Determination of precise and accurate traditional and non-traditional stable isotope fractionation factors for precipitation of speleothem calcite by unique novel laboratory experiments - part II

• Applicant: Dr. Maximilian Hansen
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 413105321

In the last few decades, speleothems have been established as valuable paleoclimate archives. They provide important information about past climate and environmental variability. The most commonly used paleoclimate proxies in speleothems are the stable carbon and oxygen isotopes. The interpretation of these proxies in terms of past in terms of past climate and environmental variability, remains challenging because various processes in the atmosphere, the soil, the epikast and inside the cave, may obscure these signals. The basic fractionation processes during formation of speleothems are not fully understand yet. In particular, whether isotope fractionation in speleothems is dominated by equilibrium or kinetic processes are still a matter of debate. In the framework of my current project, I extended and significantly improved a worldwide unique experimental setup, which enables to directly investigate isotope fractionation processes during formation of speleothem CaCO3 between all involved species (i.e., CaCO3, dissolved inorganic carbon (DIC), CO2(g) and H2O) under absolute controlled cave-analogues conditions. After substantial extension and improvement of the experimental system the current project was heavily affected by the global COVID-19 pandemic and the associated shut downs of the laboratories. In total a whole project year was lost and the planned experiments could not be performed. Here I apply for an additional year to finish the project as intended. I emphasize that I only apply for additional salary. Most of the project money for consumables, traveling and a student assistant are still available and can directly be transferred to the renewal project.During the experiments thin solution films of a CaCO3 solution will flow down inclined sandblasted glass plates progressively precipitating CaCO3 along the flow path. After different distances of flow and, thus, residence times on the plate pH, electrical conductivity of the solution as well as the isotope composition of both the DIC and the precipitated CaCO3 will be measured. During the experiments temperature, relative humidity, pCO2, the isotope composition of the CO2 as well as the isotope composition of the reservoir solution will be kept meticulously constant using state-of-the-art isotope ratio infrared spectroscopy. This will enable to generate quantitative fractionation factors for all participating species in the system and their dependence on several experimental parameters such as temperature, pCO2 or precipitation rate. Furthermore, the experimental setup will be used to investigate the fractionation of non-traditional stable Ca isotopes. The combination of both non- and traditional stable isotope systems may have great potential for quantitative paleoclimate reconstruction. A detailed understanding of all processes affecting stable isotope fractionation is a prerequisite for a robust interpretation of speleothem records in terms of past climate variability.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Denis Scholz