Sea-ice decline exposes Antarctic ice shelves to unprecedented retreat by wave erosion

The Antarctic continent is ringed by vast, floating platforms of ice known as ice shelves. These shelves act as a natural brake, holding back the massive glaciers flowing from the interior of the continent and slowing their journey into the ocean. When these shelves weaken or disappear, the glaciers behind them speed up, dumping more ice into the sea and causing global ocean levels to rise. For decades, scientists have understood that these shelves can be worn away from below by warm ocean water or from above by melting air. However, a critical piece of the puzzle has been missing: the role of the sea ice that usually surrounds the Antarctic coast. This sea ice acts as a protective buffer, shielding the floating shelves from the open ocean. As the climate warms, this protective ring is shrinking, leaving the ice shelves exposed to new forces that previous models have not accounted for.

A team of researchers has now uncovered a powerful, previously overlooked mechanism driving the rapid retreat of these ice shelves. By studying specific regions where the protective sea ice has vanished during the summer months, they found that the shelves are being eroded by a combination of warm water and waves. When sea ice disappears, the open ocean allows waves to reach the vertical face of the ice shelf. These waves, driven by water that is slightly warmer than the freezing point, carve out a notch at the waterline. This process undermines the ice, creating a submerged, buoyant ledge that lifts the front of the shelf upward. Eventually, the stress becomes too great, and the shelf breaks off, sending large icebergs into the sea. This cycle repeats every summer, causing the ice shelf to retreat much faster than it would from melting alone.

The researchers focused their investigation on the Amundsen Sea Polynya, an area where the sea ice has been disappearing for years, and the Ronne Entrance, a region that experienced its first complete summer without sea ice in 2025 and 2026. Using decades of satellite images, they tracked the movement of the ice fronts. They observed that in areas protected by sea ice, the ice shelves remained relatively stable, advancing and retreating in a predictable pattern. In contrast, the sections of the Getz Ice Shelf bordering the open water were retreating steadily every year. The retreat was not caused by the ice thinning from below or melting from the top, as is common in other parts of Antarctica. Instead, the ice front was being worn away at the waterline, a process the scientists describe as edge wasting.

To understand exactly how this happens, the team used high-precision satellite measurements to scan the surface of the ice. They discovered a distinct pattern: a raised ridge of ice followed by a depression, known as a rampart-moat structure. This shape forms when the waterline is eroded, leaving a submerged foot of ice that floats upward, tilting the shelf above it. The researchers calculated that this underwater foot needs to extend only about 50 to 100 meters before the upward force becomes strong enough to snap the shelf. Once this threshold is reached, the shelf calves, or breaks off, in a single event that can remove nearly 900 meters of ice. This means that a relatively small amount of erosion at the waterline can trigger a massive release of ice, a phenomenon the authors call a calving multiplier effect.

The study reveals that the speed of this retreat is alarming. In the Amundsen Sea, the ice front was retreating at a rate of roughly 680 meters per year. In the Ronne Entrance, where the sea ice was absent for the entire summer and the water was warmer, the retreat rate was even higher, exceeding 2,000 meters per year in some spots. These rates are far faster than the speed at which the ice flows forward, meaning the shelves are shrinking rapidly. The researchers noted that this process is entirely dependent on the absence of sea ice; in years when sea ice persisted, or when cold icebergs drifted into the area and cooled the water, the retreat stopped. This confirms that the loss of the protective sea ice barrier is the direct trigger for this erosion.

The implications of these findings extend far beyond the specific locations studied. The researchers analyzed data from across the entire Antarctic coast and found that as sea ice continues to decline, most ice shelves will soon be exposed to these same conditions. Currently, many ice shelves are shielded by sea ice during the summer, but this protection is disappearing. If the pattern observed in the Amundsen Sea and Ronne Entrance repeats across the continent, nearly all Antarctic ice shelves could begin to retreat year after year. This would fundamentally alter the stability of the ice sheet, potentially leading to the collapse of shelves that were previously considered safe.

This discovery highlights a gap in current predictions of sea-level rise. Existing computer models that forecast future ocean levels do not include this wave-driven erosion process. They focus on melting from warm water below and warm air above, but they miss the mechanical and thermal erosion caused by waves hitting the ice front when sea ice is gone. Because this mechanism can drive retreat at speeds much faster than previously thought, the researchers argue that current models are likely underestimating how quickly Antarctica will lose ice. As the protective sea ice vanishes, the continent's ice shelves face a new and potent threat, one that could accelerate the rise of global sea levels more rapidly than scientists have anticipated.