Variability and Controls on δ<sup>18</sup>O, d‐excess, and ∆′<sup>17</sup>O in Southern Peruvian Precipitation
Phoebe Aron, Christopher J. Poulsen, Richard P. Fiorella, Naomi E. Levin, R. Paul Acosta, Brian J. Yanites, Elizabeth J. Cassel
Abstract
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 δ 18 O p and δ 2 H p values from 15 stations in southern Peru and triple oxygen isotope data, expressed as ∆′ 17 O p , from 32 precipitation samples. Consistent with previous work, we find that elevation correlates negatively with δ 18 O p and that seasonal δ 18 O p variations are related to upstream rainout and local convection. Spatial δ 18 O 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 ∆′ 17 O p clearly differentiate evaporated and non‐evaporated samples. These results begin to establish the natural range of unevaporated ∆′ 17 O 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 δ 18 O p , d‐excess p , and ∆′ 17 O p data and helps identify the evaporation, recycling, and rainout processes that drive water cycling in the central Andes.