent of basal terracing and shows that these are remarkably stable and can be clearly identified in both seasons. They are  laterally offset  by along-flow advection and possibly also horizontal basal melting oriented perpendicular to the vertical walls. There is very little vertical difference between both datasets which is consistent with the small sub-daily melt rates derived from a continuously measuring ApRES located above a horizontal plateau linking two basal terraces at the ice base. These two 3D time slices are a unique dataset to better understand how such basal terraces initially form, how they are maintained over time and whether or not ocean-induced melting in the horizontal direction (which is typically not picked up by the ApRES data) is relevant on larger spatial scales.