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A23a was discovered in 1986 from the Filchner-Ronne ice shelf in Western Antarctica. At the time it was approximately 4000 square km in size – more than three times the size of Rome – making it the largest iceberg in the world. After remaining frozen to the ocean floor for decades, in 2020 it lost its grip and began floating in the Weddell Sea. In November 2023, it began moving rapidly away from Antarctic waters.
Driven by winds and currents, the iceberg moved about 2000 km northward towards the warm South Atlantic Ocean waters, and in May 2025 reached South Georgia Island, where it began to disintegrate.
During 2025, A23a is breaking into smaller pieces of ice, significantly reducing its size. In this image from December 20, 2025, the iceberg is about 150 km northwest of South Georgia, surrounded by numerous icebergs of various sizes. Although it has lost about three-quarters of its surface area, A23a is still one of the largest icebergs floating in open water, covering about 1000 square km.
The bright blue areas visible on its surface and on the icebergs to its south are ponds of meltwater, a clear sign of the iceberg’s rapid loss.
This disintegration is typical for icebergs that reach far north and is caused by warm ocean temperatures and weather conditions. As A23a is traveling toward even warmer water, pushed by currents, it will soon experience the same fate as other megabergs that have disintegrated in the same waters.
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