Just months ago, the world’s largest iceberg weighed about a trillion tons and covered an area nearly the size of Anchorage, Alaska. Now it’s less than half that—and rapidly disappearing.
In recent weeks, massive chunks of ice measuring up to 250 square miles (400 square kilometers) have sloughed off the ‘megaberg’ known as A23a. Smaller pieces float freely in the surrounding waters too, many of them still big enough to threaten ships.
The iceberg’s disintegration has reduced its total area to 683 square miles (1,770 square kilometers), according to an Agence France-Presse analysis of satellite images captured by the European Union Earth observation monitor Copernicus. It could disappear completely within weeks.
Andrew Meijers, a physical oceanographer from the British Antarctic Survey, told AFP that A23a was “breaking up fairly dramatically” as it drifted further north. “I’d say it’s very much on its way out…it’s basically rotting underneath,” he said. “The water is way too warm for it to maintain. It’s constantly melting.”
End of the line
This could mark the end of A23a’s 40-year-long journey, which started when the iceberg broke off Antarctica’s Filchner Ice Shelf in 1986, according to the U.S. Geological Survey. It remained grounded on the bottom of the Weddell Sea for more than 30 years before detaching and beginning its slow drift northward in 2020. Over the next four years, A23a followed the Antarctic Circumpolar Current on a path known as “Iceberg Alley” and then became trapped in an ocean vortex near the South Orkney Islands in April 2024.
After finally breaking free eight months later, the iceberg resumed its journey north. In March, it ran aground near the Southern Ocean’s South Georgia Island, sparking fears that it could disrupt large colonies of penguins and seals. Fortunately, it dislodged in May, drifting around the island and northward again.
As A23a has encountered huge waves and increasingly warmer waters, it’s been crumbling into the ocean. Losing half its size in a matter of months is staggering, but most icebergs never make it this far from the frigid waters of Antarctica, Meijers said. “This one’s really big so it has lasted longer and gone further than others,” he explained.
Still, A23a is shrinking faster than new ice can form. “I expect that to continue in the coming weeks, and expect it won’t be really identifiable within a few weeks,” Meijers said. It’s unclear how much water this megaberg contained at its peak, but the similarly sized A68a dumped more than 1 trillion tons of fresh water into the ocean during its lifetime.
A warning sign
Contrary to popular belief, melting icebergs—even giants like A68a and A23a—don’t raise global sea levels. That’s because they’re already floating in the ocean. However, their rapid disappearance is a clear sign of rising global temperatures, which do contribute to sea level rise by accelerating glacial melt.
Recent research estimates that Antarctica’s ice sheet could raise global sea levels 11 inches (28 centimeters) by 2100, and potentially more if we surpass certain warming thresholds. That said, much remains unknown about the processes that underlie accelerated sea level rise. Despite uncertainties in future projections, the disappearance of Antarctic behemoths like A23a serves as a stark reminder of how rapidly humans are reshaping this critical region.