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.