近日，加拿大阿尔伯塔大学Xueqi Liang团队研究了大氧化事件之前由铁形成记录的海水氧振荡。2025年4月23日出版的《自然—地球科学》杂志发表了这项成果。
大约24.5-22.2亿年前（Ga）的大氧化事件期间，由于海洋蓝藻产生的过量氧气（O2），地球大气经历了永久氧化。然而，由于缺乏敏感的示踪剂，对大氧化事件前海水氧化的时间和速度的理解受到了阻碍。氮（N）同位素可以作为海洋氧合的指标。研究组展示了西澳大利亚州哈默斯利盆地新太古代和古元古代带状铁地层记录的约200 Myr氮同位素振荡，这些地层沉积在相对较深的海洋陆架环境中。
结合Jeerinah组页岩记录，研究组从Marra Mamba铁组获得的数据表明，氧化条件从~2.63 Ga扩展到2.60 Ga的带状铁组沉积环境。随后，在~2.48 Ga的Dale峡谷段发生了正的δ15N偏移，标志着海水O2的下降和反硝化作用的增强。这种氧气不足之后是氧气水平上升的第二阶段，如~2.46 Ga Joffre段和2.45 Ga Weeli Wolli铁组中δ15N值逐渐恢复到中等正值所示。这些变化突显了海洋氧合的非线性历史，并揭示了大氧化事件之前海水O2水平的一种以前未被认识的振荡。
附：英文原文
Title: A seawater oxygen oscillation recorded by iron formations prior to the Great Oxidation Event
Author: Liang, Xueqi, Steken, Eva E., Alessi, Daniel S., Konhauser, Kurt O., Li, Long
Issue&Volume: 2025-04-23
Abstract: Earth’s atmosphere underwent permanent oxidation during the Great Oxidation Event approximately 2.45–2.22 billion years ago (Ga) due to excess oxygen (O2) generated by marine cyanobacteria. However, understanding the timing and tempo of seawater oxygenation before the Great Oxidation Event has been hindered by the absence of sensitive tracers. Nitrogen (N) isotopes can be an indicator of marine oxygenation. Here we present an ~200Myr nitrogen isotope oscillation recorded by Neoarchaean and Palaeoproterozoic banded iron formations from the Hamersley Basin, Western Australia, that were deposited in relatively deep marine shelf environments. Paired with the Jeerinah Formation shale record, our data from the Marra Mamba Iron Formation suggest that oxic conditions expanded to banded iron formation depositional environments from ~2.63 to 2.60Ga. Subsequently, a positive δ15N excursion occurred in the ~2.48Ga Dale Gorge Member, marking a decline in seawater O2 and enhanced denitrification. This O2 deficit was followed by a second phase of increasing O2 levels as indicated by a gradual return to moderately positive δ15N values in the ~2.46Ga Joffre Member and 2.45Ga Weeli Wolli Iron Formation. These variations underscore a nonlinear history of marine oxygenation and reveal a previously unrecognized oscillation in seawater O2 levels preceding the Great Oxidation Event.
DOI: 10.1038/s41561-025-01683-7
Source: https://www.nature.com/articles/s41561-025-01683-7