Yearly evolution of Basal Terraces at Ekström Ice Shelf (East Antarctica)

Basal terraces are characteristic stepped features with steep, near-vertical walls which are interspersed by smooth horizontal sections. They occur beneath many Antarctic ice shelves and their genesis has been linked to stable ocean stratification beneath the horizontal sections which ceases near the walls where ocean-induced melt rates intensify. However, how terraces initially form and how they evolve over time is poorly observed and understood. Here, we present temporal changes in basal topography from densely spaced GPR profiles imaging the 3D structure of a basal terrace field on Ekström ice shelf in East in 2021/22 and 2022/23. Many features can be traced coherently across time and the majority of the structures advected with ice flow, with the exception of some local modifications near some walls. A concurrent year-long time series of an ApRES situated above one of those terraces shows moderate melt rates comparable to the ice-shelf wide magnitudes, confirming previous assertions that melt rates at the terraces are low. Imaging of the 3D structure of the basal terraces now enables us to identify off-angle reflections in the ApRES time series and thus quantify if localized horizontal melting at the walls can be detected.