Reagan-era megaberg that once dwarfed Rhode Island is now rapidly breaking up — Iceberg A-23A disintegrating in the South Atlantic
Iceberg A-23A, a Reagan-era megaberg that calved from the Filchner–Ronne Ice Shelf in 1986, is rapidly disintegrating in the South Atlantic after drifting into warmer waters and shedding large fragments, with blue meltwater ponds signaling imminent breakup.
Key takeaways
- Origin and age: A-23A calved from the Filchner–Ronne Ice Shelf in 1986 and remained grounded for decades before floating free around 2020.
- Size then and now: The berg measured about 4,000 km² at calving — almost twice Rhode Island — and the U.S. National Ice Center estimated the main remnant at ~1,182 km² in early January 2026 (NASA).
- Visible breakup: Striking bright-blue meltwater ponds, long fractures and rampart–moat edges show surface melt is forcing cracks open and accelerating fragmentation (NASA).
- Scientific value: Researchers are studying seafloor interactions, Taylor-column trapping, and ecological effects as the berg disintegrates (British Antarctic Survey; JAXA).
Key information
Name and type: A-23A is a large tabular iceberg that calved from the Filchner–Ronne Ice Shelf in 1986 (NASA; Wikipedia).
A long life, then a drift
A-23A calved in 1986 — the same year Ronald Reagan was U.S. president and Top Gun premiered — and spent more than 30 years grounded on the Weddell Sea seabed. Scientists treated the berg like a slow-moving island while observing interactions with currents and the seafloor (NASA; British Antarctic Survey).
Around 2020, A-23A finally floated free and began a long drift. It moved northwest, encountered the Antarctic Circumpolar Current, and later became caught in a Taylor column — a rotating water mass over a seamount — which made it spin slowly near the South Orkney Islands. That rare behavior gave researchers an unusual opportunity to study megaberg–seafloor interactions (BAS; JAXA).
Approach to South Georgia and the South Atlantic
By early 2025 A-23A was heading north toward South Georgia. Satellite tracking showed it entering shallower continental-shelf waters where grounding was possible because the berg’s thickness matched local shelf depth. A near-collision and brief lodging near South Georgia were followed by escape into warmer South Atlantic waters, where breakup accelerated (JAXA; NASA).
From megaberg to fragments: size changes
Initial satellite estimates after breakup put A-23A at roughly 4,000 km² — nearly twice the size of Rhode Island. Over years of drift it lost mass slowly, then suffered faster calving in mid- to late-2025, with several large pieces reported in July–September 2025. By early January 2026 the U.S. National Ice Center placed the main remnant at about 1,182 km² (456 mi²), leaving A-23A still larger than New York City and among the world’s biggest icebergs (NASA; JAXA; Wikipedia).
Visible disintegration: meltwater ponds and fractures
Recent satellite images and an astronaut photograph show A-23A dotted with bright blue meltwater ponds. These pools make sections of the ice appear vividly blue and indicate surface melt soaking into structural cracks. Scientists warn the weight of ponded water forces cracks open, speeding breakup. Long striations left from when the ice was part of the shelf now channel meltwater and influence where fractures widen (NASA).
“Rampart–moat” patterns and zones of “blue-mush” mark active disintegration — the combination of surface melt and structural fracture is driving the berg toward complete breakup.
Why scientists are watching
For polar researchers, A-23A represents a rare, decades-long natural experiment: a 40-year life, long grounding, escape and breakup that reveal how megabergs interact with topography and circulation. Key study areas include:
- Interactions with seafloor topography and local currents (BAS).
- Trapping and steering by ocean currents and Taylor columns (JAXA).
- How melt ponds and water-filled cracks accelerate breakup in warmer seas (NASA).
There are ecological questions too: a long-grounded berg near South Georgia could block penguin and seal access to feeding grounds, and meltwater plus deposited sediment can release nutrients that fertilize waters and alter krill and fish dynamics, with complex effects up the food chain (BAS; JAXA).
Tracking and monitoring partners
A-23A has been followed by many agencies for decades. NASA used MODIS imagery and astronaut photos to document surface melt and fractures. The U.S. National Ice Center supplied early-2026 area estimates (reported via NASA). JAXA tracked structural changes and edge collapse via radar satellites, while EUMETSAT, NOAA/NESDIS and others compiled long-term imagery and operational tracking (Wikipedia overview).
Implications for United States
Economic and trade signals: Although A-23A and its fragments are far from U.S. waters, drifting ice poses hazard to ships in the South Atlantic and to vessels serving fisheries and research in southern oceans. U.S. commercial and scientific vessels monitor such hazards via international warnings and satellite data (NOAA/NESDIS).
Fisheries and food chains: Nutrient-rich meltwater from A-23A could alter krill and fish near South Georgia, with possible ripple effects on global seafood markets and supply chains serving American consumers and processors (BAS).
Scientific and strategic interests: U.S. satellites and research programs benefit from such events, improving forecasts of sea-ice behavior, shipping risk assessments, and ocean-circulation knowledge that affects weather and commerce (NASA; NOAA/NESDIS).
Sea-level context: The melting of a single floating iceberg like A-23A has no direct effect on global sea level beyond negligible local amounts; the event is important for research and ecosystems rather than a direct driver of sea-level rise (NASA).
Public safety and awareness: The A-23A story highlights how international monitoring by agencies such as NOAA/NESDIS, NASA, JAXA and EUMETSAT helps mariners and industry plan around hazards.
Sources and further reading
- NASA Earth Observatory: “Meltwater turns iceberg A-23A blue”
- Wikipedia: A23a overview
- British Antarctic Survey: “World’s largest iceberg A23A breaks free”
- JAXA Earthview: A-23A tracking and analyses
- EUMETSAT case study: “Iceberg A23-A through the decades”
- NOAA/NESDIS: GOES-East tracking of A-23A
Scientists will continue to monitor Iceberg A-23A, track its meltwater ponds and fractures, and watch how what was once the world’s largest megaberg changes the ocean and life around it.
