A23a, the world's largest iceberg, began moving north again after months trapped in a rotating body of water in the Southern Ocean, the British Antarctic Survey reported. Scientists expected the iceberg to continue toward the Atlantic, where warmer conditions would eventually fracture and melt the enormous mass.
The iceberg covered about 3,800 square kilometres, more than twice the area of Greater London, and was approximately 400 metres thick. Its great depth had shaped its unusually long history. After separating from Antarctica in 1986, the bottom grounded on the floor of the Weddell Sea, keeping it almost stationary for more than three decades.
A23a began travelling north in 2020. In the spring of 2024, however, it became caught near the South Orkney Islands in a Taylor column, a vertical rotating current that can hold an object over an underwater feature. Rather than progressing, the iceberg spent much of the year turning in place.
British Antarctic Survey oceanographer Andrew Meijers said the renewed movement offered researchers a chance to see whether A23a would follow routes taken by other large Antarctic icebergs. Once it leaves the colder Southern Ocean, it is likely to encounter water that accelerates breakup into smaller pieces before the ice melts.
The movement is also relevant to ecosystem research. Large icebergs release freshwater and material as they melt, and can add nutrients to waters that are otherwise relatively unproductive. Those inputs may support biological activity along an iceberg's path, but scientists are still studying how the size and origin of an individual iceberg change the effect.
Researchers aboard the RRS Sir David Attenborough sampled water around A23a about a year before the December update. Biogeochemist Laura Taylor said scientists understood that giant icebergs could fertilise the ocean around them, while the specific influence of different ice masses remained uncertain. The samples offered a way to connect observations with the iceberg's later journey.
The announcement concerned a change in drift rather than a sudden calving or immediate coastal hazard. A23a had already been afloat and moving intermittently for years, and its latest release was from an oceanographic trap, not from the seabed where it spent its first decades.
Its scale makes the voyage scientifically valuable. Tracking its course, breakup and surrounding waters can help researchers understand how exceptionally large Antarctic icebergs redistribute nutrients and freshwater as they move from polar seas toward warmer parts of the ocean.
A23a’s departure will be observed over months rather than treated as a single endpoint. Satellite tracking can show changes in direction and speed, while ships and autonomous instruments can measure surrounding chemistry. Together, those observations can connect the visible breakup of ice with less visible ocean effects.
