The Austrian Alps during the last glacial cycle

During the Quaternary, the youngest period in the Earth`s history, vast amounts of sediments were deposited in the valleys and basins of the Alps and their foreland. These gravels, sands, silts and clays not only represent economically important raw materials and harbour major groundwater resources; they are also an archive of those profound climatic changes whose rhythm of glacials and interglacials shaped the Alpine landscape. The principal challenge in reading this archive is establishing its precise chronology. The present proposal aims at applying a relatively new and exciting geochronological technique to date Late Quaternary sediments in the Eastern Alps: optically stimulated luminescence (OSL). This method has two decisive advantages over the well known radiocarbon method: OSL can date sediments devoid of wood or other organic remains, and it has a dating range from 100s of years to about 200,000 years. We propose to study two sites with the Inn Valley in western Austria, a classical region of Quaternary research in the Alps. Most significantly, new extensive drill cores as well as seismic data have become available which provide the unique opportunity to freshly re-examine this area. By applying the OSL technique and radiocarbon dating (where applicable) in conjunction with a multiproxy approach (sedimentology, pollen, macroremains) this historically unique core material will permit fundamentally new insights into the Quaternary geology and history in the Eastern Alpine realm.

How cold was the last ice age? Did forests exist in the Alps at that time? Were the Alps always ice-covered? When and how rapid did the climate change? These are exciting questions, which currently can only be answered to some extent, because finding reliable and quantifiable traces from those past times is a daunting task. Extensive sediment layers discovered in the subsurface of the Unterangerberg terrace in the Lower Inn Valley of Tyrol during drilling explorations for a railway tunnel opened the door for this research project. Below the glacial till of the last major ice advance into the alpine foreland (ca. 25,000 years ago) the boreholes encountered gravel, sand, silt and compressed peat layers which were deposited during the last glacial period when the valley was free of ice. Dating of these sediments revealed the presence of three consecutive intervals of lake formation during the last glacial cycle. The oldest lake existed between 115,000 and 105,000 years ago, the second one lasted from 70,000 to 60,000 years ago and the youngest lake phase prevailed from 52,000 to 43,000 years before present. It is these fine grained lake sediments that hold the key for a reconstruction of the past ecological and climatological conditions. Organic remains including pollen found in these sediments showed that e.g. 80,000 years ago a conifer forest existed in this inneralpine valley which soon after disappeared in response to a dramatic climate cooling. These short-lived warm intervals during the last glacial, the so- called Dansgaard-Oeschger events, which where interrupted by Siberian-like cold periods, are known from ice-core studies in Greenland and are now also identified from sediments inside the Alps based on rapid vegetation changes. An interesting question with respect to landscape evolution could also be solved in this project: why did these lakes exist? Two large landslides went down from the mountain ridge to the north of the valley and partially dammed the Inn valley. Sediments of these mass movements were penetrated by the boreholes and underpin the role of such large-scale events in setting the stage for the formation and preservation of important climate archives such as lake sediments.