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

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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.