Late Glacial glacier, permafrost and climate history in the mountains between Arlberg and Silvretta (Eastern Alps, A) - modelling of glaciers, permafrost distribution and climate fluctuations during the end of the Pleistocene.

The Alpine Lateglacial (ca. 18.000 - 11.500 cal BP / calendar years before 1950) was characterised by numerous rapid and intense climatic fluctuations which affected glacier and permafrost extents. Within the project the lateglacial and early Holocene glacier extents and permafrost distribution in the Ferwall Group (Central Alps, Western Tyrol) were mapped and reconstructed in great detail. In selected areas it was possible to absolutely date the moraines. These results formed the basis for a palaeoclimatic interpretation. The main emphasis was put on the multi-phased "Egesen Stadial" of the Alpine Lateglacial stratigraphy (Younger Dryas, 12650 - 11500 BP, Greenland Stadial-1). The mapping of the moraines and rockglaciers provided the basis for the reconstruction of the glacier extents and permafrost distribution. Stereo-orthophotos and field mapping were used together with a digital terrain model (DTM) and a geographical information system (GIS). The mapping results and the DTM were used to reconstruct the glacier topographies for various time-slices. A reliable computer-aided model for the reconstruction of glacier maps, which is based on simple glaciological relations and the GIS software ARC/Info, was developed during the project. The glacier maps provided the basis for the calculation of the equilibrium line altitude, which is an important palaeoclimatic proxy. Thus it was possible to achieve a full areal coverage of equilibrium line altitudes in the research area for several phases of the Younger Dryas. In close cooperation with the Department of Particle Physics / Paul Scherrer Institute (ETH Zürich) and the Geological Institute of the University of Berne (Switzerland), selected moraines were dated by surface exposure dating with terrestrial cosmogenic radionuclides ( 10Be, 26Al). This method gives minimum ages for the stabilisation of the moraines. Quartz samples were collected from the Egesen Maximum moraines near Konstanzer Hütte (Schönferwall), moraines of the early Holocene Kartell Stadial (Moostal) and the early Holocene Kartell Stadial (Kartell valley, Silvretta group). By now, 10 ages are available, which basically confirm the assumptions on the age of the respective moraines. The palaeoclimatic interpretation is based on the depression of the equilibrium line altitudes. Together with founded assumptions on the summer temperature change, they allow to infer changes in precipitation. In the research area, early Younger Dryas precipitation was higher than today in the west and decreased significantly towards the east and south. This is typical for a precipitation pattern which is caused by a dominantly westerly- northwesterly airflow pattern under generally cold conditions. During later phases of the Younger Dryas, glaciers shrunk considerably and climate became increasingly more continental. These results fit well into the present-day picture of Younger Dryas climate, as it can be inferred from Atmospheric General Circulation Modelling.