Glacier Variations for the Last Seven Decades in Response to the Climatic Trends, Northern Patagonia, Chile

We expose the glaciological variations for the main mountain glaciers from Hornopirén National Park, Northern Patagonia, Chile, since the 1950s. Some of the main ice tongues have experienced significant retreats, with rates of 100 m/yr between 1973 and 2001. Rates up to 224 m/yr were observed in the 2001-2019 period. Between 1973 and 2019, we observed the highest frontal retreat being of ~7 km. As a consequence of the glacier wastage, the terminus position has migrated vertically for three major glaciers. The frontal position of those glaciers were located at an average altitude of 870, 916 and 1310 m a.s.l., respectively in 1973, 2001 and 2019. Proglacial lakes appeared and developed in the new ice-free areas. These changes occur despite the cooling trends observed in the coastal regions. However, instrumental records show a clear decline in the annual precipitation amounts since the second half of the 20th century. Precipitation in Northern Patagonia are mainly controlled by frontal systems of the southern hemisphere westerly wind belt. While winter accumulation accounts for up to 70% of the annual amounts, precipitation events during the austral summer are not rare, and the average altitude of the zero degrees isotherm during the warmest months are well above the mean altitude of the glacier tongues. In this study, the relationships between glacier area reduction, frontal retreat, and climatic trends are discussed. Focus is on average zero isotherm migration, snow cover and accumulation analysis, as well as detectable changes on mass balance and atmosphere-glacier interaction. Data from nearby automatic weather stations and atmospheric soundings were used for the study as well as reanalysis products (ERA5 and CR2MET) in order to characterize air temperature trends and local accumulation patterns.