Vegetation responses to the 8200 cal. BP cold event and to long-term climatic changes in the Eastern Alps: possible influence of solar activity and North Atlantic freshwater pulses

Abstract

Subfossil pollen from two bogs in temperature-sensitive, high-altitude regions were analysed in order to reconstruct early-to mid-Holocene summer temperature fluctuations in the Eastern Alps. The pollen records showed four centennial-scale cooling intervals with low growing-season temperatures, resulting in decreasing pollen production and/or lower treeline position during the period 9000-6000 cal. BP. For the first time, the 8200 cal. BP cold event and an equivalent to the Misox cold phase in the Swiss Alps were detected in the Eastern Alps. The oscillations recorded in the pollen curves for Swiss stone pine (Pinus cembra) and sedges (Cyperaceae) at c. 8200 cal. BP match, in time and magnitude, the δ18O excursion in the Greenland GRIP ice-core record as well as sea-surface cooling in the North Atlantic. The close congruence between the pollen records covering 3000 years and climate proxy-data from both Hemispheres indicates that large-scale environmental changes, possibly caused by North Atlantic freshwater pulses and/or fluctuations in solar activity, caused decreases in pollen production and/or treeline shifts in the Alps. Although the 8200 cal. BP climatic deterioration was of a global character, its impact on biological productivity of temperature-sensitive sites at high altitude has only rarely been demonstrated. The data indicate that pollen analyses near and above the timberline within high-altitude, herb-dominated plant communities are of considerable and yet largely unexplored potential to detect abrupt short-term as well as long-term climatic variations.