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This work investigates the timing, paleoclimatic framework and inter-hemispheric teleconnections inferred from the glaciers last maximum extension and the deglaciation onset in the Arid Tropical Andes. A study area was selected to the northeastward of the Nevado Coropuna, the volcano currently covered by the largest tropical glacier on Earth. The current glacier extent, the moraines deposited in the past and paleoglaciers at their maximum extension have been mapped. The present and past Equilibrium Line Altitudes (ELA and paleoELA) have been reconstructed and the chlorine-36 ages have been calculated, for preliminary absolute dating of glacial and volcanic processes. The paleoELA depression, the thermometers installed in the study area and the accumulation data previously published allowed development of paleotemperature and paleoprecipitation models. The Coropuna glaciers were in maximum extension (or glacial standstill) 20-12 ka ago (and maybe earlier). This last maximum extension was contemporary to the Heinrich 2-1 and Younger Dryas events and the Tauca and Coipasa paleolake transgressions on Bolivian Altiplano. The maximum paleoELA depression (991 m) shows a colder (−6.4 • C) and moister climate with precipitation ×1.2-×2.8 higher than the present. The deglaciation onset in the Arid Tropical Andes was 15-11 ka ago, earlier in the most southern, arid, and low mountains and later in the northernmost, less arid, and higher mountains.

Tropical high-mountain permafrost has a unique thermal regime due to its exposure to strong solar radiation and to rough surface snow morphology, which reduce ground heat transfer from the surface. Latent heat transfer and higher albedo that occur during the snow-covered season contribute to positive feedback that supports the presence of permafrost. This preliminary study reports on the thermal state characteristics of tropical mountain permafrost in Peru. This work also evaluates the potential combined impact of the El Niño-Southern Oscillation (ENSO) in the mountain permafrost of the Coropuna and Chachani volcanic complexes, both located at the western edge of the southern Peruvian Altiplano. Temperature monitoring boreholes were established at 5,217 m at Coropuna and 5,331 m at Chachani, and electrical resistivity was surveyed in both sites. This 7-year discontinuous record of permafrost temperature data encompasses historically extreme El Niño/La Niña events. Our results show that the current lower-altitude permafrost boundary (~5,100 m a.s.l.) is critically influenced by the balance of wet and dry seasons: permafrost tends to deplete during drought years. Typical permafrost thickness was 10-20 m and contained ice-rich pore spaces. The presence of permafrost and its thermal resistance depends on ice content and on higher albedo, usually due to: (a) hydrothermal alteration, which transforms the volcanic rocks into surfaces with ideal albedo for permafrost resilience; and (b) sublimation of the snow cover, forming ice-pinnacles named penitentes.

Weather and climate conditions drive the evolution of tropical glaciers which play an important role as water reservoirs for Peruvian inhabitants in the arid coast and semi-arid Andean region. The scarcity of long-term high-quality observations over Peruvian glaciers has motivated the extensive use of reanalysis data to describe the climatic evolution of these glaciers. However, the representativeness and uncertainties of these reanalysis products over these glaciers are still poorly constrained. This study evaluates the ability of the ERA5-Land reanalysis (ERA5L) to reproduce hourly and monthly 2 m air temperature and relative humidity (T2m and Rh2m, respectively) over several Peruvian glaciers. We compared the ERA5L with data from four on-glacier automatic weather stations (AWS), whose hourly time series were completed with nearby stations, for the period January 2017 to December 2019. Results indicates a better performance of the reanalysis for T2m (r >0.80) than for Rh2m (∼0.4< r <∼0.6) in all four glaciers. Concerning the observations, both parameters show a daily cycle influenced by the presence of the glacier. This influence is more prominent during the dry months when the so-called glacier damping and cooling effects are stronger. On a monthly time scale, the ERA5L validation for both parameters are better in wet outer tropical sites (RMSE between ±0.2°C for T2m and between 3%–7% for Rh2m) rather than in dry outer tropical sites (RMSE between ±0.2°C for T2m and between 3%–7% for Rh2m). Among all sites considered in the study, the Rh2m bias is the highest in the Cavalca glacier (correlation of 0.81; RMSE 13%, MAE 11% and bias 8.3%) and the lowest in Artesonraju glacier (correlation of 0.96; RMSE 3%; MAE 2.3% and bias — 0.8%). Based on certain considerations outlined in this paper, it is appropriate to use ERA5L to characterize T2m and Rh2m conditions on Peruvian glaciers, particularly in the wet outer tropics.