The world's largest iceberg has disintegrated and is melting

Like a giant, white wall rising from the sea and stretching to the horizon: This is how researchers described "A23a," arguably the world's largest iceberg. Some of its cliffs were 400 meters high. At 3,672 square kilometers, the colossus was as large as Mallorca and weighed almost a trillion tons. But the ice walls of A23a have long since been eroded and hollowed out by seawater. It is currently disintegrating, melting, and disappearing forever in the Atlantic Ocean.

A23a broke off from the Filchner-Ronne Ice Shelf in Antarctica, an ice mass at the upper end of the Weddell Sea, in 1986. It then remained stuck to the seafloor for decades, from where it gradually broke away. Initially, however, it remained trapped in circulating currents.

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A stroke of luck for the Soviet Union at the time: The Soviet research station Druzhnaya 1, which was unoccupied at the time of the breakup, had been located on the iceberg. Initially, it could no longer be found, and it was feared that it had sunk into the sea. But then satellite images revealed that it had broken away from the mainland along with the iceberg. Because A23a hadn't yet moved very far, supplies and equipment could be recovered from Druzhnaya 1 by helicopter.

In 2023, A23a finally broke free and began its journey . Since then, it has traveled a long way. The Antarctic Circumpolar Current caused A23a to be swept into the South Atlantic. It followed the same route that many icebergs before and after it have taken, which is why it is also called Iceberg Alley.

In 2024, A23a became stuck again: It circled for several months in a whirlpool off the South Orkney Islands, north of the Antarctic Peninsula. Researchers had suspected that A23a could survive there for years. But at the end of 2024, it broke free of the whirlpool and has since drifted toward the island of South Georgia. Initially, there were fears that A23a could threaten populations of penguins and seals there.

When ice masses move between the sea and breeding colonies on land, these colonies can either be completely cut off from the food supply from the sea. Or the animals have to travel longer distances – which can be too energy-intensive to survive. In 2004, the drift of iceberg A38 off South Georgia already led to an animal death. Thousands of penguin chicks and howlers starved to death on the beaches.

But in the case of A23a, things turned out well, at least for the animals: In March of this year, it ran aground in the shallow waters off South Georgia. It didn't break free until May. Since then, it has been drifting in a current that circles South Georgia, the Southern Antarctic Circumpolar Current Front (SACCF).

But now the bad news: It has now broken into several large pieces in just a few days, the polar research institute British Antarctic Survey announced at the beginning of September.

"The iceberg is rapidly breaking apart, shedding huge chunks, which are themselves referred to as large icebergs," Andrew Meijers, an iceberg expert at the institute, told the dpa news agency. As a result, A23a has shrunk to 1,700 square kilometers. The world's largest iceberg is now D15A: an iceberg off the Antarctic coast that, at around 3,000 square kilometers, is about twice the size of the remaining piece of A23a, Meijers said.

A23a is still the second-largest iceberg. However, this is likely to change in the coming weeks, according to the sea ice researcher. "I expect its fragmentation to accelerate," says Meijers. Since the beginning of 2024, A23a has been melting at an ever-increasing rate and is located in waters with temperatures well above freezing. With spring now approaching in the Southern Hemisphere, the iceberg will likely soon break into such small pieces that it will no longer be possible to track it.

Icebergs like A23a are being closely monitored not only because they are so fascinating: they can hinder and endanger international shipping. Furthermore, their melting process can have an impact on the environment. Melting icebergs release nutrients like iron into the water , which can alter ecosystems. The exact consequences are still being researched.

What's special about A23a is that it has aged so much, Daniela Jansen, a glacier researcher at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, told dpa. This is because it was trapped in cold waters for a long time.

Jansen also said that while it's a normal process for icebergs to break off from the Antarctic ice shelf, this is intensifying due to climate change: "A warming of the ocean and the atmosphere can cause ice shelves to become unstable and completely disintegrate." This could then lead to increased ice flow from the land into the sea, causing sea levels to rise. However, if a floating iceberg melts, it doesn't change sea level.