New Chicago-sized iceberg breaks off Antarctica

The new iceberg A-84 spent part of the 2024-2025 austral summer in the southern hemisphere bouncing off parts of the Antarctic coast. It measures 30 kilometers long by 17 kilometers wide, the size of the city of Chicago.

Over the past month, the potato-shaped iceberg has drifted about 250 kilometers (155 miles) from its point of origin near the southern end of the George VI Ice Shelf along the base of the Antarctic Peninsula.

The iceberg's journey is shown in an animation released by NASA Earth Observatory, using satellite images acquired between January 15 and February 15, 2025. The images come from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments on NASA's Terra and Aqua satellites, and the Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite.

In late 2024, a crack was observed in the remnant of the George VI Ice Shelf, but the future iceberg was still surrounded by sea ice at the Ronne Entrance, the bay that borders the southern end of the ice shelf. The George VI Shelf is unusual in that it has an ice front to both the north and south. By January 2025, much of the seasonal sea ice had melted and ocean currents carried the new iceberg along.

"It's amazing how fast it moved in the longshore current," Christopher Shuman, a retired glaciologist at the University of Maryland, said in a statement. "It makes you wonder what's going on in the water beneath the ice shelf."

Iceberg calving is a normal occurrence on ice shelves. However, warming air and water, along with the decline of protective sea ice, can accelerate the process and lead to collapse, as has happened with several shelves along the Antarctic Peninsula.

Observations by explorers in the 1940s and later by remote sensing show that George VI has lost shelf ice. For now, the retreat has been gradual, helped by the stability provided by its unique location between the Antarctic Peninsula and Alexander Island.

The A-84 iceberg is one of the most recent to break off in Antarctica, a phenomenon that has become increasingly frequent due to climate change. The George VI Ice Shelf, where it originated, is one of the largest on the Antarctic Peninsula , stretching for approximately 24,000 km². Its stability is due in part to the fact that it is contained between two land masses, but studies have shown that the shelf has thinned in recent decades, which could make it more vulnerable to future fractures.

The movement of iceberg A-84 is consistent with the behaviour of other icebergs that break off from Antarctic shelves and are carried by the Antarctic Circumpolar Current. Its speed of movement depends on factors such as wind, ocean currents and interaction with other ice blocks. By comparison, the famous iceberg A-68, which broke off from the Larsen C shelf in 2017, travelled more than 1,500 km in its first year adrift.

Ocean warming is a key factor in accelerating these processes. Data from the Southern Ocean Climate Observation Program have shown rising temperatures in the deep waters surrounding Antarctica, contributing to the melting of ice shelves from below, weakening them and facilitating the formation of cracks like the one that gave rise to A-84.