Investigating cold based summit glaciers through direct access to basal ice: A case study constraining the maximum age of Chli Titlis glacier, Switzerland

Abstract

Cold glaciers at the highest locations of the European Alps have been investigated with great success by drilling ice cores to retrieve their stratigraphic climate records. Findings like the Oetztal ice man have demonstrated that small ice bodies at summit locations of comparatively lower altitudes may also contain old ice if comprising ice frozen to the underlying bedrock. In this case, constraining the maximum age of their basal ice part may help to identify past periods with minimum ice extent in the Alps. Facing ongoing warming and recent years with extremely negative glacier mass balance, these sites may not preserve their unique climate information for much longer, however. Since sampling and dating the lowermost ice is essential, and usually requires substantial logistical (drilling) effort, we utilize here the direct access to basal ice offered by an existing ice cave at Chli Titlis (3030 m), Central Switzerland. Our dedicated approach comprises a combination of standard glaciological tools with the analysis of the isotopic and physical properties and sophisticated radiocarbon dating techniques. By this means we demonstrate that, in comparison to an earlier study at Chli Titlis, stagnant cold basal ice conditions still exist fairly unchanged more than 25 years after the pioneering exploration. Our radiocarbon analysis constrains the maximum age of the ice at Chli Titlis to about 5000 years before present. By this means, the approach presented here will contribute to a future systematic investigation of cold-based summit glaciers also targeting the Eastern Alps.