Drivers of δ¹⁸O Variability Preserved in Ice Cores from Earth’s Highest Tropical Mountain

Abstract In 2019, four ice cores were recovered from the world's highest tropical mountain, Nevado Huascarán (Cordillera Blanca, Peru; 9.11°S, 77.61°W). Composite hydroclimate records of the two Col cores (6,050 masl) and the two Summit cores (6,768 masl) are compared to gridded gauge‐analysis and reanalysis climate data for the most recent 60‐year. Spatiotemporal correlation analyses suggest that the ice core oxygen stable isotope (δ 18 O) record largely reflects tropical Pacific climate variability, particularly in the NINO3.4 region. By extension, the δ 18 O record is strongly related to rainfall over the Amazon Basin, as teleconnections between the El Niño Southern Oscillation and hydrological behavior are the main drivers of the fractionation of water isotopes. However, on a local scale, modulation of the stable water isotopes appears to be more closely governed by upper atmospheric temperatures than by rainfall amount. Over the last 60 years, the statistical significance of the climate/δ 18 O relationship has been increasing contemporaneously with the atmospheric and oceanic warming rates and shifts in the Walker circulation. Isotopic records from the Summit appear to be more sensitive to large‐scale temperature changes than the records from the Col. These results may have substantial implications for modeling studies of the behavior of water isotopes at high elevations in the tropical Andes.