Multiple mercury enrichments reveal volcanism-driven hydrological and carbon cycle changes in the Ladinian–Carnian sedimentary record, northeastern Paleo-Tethys

Extreme hydroclimatic changes linked to greenhouse gas emissions from large igneous provinces are exemplified by the Carnian Pluvial Episode (CPE; ca. 233 Ma), during which volcanic activity drove shifts in the hydrological cycle, though marine records offer only indirect evidence of terrestrial changes. There were multiple volcanism and humid events in the northeastern Paleo-Tethys. Still, the reliability of the data is difficult to evaluate, due to the absence of detailed sampling and information on mechanisms. We present a study of volcanic activity and its consequential impact on hydrological change, elucidated through examining a terrestrial sedimentary record of the Ladinian–Carnian in the northeastern Paleo-Tethys. Here we present a multiproxy analysis (including organic carbon isotopes, mercury [Hg] concentrations and isotopes, trace elements, and zircon U-Pb dating) in the Ordos Basin, North China. We can identify the onset of volcanic activity in this record based on Hg enrichment and near-zero mass-independent fractionation of Hg isotopes, which serve as proxies for volcanism, and find that these three onsets are broadly coeval with enhanced terrestrial runoff and rapid lake expansion. The most obvious episode of Hg enrichment and negative carbon isotope excursions during interval I is consistent with massive releases of local volcanogenic Hg and carbon to the Earth-surface system. Within the CPE interval, carbon isotope and sedimentary records indicate that the latter two pulses of depleted carbon into the atmosphere–lacustrine system were linked to discrete enhancements of the hydrological cycle. Our results provide a direct link between volcanism and its impact on the hydrological and carbon cycles.