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Volcanic ash interbeds in the Late Ordovician strata in South China record high-frequency volcanic activity. To assess the impact of these volcanic events on the climate and marine biological evolutionary crisis during the Late Ordovician Mass Extinction (LOME), we present high-resolution measurements of mercury (Hg) concentrations and organic carbon isotope ratios (d13Corg) in an Ordovician-Silurian sedimentary succession (Muchanggou section). The results show that high-frequency volcanic ash layers and Hg enrichments developed synchronously in the Katian graptolite P. pacificus (Lower Subzone) and T. typicus biozones and are coupled with a negative shift of ~1? in d13Corg, which reflects the perturbation of the surface carbon and mercury cycles by intense volcanic activity. Based on volcanic Hg fluxes, it is estimated that more than 1.1 × 1013 tons of CO2 were emitted by the Katian volcanic activities in South China, which interrupted the growth of the polar ice sheet and the rapid cooling of tropical oceans in the mid-Boda event. As volcanism weakened, increased weathering led to the growth of the polar ice sheet and cooling in the Hirnantian. Both regional and global biodiversity declined rapidly with the end of volcanism, which suggests that the marine ecological crisis was related to a series of disruptions in biogeochemical cycles in the post-volcanic period. [ABSTRACT FROM AUTHOR]