Here’s what happened to the Delaware-sized iceberg that broke off Antarctica

Scientists have identified a previously unknown mechanism for large berg breakups

Iceberg A68a (shown in July 2020) was the largest remnant of a Delaware-sized chunk of ice that split off from Antarctica in 2017.

Copernicus Sentinel-1/ESA (CC BY-SA 3.0 IGO)

By Carolyn Gramling

October 26, 2022 at 7:00 am

It was the rift watched ‘round the world.

In July 2017, after weeks of anticipation, a massive iceberg about the size of Delaware split from the Antarctic Peninsula (SN: 7/12/17). Satellite images show that the orphaned iceberg, known as A68, ultimately disintegrated in the Southern Ocean. Now, researchers say they have pieced together the powerful forces that led to that final breakup.

Polar scientist Alex Huth of Princeton University and colleagues combined observations of the iceberg’s drift with simulations of ocean currents and wind stress. Iceberg A68a, the largest remaining chunk of the original berg, was caught in a tug-of-war of ocean currents, and the strain of those opposing forces probably pulled the iceberg apart, the team reports October 19 in Science Advances.

After A68’s separation from the Larsen C ice shelf, researchers had questions — such as what creatures live on the seafloor in the ice’s dark shadow (SN: 2/8/19). As for the iceberg itself, it took a while to get moving, lingering in the neighborhood for about a year (SN: 7/23/18). By December 2020, satellite images show, the berg had clearly seen some action and was just two-thirds of its original size.

Three photos of Iceberg A68a, the first on December 19 with the large "finger" section still attached to the main body. In the center image from December 21, two cracks from a "T" shape along the bottom third of the iceberg. The final image from December 22 shows the "finger" section breaking away from the main iceberg in several sections. — On December 19, 2020, a European Space Agency satellite spotted iceberg A68a with its slender “finger” still intact in the Southern Ocean. Two days later, the berg was crisscrossed with rifts, now thought to be the result of strain due to ocean currents. By the next day, the iceberg had fractured into smaller pieces that eventually disintegrated. A. Huth *et al*/*Science Advances* 2022On December 19, 2020, a European Space Agency satellite spotted iceberg A68a with its slender “finger” still intact in the Southern Ocean. Two days later, the berg was crisscrossed with rifts, now thought to be the result of strain due to ocean currents. By the next day, the iceberg had fractured into smaller pieces that eventually disintegrated. A. Huth *et al*/*Science Advances* 2022

The new simulations suggest how A68a probably met its fate. On December 20, 2020, the long, slender “finger” at one end of the iceberg drifted into a strong, fast-moving current. The rest of the ice remained outside the current. The tension rifted the berg, and the finger sheared off and broke apart within a few days.

Shear stress is a previously unknown mechanism for large iceberg breakup, and isn’t represented in climate simulations, the team says. In the Southern Ocean, the melting of massive bergs can be a large source of cold freshwater to the ocean surface. That, in turn, can have a big impact on ocean circulation and the global climate.