The early Toarcian (∼183 Ma) was characterized by pronounced climate warming associated with massive release of 13C-depleted carbon to the exogenic system, as evidenced by globally recognized negative carbon-isotope excursions (N-CIE) in biospheric carbon reservoirs. Global warming during this interval triggered a variety of environmental perturbations, of which large-scale marine deoxygenation (as indicated by the presence of widespread organic carbon-rich deposits) is arguably diagnostic and led to the naming of the interval in question as the Toarcian Oceanic Anoxic Event (T-OAE). Nevertheless, the spatial variability of water-column redox during the T-OAE is unclear because most sedimentological and geochemical methods used to infer marine redox are likely reflective of bottom-water and/or pore-water conditions. Here we report new I/(Ca + Mg) and Cerium (Ce)-anomaly data from two carbonate successions from northern Italy that encompass the T-OAE interval. Both successions were deposited in the Alpine-Mediterranean Tethys; one in a shallow-water platform setting and the other within a pelagic environment. Both successions record an abrupt drop in I/(Ca + Mg) values, coupled with positive excursions in Ce-anomaly records at the onset of the T-OAE N-CIE. The synchronized changes in marine iodate depletion and Ce enrichment suggest widespread and significant upper-ocean deoxygenation in the Alpine-Mediterranean Tethys. This redox pattern is attributed to an expanded oxygen minimum zone (OMZ) formed as a result of sluggish oceanic circulation under climate warming, augmented by enhanced dissolved oxygen consumption due to increased nutrient availability and the consequent eutrophication in both proximal and distal settings. Because reduced seawater dissolved oxygen [O2] would increase the ecological stress and constrict any potentially hospitable habitats, the broad synchroneity between biotic turnovers and upper-ocean deoxygenation in the Alpine-Mediterranean Tethys is compatible with a potential causal link.

中文翻译：

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Toarcian Oceanic Anoxic Event 期间阿尔卑斯-地中海特提斯 （Tethys） 广泛的上层海洋脱氧


早期Toarcian（∼183 马）的特征是明显的气候变暖，与向外生系统大量释放13C耗尽的碳有关，全球公认的生物圈碳储层中的负碳同位素偏移（N-CIE）证明了这一点。在此期间的全球变暖引发了各种环境扰动，其中大规模的海洋脱氧（如广泛存在的富含有机碳的矿床所表明的那样）可以说是诊断性的，并导致将所讨论的间隔命名为 Toarcian 海洋缺氧事件 （T-OAE）。然而，T-OAE 期间水柱氧化还原的空间变化尚不清楚，因为大多数用于推断海洋氧化还原的沉积学和地球化学方法可能反映了底层水和/或孔隙水条件。在这里，我们报告了来自意大利北部的两个碳酸盐岩序列的新 I/（Ca + Mg） 和铈 （Ce） 异常数据，其中包括 T-OAE 层间。这两个继承都存放在阿尔卑斯-地中海特提斯;一个在浅水平台环境中，另一个在远洋环境中。两次演替都记录了 I/（Ca + Mg） 值的突然下降，再加上在 T-OAE N-CIE 开始时 Ce-异常记录的正偏移。海洋碘酸盐消耗和 Ce 富集的同步变化表明阿尔卑斯-地中海特提斯地区存在广泛而显著的上层海洋脱氧。这种氧化还原模式归因于气候变暖下海洋环流缓慢而形成的扩大的最低氧区 （OMZ），由于营养物质可用性增加而增加的溶解氧消耗以及随之而来的近端和远端富营养化。 由于海水溶解氧 [O2] 减少会增加生态压力并限制任何可能适宜居住的栖息地，因此阿尔卑斯-地中海特提斯的生物周转和上层海洋脱氧之间的广泛同步性与潜在的因果关系是兼容的。