Late-Holocene climatic variability south of the Alps as recorded by lake-level fluctuations at Lake Ledro, Trentino, Italy

Abstract

International audienceA lake-level record for the late Holocene at Lake Ledro (Trentino, northeastern Italy) is presented. It is based on the sediment and pollen analysis of a 1.75 m high stratigraphic section observed on the southern shore (site Ledro I) and a 3.2 m long sediment core taken from a littoral mire on the southeastern shore (site Ledro II). The chronology is derived from 15 radiocarbon dates and pollen stratigraphy. The late-Holocene composite record established from these two sediment sequences gives evidence of centennial-scale fluctuations with highstands at c. 3400, 2600, 1700, 1200 and 400 cal. BP, in agreement with various palaeohydro-logical records established in central and northern Italy, as well as north of the Alps. In addition, high lake-level conditions at c. 2000 cal. BP may be the equivalent of stronger river discharge observed at the same time in Central Italy's rivers. In agreement with the lake-level record of Accesa (Tuscany), the Ledro record also suggests a relatively complex palaeohydrological pattern for the period around 4000 cal. BP. On a millennial scale, sediment hiatuses observed in the lower part of the Ledro I sediment sequence indicate that, except for a high-stand occurring just after 7500 cal. BP, lower lake levels generally prevailed rather before c. 4000 cal. BP than afterwards. Finally, the lake-level data obtained at Lake Ledro indicate that the relative continuity of settlements in humid areas of northern Italy during the Bronze Age (in contrast to their general abandonment north of the Alps between c. 3450 and 3150 cal. BP), does not reflect different regional patterns of climatic and palaeohy-drological conditions. In contrast, the rise in lake level dated to c. 3400 cal. BP at Ledro appears to coincide with a worldwide climate reversal, observed in both the hemispheres, while palaeoenvironmental and archaeological data collected at Lake Ledro may suggest, as a working hypothesis, a relative emancipation of proto-historic societies from climatic conditions

Holocene palaeohydrological changes in the northern Mediterranean borderlands as reflected by the lake-level record of lake ledro, northeastern Italy

“…In addition to previous lake-level data (Magny et al, 2009a) obtained from the stratigraphic section of site Ledro I and from core Ledro II-1 (Fig. 1), the present study examines three new sediment profiles recently sampled on the south-eastern shores of Lake Ledro ( Fig.…”

“…8-m-long sediment sequence mainly composed of carbonate lake-marl. It continuously documents the early to mid-Holocene, and it completes the late Holocene data obtained from core Ledro II-1 (Magny et al, 2009a ;Fig. 1, panel C).…”

“…Panel C. Lithostratigraphic correlations between cores examined at site Ledro II. Note (1) the revised altitude of cores Ledro II-1 and Ledro II-3 (by comparison with that published by Magny et al, 2009a), and (2) lateral variations of lithofacies illustrated by sediment profiles of cores Ledro II-1, Ledro II-3, and that of core 2 studied by Beug (1964). Two vertical brackets indicate the parts studied in cores Ledro II-1 and Ledro II-3, i.e.…”

“…An earlier paper (Magny et al, 2009a) focused on the reconstruction of lakelevel changes at Lake Ledro during the late Holocene (last 4000 yr), and on problems relative to the development of settlements in humid areas of northern Italy during the Bronze Age. This study (1) presents the results of supplementary cores and sediment profiles, and (2) combines these new data with earlier ones to establish a lake-level record for the entire Holocene at Lake Ledro.…”

“…and the early to mid Holocene in core Ledro II-3 (below level 648.4 m a.s.l.). Panel D. Sediment profiles of site Ledro I and core Ledro II-1 with radiocarbon dates and reconstructed lake-level phases (Magny et al, 2009a). ES: erosion surface; SH: sediment hiatus.…”