Lateglacial glacier fluctuations: Alpine N-S traverse

The Last Termination / Lateglacial (ca. 18.000 - 11.500 cal.BP) was characterised by numerous rapid and intense climatic fluctuations. As a consequence, the general downwasting of the glaciers in the Alps after the maximum around 20.000 B.P. was interrupted by several readvance periods. The moraines and related deposits of these readvances are well preserved in many valleys and cirques. Along an E-W-axis in the central Alps, they are well documented and form the basis for a stratigraphy of the lateglacial glacial advances, which can at least partially be correlated with the "event-stratigraphy" based on the Greenland Ice Cores. There are, however, significant gaps of knowledge of the lateglacial glacier history along the northern rim of the Alps. In the Southern Alps, relevant information is virtually absent. The aim of the project is to increase and to improve the knowledge of lateglacial glacier fluctuations and to derive high-resolution palaeoglaciologic and palaeoclimatic parameters along a transect in the Alps around 1130` E between the Karwendel massif in the N and the Presanella group in the S. Mapping of the moraines and related permafrost deposits in selected areas and absolute dating of moraines with the still novel technique of surface exposure dating with cosmogenic radionuclides, which has been successfully employed at several locations in the Alps, is intended to be a major part of the project. GIS-based modelling of former glacier topographies will provide the basis for the inference of palaeoglaciologic parameters (equilibrium line altitudes (ELA), basal shear stresses, ELA depressions), which, in turn, can be used as input data for a more detailed palaeoclimatologic interpretation of the glacier fluctuations at selected time slices of the Lateglacial. This should lead to a better understanding of glacier and climate fluctuations of the Lateglacial period with the main emphasis on the Younger Dryas climate in the research area. As additional information, the palaeoclimatologic interpretation will use available palaeobotanical data, e.g. on timberline fluctuations. Then, using various stochastic and glacial-meteorologic glacier-climate-models, it is possible to rather accurately estimate changes in accumulation / precipitation with a high spatial resolution in an area of the Alps, where such kind of information is presently absent. As regional precipitation patterns are closely related to synoptic-scale airflow, it will be possible to use the results of the palaeoclimatic interpretation to evaluate the information provided by Atmospheric General Circulation Models for the Lateglacial, in particular the Younger Dryas.

The general decay of the alpine glaciers after the Last Glacial Maximum was interrupted by a number of readvance periods, which are documented by moraine systems. Mapping and dating of the moraines with the cosmogenic isotopes 10Be and 36Cl exhibits two major phases with glacier-friendly conditions. During the first phase around 16 ky ago the large alpine valleys were still completely covered by glaciers of the arctic type. Climate was very cold and dry. Summer temperatures were 9 - 11 K colder than today and annual precipitation totals were about one third of present-day amounts. The present-day Canadian Arctic is a good example for the conditions then prevailing in the Alps. The number of documented glacier topographies from that period could be significantly increased in the North and South of the project area. They show that the glacier covered area in the Alps during that period was only a small fraction of the area, which was glacier covered during the LGM about 22.000 years ago. During the second main phase from 12.7 to 11.5 ky ago (Younger Dryas), alpine glaciers were already considerably smaller than during the first phase and confined to the upper valleys and cirques. Presently the data base consist of about 180 well documented glacier topographies from the northern, central and southern Alps. Summers were about 3.5 K to 5 K colder than today with a 5 K cooling as the upper maximum. The northern Alps were more humid than today, whereas the central and southern Alps were considerably drier. This points to an atmospheric circulation pattern dominated by westerly to northwesterly airflow. Towards the end of the Younger Dryas, climate became increasingly drier. The dating of the moraines shows that glacier-friendly conditions continued for at least 500 years into the early Holocene, a period from which not very much is known in the alpine area. The palaeoclimatic interpretation is based on the glacier topographies and equilibrium line altitudes. These data are interpreted with analytical and empirical glacier-climate-models in terms of summer temperature and annual precipitation sums. The methods can also be used to predict future changes in the glacier extent und changing climatic conditions. The mass balance gradients along a glacier tongue can be calculated with glacier flow models. They are an important indicator for the climatic regime of a glacier. The interpretation of the mass balance gradients for different scenarios with the energy and mass balance equation seems to be a promising approach to get more insight into the climate for periods of the recent geological past, from which other palaeoclimatic proxies are rare or missing.