World's largest iceberg A23a disintegrates near penguin refuge

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 glacier, covering an area of about 3,100 square kilometres, is beginning to crumble, especially on its northern edge. “Thousands of iceberg pieces litter the ocean surface near the main berg, 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 glacier 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 glacier 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 glacier is less than 100 kilometres from South Georgia Island. The glacier probably got stuck on a shallow underwater shelf around the island, which has previously stopped other Antarctic glaciers on their northern drift to warmer southern Atlantic waters. Although its position remains largely unchanged, the glacier'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, including one of the largest colonies of king penguins Aptenodytes patagonicus. The presence of a large glacier nearby can be problematic for them, as penguins might be forced to travel hundreds of additional kilometres to reach their food sources. Scientists observe that meltwater released from trapped icebergs has the potential to alter both the temperature and salinity of the surrounding environment.

The A23a glacier 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 glacier melting, more such giant icebergs are expected to drift near South Georgia in the coming decades.