New study by Kiel University and Alfred Wegener Institute shows how a retreating ice sheet’s grounding line stabilized itself over a long period of time — important reference points for models of ice-sheet behavior.
Off the coast of East Antarctica and embedded in the seafloor of Vincennes Bay, researchers led by Kiel University (CAU) and the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), have investigated an exceptionally large sedimentary body: a so-called “grounding-zone wedge” — symmetrical, wedge-shaped, approximately 260 meters high and 65 kilometers long. With a volume of more than 580 cubic kilometers, it is the largest known isolated grounding-zone wedge on a glaciated continental shelf to date and constitutes an exceptional archive of East Antarctica’s past glacial history.
The sediment wedge formed within the grounding zone, the transition area between ice resting on the seafloor and a floating ice shelf. During the retreat of the East Antarctic Ice Sheet (EAIS) following the end of the last glacial period, the grounding zone temporarily stabilized, then advanced seaward by about 65 kilometers, and finally retreated permanently. High-resolution geophysical surveys now reveal — for the first time — in detail how such massive sediment bodies are structured. The researchers demonstrated that the stability of the grounding zone depends not only on climatic changes but also, to a significant extent, on the shape and composition of the seafloor. The study, recently published in the journal Geophysical Research Letters, provides important reference points for modeling the behavior of the EAIS.
“We can clearly see that an ice sheet does not simply retreat uniformly across all bays. Depending on the characteristics of the substrate, the grounding zone can remain locally stable over long periods of time and may even shift seaward again due to sediment deposition,” says Chiara Tobisch, first author of the study and a doctoral researcher in the Marine Geophysics and Hydroacoustics research group at the Institute of Geosciences at Kiel University. “What’s new is that, for the first time, we were able to image these dynamics very precisely using high-resolution methods and reconstruct the formation process based on the internal structure of the grounding-zone wedge.”
A 65-kilometer-long archive of past glacial history
Grounding zone wedges form where the transition zone between grounded and floating ice remains stable for an extended period during overall ice-sheet retreat. If the grounding zone remains stationary for a long time, subglacial sediment is deposited there. The formation of such a wedge-shaped structure allows the grounded ice to advance slightly seaward, resulting in new sediment deposition on the seaward side of the wedge. The combination of sediment deposition and ice advance leads to a gradual advance of the grounding line towards the sea. The architecture of these sediment bodies provides insight into how and under what conditions past stabilization processes occurred. Their location, age, and formation mechanism serve as important reference points for verifying simulations of past and present ice-sheet dynamics.
Researchers close knowledge gap on internal structure and formation processes
Until now, relatively little was known about the internal structure and formation processes of these sometimes massive structures. An international research team including scientists from Kiel University, the AWI, the University of Bremen, the University of Tasmania, and the Australian Center for Excellence in Antarctic Science has now closed this gap for one of the most important regions of the East Antarctic continental shelf.
The study is based on 340 kilometers of high-resolution seismic reflection data collected during Expedition PS141 aboard the German research vessel Polarstern in early 2024 in Vincennes Bay offshore the Aurora Subglacial Basin. These data were combined with bathymetric and sediment echo-sounder data. For the first time, the internal layering of such a wedge can be visualized in unprecedented detail. The data clearly reveal distinct sediment layers progressing seaward. They document how material from the hinterland was transported beneath the ice and deposited at the grounding zone.
The location at the landward end of the grounding-zone wedge is particularly revealing, as it marks the point where retreat halted and the grounding zone stabilization began. There, the slope of the seafloor changes, while geophysical data indicate a more consolidated subsurface. These two factors contributed to slowing down ice retreat, stabilizing the grounding zone, and enabling it to advance approximately 65 kilometers seaward. The researchers assume that the wedge formed after the Last Glacial Maximum around 20,000 years ago. A model estimate based on simplified sediment-flux assumptions suggests a formation period of approximately 4,000 years.
Why the seafloor is important for future predictions
The EAIS is the largest ice mass on Earth. If it were to melt completely, it would cause a global sea-level rise of about 52 meters. How rapidly the region changes under a warming climate depends on the interaction between ice, the ocean, and the underlying geology. Vincennes Bay is particularly important because it is fed by the Vanderford Glacier — one of the fastest-retreating glaciers in East Antarctica. The glacier provides a direct connection to the deep Aurora Subglacial Basin and may therefore contribute to the highly dynamic behavior of the EAIS. In addition, relatively warm modified Circumpolar Deep Water currently accelerates ice loss in the region.
The new study demonstrates that the response of ice grounded on the seafloor is not solely determined by external drivers such as ocean temperature or sea level. “Local changes in seafloor slope and the geological properties of the seafloor can also be crucial. Even small changes in these factors can influence the resistance beneath the ice and thus alter the stability of the grounding zone. So far, these factors remained largely obscure and therefore not sufficiently represented in numerical ice sheet models,” adds Dr Johann Klages, co-author and geoscientist at AWI.
“Our results show that the geometry of the seafloor can play a much greater role in grounding-zone development than would be expected from considering only large-scale climatic and oceanographic changes,” says Professor Sebastian Krastel, head of the Marine Geophysics and Hydroacoustics research group at Kiel University. “If we want to model the future evolution of the Antarctic Ice Sheet, we must therefore also account for the small-scale structures of the seafloor as realistically as possible.” The newly discovered grounding-zone wedge in Vincennes Bay provides an exceptionally detailed reference point for validating such models.
Founding
The study was funded by the German Research Foundation (DFG) as part of DFG Priority Program 1158 “Antarctic Research” and by the AWI research program “Changing Earth – Sustaining our Future.” Furthermore, the study contributes to the international research program “Instabilities and Thresholds in Antarctica” (INSTANT) of the Scientific Committee on Antarctic Research (SCAR).
This news story was first published by Christian-Albrechts University of Kiel (CAU).
Original publication
Tobisch, C. A., Klages, J. P., Barrett, R. S., Hochmuth, K., Mühlberger-Krause, T., Baumann, L. M., et al. (2026). Internal structure and formation process of a giant East Antarctic grounding-zone wedge. Geophysical Research Letters 2026. DOI: https://doi.org/10.1029/2025GL121369
