Nearly four decades after it first broke away from Antarctica, one of the largest and oldest icebergs ever recorded is now in its final stages of existence. The giant slab of ice, known as A23a, is rapidly disintegrating in the warmer waters of the South Atlantic and could disappear entirely within weeks. Earlier this year, A23a still weighed just under a trillion tonnes and was more than twice the size of Greater London. At its peak, the iceberg was unrivalled in scale, so vast that scientists described it as a “megaberg”.
Once a frozen freshwater behemoth, A23a has since diminished to less than half its original size, though it remains a formidable presence. Current satellite imagery analysed by the European Union’s Copernicus Earth observation programme places its surface area at 1,770 square kilometres (683 square miles), with a maximum width of 60 kilometres (37 miles). In recent weeks, enormous chunks – some spanning 400 square kilometres – have fractured away, while smaller fragments, still large enough to pose hazards to shipping, now litter the surrounding sea. “It’s breaking up fairly dramatically,” explained Dr Andrew Meijers, a physical oceanographer at the British Antarctic Survey, in conversation with AFP. “It’s basically rotting underneath. The water is way too warm for it to maintain. It’s constantly melting.” He added that the iceberg would likely cease to be identifiable within weeks.
A Frozen Journey Through Iceberg Alley
A23a originally calved from the Antarctic ice shelf in 1986 but soon became grounded in the Weddell Sea, where it remained stuck on the seabed for more than 30 years. It finally broke free in 2020 and began drifting northwards along the route known as “iceberg alley”, carried by the powerful Antarctic Circumpolar Current. By March 2024, the iceberg had run aground near South Georgia, a remote island in the South Atlantic. Scientists voiced concerns at the time that its massive bulk could obstruct access to feeding grounds for colonies of penguins and seals raising their young. Fortunately, A23a dislodged in late May and continued its journey northwards. In recent weeks, it has accelerated, at times covering 20 kilometres in a single day. Exposed to warmer waters and pounded by heavy seas, the iceberg has entered a rapid state of collapse.
Scientists admit they were surprised by how long A23a endured. “Most icebergs don’t make it this far. This one’s really big, so it has lasted longer and gone further than others,” said Dr Meijers. Nevertheless, its fate was inevitable. “Once icebergs leave the freezing protection of Antarctica, they’re doomed,” he noted. Iceberg calving – the process of large chunks of ice breaking off glaciers or ice shelves – is a natural part of Antarctica’s life cycle. However, researchers warn that the rate of ice loss is accelerating, a trend likely driven by human-induced climate change. The story of A23a, a relic of the 1980s now meeting its end in the turbulent Atlantic, offers a dramatic reminder of the forces at play in Earth’s polar regions – and of how the world’s oceans are transforming in a warming climate.
