Reagan‑era iceberg A‑23A — once nearly twice the size of Rhode Island — is now breaking apart in the South Atlantic
Iceberg A‑23A, calved from the Filchner‑Ronne Ice Shelf in 1986, is rapidly disintegrating in the South Atlantic. Once the world’s largest, its fragmentation and blue meltwater ponds are under study for ecological and oceanographic impacts.
Key takeaways
- A‑23A formed in 1986 from the Filchner‑Ronne Ice Shelf and was about 4,000 km² at birth — nearly twice the area of Rhode Island (NASA Earth Observatory; Wikipedia: A23a).
- After decades grounded in the Weddell Sea, it escaped around 2020 and drifted north, later stalling in a Taylor column before moving toward South Georgia (British Antarctic Survey).
- Now rapidly breaking up: as of Jan. 9, 2026 the main block was ~1,182 km² (456 sq mi) and showing extensive blue meltwater ponds and structural failure signs (U.S. National Ice Center; NASA Earth Observatory).
- Scientific and navigational stakes: researchers are studying meltwater, blowouts and ecosystem impacts, while fragmented pieces pose shipping hazards in the South Atlantic (NOAA/NESDIS).
Origin and long grounding
A‑23A is a tabular iceberg that calved from the Filchner‑Ronne Ice Shelf in 1986. At birth it covered roughly 4,000 square kilometers — nearly twice the area of Rhode Island (NASA Earth Observatory; Wikipedia: A23a).
Shortly after calving the berg grounded on the seabed in the Weddell Sea and remained stuck for more than three decades, behaving like a semi‑permanent feature. During that time ocean water slowly eroded its base and thinned the ice from below, weakening the berg over years (British Antarctic Survey).
Escape, trapping and renewed drift
Around 2020 the iceberg thinned enough to free itself from the seafloor and began moving. In 2023 it drifted north, rounded the Antarctic Peninsula, and entered the Antarctic Circumpolar Current. By late 2023 it was tracked as the largest iceberg in the world by area (NOAA/NESDIS; Wikipedia: A23a).
In early 2024 A‑23A became trapped in a Taylor column near the South Orkney Islands, spinning about 15° per day while largely staying over the same spot. That unusual stall delayed northward progress (British Antarctic Survey).
By late 2024 the berg escaped the Taylor column and resumed northward drift toward South Georgia, attracting attention for potential ecological impacts if it grounded near the island.
Grounding, sampling and risk to ecosystems
As A‑23A approached South Georgia, scientists feared a megaberg could alter currents, scour seafloor habitats and block predator access to feeding grounds. That prompted targeted sampling: in December 2023 the RRS Sir David Attenborough collected water and biogeochemical samples to measure changes in nutrients, freshwater inputs, and plankton communities (British Antarctic Survey).
Grounding impacts: icebergs can damage benthic habitats by scouring the seabed and alter krill distribution and local circulation, with downstream effects on penguins, seals and other predators.
Breakup, fragmentation and blue meltwater ponds
After moving north of South Georgia into warmer waters, A‑23A began fragmenting rapidly through 2025. Large chunks calved off, creating many hazardous smaller icebergs; satellite analyses documented separated chunks as large as 400 km² in 2025 (Wikipedia: A23a).
NASA imagery in late December 2025 revealed the remaining mass covered in extensive blue meltwater ponds and linear blue‑white bands — signatures of advanced surface melting and structural channeling of water. Rampart‑moat patterns and long glacial striations on the berg guided meltwater into elongated ponds and streams, concentrating surface melt. These features, plus observed “blowouts” where pond water forces cracks open, indicate the berg is structurally failing (NASA Earth Observatory).
“Blowouts and widespread ponding point to advanced structural weakening and make catastrophic breakup more likely.” — NASA Earth Observatory reporting.
Current status and measurements
The U.S. National Ice Center reported that on Jan. 9, 2026 the main A‑23A block measured about 26 by 22 nautical miles, with an area near 301.77 nautical miles² — roughly 1,182 km² (456 sq mi). The berg’s position in early January 2026 was in the South Atlantic, between South America and South Georgia, near 52°59′ S, 40°53′ W.
Glaciologists cited by NASA emphasize that regional sea temperatures around 3 °C, combined with extensive surface ponds, blowouts and edge erosion, place A‑23A in its final coherent phase. Scientist Chris Shuman predicted the berg likely would not survive the austral summer, expecting breakup within days to weeks of the December imagery; oceanographer Walt Meier noted the berg is moving into even warmer zones that will accelerate melt (NASA Earth Observatory).
Why A‑23A matters to science and shipping
A‑23A is a rare, decades‑long natural experiment. Its extended grounding and late escape provide insight into iceberg‑current interactions, seamount trapping (Taylor columns), and ecological consequences of megaberg meltwater. Sampling campaigns examined how meltwater changed nutrient levels and plankton downstream (British Antarctic Survey; NASA Earth Observatory).
For shipping, the shedding of large fragments creates a dispersed hazard field across the South Atlantic, complicating routing and increasing risk to vessels — a concern highlighted in tracking by NOAA/NESDIS and iceberg products from the U.S. National Ice Center.
Implications for San Diego, California
Economic and scientific ties: San Diego’s oceanographic institutions and universities can use A‑23A data to refine models of circulation, nutrient transport and iceberg‑ocean interactions, creating collaboration opportunities with polar-monitoring groups (NASA Earth Observatory; British Antarctic Survey).
Fisheries and markets: Southern Ocean productivity affects global carbon uptake and fisheries; shifts there can ripple through seafood markets and management concerns relevant to San Diego’s fishing industry.
Maritime safety: although fragments will not reach the North Pacific, lessons about dispersed iceberg hazards can inform long‑range ship routing, satellite monitoring and international coordination — areas of interest for San Diego ports and naval operations (NOAA/NESDIS).
Public awareness and education: dramatic imagery and the berg’s long life form a vivid teaching moment for schools, museums and media to explain polar processes, ocean warming and distant connections to local science.
Research funding and policy: data from A‑23A’s breakup underline the value of sustained satellite monitoring, ship campaigns and international data sharing — priorities local policymakers and funders may choose to support (NOAA/NESDIS; British Antarctic Survey).
Other giant icebergs and outlook
Other large bergs such as A‑81, B22A and D15A remain around Antarctica; the Southern Ocean may see repeated events of large bergs drifting, grounding and fragmenting in coming years. Continued satellite and shipborne monitoring will track these events and their ecological, climatic and navigational consequences (NASA Earth Observatory).
