A Giant Grounding Zone Wedge in Vincennes Bay, East Antarctica: Geomorphological Characteristics and Internal Structure

The East Antarctic Ice Sheet (EAIS) is losing mass from its marine-based portions in response to a warming climate. This warming causes the west wind drift to migrate southwards leading to upwelling of relatively warm deep waters. The assumed future behaviour of the EAIS mainly relies on numerical models, which, however, are rarely validated against precise past ice sheet constraints. This significantly affects their ability to reliably simulate potential future change. In particular, there is a dearth of data for the sectors of the East Antarctic continental shelf situated offshore major subglacial basins, such as Vincennes Bay on the Mawson Sea shelf offshore the Aurora Subglacial Basin. Past dynamic grounding zone changes are recorded here by glacial morphological structures. Those structures, including glacial troughs, glacial lineations, and grounding zone wedges (GZW), can be systematically mapped to provide important information about regional fast and slow flowing ice sheet portions, meltwater pathways, ice sheet extent, and grounding zone stabilisation processes. Here we particularly focus on GZWs, which record grounding zone stabilisation periods in a particular location during overall post-Last Glacial Maximum retreat.

We collected 230 km of high-resolution 2D multi-channel seismic reflection as well as deep-penetrating seismic profiles, multibeam and sediment echo-sounding data, during RV Polarstern Expedition PS141 (EASI 3) in early 2024 to study the morphology and architecture of glacial structures seaward of the Vanderford glacier front in Vincennes Bay. These data reveal a giant GZW that is up to 260 m high and extends 60 km along the previous ice stream bed. To our knowledge, this is the largest GZW discovered on the Antarctic continental shelf to date. The GZW consists of prograding sequences of different inclinations, suggesting multi-phase development of the GZW and a stabilisation process that led the grounding zone to grow and re-advance by several kilometres. Our findings present a significant step forward in understanding past ice sheet behaviour in Vincennes Bay, and thus provide important constraints for the evolution of the EAIS. Our new data therefore provide an important benchmark for testing and improving numerical ice sheet simulations.