A paleoclimatic record from the isotopic composition of the Mt Ortles ice cores, Eastern Alps, Italy

The vast majority of low and mid latitude mountain glaciers have been quickly retreating over the last decades, lowering the possibility of the preservation of climatic records in their ice. While several drillings have been carried out in the Alps for the last 50 years, very few attempts to obtain temperature reconstructions from the isotopic records of Alpine cores have been successful. The presence of a dense network of meteorological stations, which have been operating for over two centuries, as well as the proximity to a densely populated and developed area, make the Alpine glaciers a unique spot to obtain paleoenvironmental and paleoclimatic information through ice coring. In autumn 2011, four cores were drilled on the Alto dell’Ortles glacier (3859 m a.s.l.), three down to bedrock at an approximate depth of 75 m. The glacier is currently transitioning from a cold to a temperate state: the firn can reach the pressure melting point, while the ice below 30 m of depth is still cold. Carbon-14 determination on Water Insoluble Organic Carbon (WIOC) supported a time scale dating back to ̴7000 years before present, making the Ortles paleoclimatic record one of the very few in the Alps covering most of the Holocene. A refinement of the Ortles chronology was obtained through a novel approach: here we compare the d18O records from core #1, #2 and #3, based on the revised chronology, to the instrumental temperature series since XVIII century, using different low-pass gaussian filters with increasing sigma values. The linear regression between temperature and isotopic data shows an increasing R2 and slope when increasing the sigma of the low-pass gaussian filter. While few periods are characterized by opposing trends, the overall agreement between temperature and d18O is robust.