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

Perchlorate (ClO₄⁻) in polar ice preserves past chlorine oxidation chemistry; however, multi-centennial Antarctic ClO₄⁻ records and the mechanisms controlling their variability remain poorly constrained. Here, we present the first 400-year (1616−2016) ClO₄⁻ record from an Antarctic ice core, revealing two regimes separated around 1980. Before 1980, ClO₄⁻ variability is primarily controlled by natural drivers. Annual ClO₄⁻ deposition fluxes covary with sunspot group number, suggesting UV-driven modulation of stratospheric chlorine activation. And elevated ClO₄⁻ levels follow stratospheric volcanic eruptions, likely reflecting enhanced heterogeneous chlorine activation on stratospheric sulfate aerosols. After 1980, annual ClO₄⁻ 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 ClO₄⁻ production since 1980. These results highlight ClO₄⁻ as a proxy for reconstructing stratospheric chlorine chemistry and Antarctic ozone depletion.