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

• 成果类型: Article
• 署名作者: Remirez, Mariano N.; Gilleaudeau, Geoffrey J.; Gan, Tian; Kipp, Michael A.; Tissot, Francois L. H.; Kaufman, Alan J.; Parente, Mariano
• 署名单位: George Mason University; University System of Maryland; University of Maryland College Park; University System of Maryland; University of Maryland College Park; Duke University; California Institute of Technology; University of Naples Federico II
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-10909
• DOI: 10.1073/pnas.2406032121
• 发表日期: 2024-07-02
• 关键词: platform; EVOLUTION; molybdenum; seawater; fractionation; stratigraphy; PRODUCTIVITY; sedimentary; extinction; basin

摘要

The Toarcian Oceanic Anoxic Event (T-OAE; similar to 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 (delta U-238) 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 delta U-238 excursion (similar to 0.4 parts per thousand) 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 delta U-238 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 similar to 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 delta U-238-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.