Tracing stratospheric transport using sub-annual 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 sub-annual plutonium-239 (239Pu) deposition records from Greenland and Antarctic ice cores (1940–1980 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 the understanding of global aerosol dispersion and offer additional insight for modeling atmospheric processes, including those related to volcanic eruptions and geoengineering.