Volcanic Eruption Signatures in the Isotope‐Enabled Last Millennium Ensemble

Explosive volcanic eruptions are one of the largest natural climate perturbations, but few observational constraints exist on either the climate responses to eruptions or the properties (size, hemispheric aerosol distribution, etc.) of the eruptions themselves. Paleoclimate records are thus important sources of information on past eruptions, often through the measurement of oxygen isotopic ratios ( δ 18 O) in natural archives. However, since many processes affect δ 18 O, the dynamical interpretation of these records can be quite complex. Here we present results from new, isotope‐enabled members of the Community Earth System Model Last Millennium Ensemble, documenting eruption‐induced δ 18 O variations throughout the climate system. Eruptions create significant perturbations in the δ 18 O of precipitation and soil moisture in central/eastern North America, via excitation of the Atlantic Multidecadal Oscillation. Monsoon Asia and Australia also exhibit strong precipitation and soil δ 18 O anomalies; in these cases, δ 18 O may reflect changes to El Niño‐Southern Oscillation phase following eruptions. Salinity and seawater δ 18 O patterns demonstrate the importance of both local hydrologic shifts and the phasing of the El Niño‐Southern Oscillation response, both along the equator and in the subtropics. In all cases, the responses are highly sensitive to eruption latitude, which points to the utility of isotopic records in constraining aerosol distribution patterns associated with past eruptions. This is most effective using precipitation δ 18 O; all Southern eruptions and the majority (66%) of Northern eruptions can be correctly identified. This work thus serves as a starting point for new, quantitative uses of isotopic records for understanding volcanic impacts on climate.