Shelf Life: Icebergs are large masses of frozen freshwater that measure at least 15 meters in length. The largest ones typically break off from the Ross Ice Shelf in Antarctica before slowly melting as they drift into warmer ocean waters. A23a, currently the largest known iceberg, is nearing the end of its unusually long journey.
Nearly 40 years after breaking away from the Filchner – Ronne Ice Shelf in Antarctica, the A23a iceberg is finally beginning to melt and merge into the ocean for good. A23a ranks among the oldest and largest icebergs ever recorded and remains the biggest block of frozen freshwater on the planet.
Nicknamed the "megaberg," A23a weighed roughly one trillion tons earlier this year. Although it has since lost more than half its original mass, the iceberg still measures about 1,770 square kilometers in area and spans 60 kilometers at its widest point. Researchers have tracked its decline using satellite imagery from the European Copernicus observatory.
Recent data shows that A23a has begun to fragment into "smaller" pieces, some as large as 400 square kilometers. These chunks are further breaking apart into even smaller icebergs, many of which still pose navigational hazards for ships at sea.
According to Andrew Meijers, a physical oceanographer with the British Antarctic Survey, the changes underway in A23a can be described as nothing short of "dramatic." The megaberg is essentially nearing the end of its life, "rotting" from beneath as it drifts into waters that are simply too warm to sustain it. Constant melting is now unavoidable.
The process will continue in the weeks ahead, Meijers said, until A23a is no longer clearly identifiable. The iceberg originally calved from Antarctica's massive ice shelf in 1986, before "grounding" in the Weddell Sea, where it remained stuck on the seafloor for more than 30 years.
It finally broke free in 2020, carried by Antarctic currents into the South Atlantic Ocean. In March 2025, A23a briefly posed a threat to penguin and seal colonies after becoming stranded in shallow waters off South Georgia Island, though it moved on a couple of months later.
Together with parts of the Arctic ice pack, Antarctica's icebergs contain some of the planet's largest reserves of frozen freshwater. But they are melting slowly and inexorably, with profound consequences for human activity and natural habitats worldwide.
The world's largest iceberg is rapidly breaking apart and melting away
