How A Melting Iceberg Is Reshaping Marine Ecosystems

A massive iceberg, A-68, which broke off from Antarctica's Larsen C Ice Shelf in 2017, has created a distinctive marine environment during its four-year drift, according to recent scientific analyses. In July 2017, the massive iceberg, later named A-68, broke off in an event called ‘calving,' and began a journey across the Southern Ocean. It became the largest iceberg adrift at the time.

Initially covering over 2,200 square miles (over 5,698 km) — more than twice the size of the European country Luxembourg — the iceberg captured global attention as it drifted north, propelled by ocean currents and winds.

Concerns rose in late 2020 when A-68 neared South Georgia Island, a critical breeding ground for threatened species. “South Georgia is an incredibly rich, dynamic marine ecosystem,” Geraint Tarling, a polar ecologist at the British Antarctic Survey in Cambridge, UK, told the BBC. The island's nutrient-rich waters support phytoplankton, krill and larger marine animals. Its shores are home to breeding colonies of threatened species, including king penguins and wandering albatrosses.

But the iceberg avoided a catastrophic collision with the island. It began to collapse in December 2020 and gradually broke apart and melted into smaller fragments over the course of 2021.

As it dissolved, A-68 released billions of tons of freshwater into the ocean, significantly altering the surrounding marine habitat. The iceberg created conditions that scientists say supported diverse ecosystems, functioning as a temporary sanctuary for various species.

Nutrient levels in the surrounding waters rose, drawing in ice-associated algae, which created temporary micro-ecosystems teeming with life. Zooplankton flocked to feed on the algae, and Tarling speculated larger animals like baleen whales would likely have followed.

“You have this sort of halo effect,” he said, as algae bloomed around the iceberg fragments.

"Everything was happening so fast it just completely changed the whole dynamic of that," Tarling added. “What was happening is that huge dumps of water were coming in.” The weight of the freshwater pushed down the underlying layers, causing conditions that would typically exist at 164 feet to occur at depths of 328 feet instead.

Any food particles drifting in the water were also forced downward. “This deepening of the water masses is creating an effect that we've never seen before, taking all this particulate material down with it,” he said.

This phenomenon may have actually increased the amount of carbon buried at the bottom of the Southern Ocean. Typically, organic material descends slowly through the water, with some being consumed, so only a small portion reaches the seabed to be trapped there. However, the immense weight of the freshwater from A-68a as it melted might have accelerated the descent of carbon-based material to depths where it is less likely to be consumed.

“No one's ever reported this,” Tarling said. This suggests that large icebergs like A-68 could play a role in driving carbon deep into the ocean, potentially reducing greenhouse gas concentrations in the atmosphere.

During its journey after breaking away from the Antarctic ice shelf, A-68 shed a staggering 802 billion tonnes of ice. Between late 2020 and early 2021, it released around 152 billion tonnes of freshwater into the ocean — equivalent to nearly 61 million Olympic-sized swimming pools.