European lakes as palaeohydrological and palaeoclimatic indicators

Abstract

Lakes in temperate regions have fluctuated in size on annual to millenial time scales. Changes in water level or depth can be reconstructed by applying geomorphic, sedimentological and biostratigraphic methods to transects of sediment cores. This systematic, field-based approach has been used at a number of sites in Europe. It is illustrated by reconstructions of water-level changes in lakes from southern Sweden. These lakes have shown broadly synchronous changes during the Holocene. Such synchronous changes in water levels at several sites in a region reflect climatic changes. Inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction, magnitude and timing of lake-level changes between regions. Continental compilations of lake-level data are therefore necessary. Detailed studies are not available from enough sites, but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake-level changes has greatly increased the number of sites available for a continental-scale synthesis in Europe. This eclectic, literature-based approach is illustrated with examples from southern Europe. Lakes in the Mediterranean region were high around the glacial maximum and again somtime during the first half of the Holocene. In the western Mediterranean, the peak of late-glacial aridity occurred at 15,000–16,000 BP and the lakes were already high again by 12,000 BP. In the east, maximum late-glacial aridity occurred between 13,000 and 11,000 BP and there was a gradual return to wetter climates during the early Holocene such that 9000 BP was more arid than 6000 BP. Most lakes in the Mediterranean region were high at 6000 BP. The transition to arid conditions after 5000 BP occurred abruptly in the west and more gradually in the east. The lakes of southern Sweden indicate drier climates in the early Holocene (ca. 9000 BP), more effective moisture between 8000 and 6000 BP, increased aridity between 5500 and 3500 BP, and increased effective moisture again during the last 3000 years. The history of lake-level changes in southern Sweden and the Mediterranean region can be partially explained in terms of changes in the direct effects of insolation, and in the strength and position of the Westerlies and of the subtropical high pressure cell during the Late Quaternary.