Fig. 2: Simulated Hg enrichment and Δ¹⁹⁹Hg shift in model runs #1 and #3.

Simulated Hg enrichment factor (EF) and Δ¹⁹⁹Hg shift in the coastal sediments in response to an increase in volcanism only (a), combined volcanism and soil erosion (b), and volcanism and coastal PZE (c). The amounts of soil erosion are expressed as times background soil erosion rate coefficients (k_{se_bg}); the intensities of PZE are expressed as increasing isotope enrichment factors of odd-MIF associated with photoreduction of Hg(II) in the coastal ocean (E_{occ(II-0),pho}). The thick and thin solid lines represent simulations under high and low volcanic Hg emissions, respectively; the thick and thin solid lines of Δ¹⁹⁹Hg shift are largely overlapped due to insensitive response of Δ¹⁹⁹Hg to volcanic Hg emissions. The vertical shading and dashed lines are the same as Fig. 1. The simulated EF and Δ¹⁹⁹Hg shifts (lines) are calculated relative to their background steady-state values of the model. The measured EF and Δ¹⁹⁹Hg shifts (data symbols) are calculated relative to their background Hg/TOC (40 ppb/%) and Δ¹⁹⁹Hg values (0.09‰) of the Late Permian. Note two samples with high EF values (45 and 78) at ~251.941 Ma (onset of the EPME) are excluded due to low TOC values (<0.2%). F_{subaerial Hg_bg}: background subaerial volcanic Hg flux.