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<p>Following the most severe mass extinction event of the Phanerozoic Eon, the Early Triassic marked a critical stage of ecosystem recovery under persistent environmental stress. While previous studies have examined the nitrogen cycle during this interval to understand biotic recovery and environmental dynamics, quantitative reconstructions of marine nitrate levels remain limited. In this study, we compiled global <i>δ</i><sup>15</sup>N data from the Early Triassic and used a steady-state box model to reconstruct temporal variations in marine nitrate availability. The results reveal that the fraction of nitrogen buried from the assimilatornitrate reservoir (<i>f</i><sub>assimilator</sub>) in South China evolved through three distinct stages: remaining low (∼0.06) from the Permian-Triassic boundary (PTB) to the Smithian-Spathian boundary (SSB), increasing to ∼0.2 after the SSB, and declining to ∼0.09 during the late Spathian. This evolution was primarily controlled by temperature-driven changes in ocean stratification, up-welling intensity, and redox conditions. Furthermore, <i>f</i><sub>assimilator</sub> values differed substantially between South China and northwestern Pangea. Prior to the SSB, these regional differences likely reflected variations in marine nitrate inventories, whereas after the SSB, they may be governed by spatially variable responses to climatic cooling. The persistence of nitrate depletion in Early Triassic oceans favored bacteria-dominated phytoplankton communities. This low-productivity state, together with ammonium toxicity to metazoans, may have delayed marine ecosystem recovery after the end-Permian mass extinction.</p>

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Prolonged nitrate depletion delayed marine ecosystem recovery after the end-Permian mass extinction

  • 期刊论文

  • 发表日期：

    2025年7月28日

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  • Youren Ma,
  • Zhaoxia Ge,
  • Jiaheng Shen

摘要

Following the most severe mass extinction event of the Phanerozoic Eon, the Early Triassic marked a critical stage of ecosystem recovery under persistent environmental stress. While previous studies have examined the nitrogen cycle during this interval to understand biotic recovery and environmental dynamics, quantitative reconstructions of marine nitrate levels remain limited. In this study, we compiled global δ15N data from the Early Triassic and used a steady-state box model to reconstruct temporal variations in marine nitrate availability. The results reveal that the fraction of nitrogen buried from the assimilatornitrate reservoir (fassimilator) in South China evolved through three distinct stages: remaining low (∼0.06) from the Permian-Triassic boundary (PTB) to the Smithian-Spathian boundary (SSB), increasing to ∼0.2 after the SSB, and declining to ∼0.09 during the late Spathian. This evolution was primarily controlled by temperature-driven changes in ocean stratification, up-welling intensity, and redox conditions. Furthermore, fassimilator values differed substantially between South China and northwestern Pangea. Prior to the SSB, these regional differences likely reflected variations in marine nitrate inventories, whereas after the SSB, they may be governed by spatially variable responses to climatic cooling. The persistence of nitrate depletion in Early Triassic oceans favored bacteria-dominated phytoplankton communities. This low-productivity state, together with ammonium toxicity to metazoans, may have delayed marine ecosystem recovery after the end-Permian mass extinction.