Largest Iceberg A23a Reaches End of Its 40-Year Journey in South Atlantic Ocean, Offering Insights into Giant Glaciers and Sea Level Rise

The world’s largest iceberg, designated as A23a, is in its final stages, disintegrating rapidly in the warmer waters of the South Atlantic Ocean. This massive ice structure, once comparable to the Hawaiian island of Oahu, is now breaking up into substantial pieces, according to scientists from the British Antarctic Survey (BAS).

First calved off the Filchner-Ronne ice shelf in Antarctica in 1986, A23a has been a subject of interest for scientists since then. Over the years, it has taken turns as the largest iceberg, occasionally losing its title to larger but shorter-lived icebergs only to regain it when they disintegrated.

At nearly 40 years old, A23a is not just the oldest current iceberg but also one that has managed to slow its natural decay by getting stuck twice after calving from its parent-berg. However, the ice giant now finds itself in the terminal phase of its journey.

“The iceberg is quickly breaking up, shedding large chunks that are themselves designated as large icebergs by the U.S. National Ice Centre,” shared Andrew Meijers, an oceanographer at BAS, via email to NPR last Thursday.

A23a has currently shrunk to approximately 1,700 square kilometers (656 square miles), roughly equivalent to Greater London’s size, as per Meijers’ estimation. Its northward drift has placed it in waters where icebergs of its magnitude can no longer survive, according to Ted Scambos, a senior research scientist specializing in polar regions at the University of Colorado Boulder.

Scambos explains that this phase is part of the normal life cycle of icebergs, an event that has occurred for millennia and appears unrelated to climate change. However, A23a’s journey to reach this stage has been far from ordinary. After being grounded for decades in the seafloor of the Weddell Sea following its calving in the 1980s, it freed itself in 2020 and headed towards the open ocean by late 2023.

Yet, in August 2024, it got stuck again—this time within an ocean vortex known as the Taylor column. There it remained for several months before breaking free once more late last year, propelled northwards by strong currents. In a dramatic finale earlier this year, A23a appeared to be on a collision course with South Georgia Island, potentially threatening seal and penguin colonies, but grounded around 50 miles off the coast by March.

Currently, A23a finds itself in water well above freezing, leading Meijers at BAS to predict that it will disintegrate rapidly into pieces too small to track within weeks. “This, combined with its northward movement and the approaching southern spring, means it is likely to swiftly crumble into bergs too minute for further tracking,” he explains.

Eventually, A23a will become too tiny to be detected by satellites—marking the end of a decades-long era for the scientists who have observed its journey. Yet, even in its demise, A23a continues to offer valuable insights to scientists studying colossal icebergs and their impact on the surrounding environment.

Scientists at BAS have recently collected samples from areas affected by A23a’s path, providing insight into potential ecosystem changes as fresh water mixes with saltwater and alterations in oceanic carbon levels. According to Scambos at the University of Colorado Boulder, research like this can contribute significantly to future-focused science.

“It’s another opportunity to comprehend processes governing those mega glaciers,” he says. “And these are crucial in terms of regulating sea level rise over extended periods—decades to centuries.”