Abstract/Summary

The oxygen isotope composition of speleothems is a widely used proxy for past climate change. Robust use of this proxy depends on understanding the relationship between precipitation and cave drip water d18O. Here, we present the first global analysis, based on data from 163 drip sites, from 39 caves on five continents, showing that drip water d18O is most similar to the amount-weighted precipitation d18O where mean annual temperature (MAT) is < 10 °C. In contrast, for seasonal climates with MAT > 10 °C and < 16 °C, drip water d18O records the recharge-weighted d18O. This implies that the d18O of speleothems (formed in near isotopic equilibrium) are most likely to directly reflect meteoric precipitation in cool climates only. In warmer and drier environments, speleothems will have a seasonal bias toward the precipitation d18O of recharge periods and, in some cases, the extent of evaporative fractionation of stored karst water.