Multiproxy evidence for terrestrial and aquatic ecosystem responses during the 8.2 ka cold event as recorded at Højby Sø, Denmark

A sediment succession from Højby Sø, a lake in eastern Denmark, covering the time period 9400-7400cal yr BP was studied using high-resolution geochemistry, magnetic susceptibility, pollen, macrofossil, diatom, and algal pigment analysis to investigate responses of the terrestrial and aquatic ecosystems to the 8.2ka cold event. A reduced pollen production by thermophilous deciduous tree taxa in the period c. 8250-8000cal yr BP reveal that the forest ecosystem was affected by low temperatures during the summer and winter/early-spring seasons. This finding is consistent with the timing of the 8.2ka cold event as registered in the Greenland ice cores. At Højby Sø, the climate anomaly appears to have started 200-250yr earlier than the 8.2ka cold event as the lake proxy data provide strong evidence for a precipitation-induced distinct increase in catchment soil erosion beginning around 8500cal yr BP. Alteration of the terrestrial environment then resulted in a major aquatic ecosystem change with nutrient enrichment of the lake and enhanced productivity, which lasted until c. 7900cal yr BP.