Periodic Release of Terrestrial Mercury Punctuated Marine Biodiversification During Late Carboniferous Icehouse

The Carboniferous–Permian Biodiversification Event witnessed an approximate threefold increase in marine species diversity, yet this diversification was sharply interrupted during the late Moscovian, and its drivers remain poorly understood. Here, we present high-resolution geochemical records from astrochronologically calibrated deep-marine successions in the South China block. Our data reveal eccentricity-paced cyclic variations in mercury (Hg) enrichments, Hg mass-independent fractionation (Δ199Hg) and mass-dependent fractionation (δ202Hg). We propose that volcanism-derived Hg was repeatedly remobilized from coastal wetlands during periods of tropical rainforest expansion. Eccentricity-modulated cooling pulses likely impaired vegetation freeze-intolerance, promoting erosion and silicate weathering. Such processes would have increased terrestrial Hg fluxes, leading to marine poisoning and photic-zone euxinia, which ultimately disrupted marine biodiversification. Our study highlights how complex terrestrial systems, influenced by both internal and external Earth system processes, can contribute to marine stress, driving biotic crises during the Late Paleozoic Ice Age.