美国乔治梅森大学Remírez, Mariano N.和Gilleaudeau, Geoffrey J.小组近日取得一项新成果。他们的最新研究提出了碳酸铀同位素记录了Toarcian海洋缺氧事件期间海洋缺氧的全球扩张。2024年6月24日，国际知名学术期刊《美国科学院院刊》发表了这一成果。

据悉，Toarcian海洋缺氧事件(T-OAE)；约183Mya)是一个全球性的显著碳循环扰动，与富有机质沉积物的广泛沉积、火山释放大量二氧化碳、海洋动物灭绝、海平面上升、海洋酸化引起的碳酸盐生产危机以及海水温度升高有关。尽管人们认识到T-OAE是未来海洋缺氧的潜在模拟物，但目前对全球海洋缺氧严重程度的了解主要局限于，对黑色页岩的微量元素和同位素组成的研究，这些研究通常受局部过程的影响。

本文首次利用特提斯洋东南部开阔海台地灰岩的碳酸铀同位素(δ²³⁸U)记录了T-OAE，作为全球海水氧化还原条件的代表。在T-OAE的负碳同位素偏移开始之前，记录了一个显著的负δ²³⁸U偏移(约0.4‰)，随后δ²³⁸U值长时间恢复，这证实了T-OAE代表了海洋缺氧的全球扩张。

利用贝叶斯反同位素质量平衡模型，研究人员估计在T-OAE高峰期间，缺氧水域覆盖了全球海底的6%至8%，是现代海洋缺氧程度的28至38倍。这些数据，结合其他由二氧化碳驱动的显生宙OAEs基于δ²³⁸U的海底缺氧面积的估计，表明海洋缺氧对碳释放的共同响应，从而改进了对未来人为引起的海洋脱氧的预测。

附：英文原文

Title: Carbonate uranium isotopes record global expansion of marine anoxia during the Toarcian Oceanic Anoxic Event

Author: Remírez, Mariano N., Gilleaudeau, Geoffrey J., Gan, Tian, Kipp, Michael A., Tissot, Franois L. H., Kaufman, Alan J., Parente, Mariano

Issue&Volume: 2024-6-24

Abstract: The Toarcian Oceanic Anoxic Event (T-OAE; ~183 Mya) was a globally significant carbon-cycle perturbation linked to widespread deposition of organic-rich sediments, massive volcanic CO₂ release, marine faunal extinction, sea-level rise, a crisis in carbonate production related to ocean acidification, and elevated seawater temperatures. Despite recognition of the T-OAE as a potential analog for future ocean deoxygenation, current knowledge on the severity of global ocean anoxia is limited largely to studies of the trace element and isotopic composition of black shales, which are commonly affected by local processes. Here, we present the first carbonate-based uranium isotope (δ²³⁸U) record of the T-OAE from open marine platform limestones of the southeastern Tethys Ocean as a proxy for global seawater redox conditions. A significant negative δ²³⁸U excursion (~0.4‰) is recorded just prior to the onset of the negative carbon isotope excursion comprised within the T-OAE, followed by a long-lived recovery of δ²³⁸U values, thus confirming that the T-OAE represents a global expansion of marine anoxia. Using a Bayesian inverse isotopic mass balance model, we estimate that anoxic waters covered ~6 to 8% of the global seafloor during the peak of the T-OAE, which represents 28 to 38 times the extent of anoxia in the modern ocean. These data, combined with δ²³⁸U-based estimates of seafloor anoxic area for other CO₂-driven Phanerozoic OAEs, suggest a common response of ocean anoxia to carbon release, thus improving prediction of future anthropogenically induced ocean deoxygenation.

DOI: 10.1073/pnas.2406032121

Source: https://www.pnas.org/doi/abs/10.1073/pnas.2406032121