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

钙同位素比值在古海洋学中是一个有用的工具，但对沉积物中流固相互作用过程中的钙同位素分馏过程以及对替代信号的潜在影响知之甚少。本项目的目的是研究孔隙流体中早期成岩反应，特别是吸附-解吸反应中钙同位素的分馏。本项目第一部分的结果表明，钙离子在粘土矿物表面吸附时的脱水不会导致同位素分馏。这对于理解碳酸钙沉淀过程中的同位素分馏也有一定的意义。然而，我们在部分解吸过程中观察到了钙同位素的分馏，程度取决于解吸量和温度。这项实验工作的结果对于更好地理解天然海洋孔隙水中的过程是必不可少的。在这个项目的最后部分，我们将测定沉积物中的钙交换反应速率。这将提供有关沉积物中钙的解吸速率以及吸附和孔隙水中钙的平衡时间的信息。最后的吸附-解吸实验将在海洋沉积物中进行，以将我们从纯粘土矿物获得的结果与天然沉积物相关联。

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.