This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Off the coast of East Antarctica, 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 embedded in the seafloor of Vincennes Bay: a so-called "grounding-zone wedge"—symmetrical, wedge-shaped, approximately 260 meters (853 feet) high and 65 kilometers (40 miles) long. With a volume of more than 580 cubic kilometers (139 cubic miles), 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 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 (40 miles) 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." 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 toward 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. 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.
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