Stable isotope fractionation in minerals as a tool for climate reconstruction: insights from molecular modelling

矿物中的稳定同位素分馏作为气候重建的工具：来自分子模型的见解

• 批准号: 2890069
• 金额: --
• 依托单位: University of Reading
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2890069
• 关键词: Stable; isotope; fractionation; minerals; tool

Subtle changes in the ratio of stable isotopes in natural climate archives such as sediments in oceans, polar ice caps or speleothems can be precisely measured to reconstruct climate history. For example, by measuring the ratio of oxygen isotopes in shells found in marine sediments, it is possible to determine changes in seawater temperature and global ice volume over time, because the isotope ratio is affected by both factors. The interpretation of isotope records requires a detailed understanding of the complex processes governing isotope exchange and fractionation, which has motivated the development of theoretical models to predict and rationalise the fractionation of stable isotopes between different phases. Such approaches are typically based on molecular-level considerations: the vibrational behaviour of atoms depends on the isotopic masses involved, affecting equilibrium free energies and kinetic barriers. Molecular modelling techniques based on quantum chemistry or classical forcefields can then be used to predict the fractionation of stable isotopes between phases. While significant progress has been achieved in recent years in this research direction, some important challenges remain, because drastic approximations must often be made to avoid the huge computational cost of the atomistic-level simulations: e.g.: i) interatomic interactions are simplified; ii) isotope fractionations are predicted considering only the mineral bulk behaviour, neglecting the mineral-aqueous interface; and iii) non-equilibrium (kinetic) effects are usually ignored. In this project, we will take advantage of recent major advances in molecular modelling to overcome these limitations and achieve a faster and more accurate prediction of stable isotope fractionation, with the potential to transform the interpretation of isotope records. We will employ molecular dynamics simulations to model isotope exchange between minerals and aqueous solution, considering: i) accurate quantum-mechanical representation of interatomic interactions; ii) the effect of the mineral-aqueous interface and therefore of particle size on the overall fractionation ratios; iii) non-equilibrium and kinetic effects. To afford the drastic increase in computational cost that such improvements require, we will combine quantum chemistry with machine-learning (ML) techniques, where the latter are used to vastly accelerate the former without significant accuracy sacrifice.

自然气候档案中稳定同位素比率的微妙变化，如海洋沉积物、极地冰盖或洞穴沉积物，可以被精确测量，以重建气候历史。例如，通过测量海洋沉积物中发现的贝壳中氧同位素的比例，可以确定海水温度和全球冰量随时间的变化，因为同位素比例受到这两个因素的影响。同位素记录的解释需要详细了解同位素交换和分馏的复杂过程，这促使理论模型的发展，以预测和合理化不同阶段之间的稳定同位素的分馏。这些方法通常基于分子水平的考虑：原子的振动行为取决于所涉及的同位素质量，影响平衡自由能和动力学势垒。基于量子化学或经典力场的分子建模技术可以用来预测稳定同位素在相之间的分馏。虽然近年来在这一研究方向上取得了重大进展，但仍然存在一些重要的挑战，因为通常必须进行激烈的近似以避免原子级模拟的巨大计算成本：例如：i）原子间的相互作用被简化; ii）同位素分馏被预测为仅考虑矿物本体行为，忽略矿物-水界面;以及iii）非平衡（动力学）效应通常被忽略。在这个项目中，我们将利用分子建模的最新重大进展来克服这些局限性，实现更快，更准确的稳定同位素分馏预测，并有可能改变同位素记录的解释。我们将采用分子动力学模拟来模拟矿物和水溶液之间的同位素交换，考虑：i）原子间相互作用的精确量子力学表示; ii）矿物-水界面的影响，因此粒度对整体分馏比的影响; iii）非平衡和动力学效应。为了提供这种改进所需的计算成本的急剧增加，我们将联合收割机与机器学习（ML）技术相结合，后者用于大大加速前者而不会显着牺牲精度。