World’s largest iceberg A23a runs aground near South Georgia

The iceberg, weighing nearly a trillion tonnes, has remained stationary since March 1, approximately 90 km (56 miles) from land. Researchers are monitoring its impact on local ecosystems and marine navigation, as its gradual breakup could disrupt commercial fisheries and alter ocean chemistry.

The British Antarctic Survey (BAS) is closely monitoring A23a to assess its influence on ocean chemistry and marine ecosystems. The melting iceberg releases nutrients, including iron and nitrogen, which can stimulate phytoplankton blooms. The microscopic organisms play an important role in the marine food web and carbon sequestration.

“If the iceberg stays grounded, we don’t expect it to significantly affect the local wildlife of South Georgia. In the last few decades, the many icebergs that end up taking this route through the Southern Ocean soon break up, disperse, and melt. Commercial fisheries have been disrupted in the past, however, and as the berg breaks into smaller pieces, this might make fishing operations in the area both more difficult and potentially hazardous,” Dr. Andrew Meijers, an oceanographer at BAS, explained.

In December 2023, researchers aboard the RRS Sir David Attenborough collected water samples from around the iceberg to analyze its effects on marine life. Melting icebergs like A23a can alter ocean circulation and nutrient distribution, influencing marine biodiversity, according to BAS scientists.

While large icebergs grounding near South Georgia are not uncommon, A23a’s immense size raises concerns. If the iceberg remains intact, it may obstruct access to feeding grounds for penguins and seals. Historical events, such as the grounding of iceberg A38 in 2004, resulted in food shortages for thousands of seabirds and marine mammals.

Researchers are still uncertain about A23a’s fate. If the iceberg begins to fragment, smaller icebergs could disperse across the region, creating hazards for shipping and fishing vessels. The BAS has previously deployed robotic ocean gliders to measure how icebergs impact ocean circulation, freshwater input, and the release of vital micronutrients.

“Now it’s grounded, it is even more likely to break up due to the increased stresses, but this is practically impossible to predict. Large bergs have made it a long way north before – one got within 1 000 km [620 miles] of Perth, Australia, once – but they all inevitably break up and melt quickly after,” Dr. Meijers added.

A23a originally calved from Antarctica’s Filchner Ice Shelf in 1986 and remained grounded in the Weddell Sea for more than 30 years. It began drifting in 2020, following ocean currents toward South Georgia. Satellite data confirmed that by January 17, 2025, the iceberg had reached the vicinity of the island. It eventually became trapped on the continental shelf by March 1.

The iceberg was caught in a Taylor Column, a rotating oceanic vortex above a seamount, for several months in late 2024. This phenomenon temporarily stalled its movement before it resumed its northward journey toward the island.

References:

¹ World’s largest iceberg grounds near sub-Antarctic Island of South Georgia – BAS – March 4, 2025