by Mick the Ram

After 30 years of being stuck to the ocean floor, the world’s biggest iceberg is finally on the move.

Given the name A23a, the monster berg split from the Antarctic coastline back in 1986, but it quickly became grounded in the Weddell Sea, becoming what was essentially, an ice island.

Its size is a staggering 4,000 sq km (1,500 sq miles) in area. In the past 12 months it has begun to drift, gathering momentum driven by winds and currents and it now seems that it is about to spill beyond the Antarctic’s waters.

It is currently passing the northern tip of the continent’s Peninsula, following a path similar to the one that Sir Ernest Shackleton exploited back in 1916, as he made his escape following the loss of his ship, the Endurance, in crushing sea-ice.

At that time he aimed his lifeboat for the British Overseas Territory of South Georgia, and pattern has emerged over time that has seen many of Antarctica’s icebergs head in the same direction and then get pinned on the island’s shallow continental shelf.

Former home of Soviet research station

A23a was part of a mass outbreak of bergs from the White Continent’s Filchner Ice Shelf. To put into a time context, at the point of its initial breakaway it was playing host to a Soviet research station.

Its journey came to an abrupt halt when it anchored itself to the bottom-muds and there it stayed for more than 30 years, but it seems that it has shrunk sufficiently to loosen its grip and free itself to start moving again.

Breaking free

The iceberg is incredibly thick at around 400m, which to give some perspective to, is greater than the height of Europe’s tallest skyscraper, the Shard building in London, which is 310m tall.

Movement was first identified back in 2020, but in recent months it has definitely increased into a spurt and now seems destined for the South Atlantic and an area that has earned itself the nickname of “iceberg alley”.

Threat to marine life

Scientists will be monitoring what happens with a keen eye as it could have a detrimental effect on on animal life. As these giant bergs crumble and melt, they dump billions of tonnes of freshwater into the local marine environment, causing disruption to normal foraging routes for penguins and seals and upsetting seabirds breeding grounds. 

No way past South Georgia

South Georgia which seems to be its inevitable destination has a continental shelf which extends typically more than 50km from the coast and has an average depth of about 200m, so when a mega-berg reaches the close vicinity of the island, they tend to ground themselves and then and slowly decay.

Big changes ahead

Oceanographer Dr Mark Brandon, remarked: “The scale of some of these icebergs is something else.” He explained that the freshwater released by the iceberg will have a measurable effect on the structure of the water column around the island.

“It changes the currents on the shelf because it changes the seawater’s density. It makes the seawater quite a lot cooler as well,” Dr Brandon said.

Shackleton’s heroic exploits saved crew

The epic journey of explorer Ernest Shackleton and his crew more than 100 years ago is legendary. He led three expeditions to the Antarctic, but it was his voyage in lifeboats first of all from Elephant Island before finally heading onto South Georgia, after the sinking of his ship which had become trapped in pack ice, that he is most famed for.