MOLLUSCA STABLE ISOTOPE RECORD OF A CORE FROM LAKE FRASSINO, NORTHERN ITALY: HYDROLOGICAL AND CLIMATIC CHANGES DURING THE LAST 14 KA

Abstract

A core retrieved from Lake Frassino (northern Italy) provided evidence of palaeohydrological change in this area during the last 14 ka. Lithological, malacological and, in particular, stable isotope composition of freshwater shells allowed the delineation of the main phases of lake evolution between the Lateglacial and Holocene. Lateglacial conditions were drier than the Holocene, although a wetter period was inferred before c. 14 ka. According to the oxygen isotope composition of freshwater shells, the Holocene showed a clear bipartition. The first part, which lasted from ?9100 to 7000 yr BP, was drier and was followed by a rapid increase in humidity at ? 7000-6800 yr BP. Between ? 6800 and 5000 yr BP, there were wetter and more stable conditions, as indicated by smaller ?18O oscillations of Pisidium and Valvata shells. From c. 5000 to 2600 yr BP the record is characterized by larger fluctuations, which may indicate that short-term and particularly pronounced alternation of wet and dry periods occurred.