Subseasonal Variations of Stable Isotopes in Tropical Andean Precipitation

The tropical Andes of southern Peru and northern Bolivia have several major mountain summits suitable for ice core paleoclimatic investigations. However, incomplete understanding of the controls on the isotopic (delta D, delta O-18) composition of precipitation and a paucity of field observations in this region continue to limit ice-core-based paleoclimate reconstructions. This study examines four years of daily observations of delta D and delta O-18 in precipitation from a citizen scientist network on the northeastern margin of the Altiplano, to identify controls on the subseasonal spatiotemporal variability in delta O-18 during the wet season (November-April). These data provide new insights into modern delta O-18 variability at high spatial and temporal scales. We identify a regionally coherent subseasonal signal in precipitation delta O-18 featuring alternating periods of high and low delta O-18 of 9-27-day duration. This signal reflects variability in precipitation delivery driven by synoptic conditions and closely relates to variations in the strength of the South American low-level jet and moisture availability over the study area. The annual layer of snowpack on the Quelccaya Ice Cap observed in the subsequent dry season retains this subseasonal signal, allowing the development of a snow-pit age model based on precipitation delta O-18 measurements, and demonstrating how synoptic variability is transmitted from the atmosphere to mountaintop snowpacks along the Altiplano's eastern margin. This result improves our understanding of the hydrometeorological processes governing delta O-18 and delta D in tropical Andean precipitation and has implications for improving paleoclimate reconstructions from tropical Andean ice cores and other paleoclimate records.