The world’s largest iceberg, known as A23a, has become a spectacle of nature, caught in a peculiar oceanic phenomenon just north of Antarctica. A23a, which detached from the Antarctic ice shelf in 1986, initially remained grounded on the seabed of the Weddell Sea for decades. It wasn’t until 2020 that this colossal iceberg, once approximately three times the size of New York City, started drifting again. However, instead of moving towards warmer waters, A23a has been ensnared by a Taylor Column—a massive rotating cylinder of water caused by an obstruction on the seafloor.
What is this mysterious Taylor Column? A Taylor Column occurs when a current meets an obstruction on the ocean floor, creating a vortex of rotating water. In A23a’s case, the obstruction is a 100 km-wide seafloor feature called Pirie Bank. This phenomenon, first described by the pioneering physicist G.I. Taylor in the 1920s, is trapping the iceberg, causing it to rotate counterclockwise by approximately 15 degrees daily. The iceberg’s situation is peculiar because it’s floating at least a kilometer above the seabed, unlike its previous grounding in the Weddell Sea.
Surprisingly, the A23a mega iceberg is very much still with us and has postponed its expected melty journey north. This Cornwall-sized piece of ice is now just spinning in an ocean vortex near the South Orkney Islands, maintaining a chill 15° rotation per day. As polar expert Prof. Mark Brandon from the Open University told BBC, “A23a is the iceberg that just refuses to die.” The iceberg’s stationary state within this Taylor Column delays its melting, preventing it from drifting into the warmer waters of the South Atlantic, where it would likely disintegrate.
What was the iceberg’s original path? The presence of A23a within this oceanic trap has surprised scientists, as the iceberg was expected to be carried away by the powerful Antarctic Circumpolar Current (ACC). The ACC is the world’s most potent ocean current, moving 100 times more water around the globe than all Earth’s rivers combined. Instead of following this anticipated path, A23a has remained virtually immobile since early April 2023. This unexpected stillness has led to a delay in the iceberg’s decay, with its eventual break-up now postponed indefinitely.
The phenomenon highlights the significant influence of underwater topography on ocean currents and iceberg movement. As Prof. Mike Meredith from the British Antarctic Survey noted, “The ocean is full of surprises, and this dynamical feature is one of the cutest you’ll ever see.” The presence of such seafloor features affects water direction, nutrient distribution, and even global climate patterns by redistributing heat energy.
How long will A23a remain trapped? The longevity of A23a’s entrapment in the Taylor Column is uncertain. Similar instances, like the buoys placed in other Taylor Columns, have remained in place for years. In January, the British Antarctic Survey’s Andrew Fleming had even predicted that A23a might get caught in this manner, mirroring the paths of previous massive icebergs like A68 and A76a. Fleming stated, “We’ll be interested to see if it also gets caught in the same place as the previous bergs, which spun in circles for several weeks before moving on.”
While climate change significantly impacts polar regions, A23a’s journey and current situation result from natural processes rather than direct climate influences. However, the event underscores the necessity of better understanding seabed topography to predict the movement of large icebergs, which could potentially disrupt shipping routes. When A23a eventually breaks apart, its meltwater, rich in nutrients, will likely benefit marine life, provided it doesn’t cause significant disruptions in their habitats.
A23a’s fascinating journey from a static “ice island” to a trapped giant within a Taylor Column demonstrates the complex and often surprising interactions between icebergs and oceanic forces.
