A MULTIPROXY, HIGH-RESOLUTION RECORD OF LATE GLACIAL CLIMATE CHANGE IN NORTHWEST ITALY

A lacustrine sequence from Lago Piccolo di Avigliana, Piemonte, Italy, has been studied using pollen, loss-on-ignition, stable isotopic, and microtephra analysis. The data provide evidence of climate changes during the last glacial Late Glacial south of the Alps, a region whose climate is influenced at present by the Mediterranean Sea and by its position in regard to the Alpine mountain chain. Previous attempts to prove the impact of climatic shifts by means of oxygen isotopes (d¹⁸O) in this region were not completely successful (for hydrological reasons): only the Bølling warming could be demonstrated. In contrast, d¹⁸O measured on bulk carbonates at our new site reveals a similarity with classic climate sequences of Central European records (e.g. Gerzensee) or ice-core records (GRIP/GISP), where (i) major climatic events such as the rapid warming at the Oldest Dryas/Bølling transition and the onset and end of the Younger Dryas were observed, as well as (ii) minor events like the Gerzensee Oscillation, were recorded. Chronology is given by AMS ¹⁴C datings of terrestrial macrofossils, one tephra layer (LST), and regional pollen correlation. Correlation of our d¹⁸O record with other sequences where the LST was found is attempted, and synchronicity of the Gerzensee Oscillation could therefore reliably be tested.

The d¹⁸O record is taken as a signature of climate forcing against which the response of vegetation can be studied. During the Bølling warming, d¹⁸O values, organic matter, and carbonate content increased while Betula and subsequently Pinus forests established. During the Allerød and before the LST was deposited, Quercus expanded but was soon reduced in response to the Younger Dryas cold reversal. The subsequent gradual reduction of d¹⁸O values during the early Holocene suggests either a change in seasonality of rainfall or a change in source of moisture.

In conclusion, the similarity between d¹⁸O records at distant sites suggests that during the Late Glacial the Southern Alps and the North Atlantic may have been responding more or less synchronously to common forcing mechanisms. However, the contemporaneity of these climate shifts with climatic events observed in the GRIP ice-core record is difficult to establish until independent correlation proxies such as tephra layers are used to link sedimentary sequences.