Juxtaposing field evidence, isotopic dating results and ice-sheet models for the Last Glacial Maximum in the Alps.

Glaciers flowing out from local ice caps and plateau ice fields in the high Alps filled the main valleys and extended onto the forelands as piedmont lobes during the Last Glacial Maximum (LGM). Beginning already nearly 200 years ago, field mapping allowed detailed reconstruction of past ice margins. Nevertheless, determination of numerical ages has only been possible in the last few decades; 14C dating is well applicable S of the Alps while to the N 10Be is favored due to the lack of organic remnants. Recent glacier modelling by Seguinot et al. (2018) suggests the possibility of significant disparities in the timing of reaching of the maximum extent by the various foreland lobes across the Alps. Differences in flow-path length, catchment hypsometry and glacier dynamics likely contribute to the asynchrony observed in the model results. The present data set pinpoints the culmination of the last glacial cycle, as marked by formation of the outermost moraines, at around 26-24 ka. The timing of abandonment of foreland positions is given by the ages of the innermost often lakebounding moraines, which stabilized about 19-18 ka. Strikingly, the modelling shows strong variation in the number of oscillations of individual lobes over the last glacial cycle. Even during the LGM itself, ice margin fluctuations were much more frequent than interpreted from glacial-geological evidence. Yet at present, few sites in the Alps have detailed enough geomorphological constraints with well-dated ice-marginal positions for in depth discussion of outermost, innermost and in between moraines. We will present a comparison of field, dating and modelling results from both published and in progress sites both N and S of the Alps.