Abstract
Abstract. 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 37 km southwest from where the Tyrolean Iceman, ∼ 5.3 kyrs old, was discovered emerging from the ablating ice field of Tisenjoch (3210 m, near the Italian–Austrian border) in 1991. The excellent preservation of this mummy suggested that the Tyrolean Iceman was continuously embedded in prehistoric ice and that additional ancient ice was likely preserved elsewhere in South Tyrol. Dating of the ice cores from Alto dell'Ortles based on 210Pb, tritium, beta activity and 14C determinations, combined with an empirical model (COPRA), provides evidence for a chronologically ordered ice stratigraphy from the modern glacier surface down to the bottom ice layers with an age of ∼ 7 kyrs, which confirms the hypothesis. Our results indicate that the drilling site has continuously been glaciated on frozen bedrock since ∼ 7 kyrs BP. Absence of older ice on the highest glacier of South Tyrol is consistent with the removal of basal ice from bedrock during the Northern Hemisphere Climatic Optimum (6–9 kyrs BP), the warmest interval in the European Alps during the Holocene. Borehole inclinometric measurements of the current glacier flow combined with surface ground penetration radar (GPR) measurements indicate that, due to the sustained atmospheric warming since the 1980s, an acceleration of the glacier Alto dell'Ortles flow has just recently begun. Given the stratigraphic–chronological continuity of the Mt. Ortles cores over millennia, it can be argued that this behaviour has been unprecedented at this location since the Northern Hemisphere Climatic Optimum.
Highlights
Glaciers are sensitive indicators of climate change as their length, area and volume respond primarily to variations in air temperature and precipitation (e.g. Oerlemans, 2001)
While the relative inclinometric measurement does not necessarily imply a net basal sliding of the drilling site, it does indicate that currently ice layers located next to bedrock are dynamically active (38 mm (0.3 m yr−1) at 65 m; 18 mm (0.2 m yr−1) at 70 m)
The ice embedded in the deepest layers of Alto dell’Ortles dates to the demise of the Northern Hemisphere Climate Optimum (NHCO), and is among the oldest ice discovered in the European Alps, exceeded in age only by the ice more than 10 kyrs old retrieved at Colle Gnifetti (Jenk et al, 2009)
Summary
Glaciers are sensitive indicators of climate change as their length, area and volume respond primarily to variations in air temperature and precipitation (e.g. Oerlemans, 2001). At that time conditions favourable to glaciers persisted in the European Alps until 10.5 kyrs BP (Ivy-Ochs et al, 2009) when a period of climatic warming started, culminating between 6 and 9 kyrs BP during the so-called Northern Hemisphere Climatic Optimum (Vollweiler et al, 2006) At this time the Northern Hemisphere summer insolation and solar irradiance reached maximum levels during the Holocene (Berger and Loutre, 1991; Stuiver et al, 1998). In 2010, we formulated the hypothesis that an ice core record encompassing the time of the Tyrolean Iceman was embedded in the upper reaches of the Alto dell’Ortles (3859 m), the main glacier of Mt. Ortles (3905 m, Italy), which is the highest mountain of South Tyrol, located 37 km from the Tisenjoch (Gabrielli et al, 2010). Combining ice core and glaciological observations, we discuss these findings in light of the state of the knowledge of the glaciation of the eastern Alps during the Holocene
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