Tracking the Demise of One of the World’s Largest-Known Icebergs

The dying throes of A-68A, one of the world's largest known icebergs, were recently documented by researchers.

An iceberg starts to perish as soon as it is born. Waves erode the edges, air thaws it from above, and water melts it from below. One of the world's largest-known icebergs was recently recorded in similar dying throes by scientists.

Iceberg A-68 broke free from the Larsen C Ice Shelf on the Antarctic Peninsula's east coast in July 2017. It was the world's largest iceberg at the time, and the sixth-largest berg in the previous three decades of records. It was almost 5,800 square kilometers (2,200 square miles), roughly the same area as Delaware. A-68, in other terms, stood to lose a lot. The berg broke up and melted over the course of three and a half years, leaving its impact on the maritime environment, particularly near the isolated island of South Georgia.

“Icebergs are a source of cold fresh water and nutrients in the Southern Ocean,” said Anne Braakmann-Folgmann, a doctorate candidate at the University of Leeds. “However, where and how much of this is released is not very well studied and not included in ocean models yet, especially for the largest icebergs.” 

Braakmann-Folgmann and his colleagues set out to track A-68A's progress. (After a few minor parts of the main berg broke off, it was given a new name.) The researchers utilized satellite data to track changes in the iceberg's thickness, area, volume, and mass from the moment it broke free from the ice shelf in July 2017 until January 2021, when it began to rapidly disintegrate.

As it traveled north from the Weddell Sea into the Scotia Sea, the iceberg thinned out as shown in the maps above. The berg's thickness in July 2017, while it was still approaching the Larsen C Ice Shelf, is seen in the first map (left). It's thicker on the left side, where it was linked to the ice shelf, and thinner on the right, when it was exposed to the sea. At the time, it had a total average thickness of 235 meters. As the berg moved north, it came into contact with warmer air and ocean temperatures, hastening its melting. When the berg closed in on South Georgia in January 2021, it had shrunk to an average thickness of 168 meters.

About 85% of an iceberg is below the water's surface, making it difficult to determine its exact thickness. However, scientists can now determine the thickness of the iceberg by monitoring the iceberg's above-water components. The distance between the satellite and the surface of the iceberg and the sea may be determined using data from NASA's Ice, Cloud, and Land Elevation Satellite 2 (ICESat-2) and the European Space Agency's CryoSat-2 (laser and radar altimeters, respectively). The iceberg's "freeboard," or the height of the ice that rises above the sea, is the difference between these measures. By taking into consideration the densities of the iceberg, the snow layer on top, and the surrounding sea water, scientists may translate this height to thickness.

The melting from the iceberg's bottom accounted for 32% of its loss from July 2017 to January 2021, according to the experts. Melting peaked around South Georgia, with experts estimating that 152 billion metric tons (152 billion cubic meters) of fresh water was poured to the ocean over the course of three months, the equivalent of 61 million Olympic swimming pools. The impact of all this fresh water on local ocean characteristics is currently being investigated by scientists. They also want to know if the extra nutrients provided by the melting glacier to the water aided biological production.

Large sections of ice broke away from the berg's flanks, causing further ice losses. This was especially true when A-68A broke free from the sheltering sea ice near Antarctica and traveled north, where it was exposed to the open ocean's devastating waves. As the iceberg moved north, both thinning and fragmentation grew, but fragmentation eventually won out as the iceberg shattered in the Northern Scotia Sea.