Alkalinity etched in the rocks

摘要

Sulphur dioxide emitted during volcanic eruptions is oxidized to sulphate and can go on to form sulphate aerosols that can influence Earths radiation balance. Bao et al. have used sulphur and triple oxygen isotope measurements of atmospheric sulphate preserved in the rock record to investigate the specific oxidation pathways from which the sulphate was formed. They find that seven eruption-related sulphate aerosol deposition events occurred during the mid-Cenozoic (between 34 and 7 million years ago) in the northern High Plains of North America. The isotopically discrete sulphates found in the sediments would have been produced only in alkaline cloudwater that favours an ozone-dominated sulphur dioxide oxidation pathway in the troposphere. This suggests that, in contrast to the weakly acidic condition today, cloudwater in the region was frequently alkaline during the mid-Cenozoicrnera.