The world’s largest icebergs, sometimes exceeding the size of entire countries, are born as they break off the Antarctic ice sheet. These colossal ice masses, drifting and melting in the Southern Ocean, create distinct and temporary ecosystems around them.
It all began with a significant crack. Late in 2016, scientists observed a swiftly expanding fissure in the immense Larsen C Ice Shelf, which extends into the Weddell Sea from the West Antarctic Peninsula. Within months, this crack grew to an enormous scale, ultimately leading to one of the most massive icebergs ever recorded breaking away into the ocean.
The iceberg, labeled as A-68, was an immense structure, more than double Luxembourg’s area at 2,200 square miles (5,700 sq km) and around 770 feet (235m) thick. Initially, it barely moved, trapped in the seasonal Antarctic sea ice. However, it eventually began drifting northward, carried by ocean currents and wind.
This giant iceberg set out on a notable four-year voyage from the Antarctic sea ice to a distant island in the Southern Ocean. Iceberg A-68 became widely known, particularly when its travels captured attention on social media during the Christmas of 2020. During a time when Covid-19 lockdowns isolated many, people followed A-68’s journey with great interest, rooting for it as it crossed the Southern Ocean. There was even a chance of a dramatic finish, as ecologists feared A-68 could collide with South Georgia Island, potentially devastating its ecosystems.
The iceberg eventually broke apart and melted before reaching the island, dispersing billions of tons of chilled freshwater into the ocean. Over the years, it shattered into smaller pieces and gradually vanished, disappearing into slushy seawater by April 2021. This process significantly impacted the surrounding marine habitat, creating conditions that supported a unique ecosystem. Scientists tracking A-68 from its birth to its end gathered valuable insights into the effects of massive icebergs on marine environments. A-68, for its short existence, became a mobile refuge for various species.
With years of data collection, researchers can now tell A-68’s complete story and analyze its environmental impact on the ocean.
Breaking Away from Antarctica
On Antarctica’s side closest to South America, the West Antarctic Peninsula stretches into the Southern Ocean. This peninsula, home to numerous penguin colonies and other thriving life forms, is the most habitable region of the continent. To the east, it is bordered by the Larsen ice shelves, vast plains of floating glacier ice that extend tens of thousands of square kilometers. The seas beneath these ice shelves remain mostly uncharted due to the thick ice, which blocks vessel access and sunlight from reaching these regions, isolating the marine habitat beneath for thousands of years.
The Antarctic ice shelves are not stationary. Ice flows continuously from the continent towards the ocean, creating a dynamic environment as the ice interacts with the thinner seasonal sea ice. Occasionally, a significant chunk breaks off—a process known as “calving.” According to Geraint Tarling, a polar ecologist with the British Antarctic Survey, “Calving is a natural event.”
In July 2017, the growing fissure in Larsen C led to the detachment of a massive ice block, which represented about 10% of the shelf. This newly calved iceberg was the largest in the ocean at the time, and among the top six over the last 30 years. The US National Ice Center designated it as “A-68.” Within days, a portion of it broke off, creating fragments known as A-68a, A-68b, A-68c, and so on.
Embarking on Its Journey
The formation of A-68 exposed a previously hidden seabed that had remained beneath the ice for millennia. Polar scientists were eager to investigate this newly uncovered area before changes in the ecosystems began. “There was a big move to get expeditions in there,” says Tarling, noting, “Unfortunately, when it calved, there was a huge amount of ice around… The opportunity was lost.”
Thus, A-68a remained in place for a couple of years, trapped in its icy surroundings. In July 2018, it began drifting within the Weddell Gyre—a circular ocean current. By summer 2019, it had traveled about 155 miles (250 km) north. Then, as it reached the edge of Antarctica’s year-round sea ice, it drifted into “Iceberg Alley,” a path where powerful currents steer icebergs northwards.
In these waters, A-68a encountered warmer temperatures. By April 2020, a chunk measuring 67 square miles (175 sq km) had broken off, leading scientists to anticipate a collapse. Yet, A-68a persisted. Describing this iceberg as unique, Tarling notes, “It was the sixth-largest ever detected” and “stayed together for an incredibly long period.”
During the same period, Roseanne Smith, then a student researching polar and alpine change, tracked A-68a’s progress using satellite data. “I was doing it from home,” she recalls, adding, “It was a case of waking up every morning and then checking where the iceberg had moved to.”
Smith’s work at the British Antarctic Survey revealed that vast but thin layers of freshwater spread more than 620 miles (1,000 km) from the iceberg. “Satellites are only able to tell you anything about the conditions in the top few centimeters of the surface ocean,” she explains.
Approaching South Georgia Island
By the summer of 2020, the iceberg was drifting closer to South Georgia, raising concerns among scientists. South Georgia’s marine ecosystem is enriched by glacial runoff, which fertilizes surrounding waters, promoting photosynthetic plankton growth that sustains krill and other marine life. The island also serves as a breeding ground for species like elephant seals, king penguins, and wandering albatrosses.
An impact with the island’s shallow seabed could have damaged these ecosystems. “That probably would mean that there would be low levels of survival at those colonies for that particular year,” Tarling explains. This potential danger prompted an urgent attempt to arrange an expedition to assess the iceberg’s effects on the region’s marine environment.
In February 2021, the RRS James Cook vessel was directed to study the freshwater layer around A-68a, although Tarling could not join due to pandemic restrictions. The ship conducted transects, measuring water conditions and observing marine life.
The Final Break-Up
In December 2020, satellite images showed A-68a was “fraying at the edges” and developing cracks. As the iceberg approached South Georgia, one corner became lodged in the shallow waters off the island, breaking off from the main body. “It got very, very close,” says Tarling. Fortunately, this break spared the island, though it carved an indentation in the seabed.
The final break-up was driven by strong ocean currents that exerted a shearing force on the iceberg. This unusual event caused one section to break off, with pieces dispersing into the sea. Tarling’s team had to alter their research approach in response to the iceberg’s rapid disintegration, making observations around a collapsing iceberg for the first time.
In the peak of its melt, A-68a released around 1.5 billion tons of freshwater into the ocean daily. By late January 2021, as the RRS James Cook arrived, the researchers deployed gliders to monitor the icy fragments. Meanwhile, A-68a’s main body was melting at a rate of 23 feet (7 meters) per month due to the warmer northern waters near South Georgia.
Ultimately, in mid-April 2021, A-68a had disintegrated into fragments so small they no longer qualified as giant icebergs. Over three and a half years, A-68 shed a staggering 802 billion tons of ice, marking the end of its journey.
As scientists now assess the legacy of A-68, they reflect on the iceberg’s transformative effect on the ocean. This single calving event not only provided a unique glimpse into how massive icebergs influence the Southern Ocean but also highlighted the fleeting nature of such phenomena.