A 400‐Year Antarctic Ice‐Core Perchlorate Record Reveals Variability in Stratospheric Chlorine Chemistry

Abstract Perchlorate (ClO 4 − ) in polar ice preserves past chlorine oxidation chemistry; however, multi‐centennial Antarctic ClO 4 − records and the mechanisms controlling their variability remain poorly constrained. Here, we present the first 400‐year (1616−2016) ClO 4 − record from an Antarctic ice core, revealing two regimes separated around 1980. Before 1980, ClO 4 − variability is primarily controlled by natural drivers. Annual ClO 4 − deposition fluxes covary with sunspot group number, suggesting UV‐driven modulation of stratospheric chlorine activation. And elevated ClO 4 − levels follow stratospheric volcanic eruptions, likely reflecting enhanced heterogeneous chlorine activation on stratospheric sulfate aerosols. After 1980, annual ClO 4 − fluxes increase from 2.4 ± 3.2 g km −2 yr −1 to 5.5 ± 3.2 g km −2 yr −1 and become negatively correlated with Antarctic ozone. This increase coincides with rising anthropogenic chlorine emissions, indicating that anthropogenic chlorine has dominated Antarctic ClO 4 − production since 1980. These results highlight ClO 4 − as a proxy for reconstructing stratospheric chlorine chemistry and Antarctic ozone depletion.