For nearly four decades, the colossal Antarctic iceberg known as A23a has captured the imagination of scientists and the public alike. Once the world’s largest iceberg—spanning an area greater than the Hawaiian island of Oahu and weighing in at nearly a trillion metric tonnes—A23a’s long and dramatic journey is now coming to a close. As of September 2025, the giant berg is rapidly breaking apart in the warmer waters of the South Atlantic, with experts predicting it may not survive past November.
A23a’s story began in 1986, when it calved from the Filchner-Ronne ice shelf in Antarctica. According to the British Antarctic Survey (BAS), the berg was immediately remarkable: at its peak, it stretched across 3,672 square kilometers, slightly larger than the state of Rhode Island, and boasted a mass that dwarfed most other icebergs in recent history. For over thirty years, however, A23a barely budged, grounded on the seabed of the Weddell Sea—essentially frozen in place by shallow waters and the Antarctic chill.
“It has been shedding very large chunks, each of which is now tracked separately as new icebergs,” explained Dr. Andrew Meijers, an oceanographer with BAS, in an interview with CNN. This slow-motion saga took a turn in 2020, when A23a finally broke free, embarking on a long, circuitous journey north through what scientists call “iceberg alley.” Over the next few years, it became a fixture of satellite imagery and scientific curiosity, its progress closely monitored by experts around the world.
But A23a’s path was anything but straightforward. After decades of relative stillness, the iceberg’s odyssey included a series of dramatic pauses and pivots. In August 2024, for instance, A23a found itself ensnared in a swirling ocean vortex known as the Taylor column. There, it spun in place for months, a whimsical spectacle visible from space, before breaking free again late in the year. By March 2025, it had drifted perilously close to South Georgia Island, raising alarms for the region’s thriving seal and penguin colonies. Ultimately, A23a grounded about 50 miles offshore, sparing the wildlife but setting the stage for its final act.
Now, as the southern spring approaches and A23a drifts ever further north, its fate is sealed by forces as old as the planet itself. Warmer waters and powerful ocean currents are accelerating its demise. The iceberg has shrunk to about 1,700 square kilometers—roughly the size of Greater London or Houston—and continues to fragment. NASA satellite images have captured the emergence of new, smaller icebergs designated A23D, A23E, and A23F, each one a testament to the ongoing disintegration of this once-mighty megaberg.
“The iceberg is rapidly breaking up, and shedding very large chunks, themselves designated large icebergs by the U.S. national ice centre that tracks these,” Meijers told NPR. He added, “This, plus moving ever further north and the coming of southern spring means it is likely to rapidly disintegrate into bergs too small to track further.”
With its current size reduced by more than half, A23a has lost its title as the world’s largest iceberg—a distinction now held by D15a, which measures around 3,000 square kilometers and is currently near Australia’s Davis research base. Yet, A23a remains the oldest iceberg still afloat, a relic of a colder era that managed to delay its demise by getting stuck—twice—on the Antarctic seafloor.
For scientists, A23a’s breakup is both a familiar spectacle and a valuable research opportunity. “It’s really quite typical and normal. It is kind of a big, spectacular thing that our planet does as part of day-to-day operations,” Ted Scambos, a senior research scientist at the University of Colorado Boulder, told NPR. He emphasized that the current breakup is not directly linked to climate change, but rather is part of the natural life cycle of icebergs—a process that has unfolded for millennia as currents and warmer waters grind down these icy giants.
However, the context surrounding A23a’s demise is more complicated. As climate change intensifies, warmer ocean temperatures and shifting currents are causing Antarctica’s ice shelves to lose trillions of tonnes of ice. “We don’t yet know if giant icebergs are forming more often,” Meijers noted to CNN, “but we do know that human-driven warming is reshaping Antarctica in alarming ways.” While the immediate fragmentation of A23a won’t directly affect global sea levels, Scambos warned that the loss of such massive icebergs could allow more land-based glaciers to flow into the ocean, raising sea levels substantially over time.
One particularly dramatic scenario looms as A23a drifts through ever-warmer waters: a catastrophic failure, akin to an avalanche, where parts of the iceberg could disintegrate almost overnight. “A23A is becoming more vulnerable as it undergoes subtle flexing due to tidal movements and oceanic waves, which are gradually exposing weak spots that lead to its fragmentation,” Scambos told the press. The prospect of a sudden collapse during the Antarctic summer has scientists watching closely, eager to learn more about the processes that govern these icy behemoths.
Earlier in 2025, a research team from BAS visited A23a while it was still grounded near South Georgia. They collected environmental samples along its path to study the impact of such a massive influx of cold, fresh water on marine ecosystems. According to BAS, A23a’s passage likely disrupted life on the seabed and in surrounding waters, while also affecting carbon levels in the ocean. “It’s another opportunity to understand some of the processes that govern those mega glaciers,” Scambos told NPR. “And in fact, those are very important in terms of controlling sea level rise in the long term, decades to centuries from now.”
The end of A23a’s journey will mark the close of a remarkable chapter in polar science. As the iceberg breaks into pieces too small to track, its legacy will persist in the data and insights it leaves behind. Its story is not just one of ice and ocean currents, but a window into the shifting balance of our planet’s climate and the interconnectedness of its ecosystems. Even in its final days, A23a continues to teach us about the forces shaping our world—reminding us that, sometimes, the most spectacular natural events are both timeless and timely.
