Holocene climate change in the northern Alps

The alpine realm plays a special role in the current climate debate, because of the obvious rapid changes of glaciers and permafrost, but also because this region apparently warms stronger than large areas of the Northern Hemisphere. In order to reliably assess the most recent climate change (the past 150 yr) a long-term perspective of the postglacial period, the Holocene, is essential. We propose a high-resolution paleoclimate investigation of this 11000 yr-long time window at the northern margin of the Eastern Alps, which will complement previous and ongoing studies in the southern and central part of the Alps toward a N-S traverse. We shall focus on dripstones from alpine caves, a relatively new archive which currently receives a lot of attention internationally. Stalagmites will be sampled in Gassel Cave near Ebensee and in Hölloch, Allgäu Mountains, and these dripstones permit a quantitative reconstruction of air temperatures over millennia. Both caves were selected so that the results can be directly compared to those from Ammersee and Mondsee; these two perialpine lakes are currently being scrutinized within a large paleoclimate project funded by the European Science Foundation. Integrating high-resolution data from lake sediments and cave deposits of the same region is unique for the Alps and represents an important step toward a precise and quantitative climate history of this mountain chain.

The natural variability of Earth`s climate is seemingly well known. Actually, observational stations in Austria started only in the middle of the 18th century and a global meteorological network of the most important climate variables such as air temperature and precipitation is in existence only since ca. 150 years. The study of long-term climate change and trends requires a major effort in order to obtain robust climate information (so-called proxy data) from earlier time periods, e.g. the Medieval time or the Bronze Age. In the Alps, glaciers and their deposits are established climate indicators, as are pollen e.g. from mires. Some 15 years ago dripstones from caves emerged as a new, exciting archive of palaeoclimatology. The Innsbruck research group has worked on this topic during the last decade. Dripstones from two caves in the provinces of Vorarlberg and Upper Austria were analysed in this project. According to the currently available data these deposits cover the last ca. 30,000 years. Special emphasis was on climate events, which are recorded in these dripstones and were studied in the northern Alps at very high temporal resolution. For the first time in central Europe, a seasonally resolved quantitative temperature reconstruction was performed for the so-called Younger Dryas interval (12,900-11,700 years before present). The results show that the strong decrease in the mean annual air temperature was primarily due to drastic cooling during winter. These observations were made possible using a method to extract isotopic information from microscopic water inclusions residing in the crystals of dripstones and which was further developed by the Innsbruck team. This isotopic information varies as a function of the air temperature outside the cave. The studied dripstones also revealed clear-cut traces of another climate event, which resulted in markedly colder conditions in Europe some 8,300 years ago, probably caused by a short-lived slow-down of the North Atlantic deep-water circulation. A major component of this research project was the long-term monitoring of environmental parameters in these two caves, most importantly drip water. These observations allow to relate proxy data encoded in dripstones to meteorological parameters and their changes outside the cave.