Iceberg-Induced Collapse of Access Connectivity and a Dramatic Reduction in Chick Survival at the Coulman Island Emperor Penguin Colony

Rapid environmental change in Antarctica highlights that emperor penguin populations are vulnerable not only to regional sea-ice decline but also to localized physical disturbances that disrupt breeding colony access. This study examines a ~ 69% decline in springtime chick counts at Coulman Island in 2025, based on integrated multi-satellite analyses and field surveys. A giant iceberg calved from the Nansen Ice Shelf became grounded in late July along a narrow coastal margin, obstructing the colony's primary access corridor prior to chick rearing. Three-dimensional iceberg reconstruction reveals pronounced morphological asymmetry functioning as a "geometric trap": gentler ocean-facing slopes encouraged adults to ascend, while the colony-facing margin presented a sub-vertical escarpment exceeding 20 m, funneling penguins into impassable culs-de-sac. The semi-enclosed geography of Coulman Island further obscured a residual ~ 1 km passage, preventing effective detours. Very-high-resolution imagery and field observations confirmed near-total absence of guano staining and extensive chick mortality. These findings provide compelling evidence for a "functional collapse of accessibility," wherein iceberg morphology and regional topography synergistically severed the colony's energetic connectivity. As climate change increases ice-shelf instability and iceberg discharge, stochastic physical barriers may increasingly rival gradual sea-ice decline in determining emperor penguin breeding outcomes.