40-year-old 'queen of icebergs' A23a is no longer world's biggest after losing several 'very large chunks' since May

An iceberg that was once the size of Rhode Island and the biggest in the world has lost about 80% of its mass since May, scientists at the British Antarctic Survey (BAS) report.

Known as A23a, the "megaberg" has been rapidly disintegrating since becoming trapped in a current flowing counterclockwise around South Georgia Island in the South Atlantic Ocean, Andrew Meijers, a polar oceanographer with the BAS, told CNN.

A23a was swept up by the current in May after spending several months grounded on the continental shelf just off South Georgia Island. "It has been following the strong current jet known as the Southern Antarctic Circumpolar Current Front (SACCF)," Meijers said, adding that the iceberg will likely end up traveling away from the island in a northeast direction before breaking up completely.

Dubbed the "queen of icebergs," A23a broke off Antarctica's Filchner-Ronne ice shelf (which borders the Weddell Sea) in 1986. The giant berg immediately ran aground, remaining stuck to the seabed in the Weddell Sea for more than 30 years. It was crowned the biggest iceberg in the world and has only briefly been surpassed by others over the years, including iceberg A68 between 2017 and 2020 and iceberg A76 in 2021.

A23a finally made a move in 2020, probably because the ice that anchored it to the seabed melted away. But the iceberg quickly became trapped again, this time in a spinning vortex called a Taylor column, caused by an underwater mountain. It managed to free itself in December 2024 and was reported in January to be barreling toward South Georgia Island.

In January, A23a weighed almost 1.1 trillion tons (1 trillion metric tons) and measured 1,418 square miles (3,672 square kilometers), CNN reported. Now, the megaberg is not so mega anymore, measuring 656 square miles (1,700 square km), or about one-fifth of its size just eight months ago.

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"The iceberg is rapidly breaking up, and shedding very large chunks, themselves designated large icebergs by the US national ice center that tracks these," Meijers said.

A68 and A76 also began disintegrating when they drifted close to South Georgia, suggesting the SACCF is to blame for breaking up the icebergs — although A23a remained intact for longer than either A68 or A76 did in the current's wake, Meijers said.

A23a has relinquished its title of the biggest iceberg in the world to iceberg D15a, which is currently located near Australia's Davis research station in Antarctica. D15a measures around 1,160 square miles (3,000 square km) and appears to be staying in place, Meijers said.

For now, A23a is the second-largest iceberg in the world, but it will quickly drop down the ranks as it continues to fall apart over the coming weeks, he said. Eventually, fragments of A23a will become so small that scientists will stop monitoring them, with the onset of southern spring likely to contribute to their melting into mini bergs, Meijers added.

Large icebergs could end up in the waters off South Georgia Island more frequently in the future due to climate change, a BAS spokesperson told CNN. There isn't enough data at the moment to say whether more megabergs are forming or will form as a result of global warming, but the number of icebergs calving from Antarctica is increasing, Meijers said.

Antarctica is extremely vulnerable to warming and scientists are already seeing dramatic changes in the frozen continent's natural cycles.