Alpine response to Atlantic climate variability during MIS 3

Our project will study the paleoclimate archive of Banded Clays deposited in a fjord-like paleolake of the Austrian Inn Valley. A rare opportunity in the Alps, these deposits document a period of extreme climate instability 59,000 to 28,000 years ago, well known from Greenland ice and Atlantic sediment cores for the abrupt Dansgaard- Oeschger events. Their impact on Alpine paleoclimate and environment, hitherto largely unknown, will form our central objective. A recently drilled 150-m core section and two neighboring cores planned to recover the entire sediment profile, will be analyzed by state-of-the-art techniques to produce a broad set of well dated, quantitative and qualitative proxy data of paleotemperature, -productivity, -vegetation, and hydrology, with annual, in part seasonal, resolution. These records promise important evidence to validate regional climate models of abrupt climate change and the impact of changes in Atlantic overturning circulation on Alpine climate.

Clay deposits occur 15 km east of Innsbruck an were previously mined for the production of bricks. These fine-grained sediments were laid down at the bottom of a large lake which occupied the central Inn Valley prior to the last glacial maximum. Referred to as Baumkirchen Banded Clays, these sediments are a key site for ice-age research in the Alps. The aim of this project was to obtain a profile across these sediments as complete as possible, in order to refine their chronology and to reconstruct climate and its environmental impact during this time period, known from other archives, e.g. the Greenland ice cores, for their large fluctuations in temperature. Because the outcrop conditions in the abandoned clay pit had deteriorated over the years we made several drillings in order to obtain high-quality core material. In total 250 m of lake sediments were recovered, although the base was not reached. Complete cores covering such a thick lacustrine succession are unique in the Alps. Dating these sediments using luminescence techniques revealed that the lake åexisted much longer previously assumed (from about 77,000 to about 33,000 years before present) and that a major change occurred about 60,000 to 55,000 years ago. At that time, gravel was deposited in the lake basin, recording an advance of glaciers from the southern tributary valleys into the Inn Valley. Such a significant glacier advance was hitherto unknown from the Eastern Alps; westalpine glaciers, however, were much larger and supposedly reached the foreland of the Alps at that time. Pollen grains embedded in the sediments allowed to gain insights into the vegetation around this ancient lake. Two intervals of slightly milder climate, but still markedly colder and drier than today, occurred during a generally cold, Siberian-type climate. The larger of the two interstadials probably corresponds to Interstadial no. 8 known from Greenland ice cores.