Speleothem growth and stable carbon isotopes as proxies of the presence and thermodynamical state of glaciers compared to modelled glacier evolution in the Alps

Abstract

In recent years, glacier modelling proved to be an essential tool for simulating Quaternary glacier evolution in the European Alps. Yet, only sparse empirical data mostly concentrated around the Last Glacial Maximum (LGM) is available to validate these simulations. On the other hand, speleothems from the Alps are a widespread palaeoclimate archive. They provide stable carbon isotope records, which can inform about soil and vegetation conditions above a cave site but also potentially about the lack of soil during times of glacier coverage. In addition, speleothem growth in cold, high-elevation cave sites during glacials are a strong indicator of temperatures in the soil-karst-cave system above the freezing point, which is only likely to occur if the cave is covered by a warm-based glacier.Here we use existing speleothem data (growth histories and stable carbon isotopes) from Alpine caves to infer soil coverage (i.e. glacier absence) and thermodynamical states of the glaciers during the last glacial cycle and to statistically assess the compatibility with modelled glacier reconstructions. We compare data from multiple cave sites located at different elevations (870–2512 m a.s.l.) with recent glacier evolution simulations. We find a general agreement between speleothem-derived soil presence or absence and modelled glacier coverage. However, speleothem data provide evidence of surface temperatures above freezing point if covered by a glacier, which is not fully reproduced by the simulations. Our work demonstrates the unique value of speleothem-based reconstructions as proxies to assess the performance of palaeo-ice flow models in a transient manner, whereas only maximum glacier state was considered before due to lack of data.