Origin and variability of oxygen and hydrogen isotopic composition of precipitation in the Central Andes: A review

This review concerns the knowledge of the isotopic composition of current precipitation and its association with climate, geography and orography, in the Central Andes (14–28°S and 75–63°W). This knowledge is required for the evaluation of other hydrological values, especially aquifer recharge and water resources, in environments varying from rainy to hyper-arid. Since the 1960s, oxygen (δ18O) and deuterium (δ2H) isotope composition of natural water have been used as tracers of the global hydrological cycle. In the present article, the goal is to identify the origin and trajectory of air masses that produce rainfall in the Central Andes and the isotopic composition of the precipitation, as a first step to evaluate recharge and groundwater resources. The isotopic composition of rainfall varies spatially and temporarily, depending on the climatic phenomena that originate the movement of air masses, their moisture content and the isotope fractionation processes that occur until precipitation falls. Most of the significant and recent literature on the mechanisms of δ18O and δ2H transport and fractionation in precipitation along the Central Andes has been collected and summarized in this review. Precipitation in the eastern and central Andes comes mainly from the humidity generated in the Atlantic Ocean. Although the processes involved in isotope content variability of precipitation are well known, the processes involved in isotopic variability in the Western Cordillera remain poorly understood. This is mostly due to mixing of different moisture sources: from the Atlantic Ocean in summer and from the Pacific Ocean in winter. In general, winter rainfall is more enriched in δ18O and δ2H than summer rainfall. Looking at existing data, their distribution is far from being homogeneous and well-distributed, so spatial accuracy is poor in some areas, especially in the Altiplano. Hydrological and hydrogeological research and water resources evaluation in the Central Andes would greatly benefit from initiatives to obtain broader spatial coverage of rainfall collection to get isotope data for more accurate and continuous assessment of the local weather patterns. Groundwater isotope composition is a future tool to help in increasing the coverage in data scarce areas.

The authors acknowledge SQM (Chile) for their support and for sharing isotopes data of the Salar de Atacama, as well as Southern Copper (Peru) for providing isotopic information. We thank two anonymous reviewers for their valuable comments. Further to this, numerous researchers, professors and practitioners from Argentina and Chile (Daniel E. Martinez, Cristina Dapeña and Christian Herrera) have contributed published and unpublished information and their personal experience.

Peer reviewed