Early Triassic hothouse conditions limited marine productivity

The Early Triassic represents a period of prolonged recovery following the most severe extinction of the Phanerozoic. Records show this to be a period of extremely high global temperatures, likely driven by Siberian Traps eruption induced global warming. How this hothouse impacted marine ecosystems and prolonged the recovery process remains uncertain. Across northwestern Pangea, Early Triassic marine sediments are characterized by low organic matter content, despite recurrent anoxia which would create conditions more suitable for preservation, and being located on the western continental margins were the majority of primary productivity in the Panthalassa Ocean would occur. Geochemical proxies suggest the paucity of organic matter reflects a productivity collapse rather than changes in preservation. Nitrogen isotopes show a progressive negative shift starting at the Permian/Triassic extinction and continuing through to the Smithian, indicating progressively growing nutrient limitation. High ocean temperatures likely deepened the thermocline, limiting nutrient recycling and upwelling into the photic zone driving nutrient stress. Finally ocean cooling in the Anisian is marked by widespread deposition of organic rich black shales and return of N isotopes to values consistent with active nutrient upwelling. A hyperthermal driven nutrient-limited Early Triassic ocean was likely a key inhibiter of marine recovery.