Isotopic properties of carbonate minerals: searching for hidden environmental changes and their origins

我提出的研究计划的目标是更深入地了解二价金属碳酸盐的同位素特性(1)为科学界提供多种环境指标，使我们能够追踪当前和过去的环境变化；(2)建立可靠的生物特征指标，可用于区分不同来源的碳酸盐（原生与次生，无机与生物）。几十年来，天然碳酸盐的同位素特性被广泛用于重建过去的气候变化。然而，大多数研究都集中在碳酸钙的“氧”和“碳”同位素性质上，这是由于成熟的分析技术和矿物的普遍存在。碳酸钙和其他二价金属碳酸盐中其他元素的同位素性质引起的注意少得多，因此还没有得到彻底的研究。因此，我建议在各种二价金属碳酸盐-水体系中研究非传统稳定同位素（如B、Ca、Li和Fe）以及团块同位素（如Ca13C18O16O2）的同位素系统。我的研究计划的第一个目标是量化碳酸盐-水系统中多种稳定同位素的“平衡”同位素分馏，作为温度和溶液化学的函数。例如，方解石-海水体系中的Ca-C-O-B-(Li)同位素系统将被表征，以开发新的多元素环境代用物，使我们能够重建古气候、pH或海洋化学。第二个目标是根据在不同实验条件下进行的一系列实验室实验中收集的多维稳定同位素数据阵列，通过将这些重要效应与非生物“非平衡”同位素效应分离开来，识别多种同位素的生物“非平衡”同位素效应。该研究项目的成果将为无机系统建立可靠的数据集，用于解释陆地和外星碳酸盐标本的传统和非传统稳定同位素组成。

The goal of my proposed research program is to gain a deeper understanding of the isotopic properties of divalent metal carbonates (1) to provide the scientific community with versatile environmental proxies that allow us to trace current and past environmental changes and (2) to establish reliable biosignature-indicators that can be used to differentiate carbonates of various origins (primary vs. secondary, inorganic vs. biogenic). For several decades, isotopic properties of natural carbonates have been extensively used to reconstruct past climate variations. Nevertheless, most studies focused on the "oxygen" and "carbon" isotope properties of calcium carbonates because of the well-established analytical techniques and the ubiquity of the minerals. The isotopic properties of other elements in calcium carbonates and those of other divalent metal carbonates have attracted far less attention and thus have not been thoroughly investigated. For this reason, I am proposing to investigate the isotopic systematics of non-traditional stable isotopes (e.g., B, Ca, Li, and Fe) as well as clumped isotopes (e.g., Ca13C18O16O2) in a variety of divalent metal carbonate-water systems. The first objective of my research program is to quantify the "equilibrium" isotope fractionations of multiple stable isotopes in the carbonate-water system as a function of temperature and solution chemistry. For example, the Ca-C-O-B-(Li) isotope systematics in the calcite-seawater system will be characterized to develop new multi-element environmental proxies that will allow us to reconstruct paleo-climate, pH, or ocean chemistry. The second objective is to identify biogenic "non-equilibrium" isotope effects of multiple isotopes by disentangling these vital effects from the abiogenic "non-equilibrium" isotope effects on the basis of multi-dimensional stable isotope data arrays collected from a series of laboratory experiments conducted under various experimental conditions. The outcomes of the research program will establish reliable datasets for inorganic systems that will serve to interpret traditional and non-traditional stable isotope compositions of terrestrial and extraterrestrial carbonate specimens.