World’s biggest iceberg, A23a, has broken up

An aerial view shows iceberg A23a in the South Atlantic Ocean near South Georgia and the South Sandwich Islands on Nov. 24, 2024. (MOD / Getty Images via CNN Newsource)

The world’s largest iceberg is “rapidly breaking up” into several large “very large chunks,” scientists from the British Antarctic Survey (BAS) have said.

Previously weighing nearly a trillion metric tonnes (1.1 trillion tonnes) and spanning an area of 3,672 square kilometers (1,418 square miles) — slightly bigger than Rhode Island — the A23a iceberg has been closely tracked by scientists ever since it calved from the Filchner-Ronne ice shelf in Antarctica in 1986.

A23a has held the “largest current iceberg” title several times since the 1980s, occasionally being surpassed by larger but shorter-lived icebergs, including A68 in 2017 and A76 in 2021.

Andrew Meijers, an oceanographer at BAS, told CNN in an email Wednesday: “The iceberg is rapidly breaking up, and shedding very large chunks, themselves designated large icebergs by the US national ice centre that tracks these.”

The “megaberg” has now shrunk to about 1,700 square kilometres (656 square miles), according to Meijers, which equates to roughly the size of Greater London.

A23a remained grounded on the Antarctic’s Weddell Sea floor for more than 30 years, probably until it shrank just enough to loosen its grip on the seafloor.

Then in 2020, it was carried away by ocean currents before it became stuck again in a Taylor column — the name given to a spinning vortex of water caused by ocean currents hitting an underwater mountain — until it was reported to be on the move again last December. In March this year it ran aground on a continental shelf before floating loose again in May.

Meijers explained the circumstances that led to the iceberg’s breakup. “It has been following the strong current jet known as the Southern Antarctic Circumpolar Current Front (SACCF) anti-clockwise around South Georgia ever since it floated loose in May, after grounding on the continental shelf for a few months in March.

“This jet is likely to ultimately take away the berg and its bits off to the north east — still as part of iceberg alley.”

He said A23a is “following a similar fate” to other megabergs, such as A68 in 2021 and A76 in 2023, which also disintegrated around South Georgia, a British Overseas Territory in the southern Atlantic Ocean, though it has stayed in one piece for longer than either of those.

The disintegration means the crown for world’s largest iceberg is now held by D15a, which measures around 3,000 square kilometres (1,158 square miles) and, according to Meijers, is “fairly static on the Antarctic coast near the Australian Davis base.”

A23a currently still holds the title of the world’s second-largest iceberg, but Meijers said this is likely to “rapidly change” as it continues to “fragment in the coming weeks.” Warmer water temperature and the onset of southern spring means it will probably break into “bergs too small to track further,” he said.

Iceberg calving is a natural process and there haven’t been enough megabergs for scientists to know if they are increasing as the world warms, Meijers said. What is clear, however, is that ice shelves have lost trillions of tonnes of ice through increased iceberg formation and melting over the past few decades, much of which is due to warming ocean water and changes in ocean currents, he added.

Human-caused climate change is driving alarming changes in Antarctica, which could lock in catastrophic sea level rise.