Separating isotopic impacts of karst and in-cave processes from climate variability using an integrated speleothem isotope-enabled forward model

Speleothem δ18O values are commonly used to infer past climate variability. However, both non-linear karst hydrological processes and in-cave disequilibrium isotope fractionation are recognised and hinder the interpretation of δ18O values. In recent years, proxy system models (PSMs) have emerged to quantitatively assess the confounding effects of these processes. This study presents the first integrated stalagmite δ18O PSM (Karstolution) by coupling an existing karst hydrology with an in-cave fractionation PSM. The new modelling framework not only couples the two models, but also includes diffuse flow modelling, coupling of drip rate with infiltration, linking of surface with cave temperature, and incorporates cave seasonality effects. We test Karstolution using a cave monitoring dataset from Golgotha Cave, SW Australia. The predictive capacity of the model is assessed by comparing the output to stalagmite δ18O values. By comparing with observed stalagmite δ18O values, this study is also the first to quantify in-cave disequilibrium both kinetic isotopic fractionation in a speleothem and informs the conclusion that hydroclimatic processes contributes more to the variability of stalagmite δ18O values at Golgotha Cave than does in-cave processes. This is further supported via a sensitivity analysis performed by simulating the impacts of a wider range of cave temperature, ventilation, drip interval and pCO2 values than measured.