Late Pleistocene climatic variations as recorded in two Italian maar lakes (Lago di Mezzano, Lago Grande di Monticchio)

Sediment profiles from two maar lakes, Lago di Mezzano (central Italy) and Lago Grande di Monticchio (southern Italy), were investigated with respect to their minerogenic and biogenic sediment accumulation rates for a time window spanning the final 20,000 yr of the last glaciation. The chronological framework is provided by calibrated radiocarbon ages, varve counting, calculation of sedimentation rates and tephrochronology. In the time slice between 34,000 and 14,000 cal BP periods of increased minerogenic input are observed in both lacustrine records, interrupted by periods of low minerogenic input. These cyclic variations have an average recurrence time of 1785 yr for Lago di Mezzano and 2875 yr for Lago Grande di Monticchio, comparing well with marine and ice core data. Explanations for these pulses of increased minerogenic sedimentation include enhanced erosion and runoff. The higher precipitation/evaporation ratio required for this interpretation was possibly restricted to winter months as earlier published pollen analyses on sediments from Lago Grande di Monticchio show a contemporary development of steppe vegetation, an indicator for cool/dry climatic conditions. This may be connected with a southward shift of the westerlies and a reinforced jet stream. Agreement of lacustrine data from Italy with late Pleistocene glacial events in central Italy, with events recorded in marine archives from the North Atlantic (Heinrich events) and with oxygen isotope data from Greenland ice cores is interpreted as evidence for the Late Pleistocene climate in Europe being influenced by North Atlantic climatic forcing which may be related to Dansgaard-Oeschger cycles. (C) 1999 Elsevier Science Ltd. All right reserved.