A trillion tonnes of ice that broke off Antarctica the same year Chernobyl exploded is nearing its end, dissolving in the warm waters of the South Atlantic after four decades of defying every prediction scientists threw at it.
The berg, known as A23a, once stretched across 4,000 square kilometres, nearly twice the size of Greater London, and spent over 30 years grounded on the ocean floor before quietly resuming its drift in 2020.
Now, battered by summer heat, warm currents, and its own crumbling weight, it is in its final weeks. Scientists say it will be gone entirely soon, and the world will lose the oldest tracked iceberg in recorded history.
WHAT WAS ICEBERG A23A, AND HOW BIG WAS IT?
In 1986, a massive slab of ice split away from Antarctica’s Filchner-Ronne Ice Shelf and dropped into the Weddell Sea.
That process, called calving, is a term used to define a phenomenon in which a chunk of ice breaks off a glacier or ice shelf and becomes a free-floating berg.
The colossus weighed nearly a trillion tonnes. At roughly 4,000 square kilometres, it was larger than many countries’ capital cities.
What happened next was strange. Instead of drifting off, A23a sank into the muddy seabed and stayed put for over 30 years, completely grounded, going nowhere.
Then in 2020, without much fanfare, it began to move. Scientists noticed, started tracking it, and quickly realised they were watching something extraordinary.
HOW DID THIS GIANT CHUNK OF ICE TRAVEL SO FAR?
Ocean currents pushed A23a northwards along a route researchers call Iceberg Alley, a pathway commonly followed by Antarctic icebergs moving into the South Atlantic.
Along the way, A23a got pulled into a Taylor Column, which is a rotating cylinder of ocean water that forms above underwater mountains. It is a giant natural whirlpool.
The iceberg spent eight months spinning near the South Orkney Islands.
It then drifted towards South Georgia, a graveyard for most icebergs, broke free, and kept going north.
By early 2026, it had travelled further from Antarctica than any iceberg currently being tracked, sitting closer to the equator than London.
WHY DID IT SUDDENLY START FALLING APART?
In January 2025, its estimated area was 3,640 square kilometres, still the largest iceberg in the world. By September, it had shrunk to 1,700 square kilometres after several chunks broke away.
Then the Southern Hemisphere summer arrived and finished the job. By December, the berg was covered in pooling blue meltwater as it drifted between the eastern tip of South America and South Georgia Island. That vivid blue was not pretty. It was a warning.
The disintegration was being driven by hydrofracturing, a process where meltwater pools on the surface exert enormous pressure on the ice, forcing cracks open from the inside until the whole structure gives way.
Ted Scambos, a senior research scientist at the University of Colorado Boulder, explained it to Nasa: “You have the weight of the water sitting inside cracks in the ice and forcing them open.”
WHAT DO SCIENTISTS HOPE TO LEARN FROM THIS?
The end of A23a is not just a spectacle. It is a laboratory. Researchers aboard the British Antarctic Survey’s RRS Sir David Attenborough conducted studies around the berg in December 2023 to assess its impact on marine environments.
Dr Laura Taylor, a biogeochemist with the British Antarctic Survey, said: “We know that these giant icebergs can provide nutrients to the waters they pass through, creating thriving ecosystems in otherwise less productive areas.”
As they melt, large icebergs release nutrients like iron and nitrogen into the surrounding ocean, stimulating phytoplankton growth and feeding entire marine food webs.
But scientists are watching for something bigger too. Antarctica’s ice shelves, the floating extensions of glaciers, are under increasing pressure from rising temperatures.
If they collapse, the glaciers behind them speed up, and sea levels rise. How A23a fell apart is giving researchers a clearer picture of how that could unfold.
WHEN WILL IT COMPLETELY DISAPPEAR?
China’s Fengyun-3D satellite, operated by the China Meteorological Administration, confirmed in January 2026 that the main body had shrunk to just 506 square kilometres, less than one-eighth of its original size.
It has kept shrinking since. According to the US National Ice Center, once it drops below roughly 70 square kilometres, scientists will stop tracking it altogether.
Retired glaciologist Chris Shuman, formerly of the University of Maryland, Baltimore County, told NASA plainly: “I certainly don’t expect A-23A to last through the austral summer.”
That summer is nearly over. And so is the berg.
