The world’s largest iceberg, designated A23a, is drifting northwards from Antarctica towards South Georgia, a British territory and wildlife haven, where it could ground and break into pieces. If that happens, it poses a grave threat to King Emperor penguins’ colonies, millions of elephant seals, and fur seals on the island.

In addition to being currently the largest iceberg adrift in Antarctic waters, A23a is also one of the oldest. In 1986, the massive iceberg, more than three times larger than New York City, calved off West Antarctica’s Filchner-Ronne Ice Shelf and immediately grounded on the floor of the Weddell Sea, where it remained stuck for almost four decades until it broke free in late 2023.

Then, instead of drifting off on the Antarctic Circumpolar Current into “iceberg alley,” A23a became stuck in a massive oceanic eddy just north of South Orkney Islands, turning in an anti-clockwise direction by about 15 degrees a day, where it remained for almost a year before escaping the vortex in mid-December.

The warmer waters north of Antarctica are melting and weakening its huge cliffs, but the latest satellite pictures show it’s still roughly the size of Cornwall.

A23a could continue on its current course and hit South Georgia or could begin to break up any day.

Five years ago, there was considerable concern that iceberg A68a, which was then the largest iceberg in the world, was drifting straight toward South Georgia.  Fortunately, it broke up before colliding 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 pups dead on local beaches. 

A23a megaberg escapes after months in ocean vortex

Thanks to Alaric Bond and David Rye for contributing to this post.