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理解，并将对理解地球的碳循环和矿物基质中碳固存的潜力产生实际影响。矿物的化学分解（“矿物溶解”）在空间和时间的范围内调节碳和其他营养元素的可用性。这意味着了解矿物溶解是地球系统研究的基础，特别是对地球气候和生物圈的研究。已知矿物质溶解的速率取决于许多因素。其中，生物活性的作用和热力学平衡的方法仍然特别缺乏了解。这一知识差距阻碍了开发模型的努力，这些模型将实验室观测的规模扩大到实地条件，并使其难以利用实验研究的结果来解决大规模地球系统问题。与此同时，自然系统中的风化研究往往受到多个变量的干扰。这里提出的项目将使用新的实验方法，在了解微生物活性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，并被提议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。大量野外观察表明，生物活动导致硅酸盐风化速率增加，但是缺乏对机制的理解，因为先前的实验努力已经被生物体内和之间的活性和表型表达的变化所复杂化。实验为了最大限度地减少这种变异性，将使用具有靶向基因突变的微生物进行拟定研究中的实验。通过这种方法，可以在一系列环境条件下分离和量化单个微生物过程的影响，从而比以前更可靠地确定生物活性对橄榄石溶解速率的影响。矿物溶解速率对热力学平衡偏离的依赖性是控制自然环境中溶解速率的关键因素。理论预测在热力学平衡依赖性的函数形式以及观察到速率显著变化的热力学平衡值方面都有显著差异。对于橄榄石，近平衡实验是复杂的，因为溶液变得相对于以不可忽略的速率沉淀的次生硅酸镁矿物过饱和，使得不可能使用标准方法量化溶解速率。为解决这一问题，将采用一种通过同位素稀释确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，由他指导传统上代表性不足的高中生。博士生还将领导实验室练习的开发，该练习在教授基本科学概念的同时展示矿物橄榄石的二氧化碳封存潜力。这项练习将在南加州大学展出，并将通过因特网免费提供给其他机构用于教学。

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.