Fig. 3.

Conceptual model for environmental changes across the P−Tr boundary, depicting the shelf settings that are prone to be affected in a scenario of intensified continental influx. Preextinction Late Permian marine communities would consist of multiple trophic levels. Authigenic pyrite formation is supported by sulfide production during anaerobic OC remineralization via MSR and nonlimiting iron availability. The extinction event marks an increased terrigenous influx causing local eutrophication as well as the input of isotopically depleted sulfur, aided by an intensified hydrological cycle forced by global warming. Increased sediment load and turbulence of river discharge flocculates iron as Fe oxy(hydr)oxides in estuaries, reducing the ocean Fe_(HR) inventory. Consequential OC remineralization by MSR and Fe_(HR) limitation raises seawater H₂S. Sulfide toxicity alongside marine anoxia sustains a low-species richness but a high-biomass marine community. Pyrite sedimentation is limited to small amounts of syngenetic pyrite precipitation. Relaxation of physical continental weathering reduces ocean input of nutrients and raises Fe_(HR) delivery to the postextinction ocean, thereby reducing sulfidic water column conditions and relocating pyrite sedimentation toward the sediments, where decreased O₂ irrigation due to a less active benthic community stimulates authigenic pyrite formation. The enlarged OC pool is sustained due to carbon recycling by an active microbial community.