What does it look like when a one trillion tonne iceberg collides with an island half its size?

Given its current trajectory observed through satellite tracking and with all considerations made – such as the slope of the ocean surface and the strength of the currents surrounding it – scientists anticipate we should have our answer within the next month.

Of course, there’s always the chance ocean turbulence or even some high winds could knock the mega iceberg, A23a – a colossal iceberg, currently the size of Cornwall – off its current course, influencing the behemoth to simply brush past the coast of the remote island of South Georgia, instead. If the ocean is an unpredictable environment, let it be known that the movements of icebergs are even more so.

But, as things stand – and will all considerations taken and observations calculated – the team at British Antarctic Survey suggests that it seems most likely that A23a will have arrived at the continental shelf of South Georgia within the month.

It paints a vivid and dramatic image. One that all feels like the plot of a disaster movie; a one-trillion-tonne iceberg double the size of Greater London breaks free from its position north of the South Orkney Islands in late 2024 and within a month finds itself on a collision course with the British-owned South Georgia an island half the size of the colossal iceberg itself.

What’s more, currently measured at a distance of just 173 miles from impact, you’d be forgiven for thinking that tensions on the island must be pretty high.

Except, the team of experts at the British Antarctic Survey assure us, this is all a perfectly natural part of the lifecycle of ice. Icebergs are formed and break from their anchorage to land pretty much all the time.

Icebergs are formed when ice sheets are ‘pushed’ out into the ocean by the weight of continental ice behind them, where they begin to float as ice shelves. Eventually, they break off as icebergs due to a combination of flexure by winds, waves, tides, and ocean melting. 

The arrival of A23a, an iceberg measuring some 3,672 square kilometres, will deliver, however, rather sizeable impact. But who – or what – stands to be most affected? And what will the reverberations be for life on the island? The answer rests, primarily, among South Georgia’s population of penguins.

The island of South Georgia is somewhat of a haven for wildlife, with beaches filled with marine mammals and species of seabird. It’s according to the South Georgia Heritage Trust that species such as these thrive on the abundant plankton that populate the island’s surrounding waters. These waters are naturally fertilised through nutrients being stirred from deeper depths and run-off from the island shelf.

As such, this time of year is a critical one for the island’s resident penguins – mostly Emperor – and seals that make short and frequent trips to feed off a particular type of plankton called krill, before returning home to their chicks and pups before they get too hungry.

This process is about to receive a one-trillion tonne upset. It’s anticipated that the continental shelf of South Georgia – at several hundred metres deep – should be just shallow enough to ground the runaway iceberg, presenting what will be a rather sizeable hurdle for penguins and seals to surmount when carrying out the daily food run. This could force its residents to take on a mammoth detour to reach their food.

“An iceberg grounding close to South Georgia could result in them having to make large diversions to their feeding grounds and not getting back to their young in time,” Professor Geraint Tarling, science leader of the ecosystems team at the British Antarctic Survey, tells Oceanographic Magazine. 

Twenty years ago, in 2004, a similar iceberg – called A38 – became grounded in the waters near the island, blocking access to feeding grounds for South Georgia’s wildlife. It was an event that led to the death of many animals. Experts now fear a repeat of the event which has the potential to ‘last for years’.

South Georgia is also an important hub for commercial fishing, but large icebergs often make navigation difficult for vessels. The remains of a previous iceberg, a “game-changing” iceberg known as A76, are still floating in the region, which has complicated fishing operations.

It’s anticipated that once aground, the iceberg – which, as it has entered warmer waters along its journey northwards, has already lost mass through meltwater – will break up into smaller chunks, creating what has been envisioned by some as a “floating city of ice” before it eventually melts into the sea surrounding it. 

“The iceberg is melting faster as it moves northwards, but this is largely set by the ocean temperature; it’s in colder water right now compared to other similar icebergs from recent times, so it may not break up quite as soon,” says Dr Andrew Meijer, a member of the polar oceans team at the British Antarctic Survey. 

“However, this is very hard to tell and satellite observations aren’t really good enough to know the state of the ice itself. If it grounds, it is even more likely to break up due to increased stresses, but this is practically impossible to predict.”

In whatever state it does eventually arrive on the door step of the island of South Georgia, it’s likely to be met with mixed feelings from the South Georgia locals. It’s true that an iceberg of this magnitude will play havoc with the island’s shipping and fishing fleets. But it’s also true that icebergs do bring with them a tranche of positive impacts upon the environments they find themselves.

To find the silver lining, you just have to look a little closer.

“Their melt can actually fertilise the ocean, allowing both phytoplankton and zooplankton to thrive,” continues Dr Tarling. “These organisms can soak up large amounts of CO2 from the atmosphere, counteracting at least some of what we emit into the atmosphere.”

We know this because organisations, like the British Antarctic Survey have been studying icebergs similar to A23a for a long time. In fact, it was back in December 2023 that the team took samples from A23a itself to investigate what impact it would have on the biogeochemistry of the water it was passing through.

“Increased phytoplankton growth due to supply of nutrients from a giant iceberg can be responsible for increasing carbon sequestration from the surface ocean to the deep,” explains Dr Meijers. “The delivery of important micronutrients – such as iron – to the ocean via melt is one very active area of research, as is the stirring up of deep nutrient rich waters.

“Both are important components for generating ocean blooms of phytoplankton, which can support the higher food chain as well as potentially sequester atmospheric carbon into the ocean.”

Atmospheric carbon sequestration via the ocean mechanism is, of course, a highly active area of research right now. And icebergs are a “very interesting aspect of this” process. Of course, this could be down to the growing frequency in the number of large-scale icebergs, like the A23a, witnessed in the last two decades. Likening them to the growing reports of wildfires in polar regions, icebergs like the behemoth A23a are both a “completely normal part of the lifecycle of the Antarctic (and Greenland) ice sheets” and a result of climate change. 

“Observations show that since 2000, ice shelves have lost around six billion tonnes of their mass. This is roughly matched by an increase in straight up melt of the ice shelves, and aligns with a measured mass loss of the grounded ice of Antarctica – attributed to anthropogenic climate change,” says Dr Meijer.

“This loss of ice shelf mass has significant implications for ocean circulation, due to the addition of freshwater, acceleration of sea level rise, the possible irreversible ‘tipping points’, particularly in the vulnerable west Antarctic,” he continues.

So, what does it look like when a one trillion tonne iceberg sets a collision course with a remote island, half its size? Well, it could all come down to a matter of perspective.

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