Stable water isotope signals and their relation to stratiform and convective precipitation in the tropical Andes

Abstract

Stratiform and convective precipitation are known to be associated with distinct isotopic fingerprints in the tropics. Such rain type specific isotope signals are of key importance for climate proxies based on stable isotopes like for example ice cores and tree rings and can be used for climate reconstructions of convective activity. However, recently, the relation between rain type and isotope signal has been intensively discussed. While some studies point out the importance of deep convection for strongly depleted isotope signals in precipitation, other studies emphasize the role of stratiform precipitation for low concentrations of the heavy water isotopes. Uncertainties arise from observational studies as they mainly consider oceanic regions and mostly long aggregation timescales, while modelling approaches with global climate models cannot explicitly resolve convective processes and rely on parametrization. As high-resolution climate models are particularly important for studies over complex topography, we applied the isotope-enabled version of the high-resolution climate model from the Consortium for Small-Scale Modelling (COSMOiso) over the Andes of tropical south Ecuador, South America, to investigate the influence of stratiform and convective rain on the stable oxygen isotope signal of precipitation (δ18OP). Our results highlight the importance of deep convection for depleting the isotopic signal of precipitation and increasing the secondary isotope variable deuterium excess. Moreover, we found that an opposing effect of shallow and deep convection on the δ18OP signal. Based on these results, we introduce a shallow and deep convective fraction to analyze the effect of rain types on δ18OP.