“Stable isotope fractionation processes (∂18O and ∂ 13C) during precipitation of speleothem calcite: systematic investigation in laboratory experiments“
The most widely applied climate proxies in speleothems are stable carbon and oxygen isotopes (∂13C and ∂18O). They can be measured at very high resolution, and in combination with precise absolute dating by the 230Th/U method, they enable palaeoclimate reconstruction at monthly to annual resolution. The interpretation of the stable isotope signals in terms of past temperature and/or precipitation variability, however, is complex because both ∂18O and ∂13C depend on a complicated interplay of various processes in the atmosphere, the soil and karst above the cave and the surface of the stalagmite. Quantitative reconstruction of temperature and precipitation has, thus, remained impossible so far.
We have developed several new laboratory experiments aiming to understand the basic physical and chemical processes influencing the ∂18O and ∂13C signals in speleothems. The experiments are performed under completely controlled conditions, which are very similar to those in natural caves.
In particular, we want to quantify the influence of kinetic isotope fractionation in speleothems and verify and expand recent modelling studies. Furthermore, we will quantitatively determine the corresponding isotope fractionation factors and the time constants of the isotope-geochemical (exchange) reactions. In the framework of further experiments, we will examine the fractionation of "clumped isotopes" and determine distribution coefficients for several trace elements, such as Mg, Sr, Ba, P and U.
Hansen, M., Scholz, D., Froeschmann, M.-L., Schöne, B. R., and Spötl, C., 2017. Carbon isotope exchange between cave air and thin solution films on speleothem surfaces: Artificial cave experiments and a complete diffusion-reaction model. Geochimica et Cosmochimica Acta 211, 28-47.
Dreybrodt, W., Hansen, M., and Scholz, D., 2016. Processes affecting the stable isotope composition of calcite during precipitation on the surface of stalagmites: Laboratory experiments investigating the isotope exchange between DIC in the solution layer on top of a speleothem and the CO2 of the cave atmosphere. Geochimica et Cosmochimica Acta 174, 247-262.
Hansen, M., Dreybrodt, W., and Scholz, D., 2013. Chemical evolution of dissolved inorganic carbon species flowing in thin water films and its implications for (rapid) degassing of CO2 during speleothem growth. Geochimica et Cosmochimica Acta 107, 242-251.