After being grounded for over 30 years, the world’s largest iceberg, A23a, has started drifting in the Southern Ocean. This massive iceberg, which is roughly double the size of Greater London and weighs approximately one trillion tonnes, broke off from Antarctica’s Filchner Ice Shelf in 1986. Since then, it had remained stuck on the seabed near the South Orkney Islands in the Weddell Sea until it began its slow movement northwards in 2020.
“It’s exciting to see A23a on the move again after periods of being stuck. We are interested to see if it will take the same route the other large icebergs that have calved off Antarctica have taken. And more importantly what impact this will have on the local ecosystem,” said Dr Andrew Meijers, who is an oceanographer with the British Antarctic Survey.
A23a’s journey
The journey of iceberg A23a has been marked by fascinating scientific events. A23a broke free from Antarctica in 1986 but got stuck in the Weddell Sea’s bottom mud for 30 years. It remained a static “ice island” until 2020 when it finally began to drift again. Slowly at first, it then accelerated northward, moving towards warmer air and waters.
For several months, the iceberg was trapped in a rare oceanographic phenomenon known as a Taylor Column, where rotating water above a seamount held it in place. This unusual event caused A23a to spin in a single spot, delaying its expected rapid drift north.
As A23a continues on its journey, it is anticipated to follow the Antarctic Circumpolar Current into the Southern Ocean. This current is likely to drive the iceberg towards the sub-Antarctic island of South Georgia. Once it reaches this region, A23a will encounter warmer waters, leading to its eventual break-up into smaller icebergs and subsequent melting.
Biogeochemist Laura Taylor, who was on board a research vessel, expressed hope that scientists would be able to study the impact of the massive iceberg A23a on the surrounding ecosystems as it melts and breaks apart.
“We know that these giant icebergs can provide nutrients to the waters they pass through, creating thriving ecosystems in otherwise less productive areas,” Ms Taylor said.
“What we don’t know is what difference particular icebergs, their scale, and their origins can make to that process. We took samples of ocean surface waters behind, immediately adjacent to, and ahead of the iceberg’s route. They should help us determine what life could form around A23a and how it impacts carbon in the ocean and its balance with the atmosphere,” she added.