Giant Antarctic iceberg A23a is rapidly breaking apart in the South Atlantic
Antarctic iceberg A23a, which calved from the Filchner-Ronne Ice Shelf in 1986, is rapidly breaking apart in the South Atlantic as of early September 2025, leaving fragments up to 400 km2 (154 mi2) adrift.
Image credit: U.S. National Ice Center (USNIC)
Antarctic iceberg A23a, which calved from the Filchner-Ronne Ice Shelf in 1986, is rapidly breaking apart in the South Atlantic as of early September 2025.
Recent Copernicus satellite analyses indicate that sections measuring around 400 km2 (154 mi2) have detached in recent weeks, with numerous smaller but still hazardous fragments drifting nearby.
A23a has held the “largest current iceberg” title several times since the 1980s, occasionally being surpassed by larger but shorter-lived icebergs, including A68 in 2017 and A76 in 2021.
It was the world’s largest freely floating iceberg through mid-2025, measuring 3 460 km2 (1 336 mi2) in early March 2025. However, by July 22 it had been reduced to 2 510 km2 (969 mi2).
As of September, it measures about 1 770 km2 (683 mi2), with a maximum width of 60 km (37 miles). Its mass is estimated at nearly 1 trillion tonnes (1.1 trillion tons).
The iceberg remained grounded in the Weddell Sea for over three decades before currents carried it northward in 2020.
Since then, it has entered progressively warmer waters of the South Atlantic, where basal melting has weakened its structure. “It is breaking up fairly dramatically,” said Andrew Meijers of the British Antarctic Survey (BAS), adding that the iceberg is “rotting underneath” and may become unidentifiable within weeks.
In 2020, it was carried away by ocean currents before becoming stuck again in a Taylor column — a spinning vortex of water caused by ocean currents hitting an underwater mountain — until it was reported on the move again in December 2024. In March 2025 it ran aground on a continental shelf before floating loose again in May.
Meijers explained the circumstances that led to the breakup. “It has been following the strong current jet known as the Southern Antarctic Circumpolar Current Front (SACCF) anti-clockwise around South Georgia ever since it floated loose in May, after grounding on the continental shelf for a few months in March.
“This jet is likely to ultimately take the berg and its bits off to the north-east — still as part of iceberg alley.”
He said A23a is “following a similar fate” to other megabergs, such as A68 in 2021 and A76 in 2023, which also disintegrated around South Georgia, a British Overseas Territory in the southern Atlantic Ocean, though A23a has remained intact longer than either of those.
The disintegration means the crown for the world’s largest iceberg is now held by D15a, which measures around 3 000 km2 (1 158 mi2) and, according to Meijers, is “fairly static on the Antarctic coast near the Australian Davis base.”
In early March 2025, A23a grounded on South Georgia’s continental shelf, raising concerns over access to feeding areas for seals and penguins.
It dislodged in late May and continued northward. BAS assessed impacts on wildlife as unlikely, although smaller fragments may complicate fishing operations.
The U.S. National Ice Center (USNIC) has confirmed the calving of several large daughter bergs during 2025, including A-23B in January, A-23D and A-23E in July, and A-23F in mid-August.
While iceberg calving is a natural process in Antarctica, satellite observations show that ice-shelf mass loss has increased since 2000, with more than 6 000 gigatonnes (6 615 billion tons) of ice lost.
I am an Assistant Editor and Severe Weather & Science Journalist at The Watchers, specializing in real-time severe weather coverage, geophysical event reporting, and research-driven scientific analysis. You can reach me at rishav(at)watchers(.)news.
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