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Systematic investigation of stable isotope fractionation in speleothems with novel laboratory experiments

通过新颖的实验室实验系统研究洞穴中的稳定同位素分馏

基本信息

批准号：
242129757
负责人：
Professor Dr. Wolfgang Dreybrodt
金额：
--
依托单位：
Fachbereich 01: Physik und Elektrotechnik
依托单位国家：
德国
项目类别：
Research Grants
财政年份：
2013
资助国家：
德国
起止时间：
2012-12-31 至 2018-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/242129757?language=en
关键词：
Systematic investigation stable isotope fractionation

项目摘要

Despite of intensive research in recent years, the basic processes during speleothem growth influencing the stable isotope signals (d13C and d18O) have not been understood in detail yet. In particular, the influence of kinetic isotope fractionation is difficult to quantify. Currently, two different models developed by the two principle investigators of this proposal are available. The major uncertainties, however, arise from the relatively uncertain isotope fractionation factors used in the models. Kinetic isotope fractionation factors for the system Ca2+-CO2-H2O have not been determined yet.We have developed a novel experimental setup in order to investigate the basic processes during precipitation of CaCO3 from thin films of water and the resulting effect on stable isotope fractionation. The conditions of natural cave systems are precisely simulated, and several parameters, such as the thickness of the water film, pH and the Ca2+ content of the solution, can be precisely adjusted and controlled during the experiment. Our approach allows studying the evolution of the d18O and d13C values of both the dissolved HCO3- and the precipitated CaCO3. These are important developments in comparison to previous experiments. Furthermore, our experimental setup can also be used without further modifications to study the fractionation of clumped isotopes and the distribution coefficients of trace elements between the solution and the precipitated CaCO3.On the basis of our models, we will use our setup in order to perform several experiments in order to improve the basic understanding of stable isotope fractionation in speleothems. We will quantitatively determine the corresponding isotope fractionation factors and the time constants of the geochemical (isotope exchange) processes. The results will be used to validate and, if necessary, improve the available models.Furthermore, we will perform comparable experiments to investigate the fractionation of clumped isotopes and to determine the distribution coefficients of trace elements (e.g., Mg, Sr, Ba, P, U) between the solution and the precipitated CaCO3.

尽管近年来的研究十分深入，但洞穴沉积物生长过程中影响d13 C和d18 O稳定同位素信号的基本过程还没有得到详细的了解。特别是，动力学同位素分馏的影响很难量化。目前，该提案的两位主要研究人员开发了两种不同的模型。然而，主要的不确定性来自于模型中使用的相对不确定的同位素分馏因子。Ca ~（2+）-CO_2-H_2 O体系的动力学同位素分馏因子尚未确定，为了研究CaCO_3从水膜中沉淀的基本过程及其对稳定同位素分馏的影响，我们建立了一套新的实验装置。该方法精确模拟了天然洞穴系统的条件，可以精确调节和控制水膜厚度、溶液pH值和Ca 2+含量等参数。我们的方法允许研究的d18 O和d13 C值的溶解HCO 3-和沉淀碳酸钙的演变。与以前的实验相比，这些都是重要的发展。此外，我们的实验装置也可以直接用于研究成团同位素的分馏以及微量元素在溶液和沉淀CaCO 3之间的分配系数。在我们的模型的基础上，我们将利用我们的实验装置进行一些实验，以提高对洞穴沉积物中稳定同位素分馏的基本认识。我们将定量地确定相应的同位素分馏因子和地球化学（同位素交换）过程的时间常数。研究结果将用于验证和改进现有的模型。此外，我们将进行可比实验，以研究聚集同位素的分馏，并确定微量元素的分布系数（例如，Mg、Sr、Ba、P、U）。