Physical and glaciochemical signals of the ~25.3 ka Ōruanui supereruption in ice cores across Antarctica

Abstract. Supereruptions are the largest-scale explosive volcanic events, injecting large amounts of sulfate, halogens, and ash into the stratosphere, yet their resulting impacts on global climate and environment remain uncertain. Polar ice cores can preserve glaciochemical anomalies and volcanic glasses from past eruptions, providing high-resolution records of their timing, source, and potential impacts on the climate and environment. We examined nine Antarctic ice cores to evaluate the variability in preservation of glaciochemical signatures from the youngest known supereruption, the ~25.3 ka Ōruanui event, from Taupō volcano, New Zealand. We identified glaciochemical anomalies related to the eruption in six of these cores, and fingerprinted Ōruanui volcanic glass shard populations in three cores: West Antarctic Ice Sheet Divide (WDC06A), EPICA Dronning Maud Land (EDML) and Dome Fuji 2 (DF2). Shard sizes and abundances vary between sites, which we attribute to spatially heterogeneous dispersal of the volcanic plume due to varying transport and settling processes in the atmosphere, supported by model simulations of ash deposition across the Southern Hemisphere (SH). Glaciochemical signals also vary substantially between cores and are best explained by broadly uniform stratospheric sulfate transport followed by heterogeneous tropospheric deposition pathways, and varying site-specific post-depositional processes. We use ice core sulfate concentrations to refine estimates of sulfate deposition over Antarctica to ~270 kg km^-2, estimate a stratospheric sulfur injection of ~114 ± 33 Tg S, and estimate a maximum monthly global radiative forcing from the Ōruanui event of -8.6 W m^-2, suggesting that there were severe short-term global climatic impacts. Coupled chemistry climate model simulations (CESM2/WACCM6), constrained by stratospheric sulfur and variable halogen injection scenarios, indicate global average cooling of up to 3 K and stratospheric increases of aerosol optical depth (AOD) lasting 4–5 years, with ozone impacts potentially lasting beyond 5 years. However, consistent with other recent supereruption impact studies, our results suggest that the eruption likely did not trigger decadal-centennial scale climate shifts.