Impacts of Recent Warming and the 2015/2016 El Niño on Tropical Peruvian Ice Fields

Data collected between 1974 and 2016 from snow pits and core samples from two Peruvian ice fields demonstrate the effect of the recent warming over the tropical Andes, augmented by El Nino, on the preservation of the climate record. As the 0°C isotherm is approaching the summit of the Quelccaya ice cap in the Andes of southern Peru (5,670 meters above sea level (masl)), the distinctive seasonal δ18O oscillations in the fresh snow deposited within each thermal year are attenuated at depth due to melting and percolation through the firn. This has become increasingly pronounced over 43 years. In the Andes of northern Peru, the ice field on the col of Nevado Huascaran (6050 masl) has retained its seasonal δ18O variations at depth due to its higher elevation. During the 2015/2016 El Nino, snow on Quelccaya and Huascaran was isotopically (δ18O) enriched and the net sum of accumulation over the previous year (NSA) was below the mean for non–El Nino years, particularly on Quelccaya (up to 64% below the mean) which was more pronounced than the NSA decrease during the comparable 1982/1983 El Nino. Interannual large-scale oceanic and middle to upper-level atmospheric temperatures influence δ18O in precipitation on both ice fields, although the influences are variably affected by strong El Nino–Southern Oscillation events, especially on Quelccaya. The rate of ice wastage along Quelccaya's margin was dramatically higher during 2015/2016 compared with that of the previous 15 years, suggesting that warming from future El Ninos may accelerate mass loss on Peruvian glaciers.