A23a, one of the world’s oldest and once the largest iceberg, is nearing the end of its 40-year journey across the Southern Ocean. This colossal iceberg has captivated scientists with its extraordinary longevity and unpredictable path. This “megaberg” broke off from Antarctica’s Filchner-Ronne Ice Shelf in 1986, covering an area of approximately 4,000 square kilometres, more than twice the size of Greater London. Soon after breaking away, it ran aground in the Weddell Sea, where it remained stuck on the seafloor for more than three decades.
In 2020, A23a finally broke free and began drifting north, propelled by ocean currents and winds. During its journey, it moved along the route known as “Iceberg Alley” and at one stage became trapped in a rotating ocean vortex called a Taylor column, which caused it to spin in place.
After entering warmer waters in the South Atlantic, the iceberg began to deteriorate rapidly. Satellite observations show it shrinking dramatically. According to a recent report by the BBC, A23a has “melted”, “fractured” and “disintegrated” over the past year.
“Its journey is really pretty impressive, just for sheer longevity,” Dr Christopher Shuman, a retired scientist formerly with the University of Maryland, Baltimore County, in the US, said as quoted.
By January 2026, it had shrunk to around 506 square kilometres, with several large fragments breaking off. The report mentioned that the iceberg was still massive after 39 years, last year. In 2025 January, A23a was about 3,600 sq km. But on March 5, it was reduced to 180 sq km.
