PREVIEW

BY MARK WORGAN

One of the largest icebergs ever recorded has finally disintegrated after an incredible four decades in the ocean.

Iceberg A-23A was among the giants to “calve” from the continent, detaching from the Filchner Ice Shelf in 1986 and for many years was the world’s largest due to its size and longevity.

After forming in the Weddell Sea, its journey ultimately ended in the South Atlantic Ocean in early April 2026 - just months short of its 40th anniversary. It owed its longevity to becoming wedged on the ocean floor where the temperatures were cold enough to keep it preserved.

Satellite images captured the iceberg both at the beginning and the end of its life. Early observations showed A-23A alongside several other large icebergs formed during the same calving event, all of which it eventually outlasted.

By April 2026, what remained of the iceberg had drifted more than 2,300km north of its origin, into warmer waters near South Georgia and the South Sandwich Islands. There, it rapidly melted, fractured and shrank.

In its final months, A-23A underwent extensive melting and break-up. By late March 2026, scientists estimated it had shrunk to just over 170 sq km - a small fraction of the more than 6,000 sq km it covered in 2020 when it was still grounded off Antarctica.

Pools of deep-blue meltwater formed across its surface, weakening the structure and likely contributing to its collapse.
Cloud cover obscured some of its final moments from satellites.

“I noticed in recent weeks how Mother Nature seemed to keep a veil (of clouds) over the dying iceberg as if trying to give it some privacy at this stage,” said Jan Lieser of Bureau of Meteorology.
There were still enough observations, however, to capture glimpses of its final break-up, as well as the many stages of its long and winding journey.

A-23A’s lifespan coincided with major advances in Earth observation. The Landsat program tracked it from the 1980s onwards, while later missions such as Terra satellite and Aqua satellite provided regular, wide-area coverage.

In more recent years, a growing fleet of satellites has offered unprecedented detail — from changes in the iceberg’s shape to its impact on surrounding marine ecosystems. Astronauts aboard the International Space Station also captured close-up views.

“The technology that allows us to tell ‘iceberg stories’ is a tribute to the engineers and funding that put crucial sensors into orbit to collect those data and make them accessible,” said Christopher Shuman, formerly of the University of Maryland. “Through time, these efforts have allowed us to understand the general patterns of iceberg movement around Antarctica, especially in the last handful of decades.”

Despite decades of observations, scientists say many questions remain about how icebergs move and break apart.

Researchers are continuing to investigate the roles played by ocean currents, seabed features and rotating columns of water in shaping their paths. Smaller fragments that break away from giant icebergs are of particular concern, as they can pose hazards to shipping and are difficult to track.

Even in the case of A-23A, uncertainties persist - including the nature of the seabed where it remained stuck for years after calving, and how it later became trapped in a rotating ocean vortex near the South Orkney Islands.

“We certainly do know a fair bit about the general drift patterns of icebergs and the general environment,” Lieser said. “But when it comes to individual pieces - large and small - and their tracks, there's still a fair bit to learn.”