Ground-truthing lithium paleo-proxies: Experimental study on the Li incorporation and isotope fractionation during inorganic calcite and aragonite precipitation

大陆硅酸盐岩石的化学分解（称为“风化作用”）消耗大气中的二氧化碳。在这个过程中，硅酸盐岩石中的锂（Li）被释放出来，最终由河流进入海洋。已知风化强度会影响输送到海洋中的锂的数量和同位素组成（δ7Li）。因此，海水中Li浓度及其δ7Li的变化可以为硅酸盐风化的历史和演化及其在全球碳循环和地球气候中的调节作用提供有价值的信息。已知某些海洋生物产生的碳酸钙（CaCO3）矿物会从海水中吸收微量的锂，因此它们可以用作这些变化的记录器。然而，我们目前对Li如何与CaCO3结合以及控制这一过程的因素的理解非常有限。在这项研究中，来自夏威夷大学（UH）的研究人员将进行一系列的实验室实验，以更好地了解Li并入CaCO3的机制。这项工作将为进一步开发利用海洋CaCO3矿物作为海水Li过去变化的示踪剂以及大陆硅酸盐风化铺平道路。该项目将加强夏威夷大学研究生和本科生在地球科学方面的教育和职业发展。研究小组亦会在主教博物馆举办的“为科学而疯狂”及“活着的科学”等年度开放日活动中，讨论他们的发现。研究小组亦会讨论大陆硅酸盐岩石的风化过程，并最终由河流将锂注入海洋。海水Li浓度和δ7Li的变化可以为硅酸盐风化的历史和演化及其在全球碳循环和地球气候中的调节作用提供有价值的信息。含有Li的CaCO3矿物可以作为这些变化的记录器。本研究将基于完善的无机CaCO3沉淀实验，在相同的控制条件下，系统地改变一系列溶液物理化学参数，直接比较它们对CaCO3中δ7Li和Li浓度的影响。此外，利用种子，方解石和文石样品将在相同的实验条件下合成，以研究Li掺入的多态性控制。该项目预计将提供迄今为止最完整的实验数据集，这些数据集将与表面动力学模型的使用相结合，为Li在溶液和CaCO3矿物之间的元素和同位素分配建立一个坚实的无机（动力学和平衡）基线。该项目加强了夏威夷大学研究生和本科生在地球科学方面的教育和职业发展，夏威夷大学的学生群体多样化，而且往往代表性不足。该团队还将在主教博物馆举办的“为科学而疯狂”和“活着的科学”等年度开放日活动中讨论他们的发现。该奖项反映了美国国家科学基金会的法定使命，并通过基金会的智力价值和更广泛的影响评估标准进行了评估，认为值得支持。

Chemical break down of continental silicate rocks (referred to as “weathering”) consumes atmospheric CO2. During this process, lithium (Li) contained in silicate rocks is released and eventually delivered into the ocean by rivers. Intensity of weathering is known to influence the amount and isotopic composition (δ7Li) of Li delivered into the ocean. Thus, changes in the concentration of Li in seawater and its δ7Li can provide valuable information on the history and evolution of silicate weathering and its roles in regulating global carbon cycle and the Earth’s climate. Calcium carbonate (CaCO3) minerals produced by certain groups of marine organisms are known to incorporate trace amounts of Li from seawater, and thus they can be used as a recorder for those changes. However, our current understanding on how Li is incorporated into CaCO3 and what controls the process is extremely limited. In this study, researchers from the University of Hawaii (UH) will perform a series of laboratory experiments to better understand the mechanism of Li incorporation into CaCO3. This work will pave the road for further development in the use of marine CaCO3 minerals as the tracer for past changes in seawater Li and hence continental silicate weathering. The project will enhance education and career development in the geosciences for graduate and undergraduate students at the University of Hawaii. This team will also talk about their findings in the annual open house events such as “Mad About Science” and “Science Alive” at the Bishop MuseumWeathering of continental silicate rocks while releasing and eventually delivering Li into the ocean by rivers. Changes in seawater Li concentration and δ7Li can provide valuable information on the history and evolution of silicate weathering and its roles in regulating global carbon cycle and the Earth’s climate. CaCO3 minerals that incorporate Li can be used as a recorder for those changes. This study will be based on well-established inorganic CaCO3 precipitation experiments, where an array of solution physicochemical parameters will be systematically varied from the same control condition for straightforward comparisons of their impacts on δ7Li and Li concentrations in CaCO3. Furthermore, with the use of seeds, both calcite and aragonite samples will be synthesized under identical experimental conditions to examine the polymorphic controls on Li incorporation. This project is expected to provide by far the most complete experimental datasets, which will be combined with the use of surface kinetic modelling to establish a firm inorganic (kinetic and equilibrium) baseline for the elemental and isotopic partitioning of Li between solution and CaCO3 minerals. The project enhances education and career development in the geosciences for graduate and undergraduate students at the University of Hawaii, where the student population has diverse and often underrepresented ethnic background. This team will also talk about their findings in the annual open house events such as “Mad About Science” and “Science Alive” at the Bishop MuseumThis award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.