Coupled Hg isotope dynamics reveal eruption pulses across the Permian-Triassic mass extinction

The Permian-Triassic mass extinction, the most severe biodiversity crisis of the Phanerozoic, is widely linked to Siberian Traps volcanism, yet mercury (Hg) isotope responses to eruptive phases remain poorly constrained. Here we identify a pronounced negative correlation between Δ¹⁹⁹Hg and δ²⁰²Hg that occurs exclusively during three coupled volcanic-environmental-biotic crisis intervals ( ~ 150 kyr) and is absent under background conditions. Across multiple sections, crisis-interval samples converge between terrestrial, marine carbonate, and volcanic source fields, whereas background samples are more dispersed, indicating distinct isotopic behaviour. Hg/total organic carbon ratios normalized to background values strongly correlate with the Δ¹⁹⁹Hg-δ²⁰²Hg relationship, linking Hg loading to isotopic systematics. These results reveal a previously unrecognized isotopic structure and suggest enhanced large-scale source control during crisis intervals, providing a framework for resolving eruptive pulses and tracing volcanism-driven environmental change.