Accounting for kinetic isotope effects in Soreq Cave (Israel) speleothems

There is growing evidence that speleothem calcite grows out of isotopic equilibrium with cave drip water, with clumped isotope analysis providing a sensitive indicator for disequilibrium. This disequilibrium is primarily the result of CO₂ degassing from a thin film of water, leading to irreversible ¹³C enrichment and reversible ¹⁸O enrichment and δ₄₇ depletion. Here we examine isotopic disequilibrium in Soreq Cave (Israel) using multiple modern-day and late Holocene speleothems. The variability observed in δ₄₇ is small, within the analytical uncertainty, but the δ₄₇-derived temperature is offset from the modern cave temperature by ~4°C, reflecting degassing related disequilibrium that is fairly constant spatially. δ¹⁸O is more heterogeneous, reflecting short-term variability in drip water δ¹⁸O_w combined with variability in the speleothem growth rates and related fractionation between dissolved carbonate species and the growing calcite mineral. This complexity, however, is markedly reduced by spatial or temporal averaging, enabling an interpretation of the cave paleoclimate record. We examine the Soreq Cave speleothems through a comparison with 2 types of thermometers: one is based on CaCO₃ precipitation from a bulk solution and is typically used for calibration of the δ₄₇ and δ¹⁸O thermometers; a second that is based on CaCO₃ precipitating at the surface of the solution thus focusing and amplifying the thin film characteristics of speleothem formation. Soreq Cave speleothems are intermediate between these thermometers, providing a cave-specific thermometer calibration.