The largest iceberg in the world, designated A23a, has garnered the attention of experts as it returned to its original position after more than five months of “wandering” past the northern tip of the Antarctic Peninsula.
A23a seen from above. (Photo: Andrew Miller).
On August 4, BBC reported that A23a had returned to its original position, which is north of Antarctica, while it was expected to drift along the strongest ocean current on Earth.
A23a began to break away from the Filchner-Ronne Ice Shelf in West Antarctica in 1986 but became trapped in the Weddell Sea.
For nearly three decades, the 1 trillion-ton iceberg remained almost “asleep” in this area. It was not until 2020 that A23a began to move again, slowly drifting before reaching warmer waters. In November 2023, satellite images showed the iceberg drifting past the northern tip of the Antarctic Peninsula due to strong winds and ocean currents, according to Reuters.
Close-up of A23a. (Photo: Nguyễn Ngọc Thiện).
In early April, A23a drifted into the Antarctic Circumpolar Current (ACC)—the largest ocean current today, flowing clockwise from west to east around Antarctica. Given this situation, scientists predicted that A23a would drift along the current towards the South Atlantic and then melt.
However, its actual position proved this scenario wrong. The world’s largest iceberg remains just north of the South Orkney Islands, moving counterclockwise about 15 degrees each day, according to BBC. Based on its current speed, A23a’s lifespan will be extended.
Professor Mark Brandon, an expert on polar regions, stated that icebergs typically have a temporary nature; they will break apart and melt. However, A23a is not like that.
“It is an iceberg that refuses to ‘die’, “ the professor remarked.
Illustration of A23a stuck due to an obstruction. (Photo: IBSCO/NASA, BBC).
A type of eddy, first described around 1920 by physicist Sir Geoffrey Ingram Taylor, has blocked A23a from following the current. Specifically, the obstruction is a ridge approximately 100 km long at the ocean floor, known as Pirie Bank.
Professor Taylor previously explained in detail how and what happens when a current encounters an obstruction on the ocean floor. According to the British physicist, when faced with an obstacle, if conditions are suitable, the flow will split into two separate streams and create a circular body of water with a certain depth surrounding the obstruction.
In the case of A23a, this eddy flows around A23a and Pirie Bank.
BBC notes that the iceberg, which is three times the size of New York, serves as a real-world example for studying the shape of the ocean floor. Mountains, valleys, and ridges significantly affect ocean currents.
