In Vincennes Bay, off East Antarctica, a large deposit of seafloor sediment records a striking sequence: the ice sheet’s grounding zone paused as the ice retreated, shifted seaward by about 65 km (roughly 40 miles), then retreated permanently. The finding shows that retreat can be locally interrupted by the shape and composition of the seafloor; it does not mean the whole East Antarctic Ice Sheet advanced at once.
What the seafloor feature reveals
A grounding zone is the boundary where ice resting on the seafloor transitions into a floating ice shelf. Researchers describe a grounding-zone wedge in this transition area in Vincennes Bay. High-resolution geophysical surveys revealed its internal structure, and its position marks where retreat halted and stabilization began, according to the Alfred Wegener Institute’s announcement on 7 October 2026.
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The wedge is approximately 260 metres high and 65 kilometres long, with a volume greater than 580 cubic kilometres. These are figures reported by the institute, not independently recalculated here; the announcement does not provide numerical uncertainty for them.
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- Retreat slowed and paused. As the ice sheet withdrew after the last glacial period, its grounding zone reached a location where it remained locally stable for a time.
- The grounding zone shifted seaward. Sediment accumulating on the seafloor helped form the wedge. The study’s interpretation is that this deposition accompanied a seaward advance of about 65 km—approximately 40 miles—from the halted position.
- Retreat eventually resumed. The record indicates the advance was temporary: the grounding zone later retreated permanently.
The announcement does not give age bounds, a detailed dating method or a numerical uncertainty for the reconstructed sequence, so it cannot establish from the information available exactly when each stage occurred or how long the pause lasted.
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Why local seafloor conditions matter
Ocean temperature and sea level are among the external drivers relevant to ice-sheet stability, but the Vincennes Bay record highlights another influence: the local form and composition of the seabed. Sediment deposition can alter the substrate beneath the grounding zone, helping it remain stable locally and, in this case, shift seaward again.
These influences are not alternatives to climate or ocean forcing. The study’s interpretation is that both external conditions and local bed characteristics matter, and that grounding-zone behaviour need not be uniform from one bay to another. First author Chiara Tobisch, a doctoral researcher in Kiel University’s Marine Geophysics and Hydroacoustics research group, said: “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.”
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the finding means for ice-sheet models
The geological record gives researchers evidence to use when representing grounding-zone behaviour in ice-sheet models. It supports accounting for local seafloor geometry and sediment processes alongside climate-related drivers, rather than assuming that retreat proceeds at the same pace everywhere.
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This reconstruction is not a forecast of future retreat, nor a measurement of current ice loss. It describes a past sequence at Vincennes Bay and should not be generalized to every East Antarctic coastal sector. The study was led by Kiel University and the Alfred Wegener Institute and, according to the institute announcement, appeared in Geophysical Research Letters.
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