Tracing stratospheric transport using subannual plutonium-239 fallout in polar ice cores

Polar ice cores preserve high-resolution archives of historical atmospheric transport, providing unique insights into long-term stratospheric processes. Here, we present the first subannual plutonium-239 (²³⁹Pu) deposition records from Greenland and Antarctic ice cores (1940 to 1980 CE). The limited or delayed fallout from Ivy Mike (1952 CE) compared to Operation Castle (1954 CE), despite their detonation in close proximity, exemplifies how stratospheric circulation and seasonal dynamics create periods of reduced transport to Antarctica. These records also reveal seasonal fallout patterns in Antarctica, with enhanced deposition during austral summers driven by stratosphere-troposphere exchange. Our findings refine current representations of global aerosol dispersion and provide additional constraints for modeling atmospheric processes, particularly those driven by volcanic eruptions and geoengineering interventions.