The world’s oldest and largest iceberg, known as A23a, is defying expectations and refusing to melt, according to scientists. Just a few months ago, this colossal 1,500-square-mile ice mass was anticipated to drift into warmer waters and eventually dissolve. Instead, the trillion-ton iceberg, which is twice the size of Greater London and three times that of New York City, remains stuck in an ocean vortex that could keep it stationary for years.
A23a has an intriguing history. It originally broke away from the Antarctic coast in 1986 and soon after grounded on the seabed, where it remained for over three decades. In 2020, the iceberg refloated, and by late last year, it began an exciting migration. Scientists were eager to observe its journey, as it is rare to see an iceberg of such magnitude on the move. Propelled by strong winds and ocean currents, A23a left the Weddell Sea and entered the Southern Ocean, slowly drifting towards warmer waters.
By April, the iceberg had entered a powerful ocean current that was expected to guide it into the South Atlantic, where it would break up. However, A23a has unexpectedly halted.
Iceberg A23a should have long since shot up past South Georgia into the South Atlantic, fracturing into countless pieces. But it’s been caught in a Taylor Column just north of South Orkney since early April. pic.twitter.com/a3JPyldpNo
— Jonathan Amos (@BBCAmos) August 4, 2024
“Usually you think of icebergs as being transient things; they fragment and melt away. But not this one,” said Prof Mark Brandon, a polar expert, in an interview with BBC News. “A23a is the iceberg that just refuses to die.”
Currently, the massive iceberg is slowly spinning just north of the South Orkney Islands, a desolate region of the British Antarctic Territory, uninhabited except for an Antarctic exploration base. The iceberg’s stoppage is not due to grounding on the seafloor but because it is trapped in a vortex created by the Pirie Bank, a bump on the ocean floor. As the ocean current encounters this obstruction, it splits into two flows, generating a rotating swirl of water in between.
“The ocean is full of surprises, and this dynamical feature is one of the cutest you’ll ever see,” commented Prof Mike Meredith from the British Antarctic Survey to BBC News.
Weighing nearly one trillion metric tons, A23a could remain stuck in this vortex for years, scientists predict. This persistence adds to the complex dynamics of Antarctic ice behavior.
This situation unfolds against a backdrop of significant climate concerns. Last year, the Antarctic winter sea ice fell to its lowest level on record. The British Antarctic Survey reported that there were more than two million square kilometers (800,000 square miles) less ice than usual, an area ten times the size of the UK. It noted that such a drastic reduction in ice levels is “extremely unlikely to happen without the influence of climate change.”
Persistent low sea ice levels could have far-reaching impacts on global weather systems and Southern Ocean ecosystems, affecting species such as whales and penguins. The unexpected resilience of A23a serves as a reminder of the unpredictable and interconnected nature of our planet’s climate and ocean systems.