School of Earth Sciences, Ohio State University, Columbus, OH 43210, USA.
Proc Natl Acad Sci U S A. 2011 Mar 8;108(10):3876-81. doi: 10.1073/pnas.1011836108. Epub 2011 Feb 22.
A rise in atmospheric O(2) has been linked to the Cambrian explosion of life. For the plankton and animal radiation that began some 40 million yr later and continued through much of the Ordovician (Great Ordovician Biodiversification Event), the search for an environmental trigger(s) has remained elusive. Here we present a carbon and sulfur isotope mass balance model for the latest Cambrian time interval spanning the globally recognized Steptoean Positive Carbon Isotope Excursion (SPICE) that indicates a major increase in atmospheric O(2). We estimate that this organic carbon and pyrite burial event added approximately 19 × 10(18) moles of O(2) to the atmosphere (i.e., equal to change from an initial starting point for O(2) between 10-18% to a peak of 20-28% O(2)) beginning at approximately 500 million years. We further report on new paired carbon isotope results from carbonate and organic matter through the SPICE in North America, Australia, and China that reveal an approximately 2‰ increase in biological fractionation, also consistent with a major increase in atmospheric O(2). The SPICE is followed by an increase in plankton diversity that may relate to changes in macro- and micronutrient abundances in increasingly oxic marine environments, representing a critical initial step in the trophic chain. Ecologically diverse plankton groups could provide new food sources for an animal biota expanding into progressively more ventilated marine habitats during the Ordovician, ultimately establishing complex ecosystems that are a hallmark of the Great Ordovician Biodiversification Event.
大气中氧气（O2）的增加与寒武纪生命大爆发有关。对于大约 4000 万年后开始并持续到奥陶纪大部分时间的浮游生物和动物辐射，寻找环境触发因素一直难以捉摸。在这里，我们提出了一个用于最新的寒武纪时间间隔的碳和硫同位素质量平衡模型，该模型跨越了全球公认的 Steptoean 正碳同位素激变（SPICE），表明大气中的氧气（O2）大量增加。我们估计，这个有机碳和黄铁矿埋藏事件向大气中增加了大约 19×10^18 摩尔的氧气（即从 O2 的初始起点增加 10-18%到峰值 20-28% O2），大约从 5 亿年前开始。我们还报告了来自北美、澳大利亚和中国的 SPICE 期间碳酸盐和有机物的新的配对碳同位素结果，显示生物分馏增加了约 2‰，这也与大气中氧气（O2）的大量增加一致。SPICE 之后，浮游生物多样性增加，这可能与海洋环境中宏量和微量元素丰度的变化有关，这是食物链中的一个关键初始步骤。生态多样化的浮游生物群可以为在奥陶纪期间不断向通风良好的海洋栖息地扩张的动物生物群提供新的食物来源，最终建立复杂的生态系统，这是奥陶纪生物多样性大爆发的一个标志。
