Deciphering Climate Archives: Establishing the Inorganic Basis of an Isotope Fractionation Phenomenon in Biogenic CaCO3

根据该奖项，PI将调查无机基础，以了解海洋的CO2化学和生物碳酸盐中13 C/18 O分馏之间的联系。这可能会改善古气候重建和长期气候变化的理解。大量的气候重建是基于曾经活着的生物体的化石遗迹。在海洋环境中，用于这些重建的时间尺度从几十年到数亿年的最重要的生物之一是有孔虫和珊瑚。在这些生物体分泌的CaCO 3中，发现了稳定的碳（α 13 C）和氧（α 18 O）同位素的似乎普遍的共分馏。在有孔虫中，a18 O效应似乎是由海水pH值驱动的，海水pH值在当前关于CO2和中生代气候变化的激烈辩论中起着核心作用。分馏效应的普遍性强烈表明了一种共同的机制，可能是物理化学性质的，这是迄今为止未知的。方解石晶种的无机沉淀实验将进行，首先在简单的氯化钙溶液，随后在海水中。将改变溶液的碳酸盐化学性质，以涵盖广泛的pH值范围。方解石晶体的同位素组成（d13 C，d18 O和d48 Ca），然后测量质谱。应用与13 C，18 O和48 Ca同位素掺入相结合的晶种结晶技术将允许非常精确的质量平衡计算，因此可以非常精确地确定水和方解石过度生长之间的C-和O-同位素分馏。拟议的工作将确定是否共分馏是一个热力学现象，完全由溶液的碳酸盐化学控制，或者它是否是一个生物效应。开发一个新的模型计算的碳酸盐化学和稳定同位素分馏将伴随着实验工作，以获得一个原始的和完整的图片的分馏过程。 更广泛的影响包括本科生和研究生在实验室技术，理论建模和气候/古气候研究等领域的教育。

Under this award the PIs will investigate the inorganic basis for understanding the link between the ocean's CO2 chemistry and 13C/18O fractionation in biogenic carbonates. This may improve paleoclimate reconstructions and understanding of long-term climate changes. A large body of climate reconstructions is based on fossil remains of once living organisms. In the marine environment, one of the most important organisms employed for these reconstructions on time scales ranging from decades to hundreds of million of years are foraminifera and corals. In the CaCO3 secreted by several of these organisms, a seemingly universal co-fractionation of stable carbon (a13C) and oxygen (a18O) isotopes has been discovered. In foraminifera, the a18O-effect appears to be driven by the seawater pH which plays a central role in a current, intense debate on CO2 and Phanerozoic climate change. The universality of the fractionation effect strongly suggests a common mechanism, likely of physico-chemical nature, which is hitherto unknown. Inorganic precipitation experiments on calcite seed crystals will be conducted, first in simple CaCl2 solutions and subsequently in seawater. The carbonate chemistry of the solutions will be varied to cover a wide range of pH values. The isotopic composition of the calcite crystals (d13C, d18O, and d48Ca) are then measured mass-spectrometrically. Applying a technique of seeded crystallization combined with 13C, 18O, and 48Ca isotopes spiking will allow very precise mass balance calculations and hence a very precise determination of the C- and O-isotope fractionation between water and calcite overgrowth. The proposed work will establish whether the co-fractionation is a thermodynamic phenomenon solely controlled by the solution's carbonate chemistry or whether it is a biological effect. Development of a new model for the calculation of the carbonate chemistry and stable isotope fractionation will accompany the experimental work in order to obtain an original and complete picture of the fractionation process. The Broader Impacts include education of undergraduate students and graduate students in areas such as laboratory techniques, theoretical modeling, and climate/paleoclimate research.