Die Bedeutung des Längsees in Kärnten für die Rekonstruktion der Klima- und Seenentwicklung am Ende der letzten Eiszeit

Längsee is a small meromictic lake located in the southern pre-alpine lowland (Carinthia). For climatic reconstructions a multi-proxy approach was used (diatoms, ostracods, pollen, geochemistry, mineralogy, varves, tephra). By the use of a diatom-based transfer function for summer epilimnetic water temperatures (SEWT) three major sections were distinguished: (1) a warming period (average SEWT 15.8°C, which is ca. 6°C lower than present), called Längsee oscillation, starting about 18 to 19 kyrs before present (BP). It seems to correlate with the warmer event (GS-2b) indicated by the oxygen isotopes of the so-called Greenland Stadial 2; (2) a following climate deterioration, called Längsee cold period, which could correlate with the
youngest cold event GS-2a of the Greenland Stadial GS-2 and the Heinrich I cold event from the Atlantic dated to 17.9 - 14.7 kyrs BP. The SEWT difference of ca. 9°C between inferred and modern Längsee temperatures fits also well with the temperature decline assumed for the Gschnitz stadial of the Alps. Short-term fluctuations (SEWT range between 10.6 and 15.9°C) indicate a tri-partition of this section (two colder phases are separated by a warmer fluctuation); (3) another warming period during the Lateglacial Interstadial (= Greenland Interstadial
GI-1). The lower boundary of the initial birch-rich period was dated at Längsee to 14.3 kyrs BP using varves and a tephra layer (Neapolitan Yellow Tuff, NYT, from the Vesuvian area in Italy). Three minor climate fluctuations were observed (mainly by pollen) during this interstadial. The one likely related to the Gerzensee oscillation (Switzerland) or to the sub-stadial GI-1b in the sense of the Greenland isotope event-stratigraphy (both approximately dated to 13 kyrs BP), showed a slight SEWT decline. The Younger Dryas cold period (= Greenland stadial GS-1) between ca. 12.7 - 11.5 kyrs BP appears to have been climatically heterogeneous, indicating a tri-partition in Längsee as well as in several other lake profiles of the Austrian Alps. Climate was also the main trigger of changes in nutrients and meromixis in Längsee.