Fractionation processes of Ca isotopes during synsedimentary and early diagenetic reactions in marine sediments

钙同位素比是古海洋学中的一个有用工具，但人们对沉积物液固相互作用期间钙同位素分馏过程以及对代理信号的潜在影响知之甚少。本项目的目的是研究早期成岩反应，特别是吸附-解吸反应过程中孔隙流体中Ca同位素的分馏。本项目第一部分的结果表明，钙离子在粘土矿物表面吸附过程中的脱水不会引起同位素分馏。这也有意义的理解同位素分馏过程中碳酸钙沉淀。然而，我们观察到钙同位素分馏部分解吸过程中，程度取决于钙解吸量和温度。这项实验工作的结果对于更好地了解天然海洋孔隙水的过程至关重要。在本项目的最后一部分，我们将测定沉积物中的Ca交换反应速率。这将提供有关沉积物钙解吸速率以及吸附和孔隙水钙之间的平衡时间的信息。最后的吸附-解吸实验将用海洋沉积物进行，以将我们的结果从纯粘土矿物与天然沉积物联系起来。

Calcium-isotope ratios are a useful tool in paleoceanography, yet little is known about Caisotope fractionation processes during fluid-solid interactions in the sediments and potential effects on the proxy signal. The aim of this project is to investigate the fractionation of Ca-isotopes during early diagenetic reactions in porefluids, especially adsorption-desorption reactions. The results of the first part of this project have shown that the dehydration of Ca-ions during adsorption on clay mineral surfaces does not cause isotopic fractionation. This has also implications for understanding isotope fractionation during CaCO3 precipitation. However, we observed Ca-isotope fractionation during partial desorption, the degree depending on the amount of Ca desorbed and temperature. The results from this experimental work are essential for a better understanding of processes in natural marine porewaters. In the last part of this project, we will determine Caexchange reaction rates in sediments. This will provide information on the rate of Ca desorption from sediments as well as the equilibration time between adsorbed and porewater Ca. The final adsorption-desorption experiments will be conducted with marine sediments to relate our results from pure clay minerals to natural sediments.