239Pu concentrations reconstructed using three Antarctic ice cores during 1940-1980 CE

The radioisotope Plutonium-239 (²³⁹Pu) was artificially produced to the environment by atmospheric nuclear weapons tests during 1940-1980 CE. Although ²³⁹Pu is the most abundant one among isotopes of Plutonium, it exists in Antarctic ice cores at very low level of sub-fg g^-1. Accordingly, the historical records of ²³⁹Pu fallout in Antarctica have not been well reconstructed. In this study, we determined ²³⁹Pu concentrations in three coastal ice cores in Northern Victoria Land, East Antarctica. Discrete samples with sub-annual resolution for the period 1940-1980 CE were analyzed using inductively coupled plasma sector field mass spectrometry (ICP-SFMS) without purification or preconcentration. The fallout records of the three sites showed consistent fluctuations and also agreed with the records recovered from inland dome sites (Hwang et al., 2019), which allowed for constructing an Antarctic composite record. The composite ²³⁹Pu record was characterized by two major peaks in 1954 and 1964 CE and a minor peak in 1970s, which could be ascribed to the major atmospheric nuclear test events. Those synchronous ²³⁹Pu peaks are expected to serve as useful age markers in other regions in Antarctica, which can improve depth-age relationships of ice core records and enable more precise interregional comparisons. In addition, it will contribute to a more precise comparison of ice core records with reanalysis data back to the 1950s (e.g., ERA5).