Age of the Mt. Ortles ice cores, the Tyrolean Iceman and glaciation of the highest summit of South Tyrol since the Northern Hemisphere Climatic Optimum

In 2011 four ice cores were extracted from the summit of Alto dell’Ortles (3859 m), the highest glacier of South Tyrol in the Italian Alps. This drilling site is located only ~30 km away from where the ~5.2 kyr old Tyrolean Iceman was discovered emerging from the ablating ice field of Hauslabjoch (3210 m, near the Italian-Austrian border) in 1991. The excellent state of conservation of this mummy suggested that the Tyrolean Iceman was continuously embedded in coeval prehistoric ice and that additional ancient ice was likely present elsewhere in this area. Dating of the ice cores from Alto dell’Ortles confirms this hypothesis and assigns an age of 7 kyrs to the bottom ice. 210Pb, 3H, beta emissions and 14C determinations combined by an empirical model (COPRA), are used to illustrate a chronologically ordered ice stratigraphy from the modern glacier surface down to the bottom ice layers of Alto dell’Ortles. Our results indicate that the drilling site was uninterruptedly glaciated on a frozen bedrock since 7 kyrs BP. Absence of older ice on the highest glacier of South Tyrol is consistent with melting/removal of basal ice from a temperate bedrock during the Northern Hemisphere Climatic Optimum (6-9 kyr BP), the warmest interval in the European Alps during the Holocene. The stratigraphic-chronological continuity of the Mt. Ortles cores over millennia, borehole inclinometric measurements of the glacier internal ice flow and recent lidar surveys indicate that today, likely due to the intense anthropogenic warming, a new phase of acceleration of the glacier Alto dell’Ortles just started and that this is unprecedented since the Northern Hemisphere Climatic Optimum.