The Late Ordovician Mass Extinction wiped out 85% of animal species in two phases (LOME1 and LOME2). The kill mechanisms for the extinction phases are debated, but deteriorating climate and the expansion of marine anoxia appear to have been important factors. Nevertheless, the spatial extent and intensity of marine anoxia and its temporal relationship with the extinctions are not well understood. Here, we review existing global paleoredox proxy data based on molybdenum (Mo) and uranium (U) isotopes from four paleocontinents combined with new Mo isotope data from Dob's Linn, Scotland. Individually, these sedimentary records demonstrate significant redox fluctuations, but our coupled dynamic oceanic mass balance model for the evolution of the marine Mo and U cycles reveals that globally expansive ocean anoxia is best constrained by δ²³⁸U in carbonates from Anticosti Island that record expansive anoxia during LOME2. In addition, we consider periodic sulfidic anoxia developing in well-ventilated parts of the shallow oceans (e.g. during warmer periods with greater solar insolation) to have produced temporarily high seawater δ⁹⁸Mo values during LOME1 in accordance with trends to high values observed in the sedimentary records. In this view, oceanic oxygen loss had a causal role during both extinction phases in the Late Ordovician.

奥陶纪晚期大灭绝分两个阶段（LOME1 和 LOME2）消灭了 85% 的动物物种。灭绝阶段的杀戮机制存在争议，但气候恶化和海洋缺氧的扩大似乎是重要因素。然而，海洋缺氧的空间范围和强度及其与灭绝的时间关系尚不清楚。在这里，我们回顾了基于来自四个古大陆的钼 (Mo) 和铀 (U) 同位素的现有全球古氧化还原代理数据，并结合了来自苏格兰 Dob's Linn 的新 Mo 同位素数据。单独地，这些沉积记录显示出显着的氧化还原波动，但我们用于海洋 Mo 和 U 循环演化的耦合动态海洋质量平衡模型显示，全球膨胀的海洋缺氧最好受 δ 的约束来自 Anticosti 岛的碳酸盐中的²³⁸ U 在 LOME2 期间记录了广泛的缺氧。此外，我们认为在浅海通风良好的部分（例如在阳光照射较大的温暖时期）发生的周期性硫化物缺氧在 LOME1 期间产生了暂时的高海水 δ ⁹⁸ Mo 值，这与在沉积记录。根据这种观点，在晚奥陶世的两个灭绝阶段，海洋氧损失都具有因果关系。