Incorporation and elimination of molecular oxygen signal in sulfate: Experiments and modeling

硫酸盐中分子氧信号的掺入和消除：实验和建模

• 批准号: 1251824
• 负责人: Huiming Bao
• 金额: $ 34万
• 依托单位: Louisiana State University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-15 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1251824&HistoricalAwards=false
• 关键词: Incorporation; elimination; molecular; oxygen; signal

The stable isotope composition of atmospheric Oxygen in the geological past conveys rich information on the history of Earth system. Few compounds, however, are known to record oxygen isotope composition directly and reliably. Sulfate, being a non-labile oxyanion and capable of forming weakly soluble minerals, is thus far the only viable carrier from which direct atmospheric oxygen signals in the distant past can be retrieved. Nonetheless, how the oxygen signal is initially incorporated, later removed, or finally retained in sulfate is not clear. Earlier studies and the investigator?s initial results indicate that both water and oxygen contribute to the oxygen in intermediate and final sulfoxyanions generated during pyrite oxidation to sulfate. These earlier results also revealed that the current mechanistic understanding of the sulfide oxidation process is evidently inadequate. The full potential of this oxygen archive can only be attained through a study focusing on the kinetics of sulfur redox cycling. In this project, the investigator sets to develop and test, both theoretically and experimentally, a set of non-equilibrium, dynamic models for the oxygen signal incorporation during sulfide oxidation and for the oxygen signal elimination during dissimilatory sulfate reduction. It is expected that the study will 1) present a new mechanistic interpretation of sulfide to sulfate oxidation on mineral surface and in solution; 2) account for the intrinsic dynamics of competing oxidation and exchange pathways; and 3) unify the many chemical variables that appear to be responsible for the final oxygen apportionment in sulfate. At least five model predictions will be tested by quantifying rates of oxidation and exchange reactions as reflected in the oxygen isotope composition of sulfoxyanions. The experiments will utilize three-oxygen-isotope labeled water by which subtle changes in apportionment and in the magnitude of fractionation can both be measured. Although this study is initially driven by an interest in understanding a mysterious non-mass-dependent sulfate oxygen-17 depletion found in world-wide post-glacial deposits at about 635 million years ago, the result will offer an exemplary solution to a class of science problems that involve a set of dynamic isotope fractionation processes that rarely reach equilibrium. The project will be led by a postdoctoral researcher and a graduate student along with assisting undergraduate and high-school students of diverse ethnic and cultural backgrounds. Research results will be disseminated in introductory and upper-level undergraduate classes and in two local high schools. Two teaching modules will be developed to convey scientists? efforts in exploring mineral archives for ancient atmospheric signatures.

大气氧的稳定同位素组成在地质过去传达了有关地球系统历史的丰富信息。但是，很少有化合物直接可靠地记录氧同位素组成。硫酸盐是一种非属物氧，能够形成弱溶性矿物质，是迄今为止唯一可以从遥远过去的直接大气氧信号来检索的唯一可行的载体。但是，最初如何掺入氧信号，后来去除或最终保留在硫酸盐中尚不清楚。较早的研究和研究者的初步结果表明，水和氧促进了在黄铁矿氧化对硫酸盐期间产生的中间和最终亚氧化的氧气。这些早期的结果还表明，当前对硫化物氧化过程的机械理解显然是不足的。该氧气存档的全部潜力只能通过针对硫氧化还原循环动力学的研究来实现。在该项目中，研究人员在理论上和实验上都设定了一组非平衡的动态模型，用于在硫化物氧化过程中掺入氧信号，以及在降低异化硫酸盐减少过程中消除氧气信号的消除。预计该研究将1）提出对硫酸盐对矿物表面和溶液中硫酸盐氧化的新机械解释； 2）说明竞争氧化和交换途径的内在动力学； 3）统一了似乎负责硫酸盐最终氧气分配的许多化学变量。至少将通过量化氧化和交换反应的速率来测试五个模型预测，如氧同位素的氧同位素组成所反映的。这些实验将利用三氧同位素标记的水，通过该水，分配的细微变化和分馏的大小都可以测量。尽管该研究最初是出于对理解神秘的非质量依赖性硫酸盐氧17耗尽的兴趣所驱动的，该硫酸盐氧气17耗尽大约在6.35亿年前，但结果将为一类典型解决方案提供典范的解决方案涉及一组动态同位素分馏过程的科学问题很少达到平衡。该项目将由博士后研究人员和研究生领导，并协助具有多样化的种族和文化背景的本科生和高中生。研究结果将在入门和高级本科课程以及两所当地高中进行传播。将开发两个教学模块来传达科学家？为探索古老大气签名的矿物档案的努力。