It feels a bit odd to have developed an emotional attachment to an iceberg. Then again, we have spent years following the epic and quixotic journey of the iceberg designated as A23a, an enormous mass of ice weighing roughly one trillion tons that was once the world’s largest iceberg. The huge berg was, at about 3,500 square kilometres, more than three times larger than New York City. It also proved to be the world’s oldest iceberg, having calved from West Antarctica’s Filchner-Ronne Ice Shelf almost 60 years ago. 

A23a’s career began slowly. In 1986, a massive iceberg calved off the Filchner-Ronne Ice Shelf and immediately grounded on the floor of the Weddell Sea, where it remained stuck And there it sat for almost four decades. until it broke free in 2023. The iceberg began drifting quickly past the northern tip of the Antarctic Peninsula, aided by strong winds and currents.

 As it drifted, it was being eroded by waves and melting in the relatively warmer waters of the Southern Ocean. The impact of the waves carved huge arches and caves in the 400-meter-high walls of the iceberg.

The expectations were that the berg would continue to melt as it drifted and would begin to break up, with luck, missing the British Overseas Territory of South Georgia.

Instead, A23a went precisely nowhere, as reported by the BBC. A23a became stuck in a massive oceanic eddy or vortex, a huge rotating cylinder of water that oceanographers call a Taylor Column. The phenomenon was first described by Prof GI Taylor, who showed how a current that meets an obstruction on the seafloor can – under the right circumstances – separate into two distinct flows, generating a full-depth mass of rotating water between them. In this instance, the obstruction is a 100km-wide bump on the ocean bottom known as Pirie Bank. The vortex sits on top of the bank, and  A23a became its prisoneri.

Rather than drifting off on the Antarctic Circumpolar Current into “iceberg alley, it remained in place just north of the South Orkney Islands, turning in an anti-clockwise direction by about 15 degrees a day. It remained spinning in the current for almost a year before escaping the vortex in mid-December. Being caught in the vortex prevented A23a from drifting into warmer waters and melting more rapidly.

 In 2023, scientists conducting part of the BIOPOLE project aboard the RRS Sir David Attenborough were able to get close enough to observe and study the iceberg. They were able to collect data from alongside it to investigate how Antarctic ecosystems and sea ice influence ocean cycles of carbon and nutrients, building a more accurate image of how these normally elusive objects influence global oceanographic processes.

In addition to the legions of scientists who followed the iceberg by satellite as it made its way across the Southern Ocean, millions more followed A23a online on social media.  Referred to by many online as a “megaberg”  and having earned the nickname “queen of icebergs”, A23a briefly qualified as a minor social media star.

Usually, you think of icebergs as being transient things; they fragment and melt away. But not this one,” observed polar expert Prof Mark Brandon. “A23a is the iceberg that just refuses to die,” the Open University researcher told BBC News.

When A23a finally escaped the vortex, its travels had just begun. The world’s largest iceberg was drifting northwards from Antarctica towards South Georgia, a British territory and wildlife haven. If it ran aground on the island, it could break into pieces. If that happens, it could pose a grave threat to King Emperor penguins’ colonies, millions of elephant seals, and fur seals on the island.

Unfortunately for the island, it lies directly in the path of drifting icebergs in “iceberg alley.” In 2020 and 2021, iceberg A68a, which preceded A23a as the largest iceberg in the world, drifted straight toward South Georgia. Fortunately, A68 broke up in the slightly warmer waters of the Southern Ocean before it could collide with the island.

In 2004, the island was not as lucky. The huge berg A38 grounded at South Georgia, leaving countless penguin chicks and seal pup lying dead on the island beaches, after the huge iceberg blocked access to thier feeding grounds,

In 2025, the scientific and internet iceberg fanboys ang girls held their breaths as the still massive iceberg A23a bore down on the island. The warmer waters north of Antarctica melted and weakened A23a huge cliffs. The satellite pictures still showed that the iceberg remained roughly the size of the UK’s county of Cornwall.

In the 11 days up to February 22, the now smaller, lighter berg travelled more than 700km (435 miles) north-east across the South Atlantic, hurtling along at an average of about 2.7km/h (1.7mph)

And then on Saturday, March 4, 2025, the still massive iceberg struck the shallow continental shelf about 50 miles (80km) from land and once again became firmly lodged on the bottom.

Many feared that the grounding of A23a would harm the penguins and seals feeding around South Georgia Island. Instead, scientists in Antarctica say that huge quantities of nutrients were locked inside the ice. Instead of delivering death, A23a brought an explosion of life in the ocean.

“It’s like dropping a nutrient bomb into the middle of an empty desert,” says Prof Nadine Johnston from British Antarctic Survey.

That week, Agence France-Presse (AFP) reported via multiple news outlets that A23a was in the process of breaking up, having drifted north of South Georgia. It was reported that the iceberg was less than half its original size, but still about 1,770 square kilometres (680 sq mi) and 60 km (37 mi) at its widest point, according to AFP analysis. Chunks as large as 400 square kilometres (150 sq mi) were reported to have broken off, while smaller pieces, many still large enough to threaten ships, were littering the sea around the island.

Scientists closely watched A23a’s disintegration for hints as to how Antarctica might respond to rising temperatures – specifically its ice shelves, the floating tongues of glaciers that extend into the ocean.

Ice shelves play an important role in the stability of much of the Antarctic ice sheet. But it’s by no means clear how quickly they might collapse in a warming climate and what that could mean for sea-level rise.g along at an average of about 2.7km/h (1.7mph). That journey exposed A23a to warmer waters, close to 10C at the surface – bad news for an iceberg. Over the past two weeks, A23a was carried by ocean currents in a near-complete clockwise loop in what could be its final dance,

While other icebergs have travelled further in the past, A23a traveled the furthest north of any Antarctic iceberg tracked by modern scientists It wandered closer to the equator than London.

The prolonged exposure to sea warmth means that the berg’s remains will inevitably fragment and eventually melt away, even though the Southern Hemisphere winter is on the horizon.

By early March, A23a had shrunk to approximately 180 sq km (70 sq miles), although estimates can vary slightly. Once it gets to roughly 70 sq km (27 sq miles), scientists will stop tracking it. That moment’s not far away, according to Luckman.

“All traces will probably have disappeared in a matter of weeks now, at most.”

A23a is gone but not forgotten.

Thanks to Alaric Bond for contributing to this post.