Improved accuracy of oxygen and hydrogen isotope analysis in speleothem fluid inclusions: the importance of crusher temperature

Speleothem fluid inclusion isotope analysis provides the oxygen and hydrogen isotope composition of the parent water from which the carbonate precipitated (d18OFL; d2HFL). In contrast to carbonate isotopes, it is not affected by kinetic isotope effects. Fluid inclusion isotopes can be analyzed by crushing heated speleothem fragments and measuring the isotopic composition of the released water vapor. However, during this process, analytical artifacts related to pre-crushing evaporation and/or post-crushing adsorption can occur, potentially skewing the isotope values away from their origin and biasing temperatures calculated from the combination of d18OFL and d18OCc. In d2H-d18O cross-plots, analytical (pre-crushing) evaporation has been suggested to induce very shallow slopes down to 1.4, lower than trends induced by evaporation under natural conditions in the soil or inside the cave. In this study, we used a Picarro L2140i isotope analyzer with an artificially generated moist background setup to examine the effect of analytical evaporation by quantifying the water loss prior to analysis when applying different crushing temperatures. We targeted two layers with different calcite fabrics from a flowstone of Touhami Cave (GTOF2), Morocco, as well as speleothems from Scladina Cave, Belgium and Bloukrantz Cave, South Africa.The samples have different water contents and show different isotope effects of analytical evaporation that highly depend on the crushing temperature. Our results indicate that high water content samples (>1-2 µL/g) are generally more reliable compared to low yield samples (