Evidence from sulfate mass independent oxygen isotopic compositions of dramatic changes in atmospheric oxidation following massive volcanic eruptions

Oxygen isotopic ratio measurements (δ 17 O and δ 18 O) of background and volcanic sulfate preserved in South Pole snow and ice were used to investigate the impact on the oxidation state of the atmosphere by explosive volcanic eruptions. By comparing different paleovolcanic events, we observe a difference in the SO 2 oxidation pathway between moderate (tens of teragrams (Tg) of SO 2 ) and massive (hundreds of Tg) eruptions. Both isotopic data and numerical simulations suggest the shutdown of stratospheric OH chemistry and the opening of unaccounted oxidation channels for SO 2 , such as the reaction with O( 3 P) atoms when hundreds of Tg of SO 2 are injected into the stratosphere. It is very likely that oxidation rates and pathways and concentrations of most traces gases are also dramatically affected, with potentially important implications for climate forcing.