Variability and Controls on δ18O, d-excess, and ∆′17O in Southern Peruvian Precipitation

Abstract

The isotopic composition of precipitation is used to trace water cycling and climate change, but interpretations of the environmental information recorded in central Andean precipitation isotope ratios are hindered by a lack of multi-year records, poor spatial distribution of observations, and a predominant focus on Rayleigh distillation. To better understand isotopic variability in central Andean precipitation, we present a three-year record of semimonthly δ18Op and δ2Hp values from 15 stations in southern Peru and triple oxygen isotope data, expressed as ∆′17Op, from 32 precipitation samples. Consistent with previous work, we find that elevation correlates negatively with δ18Op and that seasonal δ18Op variations are related to upstream rainout and local convection. Spatial δ18Op variations and atmospheric back trajectories show that both eastern- and western-derived air masses bring precipitation to southern Peru. Seasonal d-excessp cycles record moisture recycling and relative humidity at remote moisture sources, and both d-excessp and ∆′17Op clearly differentiate evaporated and non-evaporated samples. These results begin to establish the natural range of unevaporated ∆′17Op values in the central Andes and set the foundation for future paleoclimate and paleoaltimetry studies in the region. This study highlights the hydrologic understanding that comes from a combination of δ18Op, d-excessp, and ∆′17Op data and helps identify the evaporation, recycling, and rainout processes that drive water cycling in the central Andes.