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

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 delta O-18(p) and delta H-2(p) values from 15 stations in southern Peru and triple oxygen isotope data, expressed as increment ' O-17(p), from 32 precipitation samples. Consistent with previous work, we find that elevation correlates negatively with delta O-18(p) and that seasonal delta O-18(p) variations are related to upstream rainout and local convection. Spatial delta O-18(p) variations and atmospheric back trajectories show that both eastern- and western-derived air masses bring precipitation to southern Peru. Seasonal d-excess(p) cycles record moisture recycling and relative humidity at remote moisture sources, and both d-excess(p) and increment ' O-17(p) clearly differentiate evaporated and non-evaporated samples. These results begin to establish the natural range of unevaporated increment ' O-17(p) 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 delta O-18(p), d-excess(p), and increment ' O-17(p) data and helps identify the evaporation, recycling, and rainout processes that drive water cycling in the central Andes.

Automated summary

The study presents a three-year record of isotopic variability in central Andean precipitation, highlighting the negative correlation between elevation and delta O-18(p) values. Results show that seasonal variations in delta O-18(p) are influenced by upstream rainout and local convection. Both eastern- and western-derived air masses contribute to precipitation in southern Peru, and seasonal d-excess(p) cycles record moisture recycling and relative humidity at remote moisture sources.