A large iceberg is stuck in the sea trap

Something amazing has happened to A23a, the world’s largest iceberg.

For months now it has been circling just north of Antarctica where it must be running with the world’s strongest ocean current.

Scientists say the frozen structure, which is twice the size of Greater London, was captured on top of a giant rotating cylinder of water.

It’s a phenomenon that oceanographers call the Taylor column – and it’s possible that A23a may not escape its prison for years.

“Normally you think of icebergs as transient things; they crack and melt. But not this one,” polar expert Prof Mark Brandon said.

“A23a is an iceberg that just refuses to die,” an Open University researcher told BBC News.

Berg’s longevity is well documented. It broke off the coast of the Antarctic back in 1986, but then quickly got stuck in the mud at the bottom of the Weddell Sea.

For three decades it was a static “island of ice”. It didn’t move. It wasn’t until 2020 that it floated again and began to drift and, slowly at first, before it charged northward into warmer air and water.

In early April this year, A23a entered the Antarctic Circumpolar Current (ACC) – a juggernaut that moves a hundred times more water around the world than all the world’s rivers combined.

This was intended to put boosters on the almost trillion-tonne berg, to throw it up in the South Atlantic and not to forget something.

Instead, A23a went nowhere. It is always in the northern part of the South Orkney Islands, rotating counterclockwise about 15 degrees per day. And as long as it does this, its decay and eventual demise will be delayed.

A23a hasn’t started again; there are at least a thousand meters of water between its bottom and the sea floor.

Stopped in its tracks by the vortex type first described in the 1920s by a brilliant physicist, Sir GI (Geoffrey Ingram) Taylor.

The Cambridge academic was a pioneer in the field of fluid dynamics, and was even recruited into the Manhattan Project to demonstrate the possible stability of the world’s first atomic bomb test.

Professor Taylor has shown how an eddy current under the seabed can – under the right conditions – split into two separate currents, producing deep water circulation between them.

In this example, the barrier is a 100 km wide bulge under the sea known as the Pirie Bank. The vortex is sitting on top of the bank, and currently A23a is its prisoner.

“The ocean is full of wonders, and this dynamic feature is one of the most beautiful you’ll ever see,” said Prof Mike Meredith of the British Antarctic Survey.

“Taylor columns can also form in the air; you see them in the movement of clouds over mountains. They can be just a few centimeters across in a laboratory test tank or they can be very large as in this case where the column has a big snow-slap in the middle of it.”

How long can A23a continue to perform its spin cycle?

Who knows, but when Prof Meredith placed a scientific buoy on Taylor’s Column above another bulge on the east side of Pirie Bank, The floating bell was still hovering in its place four years later.

A23a is also a perfect illustration of the importance of understanding the topography of the ocean floor.

Seamounts, canyons and slopes have a major influence on the direction and mixing of water, and the distribution of nutrients that drive biological activity in the ocean.

And this influence extends to the climate system: the movement of large amounts of water helps to disperse heat energy around the world.

The behavior of A23a can be explained because the seabed just north of South Orkney has been well explored.

This is not the case in many countries of the world.

Currently, only a quarter of the ocean floor has been mapped with the best modern standards.