Iceberg A23a shatters: A looming threat to penguin habitats

The iceberg A23a, known as the largest in the world, is starting to break into thousands of smaller fragments near South Georgia Island in the Atlantic Ocean. The latest satellite images taken by NASA's Aqua satellite reveal that the iceberg, covering an area of about 3,100 square kilometres, is beginning to crumble, especially on its northern edge. "Thousands of ice chunks litter the ocean surface near the main iceberg, creating a scene reminiscent of a dark, starry night," wrote researchers from NASA Earth Observatory.

Although these fragments appear small in photos, many of them are at least 1 kilometre wide and pose a threat to ships. Such calving has occurred at various stages of A23a’s journey, even when it circled in a vortex in the Drake Passage in 2024. However, there are currently signs that the iceberg is becoming increasingly fragile. On its northern side, a strip of ice debris is visible, leftover from a sudden break of the edge, partly caused by several days of warm, sunny weather.

The breakup of the A23a iceberg has so far reduced its surface area by about 520 square kilometres since March when it got stuck on the sea floor. Although it remains the largest floating iceberg, its edges are gradually being eroded by waves and seasonal weather conditions. This process could take months, or even years, before the iceberg completely disintegrates unless larger fractures accelerate this process. The largest fragment that broke off from A23a, named A23c, has an area of about 130 square kilometres and is drifting south.

Satellite images taken by MODIS on NASA's Aqua satellite a few days ago show that the iceberg is less than 100 kilometres from South Georgia Island. The iceberg probably got stuck on a shallow underwater shelf around the island, which has previously stopped other Antarctic icebergs on their northern drift to warmer southern Atlantic waters. Although its position remains largely unchanged, the iceberg's surface has shrunk significantly within just two months.

Though uninhabited by humans, South Georgia Island is home to numerous species of wild fauna, including over 2 million penguins, featuring one of the largest colonies of king penguins Aptenodytes patagonicus. The presence of a large iceberg nearby can be problematic for them, as penguins might be forced to travel hundreds of additional kilometres to reach their food sources. "Meltwater coming from trapped bergs can also alter the temperature and salinity of their surroundings," scientists note.

The A23a iceberg is currently at nearly 55°S, far from the coldest waters around Antarctica. Although it has repeatedly held the title of the largest in the world since 1986, it is now only slightly larger than the next largest iceberg, D15A. As climate change accelerates Antarctic iceberg melting, more such giant icebergs are expected to drift near South Georgia in the coming decades.