A massive iceberg has triggered a catastrophic die-off of Emperor Penguin chicks in Antarctica, blocking thousands of parents from reaching their young. The event claimed the lives of approximately 14,000 chicks at the Coulman Island colony in the Ross Sea, the region’s largest breeding ground.
According to a research team led by Dr. Jeong-hoon Kim of the Korea Polar Research Institute (KOPRI), survival rates at the colony plummeted by 70 percent. Satellite analysis and drone surveys reveal that the population of new chicks fell from roughly 21,000 last year to just 6,700 this season.
A geographical trap
The primary cause of this event was an iceberg, spanning nearly 14 kilometers. Field observations by KOPRI researchers Jong-U Kim and Youmin Kim confirmed that the ice had obstructed the critical gateway connecting the breeding ground to the open ocean.
Satellite analysis indicates the iceberg calved from the Nansen Ice Shelf in March 2025. It drifted northward before grounding against Coulman Island. By late July, this blockage had effectively cut off the penguins’ migration route.
The obstruction occurred at a critical phase in the breeding cycle. Under normal conditions, females depart to forage at sea after laying their eggs in June, leaving males to incubate the clutch. The survival of the hatchlings relies on the mothers returning 70 to 80 days later to deliver the first meal.
This year, however, returning females were intercepted by an ice mass roughly the size of 5,000 soccer fields. The iceberg formed a deceptive trap. while its seaward face offered a gentle slope that allowed the penguins to ascend with ease, the side facing the inland colony dropped off into a sheer vertical cliff. Upon reaching the crest, the mothers found themselves stranded, unable to descend to the breeding ground below.
“The iceberg’s seaward approach has a gentle gradient, making it accessible, but the edge facing the breeding ground forms a precipitous cliff,” Dr. Kim explained. “Mothers following their usual route over the sea ice were suddenly confronted by this insurmountable barrier.”
Drone imagery captured a scene of desperate frustration. Hundreds of adult penguins were massed at the base of the ice cliff, pacing nervously as the topography barred them from the colony. The surrounding ice was heavily scarred with guano, evidence that the birds had been stranded there for a prolonged period.
For the males waiting above, the blockade was catastrophic. Having already fasted for more than 70 days to incubate their young, they were pushed to their physiological breaking point.
”Males must survive to ensure future breeding opportunities,” Dr. Kim explains, outlining the brutal calculus of nature. ”It is highly likely they were eventually compelled to abandon the chicks and retreat to the ocean, unable to endure the starvation any longer.”
Researchers estimate that the surviving 30 percent of chicks were fed by mothers who managed to find alternative routes around the blockage. ”If the iceberg clears before the next breeding season, there is potential for recovery,” Dr. Kim said. ”But if the blockage persists, we may see long-term impacts, including the forced relocation of the entire colony.”
Penguins pushed to the brink
The Ross Sea serves as a vital sanctuary for Emperor Penguins. Whereas areas like the Antarctic Peninsula have struggled with early ice breakup and chick fatalities, the Ross Sea has remained comparatively stable. Sheltered deep within the continent, it benefits from robust sea ice and protection from rapid temperature shifts.
However, the arrival of this iceberg introduces a volatile new threat to their survival. The incident was an anomaly. After calving from the Nansen Ice Shelf, the iceberg collided with drift ice near Coulman Island, a crash that diverted its path and sealed off the colony’s entrance. KOPRI researchers warn that this is not an isolated event but a harbinger of things to come. As global warming accelerates, frequent iceberg calving increases the risk that such blockades will occur again.
Icebergs of similar magnitude are still frequently observed in the region, traveling along drift paths that intersect with other Emperor Penguin habitats. While icebergs from the Nansen Ice Shelf typically follow established routes, analysis suggests this specific iceberg veered off course after striking underwater terrain or other ice masses—a deviation that led it straight to the colony.
The team also noted that 14km iceberg also skirted Cape Washington, another major breeding ground. Researchers warn that if a future iceberg were to collide with this site and block its migration corridor, it could trigger another mass mortality event.
Dr. Jin-ku Park, who analyzed the satellite data, expressed concern about the wider implications. “The trajectories of icebergs calving from the Nansen Ice Shelf frequently traverse other major habitats,” he said. “This indicates that the disintegration of ice shelves poses a latent but potent threat to Emperor Penguins and other Antarctic wildlife.”
KOPRI plans to submit these findings to international bodies next year, including the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). Although discussions to designate the Emperor Penguin as a ’Specially Protected Species(SPS)’ are ongoing, progress has been blocked by objections.
“Objective, scientific evidence is a prerequisite for designating a species as protected,” Dr. Kim emphasized. “The Coulman Island case will serve as critical empirical proof of just how specific and lethal the threats posed by climate change are to the Emperor Penguin.”
Since 2017, KOPRI has monitored the Antarctic ecosystem as part of a Ministry of Oceans and Fisheries initiative focused on the Ross Sea Marine Protected Area. The institute aims to use the data from this incident to refine its remote sensing techniques and accelerate Antarctic conservation efforts.
“This catastrophe underscores the unpredictable dangers climate change poses to the Antarctic ecosystem” said Dr. Hyoung-chul Shin, President of KOPRI “We plan to intensify satellite monitoring and field surveys during the next breeding season and continue investigating the impact of climate change on this fragile environment.”
The story was produced in partnership with our colleagues at Popular Science Korea.
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