Klimaschwankungen und -trends des älteren Holozäns in den südlichen Niederen Tauern: multidisziplinäre Auswertung eines Sedimentkerns aus dem Oberen Landschitzsee (Lungau)

Innsbruck

2009

S. 55-64

2 Abb., 34 Lit. Ang.

Artikel aus einer ZeitschriftUnselbständiges Werk

200155650

Lake Oberer Landschitzsee (2.067 m a.s.l.) is a key site for the reconstruction of Holocene climate changes at the southern Austrian Central Alps (Niedere Tauern, Lungau). The lake is located in a climatically sensitive ecotone close to the alpine treeline. Its radiocarbon (AMS 14C) dated sediments have been studied intensively using a multi-proxy approach. Local glaciers, which originated from the Younger Dryas cold period, have disappeared during the early Holocene warming. Subsequently, Oberer Landschitzsee was affected by two cold and wet periods. The first started about 10.5 kyrs before present (BP) and culminated at ca. 10.2 kyrs BP. The second occurred between ca. 9.5 and 9.2 kyrs BP. From ca. 9.2 to 8.7 kyrs BP a period of lake summer warming separated these older climate oscillations from younger climate deteriorations between ca. 8.7 to 7.6 kyrs BP. The latter coincided with glacier advances in the nearby Hohe Tauern (Venediger, Frosnitz), whereas in the Niedere Tauern perennial snowfields developed, which kept summer lake water temperatures low. Prolonged summer warming and late autumn mixing characterized the following three warm periods (Holocene optimum events) between ca. 7.5 to 5.3 kyrs BP, which were interrupted by two cold fluctuations. The snowfields and possibly permafrost in the catchment of the lake disappeared during the Holocene optimum events, resulting in distinct lake warming (principle of ultra-sensitive lakes). The interval between ca. 7 and 6 kyrs was more continental than the younger one from ca. 6 to 5.3 kyrs BP. The change in continentality could explain the lowering in timber/tree-line. During the following climate oscillation at ca. 5 kyrs BP, pronounced wet and snow-rich conditions altered with drier ones. The period from ca. 5 to 4 kyrs BP indicated strong seasonal divergence, most probably due to the increasing impact of the mediterranean winter-rain climate on the area south of the Alps. In sum, the time-window from ca. 11.5 to 4 kyrs BP indicated (i) increasing temperatures with a plateau between 7.5 and 5.3 kyrs BP, (ii) a long-term trend of declining continentality, probably due to the increasing influence of the mediterranean winter-rain climate, (iii) climate oscillations with a periodicity of approximately 1000 years, (iv) two marked, well-known, acyclic, short-term cold fluctuations: the 8.2 kyrs cold event and the pre-boreal oscillation at about 11.3 kyrs BP.