Iceberg A-23A, identified as one of the world's largest and longest-tracked icebergs, is approaching its complete disintegration in the South Atlantic Ocean. Recent satellite and astronaut imagery from late December 2025 has documented extensive blue meltwater pools on its surface, signaling accelerated melting as it moves into warmer waters. Scientists project that the iceberg, which calved from Antarctica's Filchner-Ronne Ice Sheet in 1986, could fully disintegrate within days or weeks.
Origin and Initial History
Iceberg A-23A detached from Antarctica's Filchner-Ronne Ice Sheet in 1986, initially measuring approximately 4,000 square kilometers. Upon its formation, it hosted a Soviet research station. Following its detachment, the iceberg remained grounded in the shallow waters of the Weddell Sea for over 30 years, with some reports indicating this period as almost 40 years. During this time, striations formed on its underside as it dragged across Antarctic bedrock.
Recent Journey and Fragmentation
A-23A became mobile in 2020, detaching from the seafloor and beginning its northward drift. It subsequently spent several months in an oceanic vortex or gyre. In 2023, the British Antarctic Survey released time-lapse satellite imagery documenting its movement. The iceberg regained the title of the world's largest iceberg in June 2023 and was measured at an estimated area of 3,640 square kilometers in January 2025.
Its journey involved approaching South Georgia island in early 2025, prompting concerns among researchers regarding a potential ecological impact on the island's penguin population. The iceberg did not make direct impact. In March 2025, it became wedged against the seafloor, freeing itself in June 2025. This period also saw the iceberg begin to break apart in May 2025, which contributed to averting a collision with South Georgia.
Throughout 2025, A-23A experienced rapid fragmentation, with significant chunks breaking off in July, August, and September. It lost its title as the world's largest iceberg in September 2025, at which point its area had reduced to approximately 1,700 square kilometers. By early January 2026, its area was estimated at 1,182 square kilometers (456 square miles) by the U.S. National Ice Center, still an area larger than New York City but a fraction of its original size.
Satellite Observations and Scientific Analysis
On December 26, 2025, NASA's Terra satellite captured images of A-23A, revealing extensive pools of blue meltwater on its surface, often described as melt ponds encircled by white ice borders. An astronaut aboard the International Space Station photographed an even more widespread melt pool on December 27, 2025, which some observations suggested indicated a more uniform blue appearance and possibly fading striations.
Scientists, including Ted Scambos from the University of Colorado Boulder, explain that the blue areas of meltwater signal ongoing disintegration. The weight of water accumulated within cracks can force these fissures to open. The distinct linear patterns of blue and white observed across the iceberg are believed to be related to striations formed hundreds of years ago when the ice was part of a glacier. These subtle ridges and valleys now direct the flow of meltwater. Walt Meier, a senior research scientist at the National Snow & Ice Data Center, noted that these cracks likely correspond to grooves on the iceberg's underside formed during its prolonged grounding.
Observations also show a thin white line around the iceberg's outer edge, which appears to contain meltwater, forming a "rampart-moat" pattern. This pattern is attributed to an upward bending of the iceberg plate as its edges melt at the waterline. Chris Shuman, a retired University of Maryland Baltimore County scientist, described a potential "blowout," where pressure from the substantial volume of surface water could create an opening at the iceberg's edges, leading to a "freshwater discharge plume" that allows meltwater to mix with surrounding ice fragments in the ocean. Satellite data also indicated a "leak" where surface water may have penetrated the ice.
Impending Disintegration
A-23A is currently located in the South Atlantic, situated between the eastern tip of South America and South Georgia island, near the Southern Ocean-South Atlantic boundary. Scientists predict its complete disintegration could occur within days or weeks. Chris Shuman stated that A-23A is not expected to persist through the austral summer, a season characterized by clearer skies and warmer air and water temperatures that accelerate the disintegration process. Walt Meier added that the iceberg is in waters approximately 3 degrees Celsius and is being pushed by currents toward even warmer waters, which will expedite its melting in a region known as an iceberg "graveyard."
The iceberg's blue coloration is attributed to rapid melting as it drifts into warmer summer waters. Icebergs exhibit varying colors; while air bubbles can make them appear white, compressed ice with fewer air bubbles appears blue.
Scientists have tracked A-23A closely, noting its extensive and complex journey, which has provided insights into "megabergs" in the Southern Ocean. While A-23A's lifecycle concludes, other large icebergs, including A-81, B22A, and D15A, each exceeding 1,500 square kilometers, are presently situated along the Antarctic shoreline. The current largest iceberg globally is D15A, with a surface area of about 3,100 square kilometers.