Giant A-68 iceberg dumped 152 billion tonnes of freshwater into the sea
The four-year saga of iceberg A-68 may be over, but its environmental impacts are still being assessed. A new study has calculated that the largest chunk, A-68A, released billions of tonnes of freshwater into the sea right near a marine nature reserve, which could have untold effects on the ecosystem.
In July 2017, A-68 broke off from the Larsen C ice shelf in Antarctica. Measuring 5,664 km2 (2,187 miles2), it was one of the largest icebergs ever recorded, and for about two years it floated around in the cold waters of the Weddell Sea, sticking close to the ice shelf. By early 2020 it had started drifting north into the open waters of the Drake Passage.
Later that year a large chunk designated A-68A was found to be on a collision course with the island of South Georgia, an important conservation site. The fear was that the iceberg would become lodged on the shallow seabed and potentially stay there for up to a decade, disrupting the feeding and breeding habits of the seals and penguins that call the island home.
Thankfully, the berg drifted away from South Georgia and broke into smaller pieces, and by April 2021 the fragments had become too small to track. But its very presence might still have had an effect on the region – specifically, how much freshwater A-68A released into the ocean as it melted.
To investigate, a new study used data from five different satellite missions to chart the changes in the iceberg’s area and thickness over time. The team calculated the changing area of the iceberg using optical imagery from the Copernicus Sentinel-3 and the Terra missions, and radar from Sentinel-1.
The CryoSat and ICESat-2 missions were able to measure the iceberg’s freeboard, which is its height above the sea surface. From this figure, the icebergs’s thickness can be determined, and, when combined with the area measurements, its entire volume can be calculated.
The team found that by the time A-68A reached the shallow waters around South Georgia, it only extended 141 m (463 ft) below the surface, narrowly avoiding getting lodged on the seabed which is around 150 m (492 ft) deep.
The researchers also estimated that A-68A released around 152 billion tonnes of freshwater into the sea near South Georgia. This can influence ocean circulation, the occurrence of plankton and the feeding habits of other animals in the area, but the team can’t be sure entirely what these effects may be like.
“This is a huge amount of meltwater, and the next thing we want to learn is whether it had a positive or negative impact on the ecosystem around South Georgia,” said Anne Braakmann-Folgmann, lead author of the study. “Because A-68A took a common route across the Drake Passage, we hope to learn more about icebergs taking a similar trajectory, and how they influence the polar oceans.”
The research was published in the journal Remote Sensing of Environment.