Abstract An investigation of the relationships among large igneous province (LIP), carbon cycling, and climate change is central to understanding Earth system. During Glacial III, the most intense phase of Late Paleozoic Ice Age, the influence of coeval LIP on the carbon cycle and climate remains debated. We address the controversy using mercury (Hg) data from a tropical, hemipelagic marine section (Naqing, South China). A combination of Hg, δ202Hg, Δ199Hg, Δ200Hg, and other geochemical proxies indicate mainly continental Hg sources delivered via the atmosphere, inconsistent with volcanic emissions in previous studies. Sedimentary and geochemical data suggest enhanced dust input that increased marine nutrient availability and bioproductivity. Coupled with mass terrestrial organic carbon burial, these processes likely contributed to the positive carbon‐isotope excursion and global cooling during Glacial III. Our findings highlight the importance of enhanced aeolian transport and terrestrial organic burial to carbon‐cycle perturbations and climate feedbacks during Earth’s penultimate icehouse.