The Cambrian Explosion was an unprecedented bioevolutionary event that witnessed rapid diversification of marine invertebrate phyla and establishment of metazoan-dominated marine ecosystems. Nitrogen is a critical nutrient element essential for all life on Earth, and its biogeochemical cycling in the ocean is tightly associated with marine redox conditions. Numerous nitrogen isotope investigations of the Ediacaran-Cambrian (E-C) transition have been undertaken, but an integrated analysis of contemporaneous nitrogen cycling has not been achieved yet. Here, we compile published nitrogen isotope data for the South China Craton over the interval from ∼550 Ma (late Ediacaran) to ∼514 Ma (late Stage 3 of early Cambrian) with the goals of identifying key changes in the nitrogen cycle and their relationship to marine redox evolution and the Cambrian Explosion. Combined with independent redox proxy data, our δ15N dataset provides insights into spatio-temporal variation in rates of denitrification and N2 fixation induced by marine redox fluctuations, which constrains the distribution of suboxic environments and the relative position of the oceanic redoxcline. On this basis, we propose a new model of marine nitrogen-cycle evolution during the E–C transition in which (1) nitrate availability modulated the ecological development and distribution of eukaryotic primary producers, and (2) nitrate-replete ecological niches for eukaryotic primary producers, especially benthic algae expanded significantly during Cambrian Age 3, and (3) increasing biological pump efficiency promoted organic burial and net O2 release, thus contributing to oceanic oxygenation and the radiation of early animals.

中文翻译：

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埃迪卡拉纪-寒武纪过渡期间的氮循环和海洋氧化还原演化


寒武纪大爆发是一次前所未有的生物进化事件，见证了海洋无脊椎动物门的快速多样化和后生动物主导的海洋生态系统的建立。氮是地球上所有生命所必需的关键营养元素，它在海洋中的生物地球化学循环与海洋氧化还原条件密切相关。已经对埃迪卡拉纪-寒武纪 （E-C） 转变进行了大量氮同位素研究，但尚未实现对同期氮循环的综合分析。在这里，我们汇编了从 ∼550 马（埃迪卡拉纪晚期）到 ∼514 马（早期寒武纪第 3 阶段晚期）期间华南克拉通的已发表氮同位素数据，目的是确定氮循环中的关键变化及其与海洋氧化还原演化和寒武纪大爆发的关系。结合独立的氧化还原代理数据，我们的 δ15N 数据集提供了对海洋氧化还原波动引起的反硝化和 N2 固定速率的时空变化的见解，这限制了亚盒环境的分布和海洋氧化还原层的相对位置。在此基础上，我们提出了一种 E-C 过渡期间海洋氮循环演变的新模型，其中 （1） 硝酸盐的可用性调节了真核初级生产者的生态发展和分布，以及 （2） 真核初级生产者的硝酸盐丰富的生态位，尤其是底栖藻类在寒武纪 3 年显着扩大，以及 （3） 提高生物泵效率促进了有机掩埋和净 O2 释放， 从而促进了海洋氧化和早期动物的辐射。