Marine anoxia and delayed Earth system recovery after the end-Permian extinction
Marine anoxia and delayed Earth system recovery after the end-Permian extinction
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DOI：
10.1073/pnas.1515080113
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发表时间：
2016-03-01
影响因子：
11.1
通讯作者：
Payne, Jonathan L.
中科院分区：
文献类型：
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作者：
Lau, Kimberly V.;Maher, Kate;Payne, Jonathan L.
二叠纪末大灭绝后地球系统的延迟恢复通常归因于严重的海洋缺氧。然而，早三叠纪缺氧的范围和持续时间仍然知之甚少。在这里，我们使用来自中国和土耳其的上二叠统-上三叠统海相石灰岩的铀浓度（[U]）和U-238/U-235同位素组成（δ U-238）的配对记录来量化全球海底氧化还原条件的变化。我们观察到[U]和δ U-238在二叠纪末灭绝水平上突然下降，从类似于3 ppm和-0.15 ppm的水平下降到类似于0.3 ppm和-0.77%的水平，随后在随后的500万年中逐渐恢复到灭绝前的值。这些趋势意味着海底缺氧程度增加了100倍，并表明存在一个抑制底栖动物多样性和海洋生态系统功能恢复的浅氧最小带。我们推测，在早三叠世的海洋中，全球生物地球化学循环和海洋生态系统结构对OMZ位置的变化更为敏感，其特征是长时间的浅层缺氧可能冲击了大陆架。在这一假设下，中三叠世底水缺氧的减少、生物地球化学循环的稳定和海洋动物的多样化共同反映了一个更深、更小范围的OMZ的发展，它调节了二叠纪末灾难后地球系统的恢复。
Delayed Earth system recovery following the end-Permian mass extinction is often attributed to severe ocean anoxia. However, the extent and duration of Early Triassic anoxia remains poorly constrained. Here we use paired records of uranium concentrations ([U]) and U-238/U-235 isotopic compositions (delta U-238) of Upper Permian- Upper Triassic marine limestones from China and Turkey to quantify variations in global seafloor redox conditions. We observe abrupt decreases in [U] and delta U-238 across the end-Permian extinction horizon, from similar to 3 ppm and -0.15 parts per thousand to similar to 0.3 ppm and -0.77%, followed by a gradual return to preextinction values over the subsequent 5 million years. These trends imply a factor of 100 increase in the extent of seafloor anoxia and suggest the presence of a shallow oxygen minimum zone (OMZ) that inhibited the recovery of benthic animal diversity and marine ecosystem function. We hypothesize that in the Early Triassic oceans-characterized by prolonged shallow anoxia that may have impinged onto continental shelves-global biogeochemical cycles and marine ecosystem structure became more sensitive to variation in the position of the OMZ. Under this hypothesis, the Middle Triassic decline in bottom water anoxia, stabilization of biogeochemical cycles, and diversification of marine animals together reflect the development of a deeper and less extensive OMZ, which regulated Earth system recovery following the end-Permian catastrophe.