Beyond isotope proxies: employing triple oxygen isotope systematics in the water cycle and in chemical sediments as quantitative tool

Carbonate classic and clumped isotope ratios (δ18O and Δ47) are used to reconstruct paleotemperature. However, kinetic isotope effects (KIE) induce a bias on absolute temperature reconstructions. High precision δ17O measurements provide a refinement proxy to identify the direction and magnitude of KIEs in carbonates. Progress on this new proxy will be discussed.

The basic concept is similar to the combination of conventional oxygen and hydrogen isotope analyses in water. Combined δ18O and δ2H analyses are commonly used to approximate the magnitude of KIEs during evaporation. Triple oxygen isotope measurements in water are now used in a similar fashion. The simultaneous utilization of both trajectories provides a powerful approach to reconstruct quantitative paleoclimate information. We applied this approach to extracted water from ancient gypsum formed in the Atacama Desert and in Cyprus during the Messinian Salinity Crisis. Quantitative information on paleo-humidity and palaeohydrology are obtained. Effectively, this information is derived by quantifying KIE.

In this example, the KIE is related to diffusion of water molecules through air. Other examples of KIE include the breaking of chemical bonds, molecular mixing effects or steady states. Triple oxygen isotope trajectories allow to distinguish between such fundamental processes. Respective concepts will be explained using examples from chert and phosphate triple oxygen isotope systematics.