Vertical decoupling in Late Ordovician anoxia due to reorganization of ocean circulation
Vertical decoupling in Late Ordovician anoxia due to reorganization of ocean circulation
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DOI：
10.1038/s41561-021-00843-9
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发表时间：
2021-11
影响因子：
18.3
通讯作者：
A. Pohl;Zunli Lu;Wanyi Lu;R. Stockey;M. Elrick;Menghan Li;A. Desrochers;Yanan Shen;Ruliang He;S. Finnegan;A. Ridgwell
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作者：
A. Pohl;Zunli Lu;Wanyi Lu;R. Stockey;M. Elrick;Menghan Li;A. Desrochers;Yanan Shen;Ruliang He;S. Finnegan;A. Ridgwell
地球化学氧化还原指标表明，海底缺氧发生在奥陶纪末次冰期，与晚奥陶纪生物大灭绝的第二次脉冲相吻合。然而，在冰川气候中的扩大缺氧与变暖相关的中生代缺氧事件形成鲜明对比，并提出了海洋脱氧的因果机制及其与灭绝的关系的问题。在这里，我们首先报告碘钙比（I/Ca）的数据，文件增加上层海洋的氧合，尽管同时扩大海底缺氧。然后，我们解决这些明显相互矛盾的意见，以及它们与全球气候的关系，通过一系列的地球系统模型模拟。应用现有的晚奥陶世（Hirnantian）的海洋表面温度估计的氧同位素研究的限制，除了我们的I/Ca数据，导致我们确定一个场景中，Hirnantian冰川条件允许海底缺氧和增加上层海洋氧化的蔓延。我们模拟的全球海洋环流的重组机制，减少了北方来源的沃茨的重要性和较差的通风和缺氧的深海与更新世的状态转换在大西洋大西洋的翻转（尽管有非常不同的大陆配置），并表明，没有简单和可预测的关系，过去的气候状态和氧化可能存在。
Geochemical redox proxies indicate that seafloor anoxia occurred during the latest Ordovician glacial maximum, coincident with the second pulse of the Late Ordovician mass extinction. However, expanded anoxia in a glacial climate strikingly contrasts with the warming-associated Mesozoic anoxic events and raises questions as to both the causal mechanism of ocean deoxygenation and its relationship with extinction. Here we firstly report iodine-to-calcium ratio (I/Ca) data that document increased upper-ocean oxygenation despite the concurrent expansion of seafloor anoxia. We then resolve these apparently conflicting observations as well as their relationship to global climate by means of a series of Earth system model simulations. Applying available Late Ordovician (Hirnantian) sea-surface temperature estimates from oxygen isotope studies as constraints, alongside our I/Ca data, leads us to identify a scenario in which Hirnantian glacial conditions permit both the spread of seafloor anoxia and increased upper-ocean oxygenation. Our simulated mechanism of a reorganization of global ocean circulation, with reduced importance of northern-sourced waters and a poorer ventilated and deoxygenated deep ocean has parallels with Pleistocene state transitions in Atlantic meridional overturning (despite a very different continental configuration) and suggests that no simple and predictable relationship between past climate state and oxygenation may exist.