ISOLUTION 1.0: an ISOtope evoLUTION model describing the stable oxygen (δ18O) and carbon (δ13C) isotope values of speleothems

Abstract

Stable oxygen and carbon isotope ratios (δ13C and δ18O) are the most applied climate and environmental proxies in speleothems allowing to infer past changes in cave drip water δ13C and δ18O related to climate and environmental variations from above the cave. However, disequilibrium isotope fractionation processes can modify δ13C and δ18O values in speleothems, which is in most cases difficult to estimate due to inter-dependencies on various cave specific parameter. To better understand the effect of these disequilibrium isotope fractionation processes proxy system models were developed in recent years, such as the ISOLUTION model. Here the code of the ISOLUTION model is made available for the public and the speleothem community to be applied to research questions that arise from e.g. monitoring programs that investigate δ13C and δ18O values of in situ calcite precipitates on watch glasses or modern speleothem calcite, respectively. Another application of the ISOLUTION model is to investigate the dependence of calcite δ13C and δ18O on the variation of one or multiple cave specific parameter, such as cave air temperature, drip interval, cave air pCO2, Ca2+ concentration of the drip water as well as on relative humidity and wind velocity. This allows to quantitatively estimate the effect of disequilibrium isotope fractionation processes in individual caves and drip sites on speleothem δ13C and δ18O values for modern and past climates and may help to further elucidate the complex interplay of kinetic and disequilibrium isotope fractionation.

Keywords

• speleothems
• proxy system model
• ISOLUTION