Model Interpretation of the Long-Term Variability of Ice-core Perchlorate

Ice-core perchlorate likely preserves unique information about chlorine chemistry in the past stratosphere, but a holistic assessment of the long-term variability of perchlorate in multiple ice cores is still lacking. We analyze published ice-core perchlorate records and find that perchlorate concentrations have no consistent correlation with concentrations of other major ions across all records and time periods. This is consistent with a primarily stratospheric origin of perchlorate. We show that ice-core perchlorate does not have a strong relationship with volcanic eruptions either, with the exception of a few events seen in the Summit, Greenland ice-core record which had a clear stratospheric influence. Comparison of satellite observations of stratospheric ozone with perchlorate ice-core records suggests that stratospheric chlorine is important for explaining the perchlorate trends. We conduct global model simulations to quantify the contribution from anthropogenic production of chlorofluorocarbons in the 20th century and natural emissions of methyl chloride to the trends and variability of ice-core perchlorate. Our results facilitate the interpretation of ice-core perchlorate records and improve our understanding of the global atmospheric chlorine cycle in the past.