Experimental study of CO2 hydration in seawater: Mechanism and kinetic isotope effects

在海洋环境中，二氧化碳（CO2）与水的化学反应是产生碳酸（H2CO3）和所有相关化学离子(碳酸盐（CO3）；氢离子（H+）和碳酸氢盐（HCO3-）是海洋中pH值的主要缓冲物质。脱水是指相反的反应，释放二氧化碳气体。通过参与重要的反应和控制pH值，这些物种控制着海洋中各种各样的化学和生物过程。令人惊讶的是，虽然涉及二氧化碳水化及其产物的重要反应已经在海洋中得到了广泛的研究，但一些基本机制仍然知之甚少，数据集也很少。特别是，人们对碳原子和氧原子的天然同位素是如何参与的几乎一无所知，这对于解释化学物质和固体碳酸钙（如珊瑚礁产生的）的观察变化至关重要。这项研究的目的是仔细地产生新的实验数据，包括海洋中二氧化碳水化前后碳和氧同位素的关键测量。由于这些碳酸盐物种在海洋科学的许多研究中被广泛使用，特别是在研究过去气候的研究中，这项研究将产生深远的影响。此外，研究结果将为海洋在气候变化中如何吸收和应对大气中二氧化碳浓度的变化提供新的基本见解。这项研究将资助一位早期职业科学家，他致力于研究生和本科教育以及向社区提供科学服务。虽然海洋中二氧化碳的水合/脱水严重影响各种海洋化学和生物过程，但人们对该反应的某些方面了解甚少。分子机制尚不清楚，因为已经提出了两种可能的途径。此外，CO2期间的动力学同位素效应还没有得到很好的研究，关于这一主题的数据也不一致。本研究旨在通过对碳氧同位素分馏的研究，不仅可以阐明反应的分子机理，而且可以为动力学同位素效应增加一个一致的数据集。这项研究的主要挑战是在重新平衡之前将产物HCO3-从二氧化碳中分离出来，但研究人员将通过快速沉淀溶解的碳作为碳酸盐来解决这个问题。由于水化过程形成的碳酸盐被认为是水化学、生物过程和整个无机碳循环的关键指标，并被广泛用于各种海洋学研究，特别是作为古代用物，因此本研究将提供基本的机制数据，这将大大推进超越物理化学测量的研究，将在这里进行。

The chemical reaction of carbon dioxide (CO2) with water in the marine environment is a fundamental process that creates carbonic acid (H2CO3) and all of the associated chemical ions (carbonate (CO3); hydrogen ions (H+), and bicarbonate (HCO3-)) that serve as the dominant buffer for pH in the ocean. Dehydration refers to the opposite reaction that releases CO2 gas. By entering into important reactions and serving to control pH, these species govern a wide variety of chemical and biological processes in the ocean. Surprisingly, while the important reactions that involve CO2 hydration and its resulting products have been extensively studied in the ocean, some of the fundamental mechanisms remain poorly understood and datasets are sparse. In particular, almost nothing is known about how the natural isotopes of the carbon and oxygen atoms are involved and this is critically needed to explain observed changes in chemical species and solid calcium carbonate such as that created by coral reefs. This research aims to carefully produce novel experimental data that includes critical measurements of carbon and oxygen isotopes before and after the hydration of CO2 in the ocean. Because these resulting carbonate species are used widely in many studies in the ocean sciences, particularly those examining past climates, this research will have far-reaching influences. Additionally, the results will provide new fundamental insight on exactly how the ocean will take up and respond to changing concentrations of atmospheric CO2 in a changing climate. The research will fund an early-career scientist who is dedicated to graduate and undergraduate education as well as scientific outreach to the community. While hydration/dehydration of CO2 in the ocean critically influences a variety of marine chemical and biological processes, there are certain aspects of the reaction that are poorly understood. The molecular mechanism is not yet clear, as there are two possible pathways that have been proposed. Additionally, kinetic isotope effects during CO2 have not been well studied, and the data regarding this topic is inconsistent. This research aims to study the carbon and oxygen isotope fractionation, which will not only clarify the molecular mechanism of the reaction but also will add a consistent dataset on kinetic isotope effects. The main challenge in this study is separating the product, HCO3-, from CO2 before re-equilibration, but the researcher will resolve this by rapidly precipitating dissolved carbon as carbonate. Since carbonates formed from the process of hydration are considered critical indicators of water chemistry, biological processes, and the inorganic carbon cycle as a whole and are used in a wide variety of oceanographic research, particularly as paleo-proxies, this research will provide fundamental mechanistic data that will greatly advance studies reaching beyond the physical chemical measurements that will be made here.