A23a refers to

A23a is currently the world's largest iceberg, covering an area of approximately 4,000 km2. It calved from the Filchner-Ronne Ice Shelf in West Antarctica in 1986 but remained grounded on the Weddell Sea floor for more than three decades. In late 2023, it began to drift significantly, moving past the Antarctic Peninsula toward the Southern Ocean. Measuring about 400 metres in thickness, it is more than twice the size of Greater London. Scientists monitor its movement closely as it enters "iceberg alley," a common path for icebergs drifting toward the South Atlantic. Its trajectory is significant because it could potentially ground near South Georgia Island, impacting the foraging routes of seals and penguins, or eventually fragment as it reaches warmer waters.