Alpine glacier oscillations and climate at the Lateglacial - Holocene transition

Well dated glacial advances constitute a valuable information source of climate history because glaciers react directly to climatic changes. In this context, the time frame from the late Younger Dryas (Greenland Stadial 1) to the end of the Boreal in the early Holocene is especially interesting. It is characterized by the onset of a very rapid warming around approximately 11.5 ka, which subsequently continues on in a more dampened way. This warming was disrupted by a number of climatic "events" (Preboreal Oscillation, Erdalen-event, 9.3 and 8.3 ka event), which brought forth short and emphasized cooling particularly in the European-Atlantic sector. These events are imbedded within a setting of generally unfavourable climate conditions for glaciers. The project aims at elucidating in detail the glacial advances within this time frame. Emphasis will be placed on a system of moraines that are especially well preserved at smaller glaciers and that are found intermediately between the moraines of the Younger Dryas and the "Little Ice Age" (modern age). Hitherto such moraines have only been dated at three localities, whereby their ages and hence chronological classification have been contradictory (Preboreal Oscillation, Erdalen event, 8.2 ka event). Consequently, the question of whether and how small Alpine glaciers reacted to the 8.2 ka event is of special interest and which implications for climate history can be derived there from. The study areas are located in areas that are convenient for climate historic interpretations and offer the corresponding moraine inventory. These are primarily the western Silvretta Group (northwestern Alpine fringe on the cross over to the central Alps), the Karwendel Mountains (northern Alpine margin), and the western Ötztal Alps (inner Alpine dry areas). The dating will take place by means of the well-proven cosmogenic nuclides 10Be and 36Cl in close cooperation with the Institute of Particle Physics at ETH Zurich. The interpretation of climate history will be supported by the use of energy and mass balance equations at the equilibrium line, empirical precipitation-temperature models and positive degree-day models. The additionally necessary climate information (especially summer temperature) will be taken from all sensible utilizable proxy data sources of the respective time segments. Therewith changes in precipitation structures throughout the Alpine region and indications of atmospheric circulation conditions in times of rapid climate change can be derived.

Alpine glacier oscillations and climate at the Lateglacial Holocene transition - A case study of the late Younger Dryas / Preboreal / Boreal time window in the Alps of western Austria. Well dated glacial advances constitute a valuable information source of climate history because glaciers react directly to climatic changes. The time frame from the late Younger Dryas, which concluded the last ice age, to the end of the Boreal in the early Holocene is especially interesting. About 11,700 years ago a very rapid warming set in that continued on in a more dampened way. This warming provided mostly unfavourable conditions for glaciers, but was interrupted by several climatic events charaterized by brief, but strong phases of cooling in the European-Atlantic sector. Glaciers advanced again during these periods. These glacier advances were investigated in the scope of this project. The focus was placed particularly on moraines that are well preserved in front of small glaciers. Their positions represent an intermediate position between the glaciers of the Younger Dryas ad those of the Little Ice Age (modern times). Our research areas are located especially convenient for climate historic interpretations. They are found in the Silvretta Mountains (transition from the northwestern Alpine fringe to the central Alps), the Karwendel Mountains and Mieminger Chain (northern Alpine fringe), the northern Stubai Alps and the western Ötztal mountains (inner Alpine dry area). The dating took place by means of the well-proven cosmogenic nuclides 10Be and 36Cl in close cooperation with the Laboratory of Ion Beam Physics at ETH Zurich. Thereby we were able to determine several different glacier advance periods. The first occurred about 11,200 years ago and was significantly greater than all subsequent advances. The second advance was several hundred years later and reached less extensive positions. Finally a glacier advance about 3,500 years ago could be determined. It coincides with the beginning of the late Holocene and had to be the reaction to a pronounced climate deterioration. In the northern Calcareous Alps the end of rock glacier activity and hence the meltout of low lying permafrost was dated to about 11,000 years before present. Climate information derived from our glacier data shows that during the cold phases at the beginning of the Holocene summer temperatures were approximately 2 to 3 C lower than at the beginning of the 21st century while precipitation was similar to today. These results fit well with those from the western Alps and form an important building block for the understanding of climate history in the Alps at the end of the last ice age.