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.

地质历史中大气氧的稳定同位素组成提供了丰富的地球系统历史信息。然而，很少有化合物能够直接可靠地记录氧同位素组成。硫酸盐是一种不稳定的含氧阴离子，能够形成弱可溶性矿物质，是迄今为止唯一可行的载体，可以从中恢复遥远过去的直接大气氧信号。尽管如此，氧信号最初是如何被结合的，后来被去除，或最终保留在硫酸盐中尚不清楚。早期研究和研究者？的初步结果表明，水和氧有助于在中间和最终硫氧阴离子在黄铁矿氧化成硫酸盐过程中产生的氧。这些早期的结果也表明，目前的硫化物氧化过程的机械理解是明显不足的。只有通过研究硫氧化还原循环的动力学，才能达到这种氧档案的全部潜力。在这个项目中，研究人员设置开发和测试，理论和实验，一组非平衡，动态模型的氧信号纳入硫化物氧化过程中和异化硫酸盐还原过程中的氧信号消除。预计该研究将：1）提出一种新的机制解释矿物表面和溶液中硫化物氧化为硫酸盐; 2）解释竞争氧化和交换途径的内在动力学; 3）统一许多化学变量，这些变量似乎是负责硫酸盐中最终氧分配的。至少有五个模型的预测将进行测试，通过量化氧化和交换反应，反映在氧同位素组成的sulfoxyanions。这些实验将利用三氧同位素标记的水，通过它可以测量分配和分馏幅度的微妙变化。虽然这项研究最初是出于对了解约6.35亿年前在全球冰后期沉积物中发现的神秘的非质量依赖性硫酸盐氧-17耗尽的兴趣，但其结果将为一类涉及一系列动态同位素分馏过程的科学问题提供示例性解决方案，这些过程很少达到平衡。该项目将由一名博士后研究员和一名研究生沿着领导，并协助不同种族和文化背景的本科生和高中生。研究成果将在本科入门和高年级班以及两所当地高中传播。将开发两个教学模块，以传达科学家？努力探索矿物档案中的古代大气特征。