The iceberg has been hovering in the same spot just north of Antarctica for the past several months, when it should have been speeding along the planet's most powerful current these days.
Scientists say the iceberg, twice the size of London, is stuck on top of a giant eddy in the ocean.
Marine experts call this situation 'Taylor Column' and it is possible that A23a could not be freed from this 'imprisonment' for several years.
"Normally you think of icebergs as ephemeral things that will eventually melt away, but this iceberg is not," says polar expert Professor Mark Brandon.
An Open University researcher told BBC News that A23a is an iceberg that never melts.
The iceberg's longevity is documented by the fact that it broke free from the Antarctic coastline in 1986, but soon after became trapped in the mud below the sea floor.
For three decades it was considered a static 'island of ice' that did not budge.
Then after 2020 it started floating again. It first began to flow slowly and then moved towards the north.
In early April of this year, A23a entered the Antarctic Circumpolar Current (ACC), a current that carries a hundred times more water than all the rivers on Earth combined.
This would have meant a multi-fold increase in the speed of the trillion-ton iceberg, which would have entered the South Atlantic and then slowly melted away to become part of the ocean.
But A23a went nowhere. It is located just north of the South Orkney Islands and is rotating at a rate of about 15 degrees a day, and as long as it continues to do so, its demise will continue to be delayed.
A23a is not connected to the sea floor again and there is at least 1000 meters of water between the two.
It is held back by a type of vortex first described in the 1920s by physicist Sir GI (Geoffrey Ingram) Taylor.
The Cambridge academic was a pioneer in the field of fluid dynamics and was even involved in the Manhattan Project to model the possible stability of the world's first atomic bomb test.
Professor Taylor showed how a current that encounters an obstacle on the sea floor can split into two separate currents under the right conditions, creating a depth in the water circulating between them.
In the case of A23a, the barrier is a 100 km wide ridge on the sea floor known as Peribank. This vortex has formed above this bulge and currently A23a is its prisoner.
Professor Mike Meredith of the British Antarctic Survey said: 'The ocean is full of surprises and this dynamic feature is one of the most beautiful ever seen.'
Taylor columns can also form in air. You see them in the movement of clouds over the mountains. These may be only a few centimeters wide in an experimental laboratory tank or be very large as in the case where there is a large avalanche in the middle of the column.
How long A23a will continue to orbit is unknown, but when Professor Meredith placed a scientific buoy in the Taylor Column above another bulge east of Perry Bank, the floating device was still orbiting in the same spot four years later.
A23a is once again a great example of the importance of understanding the composition of the ocean floor.
Seamounts, valleys and slopes have a profound effect on the direction and mixing of water and the distribution of nutrients that drive biological activity in the ocean.
This effect also extends to the climate system. It is the mass movement of water that helps disperse heat energy around the globe.
The behavior of A23a can be explained because the sea floor north of South Orkney has been adequately surveyed.
This is not the case in the rest of the world and currently only a quarter of the world's ocean floor has been mapped according to the best modern standards.
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