Storm-Scale Variations of Water Isotopes in the Tropical High Andes

Comprehensive understanding of the climatic controls on stable water isotopes (HD, δ¹⁸O) in precipitation over the tropical high Andes is fundamental to developing paleoclimatic reconstructions developed from regional ice cores. To establish how meteorological events transmit isotopic signals to snowpacks we utilize the Quelccaya Isotope Profile Utility (QUIPU), an analytical tool developed from an empirically based hypothesis that δ¹⁸O profiles in high elevation tropical Andean ice cores record mesoscale precipitation processes along moisture trajectories upstream of the site of snow deposition. QUIPU is based on isotopic fractionation according to Rayleigh distillation theory, and utilizes climatological data to simulate depth profiles of δ¹⁸O variations in wet season mountaintop snowpacks.

In this presentation, we demonstrate how QUIPU and in situ data collection offer potential to improve the interpretation of sub-seasonal to annual isotope signals preserved in low-latitude ice cores. In July 2017 our joint US-Peru-Bolivia team obtained snow pit isotope profiles from four high Andean summits at elevations between 5,670-6,265 m ASL along a 450 km linear transect (Quelccaya, Peru and Nevados Ancohuma, Huayna Potosi and Illimani, Bolivia). Storm precipitation amount and isotopic content measurements, collected daily at additional 10 sites in Peru and Bolivia by citizen scientist observers and processed through QUIPU, provide date-specific age models for each snowpit profile. The QUIPU simulations demonstrate skill at accurately reproducing high and low frequency δ¹⁸O signals and amplitudes observed in annual accumulation profiles. As such, QUIPU is enabling determination of the controls on δ¹⁸O annual layer profiles by meteorological phenomena under modern climatic conditions; this in turn informs interpretation of the climatic conditions associated with older δ¹⁸O registered prior to the instrumental era and retrievable in ice core records.