Chen Jitao, Li Shihan, Zhang Shuang, Isson Terry, Dahl Tais W, Planavsky Noah J, Zhang Feifei, Wang Xiang-Dong, Shen Shu-Zhong, Montañez Isabel P
State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China.
Nanjing College, University of Chinese Academy of Sciences, Nanjing 211135, China.
Proc Natl Acad Sci U S A. 2025 Jul;122(26):e2420505122. doi: 10.1073/pnas.2420505122. Epub 2025 Jun 23.
The Late Paleozoic Ice Age (~340 to 260 Ma) occurred under peak atmospheric O (1.2 to 1.7 PIAL, pre-industrial atmospheric levels) for Earth history and CO concentrations comparable to those of the preindustrial to that anticipated for our near future. The evolution of the marine redox landscape under these conditions remains largely unexplored, reflecting that oceanic anoxia has long been considered characteristic of carbon cycle perturbation during greenhouse times. Despite elevated O, a 10-y period of CO-forced oceanic anoxia was recently identified, but whether this short-term interval of widespread oceanic anoxia was anomalous during this paleo-ice age is unexplored. Here, we investigate these issues by building a high-resolution record of carbonate uranium isotopes (δU) from an open-marine succession in South China that permits us to reconstruct the global marine redox evolution through the deep glacial interval (310 to 290 Ma) of near peak O. Our data reveal repeated, short-term decreases in δU coincident with negative C isotopic excursions and rises in paleo-CO, all superimposed on a longer-term rise in δU. A carbon-phosphorus-uranium biogeochemical model coupled with Bayesian inversion is employed to quantitatively explore the interplay between marine anoxia, carbon cycling, and climate evolution during this paleo-glacial period. Although our results indicate that protracted, enhanced organic carbon burial can account for the long-term O increase, seafloor oxygenation, and overall low CO, episodic pulses of C emissions had the potential to drive recurring short-term periods of marine anoxia (with 4 to 12% of seafloor anoxia) despite up to 1.7 times higher atmospheric O than present day.
晚古生代冰期（约3.4亿至2.6亿年前）发生在地球历史上大气氧含量峰值（1.2至1.7倍工业化前大气水平）以及二氧化碳浓度与工业化前相当、接近我们不久将来预期水平的时期。在这些条件下海洋氧化还原格局的演变在很大程度上仍未得到探索，这反映出长期以来海洋缺氧一直被认为是温室时期碳循环扰动的特征。尽管氧含量升高，但最近发现了一段由二氧化碳驱动的长达10年的海洋缺氧期，不过在这个古冰期内，这段广泛海洋缺氧的短期间隔是否异常尚未得到研究。在这里，我们通过建立来自中国南方一个开阔海洋层序的碳酸盐铀同位素（δU）高分辨率记录来研究这些问题，这使我们能够重建接近氧含量峰值的深度冰期间隔（3.1亿至2.9亿年前）全球海洋氧化还原演变。我们的数据显示，δU反复出现短期下降，同时伴有负碳同位素偏移和古二氧化碳上升，所有这些都叠加在δU的长期上升之上。我们采用了一个碳 - 磷 - 铀生物地球化学模型并结合贝叶斯反演，来定量探索这个古冰期内海洋缺氧、碳循环和气候演变之间的相互作用。尽管我们的结果表明长期增强的有机碳埋藏可以解释氧含量的长期增加、海底氧化以及总体较低的二氧化碳水平，但尽管大气氧含量比现今高出1.7倍，间歇性的碳排放脉冲仍有可能驱动反复出现的短期海洋缺氧期（海底缺氧面积达4%至12%）。
