Climate sensitivity of the century‐scale hydrogen peroxide (H2O2) record preserved in 23 ice cores from West Antarctica

Abstract

We report new century‐scale ice core records of hydrogen peroxide (H2O2), a major atmospheric oxidant, from 23 locations across the West Antarctic Ice Sheet (WAIS) and use the spatial variability of (multi‐) annual mean H2O2 concentrations in snow and firn to investigate the sensitivity of ice core H2O2 preservation to mean annual temperature and accumulation rate. In agreement with the ice‐air equilibrium partitioning, H2O2 uptake in near‐surface firn was found to be greatest at low temperatures, while postdepositional losses from degassing increase as accumulation rates decrease. This resulted in almost complete loss of H2O2 at warm (>−25°C), low‐accumulation sites (<13 cm yr−1), but excellent preservation of records at cold, high‐accumulation sites. A two‐parameter semiempirical model fitted to the 1911–1960 H2O2 means across all sites predicts >94% deviations from the ice‐air equilibrium at high‐accumulation sites (>30 cm yr−1), but close‐to‐equilibrium values on the East Antarctic Plateau, where it is dry (<11 cm yr−1). It also estimates a weighted average of the annual atmospheric H2O2 cycle of 1–3 pptv, about 10% of the levels at the bottom of the H2O2 range observed in winter and early spring in coastal Antarctica. Sensitivities from the model fit suggest that recent changes of annual mean temperature observed in Antarctica have no noticeable effect on the H2O2 record in the interior of West Antarctica and that interannual variability of annual H2O2 is dominated by variations in regional‐scale accumulation under the current WAIS climate. Intermittent correlations between the first PC time series of accumulation rate and H2O2 concentration anomalies and the annualized SOI during the 20th century are statistically significant (r > 0.6, p < 0.05) during extended El Niño–La Niña events and explain the occurrence of significant spectral peaks at ENSO‐like periodicities (2–7 years) in the H2O2 record. Core records of H2O2 at high‐accumulation sites (>30 cm yr−1) are most suitable for detection of temporal changes in atmospheric concentration, although a long‐term H2O2 record will be well preserved under the current environment at the WAIS Divide core site.