Moderate levels of oxygenation during the late stage of Earth's Great Oxidation Event
Moderate levels of oxygenation during the late stage of Earth's Great Oxidation Event
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DOI：
10.1016/j.epsl.2022.117716
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发表时间：
2022-09
影响因子：
5.3
通讯作者：
Frantz Ossa Ossa-Frantz-Ossa-Ossa-115591413;J. Spangenberg;A. Bekker;S. König;E. Stüeken;A. Hofmann;S. Poulton;A. Yierpan
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作者：
Frantz Ossa Ossa-Frantz-Ossa-Ossa-115591413;J. Spangenberg;A. Bekker;S. König;E. Stüeken;A. Hofmann;S. Poulton;A. Yierpan
地球在大氧化事件（GOE; 2.43-2.06 Ga）期间过渡到永久含氧大气的后期阶段通常与2.22-2.06 Ga Lomagundi事件（LE）期间的“氧气过量”有关，这代表了地球最明显和最长寿命的正碳同位素漂移。然而，在地球历史上的这一关键时期，大气-海洋氧化作用的规模和程度及其对生物圈的影响仍然受到很大的限制。在这里，我们提出了氮（N），硒（Se），碳（C）同位素数据，以及生物必需元素的浓度，古元古代海洋页岩沉积在LE。这些数据提供了证据，一个高生产力和良好的含氧透光区，与内部和外部的货架海洋环境的特点是硝酸盐和硒氧阴离子充满条件。然而，氧化还原层随后侵入到内大陆架在全球尺度脱氧的大气-海洋系统在LE结束，导致局部增强水柱反硝化和硒氧阴离子的定量减少。我们建议，硝酸盐充满条件与充分氧化的大陆架设置是一个共同的特点，在LE，但硝化作用是不够广泛的好氧氮循环的影响同位素组成的全球海洋氮库存。将其置于地球更广泛的氧化历史背景下，我们的研究结果表明，大气-海洋系统中的O2水平可能远低于现代浓度。因此，古元古代早期的地球化学循环远不如新元古代氧化作用之后的循环先进。
The later stages of Earth's transition to a permanently oxygenated atmosphere during the Great Oxidation Event (GOE; ∼2.43–2.06 Ga) is commonly linked with the suggestion of an “oxygen overshoot” during the ∼2.22–2.06 Ga Lomagundi Event (LE), which represents Earth's most pronounced and longest-lived positive carbon isotope excursion. However, the magnitude and extent of atmosphere-ocean oxygenation and implications for the biosphere during this critical period in Earth's history remain poorly constrained. Here, we present nitrogen (N), selenium (Se), and carbon (C) isotope data, as well as bio-essential element concentrations, for Paleoproterozoic marine shales deposited during the LE. The data provide evidence for a highly productive and well-oxygenated photic zone, with both inner and outer-shelf marine environments characterized by nitrate- and Se oxyanion-replete conditions. However, the redoxcline subsequently encroached back onto the inner shelf during global-scale deoxygenation of the atmosphere-ocean system at the end of the LE, leading to locally enhanced water column denitrification and quantitative reduction of selenium oxyanions. We propose that nitrate-replete conditions associated with fully oxygenated continental shelf settings were a common feature during the LE, but nitrification was not sufficiently widespread for the aerobic nitrogen cycle to impact the isotopic composition of the global ocean N inventory. Placed in the context of Earth's broader oxygenation history, our findings indicate that O2levels in the atmosphere-ocean system were likely much lower than modern concentrations. Early Paleoproterozoic biogeochemical cycles were thus far less advanced than after Neoproterozoic oxygenation.