Using novel genetic and isotopic techniques to understanding how microbial activity affects rates of dissolution of the mineral olivine.

这项研究的结果将促进对地球科学的基本认识，并将对了解地球的碳循环和矿物基质中碳固存的潜力具有实际意义。矿物质的化学分解（“矿物溶解”）在一定的空间和时间尺度上调节着碳和其他营养元素的可用性。这意味着了解矿物溶解是研究地球系统的基础，特别是对地球气候和生物圈的研究。矿物质溶解的速度取决于许多因素。其中，生物活性的作用和热力学平衡的方法仍然特别不为人所知。这种知识差距阻碍了开发将实验室观测与现场条件相适应的模型的努力，并使利用实验研究的结果来解决大规模地球系统问题变得困难。同时，自然系统的风化研究常常受到多种变量的干扰。本文提出的项目将采用新颖的实验方法，在理解微生物活动和平衡方法如何影响硅酸盐矿物橄榄石的溶解速率方面迈出重要一步。橄榄石作为高耐候性岩石的主要成分，在碳循环中起着关键作用，并且已被提出作为二氧化碳封存的基质，使其成为值得关注的重点研究矿物。大量的实地观察表明，生物活动推动了硅酸盐风化速率的增加，但缺乏对机理的理解，因为先前的实验工作因实验内部和实验之间生物体的活动和表型表达的变化而变得复杂。为了尽量减少这种可变性，拟议研究中的实验将使用具有靶向基因突变的微生物进行。通过这种方法，可以在一系列环境条件下对单个微生物过程的影响进行分离和量化，从而可以比以前更可靠地确定生物活性对橄榄石溶解速率的影响。在自然环境中，矿物溶蚀速率与热力学平衡偏离的关系是控制溶蚀速率的关键因素。理论预测在热力学平衡依赖的函数形式和观察到速率显著变化的热力学平衡值两方面都有很大的不同。对于橄榄石，近平衡实验是复杂的，因为相对于以不可忽略的速率沉淀的二次硅酸镁矿物，溶液变得过饱和，使得使用标准方法无法量化溶解速率。为了解决这一问题，将采用同位素稀释法测定溶解速率的新方法来研究橄榄石的近平衡溶解动力学。该项目将支持培养一名博士生，该博士生将指导来自传统上代表性不足背景的高中生。在教授基础科学概念的同时，博士生还将领导一项实验室练习的开发，该实验将展示矿物橄榄石的二氧化碳封存潜力。这个练习将被纳入南加州大学的一个展示中，并将通过互联网免费提供给其他机构的教育使用。

The results of this research will advance basic understanding in the Earth sciences and will have practical implications for understanding Earth's carbon cycle and the potential for carbon sequestration in mineral substrates. The chemical breakdown of minerals ("mineral dissolution") regulates the availability of carbon and other nutrient elements across a range of scales in space and time. This means that understanding mineral dissolution is fundamental to the study of the Earth system, and particularly to the study of Earth's climate and biosphere. The rate at which minerals dissolve is known to depend on a number of factors. Of these, the roles of biological activity and the approach to thermodynamic equilibrium remain particularly poorly understood. This knowledge gap stands in the way of efforts to develop models that scale laboratory observations to field conditions and makes it difficult to use the results from experimental studies to address large-scale Earth system problems. Meanwhile studies of weathering in natural systems are often confounded by multiple variables. The project proposed here will use novel experimental methods to take a major step forward in understanding how microbial activity and the approach to equilibrium affect the dissolution rate of the silicate mineral olivine. Olivine plays a key role in the carbon cycle as a primary constituent of highly weatherable rocks, and has been proposed as a substrate for carbon dioxide sequestration, making it a noteworthy mineral for focused investigation.Numerous field observations have shown that biological activity drives higher increased silicate weathering rates, but a mechanistic understanding is lacking because prior experimental efforts have been complicated by variations in the activity and phenotypic expression of organisms within and between experiments. To minimize this variability, experiments in the proposed study will be preformed using microorganisms with targeted genetic mutations. With this approach, the effects of a single microbial process can be isolated and quantified over a range of environmental conditions, allowing for a more robust determination of the effects of biological activity on olivine dissolution rates than have previously been possible. The dependence of mineral dissolution rates on the departure from thermodynamic equilibrium is a critical factor that controls dissolution rates in natural environments. Theoretical predictions vary significantly in both the functional form of the thermodynamic equilibrium dependence as well as the value of the thermodynamic equilibrium at which a significant change in rate is observed. For olivine, near-equilibrium experiments are complicated because solutions become supersaturated with respect to secondary magnesium silicate minerals that precipitate at non-negligible rates, making it impossible to quantify dissolution rates using standard methodologies. To circumvent this problem, a novel method of determining dissolution rates by isotope dilution will be used to study the near equilibrium dissolution kinetics of olivine.The project will support the training of a doctoral student, who will supervise high school students from traditionally underrepresented backgrounds. The doctoral student will also lead the development of a laboratory exercise that demonstrates the carbon dioxide sequestration potential of the mineral olivine while teaching basic science concepts. This exercise will be incorporated into a display at the University of Southern California and will be provided free of charge over the Internet for educational use at other institutions.