Long-term glacier variations in the Central Andes of Argentina and Chile, inferred from historical records and tree-ring reconstructed precipitation

Snow and ice in the Central Andes of Chile and Argentina (33–36 °S) are the major source of water for the highly populated regions near the cities of Santiago and Mendoza. However, our knowledge of the forces driving the general glacier retreat in the region is limited. In order to obtain a long-term perspective of glacier fluctuations and their relationships with climate in the Central Andes, historical glacier variations were documented and compared with a tree-ring precipitation reconstruction based upon Austrocedrus chilensis trees. A multi-proxy approach (historical documents, old aerial photographs and satellite imagery) was used to map the fluctuations of eight glaciers, including the Cipreses Glacier, which provides the oldest record of glacier variations in the region starting in AD 1842. All the studied glaciers exhibited a negative trend during the 20th century with mean frontal retreats between - 50 and - 9 m y- 1, thinning rates between 0.76 and 0.56 m y- 1 and a mean ice area reduction of 3% since 1955. More than 350 tree-ring cores were combined into three tree-ring chronologies, which strongly correlate with the instrumental precipitation in Santiago de Chile (33°26' S; 70°41' W, 520 m asl). Based on these records, a 712-year precipitation reconstruction was developed. This reconstruction is characterised by a centennial oscillation indicating marked dry conditions around the years 1440 and 1600 AD. Wet conditions were prevalent in the years 1500, 1650 and particularly around 1850 AD. Since this precipitation maximum, the reconstruction shows a clear, secular, decreasing trend. The reduction in precipitation indicated by this reconstruction for the last 150 yr, in combination with a significant warming recorded in Central Chile, are the main causes of the observed current glacier retreats