The Smithian negative C-isotope excursion was one of the major perturbations of the global carbon cycle following the end-Permian mass extinction event. Profound oceanographic and biological changes occurred during the Smithian, but the mechanism driving the negative C-isotope excursion and its links with marine environmental and biotic changes remain poorly constrained. Here, we use high-resolution paired C-isotope records from the early Smithian to the early Spathian in the Jiarong section, South China, to investigate the origin of the carbon cycle perturbation and its relationship with contemporaneous environmental changes. The paired C-isotope data reveal parallel negative excursions in both δ¹³C_carb and δ¹³C_org during the Smithian that can be correlated globally. The global Smithian negative C-isotope excursion shows a good first-order correspondence with global transgression and ocean anoxia. The results of numerical box modeling suggest that the Smithian negative C-isotope excursion could have been generated by increased organic carbon oxidation in response to the upward movement of anoxic bottom waters during transgression. The oxidative decay of organic carbon is primarily fueled by the consumption of oxygen and sulfate in the atmosphere–ocean system. Hence, we use the model to quantify the oxidants consumption rate that could be required to simulate the global Smithian negative C-isotope excursion through organic carbon oxidation. The modeling results show that the organic carbon oxidation during the Smithian could have generated a high demand for oxidants in the ocean, leading to the expansion of anoxia. Our study provides quantitative constraints on the causal link between the Smithian negative C-isotope excursion and widespread anoxia. The nadir of the Smithian negative C-isotope excursion coincided with the severe loss of biodiversity, suggesting that the expansion of anoxia in response to the transgressive upward movement of anoxic waters may have driven the late Smithian extinction. Hence, it could be one of the causes of the prolonged Early Triassic biotic recovery.

史密斯负碳同位素偏移是二叠纪末大灭绝事件后全球碳循环的主要扰动之一。史密斯期间发生了深刻的海洋学和生物变化，但驱动负碳同位素偏移的机制及其与海洋环境和生物变化的联系仍然受到很大限制。在这里，我们使用华南嘉绒剖面从史密世早期到斯帕阶早期的高分辨率配对碳同位素记录，研究碳循环扰动的起源及其与同期环境变化的关系。配对的 C 同位素数据揭示了 δ ¹³ C _carb和 δ ¹³ C _{org 中的}平行负偏移在可以全局关联的史密斯期间。全球史密斯负 C 同位素偏移显示出与全球海侵和海洋缺氧的良好一阶对应。数值盒模型的结果表明，史密斯氏负 C 同位素偏移可能是由于海侵期间缺氧底水向上运动而增加的有机碳氧化产生的。有机碳的氧化衰变主要是由大气-海洋系统中氧气和硫酸盐的消耗引起的。因此，我们使用该模型来量化通过有机碳氧化模拟全球史密斯负 C 同位素偏移可能需要的氧化剂消耗率。建模结果表明，史密斯期间的有机碳氧化可能产生了海洋中对氧化剂的高需求，导致缺氧扩大。我们的研究为史密斯负碳同位素偏移与广泛缺氧之间的因果关系提供了定量限制。史密斯负 C 同位素漂移的最低点与生物多样性的严重丧失相吻合，这表明缺氧对缺氧水域的海进向上运动的反应可能导致了史密斯晚期的灭绝。因此，它可能是早三叠世生物恢复时间延长的原因之一。史密斯负 C 同位素漂移的最低点与生物多样性的严重丧失相吻合，这表明缺氧对缺氧水域的海进向上运动的反应可能导致了史密斯晚期的灭绝。因此，它可能是早三叠世生物恢复时间延长的原因之一。史密斯负 C 同位素漂移的最低点与生物多样性的严重丧失相吻合，这表明缺氧对缺氧水域的海进向上运动的反应可能导致了史密斯晚期的灭绝。因此，它可能是早三叠世生物恢复时间延长的原因之一。