Contrasting patterns of hydrological changes in Europe in response to Holocene climate cooling phases

The quantitative reconstruction of climatic parameters from pollen and lake-level data obtained at Saint-Jorioz, Lake Annecy (eastern France), gives evidence for cooler and wetter conditions during the 8.2 ka cold event. A comparison of these regional data with other hydrological records reconstructed in Europe for the same period suggests, as a working hypothesis, that mid-latitudes between ca 50degrees and 43degrees underwent wetter conditions in response to the cooling, whereas northern and southern Europe were marked by drier climate, in the latter case leading to an interruption of the sapropel I formation in the Mediterranean. A similar hydrological tri-partition of Europe can be observed during other Holocene cooling phases associated with North Atlantic IRD events. Data indicate, that the middle zone characterised by wetter climate conditions could have had a more extended latitudinal amplitude during phases of climate cooling weaker than the 8.2 ka event. The differences in expansion of the wet mid-European zone depending on Holocene climate cooling phases could reflect variations in the strength of the Atlantic Westerly Jet in relation with the thermal gradient between high and low latitudes. (C) 2003 Published by Elsevier Science Ltd.