EAR-Climate: Estimating Seawater Boron Isotope Ratios from Halite Evaporites

这项研究将通过解决海水中硼的成分如何随时间变化来改善对3600万年前海洋pH值和大气二氧化碳浓度的估计。需要知道海水中硼的组成，以便使用化石贝壳中的少量硼来确定它们生长的水的pH值以及与水平衡的二氧化碳。该项目将分析岩盐矿床，其中硼存在于盐晶体和矿物中捕获的少量蒸发海水中。通过分析这些盐沉积物中的硼，并确定古代海水中硼的组成，这项研究将使化石贝壳中的硼转化为对大气二氧化碳的更准确估计，这将提高对气候与二氧化碳之间联系的理解。该项目将支持两名早期职业女性科学家和一名代表性不足的少数民族科学家，研究人员将与芝加哥南部的一个高中教育推广项目分享他们在这些主题上的科学专业知识。该项目将调查硼在岩盐蒸发岩地层中的行为，以确定硼的赋存状态（例如散布在岩盐中的流体包裹体或微量矿物）并限制古代海水中硼的稳定同位素组成。通过测量几个含有流体包裹体的岩盐子样品的主要元素组成，将建立各种矿物和流体成分之间的混合关系，这些矿物和流体成分为大量溶解的岩盐样品提供硼，这将允许计算流体包裹体的端元组成和古海水的硼同位素组成。本项目将研究实验沉淀的岩盐、天然盐芯，最终将研究来自西班牙的约3600万年前的海洋岩盐样品。将在芝加哥大学的地球化学设施中建立用电感耦合等离子体质谱法进行硼的稳定同位素分析。除了提供对海洋pH值和碳酸盐体系的独立约束外，该研究还将确定石膏中硼的分配系数，并解决硼地球化学循环的长期演变。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This research will improve estimates of ocean pH and atmospheric carbon dioxide concentrations ~36 million years ago by resolving how the composition of boron in seawater has changed over time. The composition of boron in seawater needs to be known in order use the small amounts of boron in fossil shells to determine the pH of the water they grew in and the carbon dioxide that would be in equilibrium with that water. This project will analyze rock salt deposits where boron is present in small amounts of evaporated seawater that are captured within the salt crystals, as well as within minerals. By analyzing the boron in these salt deposits and determining the composition of boron in ancient seawater, this research will allow the boron in fossil shells to be translated into more accurate estimates for atmospheric carbon dioxide, which will improve understanding about the connection between climate and carbon dioxide. The project will support two early-career women scientists and one under-represented minority scientist, and the researchers will share their scientific expertise on these topics with a high-school educational outreach program on the South Side of Chicago.The project will investigate the behavior of boron in halite evaporite formations to determine the phases that host boron (e.g. fluid inclusions or trace minerals disseminated in the halite) and constrain the stable isotopic composition of boron in ancient seawater. By measuring major element compositions across several halite subsamples bearing fluid inclusions, mixing relationships between the various mineral and fluid components that contribute boron to bulk dissolved halite samples will be established, which will allow for calculation of the endmember composition of the fluid inclusions and the boron isotopic composition of ancient seawater. Experimentally precipitated halites, natural salt cores, and ultimately a ~36 million year old marine halite sample from Spain will be studied in this project. Stable isotope analysis of boron by inductively coupled plasma mass spectrometry will be established in the geochemical facilities at the University of Chicago. In addition to providing an independent constraint on ocean pH and the carbonate system, this research will also determine the distribution coefficient of boron in gypsum and resolve the long-term evolution of the boron geochemical cycle.This 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.