Understand · 5 November 2026
Iceberg A23a: the life and end of the world's largest iceberg
Born in 1986, stuck for more than thirty years on the floor of the Weddell Sea, trapped in an ocean vortex, then grounded off South Georgia: the story of A23a, the giant that fascinated the world, and what it teaches us.
A23a is a giant iceberg that broke away from Antarctica in 1986 and was for a long time the largest iceberg in the world, covering nearly 4,000 km², more than thirty times the area of Paris. After more than thirty years without moving, resting on the floor of the Weddell Sea, it started drifting again in 2020, was trapped for several months in an ocean vortex in 2024, then broke up near the island of South Georgia in 2025. In March 2026, the U.S. National Ice Center stopped tracking it, judging its remains too small. The title of world's largest iceberg now belongs to D15A.
Few icebergs have a biography. A23a has one, followed by satellites and told by scientists for forty years. It is a chance to understand how a giant iceberg is born, lives and dies.
What happened
Where does its name come from?
Antarctic icebergs are named by the U.S. National Ice Center when they are at least 10 nautical miles (about 18.5 km) long. The letter A means it was first sighted in the sector between 0° and 90° west longitude, which includes the Weddell Sea. The number 23 means it was the 23rd iceberg named in that sector. The final a indicates that it is a piece of a larger iceberg, A23, which had broken apart. To learn more about these names, see the page for each iceberg in our catalogue.
1986: birth
A23a broke away from the Filchner-Ronne Ice Shelf, one of the largest in Antarctica, in 1986. This process, called calving, is natural: ice shelves slowly advance over the ocean, pushed by the ice sheet, and eventually fracture and release icebergs. The calving of A23a cannot therefore be attributed to climate change.
At birth, A23a covered nearly 4,000 km², more than thirty times the area of Paris. These so-called tabular icebergs are flat, edged with vertical cliffs, and several hundred metres thick. As with any iceberg, about 90% of their volume lies underwater.
More than thirty years resting on the seabed
Shortly after its birth, A23a ran aground on the floor of the Weddell Sea. Its very deep base touched the seabed, so it stayed motionless for more than thirty years, like an island of ice. Throughout those years, it slowly melted and thinned.
2020: the great departure
Around 2020, thinned by melting, A23a lifted off the seabed and began to drift. It passed the northern tip of the Antarctic Peninsula in November 2023, by which time it had once again become the largest iceberg in the world, the other giants having broken up in the meantime. At the start of 2025, it still covered about 3,600 to 3,700 km² and weighed in the order of a trillion tonnes.
2024: trapped in a vortex
In April 2024, A23a entered the Antarctic Circumpolar Current, the great current that circles the continent. Then, above an undersea feature called Pirie Bank, near the South Orkney Islands, it became trapped in a Taylor column: a vortex that forms when a current meets an undersea mountain. For months, the iceberg spun on the spot, watched by satellites. It only broke free in December 2024.
2025: grounding off South Georgia
Once free, A23a headed north into ever warmer waters. In early March 2025, it ran aground on the continental shelf off South Georgia, a sub-Antarctic island that is home to huge colonies of penguins and fur seals. Scientists were concerned: an iceberg of this size could block the animals' access to their feeding grounds. The iceberg eventually began to break up, carried by a current that flows around the island.
2025–2026: the end of a giant
Over the southern summer of 2025, A23a lost enormous pieces. Around September 2025, it lost its title of largest iceberg in the world. On 20 March 2026, the U.S. National Ice Center measured it at just 141 km² and said it was becoming too small to track. Its fragments kept melting in the waters of the South Atlantic; by mid-2026, the iceberg was considered practically gone.
What the data say
- Birth: 1986, Filchner-Ronne Ice Shelf, about 4,000 km².
- Standstill: more than thirty years resting on the floor of the Weddell Sea.
- Departure: around 2020; passed the Antarctic Peninsula in November 2023.
- Size at the start of 2025: about 3,600 to 3,700 km², in the order of a trillion tonnes.
- Taylor column: April to December 2024, near the South Orkney Islands.
- Grounding: March 2025, off South Georgia.
- End of tracking: 20 March 2026, 141 km² according to the U.S. National Ice Center.
The new title holder, D15A, broke away in 2016 from the West Ice Shelf, in East Antarctica. According to U.S. National Ice Center reports, it measures about 94 km by 41 km, a little over 3,000 km². You can follow its position on its page: Iceberg D15A.
What A23a teaches us
A giant iceberg is not necessarily a sign of warming
This is an important nuance. The calving of large icebergs is part of the natural cycle of ice shelves, and the end of A23a, which melted as it drifted into warmer waters, is the normal fate of every iceberg. Scientists warn against the temptation to make each iceberg a symbol of climate change.
What worries researchers is not any particular iceberg, but how the ice shelves themselves are changing. When the ocean warms and melts them from below, they thin and hold back the continent's ice less effectively, so it flows faster into the sea. This mechanism makes West Antarctica one of the main sources of sea-level rise.
Icebergs feed the ocean
As it melts, an iceberg releases fresh water, but also dust and nutrients, including iron, trapped in the ice for centuries. In the Southern Ocean, where iron is scarce, this input can boost the growth of plankton, the foundation of the whole food chain. Scientists from the British Antarctic Survey took water samples around A23a to study this effect. Analyses published in 2026 suggest that, at the time of sampling, its meltwater had not significantly changed the chemistry of the local ocean.
Satellites let us follow ice everywhere
Forty years ago, tracking an iceberg in the middle of the Southern Ocean was a feat. Today, radar satellites, which see through clouds and the polar night, reveal the position and size of the large icebergs every week. It is thanks to these public data that the story of A23a could be told, and that Mon Iceberg can offer you the chance to follow real icebergs.
Why it matters
The story of A23a shows how alive and dynamic Antarctica is, and how much we depend on satellite observations to understand it. It is also a reminder that the Southern Ocean and its currents play a major role in the climate of the whole planet. Tracking icebergs means keeping an eye on the state of the ice shelves, and therefore on the future of sea level.
What everyone can do
You cannot stop an iceberg from melting, nor would you want to: it is its natural fate. But we can limit the ocean warming that weakens ice shelves. Our detailed guides help you reduce your carbon footprint:
And to keep a concrete connection with the drifting ice, you can follow, adopt or give one of the real icebergs in our catalogue, including D15A.