A screenshot of the National Oceanic and Atmospheric Administration's satellite system monitoring iceberg A23a, which was drifting in the Weddell Sea near the Antarctic Peninsula in February. //NOAA Joint Polar Satellite System Hide caption
Toggle caption // National Oceanic and Atmospheric Administration's Joint Polar Satellite System
The world's largest iceberg, A23a, has been trapped again.
The massive chunk of ice the size of Rhode Island was stranded on the ocean floor off the coast of Antarctica for more than 30 years before finally being freed in 2020 and beginning its journey out to sea this winter.
But a few months into the A23a's voyage, onlookers were astonished to see the iceberg spinning around.
The British Antarctic Survey has seen the giant iceberg rotating since January near the South Orkney Islands, about 375 miles from the Antarctic Peninsula, via satellite imagery. The survey says A32a is maintaining a “cold rotation of 15 degrees per day.”
This dancing motion is likely caused by a fluid dynamics phenomenon called a Taylor pillar, which is essentially a spinning cylinder that forms when there is an obstruction in the flow. In other words, A23a is trapped in a kind of ocean eddy.
Till Wagner, a professor at the University of Wisconsin-Madison who studies how ice interacts with the climate, said he has never seen an example of something on such a large scale.
“You know, Taylor columns are easy to make in a rotating tank experiment in the lab, but it's very rare to see them on a geophysical scale like this,” he said.
There's still a lot we don't know about how Taylor Pillars affect giant icebergs like A23a: How often they form in the ocean, and how often icebergs become trapped inside them, are unclear.
In the case of A23a, no one knows how long it will spin in the vortex. The iceberg is melting as it spins, and Wagner is curious to see how that will affect organisms in the surrounding ecosystem, such as phytoplankton.
“It will be interesting to see if there is a more vigorous phytoplankton bloom there next spring,” he said.
Iceberg A23a's origins date back to 1986, when the tip of the Filchner Ice Shelf broke off three icebergs. For decades, A23a was attached to a sandbar in shallow waters. In 2020, the main part of A23a broke off, and finally began flowing into the Southern Ocean in November.
It was expected to move north over the next year until it reaches warmer ocean waters where it will rapidly melt and break up. Currently, A23a's fate is somewhat uncertain.
