The world’s largest iceberg is on the move again after three decades trapped in the Antarctic seabed, scientists announced Wednesday, setting in motion a colossal journey that could disrupt shipping routes and ecosystems across thousands of miles of open ocean.
Iceberg A23a, measuring roughly 1,500 square miles — larger than Rhode Island — broke free from the Filchner-Ronne Ice Shelf in 1986 but promptly ran aground in the Weddell Sea. Scientists from the British Antarctic Survey (BAS) confirmed the massive ice island began drifting in 2022 and has now picked up significant momentum.
“It’s absolutely enormous — it’s hard to comprehend just how big some of these structures really are,” said Dr. Oliver Marsh, a glaciologist with the BAS who has been monitoring the iceberg’s movements. “What’s particularly interesting is how it’s managed to finally break free from the sea floor after all these years.”
A Giant Awakens
Why now, after decades of stubborn immobility? Researchers suggest that gradual thinning of the ice mass finally reduced its draft enough to float free of the seafloor. The iceberg has lost nearly 160 feet of thickness over three decades through melting and erosion.
Satellite tracking shows A23a is now caught in the powerful Antarctic Coastal Current, which is expected to propel it into the Antarctic Circumpolar Current — often called the “highway” that could carry the iceberg north toward South Georgia Island and potentially into shipping lanes in the South Atlantic.
The timing couldn’t be more significant. The movement coincides with record low sea ice levels around Antarctica, which dropped to just 6.5 million square miles this year — about 1.5 million square miles below the 1981-2010 average.
“We’re witnessing potentially historic changes in the Antarctic system,” said Professor Karen Heywood, an oceanographer at the University of East Anglia. “A23a’s movement isn’t directly caused by climate change, but it’s happening against a backdrop of rapidly transforming polar regions that should concern us all.”
Ecological Impacts
Massive icebergs like A23a don’t just reshape shipping maps — they transform entire marine ecosystems. As they drift and melt, they release enormous quantities of freshwater and nutrients that have been trapped in the ice for decades.
This “fertilization effect” can trigger phytoplankton blooms visible from space. Scientists documented such blooms following the path of previous giant icebergs, creating temporary carbon sinks as the tiny organisms absorb carbon dioxide before sinking to the ocean floor.
But the ecological story isn’t entirely positive. If A23a follows the path of previous giant bergs and grounds near wildlife-rich South Georgia Island, it could block access to critical feeding grounds for millions of penguins, seals, and other wildlife.
“These animals have evolved specific migration and feeding patterns,” explained marine biologist Dr. Emma Boland. “When a trillion-ton ice island parks itself between colonies and their food sources, the results can be catastrophic.” A previous iceberg (A68) that approached South Georgia in 2020 narrowly avoided such a disaster when it broke apart just before reaching the island.
Tracking the Behemoth
How do you keep tabs on something the size of a small country? The iceberg’s movements are being tracked through a combination of satellite imagery and ocean sensors.
The European Space Agency’s Sentinel satellites provide regular updates on A23a’s position, while oceanographic data helps scientists model its likely course. The U.S. National Ice Center has also designated the iceberg a priority for monitoring given its size and potential impact on shipping routes.
Researchers estimate A23a contains approximately 1 trillion tons of fresh water — enough to fill Lake Michigan. As it drifts into warmer waters, its melt rate will accelerate dramatically.
“The journey ahead for A23a is fascinating from a scientific perspective,” said Dr. Mark Brandon, a polar oceanographer. “Each of these giant icebergs gives us a natural experiment in how the ocean and atmosphere interact with these massive ice structures. We’re learning something new with every kilometer it travels.”
Strange as it may seem, A23a won’t hold the “world’s largest iceberg” title for long. In October, another massive berg designated D-28 calved from the Amery Ice Shelf, and scientists are monitoring several other potential calving events that could release even larger ice islands in coming years.
For now, shipping companies operating in the Southern Ocean are receiving regular updates on A23a’s position, though the iceberg remains far from major transit routes.
After three decades of stillness, this frozen colossus is finally making its grand exit — a reminder of nature’s patient, powerful rhythms playing out at a scale that dwarfs human endeavors.