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.