World's biggest iceberg spins in ocean trap

A23a is vast. Its flat, table-like top stretches to the horizon

Something remarkable has happened to A23a, the world’s biggest iceberg.

For months now it has been spinning on the spot just north of Antarctica when really it should be racing along with Earth’s most powerful ocean current.

Scientists say the frozen block, which is more than twice the size of Greater London, has been captured on top of a huge rotating cylinder of water.

It’s a phenomenon oceanographers call a Taylor Column – and it’s possible A23a might not escape its jailer for years.

“Usually you think of icebergs as being transient things; they fragment and melt away. But not this one,” observed polar expert Prof Mark Brandon.

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

View from space: A23a should have long departed for much warmer waters

The berg’s longevity is well documented. It broke free from the Antarctic coastline way back in 1986, but then almost immediately got stuck in the bottom-muds of the Weddell Sea.
For three decades it was a static “ice island”. It didn’t budge. It wasn’t until 2020 that it re-floated and started to drift again, slowly at first, before then charging north towards warmer air and waters.

The berg may be crumbling along its edges, but its greater bulk remains intact

In early April this year, A23a stepped into the Antarctic Circumpolar Current (ACC) – a juggernaut that moves a hundred times as much water around the globe as all Earth’s rivers combined.
This was meant to put boosters on the near-trillion-tonne berg, rifling it up into the South Atlantic and certain oblivion.
Instead, A23a went precisely nowhere. It remains in place just north of South Orkney Islands, turning in an anti-clockwise direction by about 15 degrees a day. And as long as it does this, its decay and eventual demise will be delayed.

A23a has not grounded again; there is at least a thousand metres of water between its underside and the seafloor.
It’s been stopped in its tracks by a type of vortex first described in the 1920s by a brilliant physicist, Sir G.I. (Geoffrey Ingram) Taylor.
The Cambridge academic was a pioneer in the field of fluid dynamics, and was even brought into the Manhattan Project to model the likely stability of the world’s first atomic bomb test.Prof Taylor showed how a current that meets an obstruction on the seafloor can – under the right circumstances – separate into two distinct flows, generating a full-depth mass of rotating water between them.
In this instance, the obstruction is a 100km-wide bump on the ocean bottom known as Pirie Bank. The vortex sits on top of the bank, and for now A23a is its prisoner.

Source: https://www.bbc.com/news/articles/cd168081wxvo