1200 years of decadal-scale variability of Mediterranean vegetation and climate at Pantelleria Island, Italy

A new sedimentary sequence from Lago di Venere on Pantelleria Island, located in the Strait of Sicily between Tunisia and Sicily was recovered. The lake is located in the coastal infra-Mediterranean vegetation belt at 2 m a.s.l. Pollen, charcoal and sedimentological analyses are used to explore linkages among vegetation, fire and climate at a decadal scale over the past 1200 years. A dry period from ad 800 to 1000 that corresponds to the ‘Medieval Warm Period’ (WMP) is inferred from sedimentological analysis. The high content of carbonate recorded in this period suggests a dry phase, when the ratio of evaporation/precipitation was high. During this period the island was dominated by thermophilous and drought-tolerant taxa, such as Quercus ilex, Olea, Pistacia and Juniperus. A marked shift in the sediment properties is recorded at ad 1000, when carbonate content became very low suggesting wetter conditions until ad 1850–1900. Broadly, this period coincides with the ‘Little Ice Age’ (LIA), which was characterized by wetter and colder conditions in Europe. During this time rather mesic conifers (i.e. Pinus pinaster), shrubs and herbs (e.g. Erica arborea and Selaginella denticulata) expanded, whereas more drought-adapted species (e.g. Q. ilex) declined. Charcoal data suggest enhanced fire activity during the LIA probably as a consequence of anthropogenic burning and/or more flammable fuel (e.g. resinous Pinus biomass). The last century was characterized by a shift to high carbonate content, indicating a change towards drier conditions, and re-expansion of Q. ilex and Olea. The post-LIA warming is in agreement with historical documents and meteorological time series. Vegetation dynamics were co-determined by agricultural activities on the island. Anthropogenic indicators (e.g. Cerealia-type, Sporormiella) reveal the importance of crops and grazing on the island. Our pollen data suggest that extensive logging caused the local extinction of deciduous Quercus pubescens around ad1750.

Climate and vegetation changes during the Lateglacial and early–middle Holocene at Lake Ledro (southern Alps, Italy)

Adding to the on-going debate regarding vegetation recolonisation (more particularly the timing) in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081) from Lake Ledro (652ma.s.l., southern Alps, Italy). Environmental changes were reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake levels, magnetic susceptibility and X-ray fluorescence (XRF) measurements) recorded climate and land-use changes during the Lateglacial and early-middle Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of tree species distribution. An altitudedependent progressive time delay of the first continuous occurrence of Abies (fir) and of the Larix (larch) development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills) in northern Italy. Preboreal oscillations (ca. 11 000 cal BP), Boreal oscillations (ca. 10 200, 9300 cal BP) and the 8.2 kyr cold event suggest a centennial-scale climate forcing in the studied area. Picea (spruce) expansion occurred preferentially around 10 200 and 8200 cal BP in the south-eastern Alps, and therefore reflects the long-lasting cumulative effects of successive boreal and the 8.2 kyr cold event. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200-7300 cal BP evidenced in high lake levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal BP, a weak signal of pollen-based anthropogenic activities suggest weak human impact. The period between ca. 5700 and ca. 4100 cal BP is considered as a transition period to colder and wetter conditions (particularly during summers) that favoured a dense beech (Fagus) forest development which in return caused a distinctive yew (Taxus) decline.We conclude that climate was the dominant factor controlling vegetation changes and erosion processes during the early and middle Holocene (up to ca. 4100 cal BP).

Orbital changes, variation in solar activity and increased anthropogenic activities: controls on the Holocene flood frequency in the Lake Ledro area, Northern Italy

Adding to the on-going debate regarding vegetation recolonisation (more particularly the timing) in Europe and climate change since the Lateglacial, this study investigates a long sediment core (LL081) from Lake Ledro (652ma.s.l., southern Alps, Italy). Environmental changes were reconstructed using multiproxy analysis (pollen-based vegetation and climate reconstruction, lake levels, magnetic susceptibility and X-ray fluorescence (XRF) measurements) recorded climate and land-use changes during the Lateglacial and early-middle Holocene. The well-dated and high-resolution pollen record of Lake Ledro is compared with vegetation records from the southern and northern Alps to trace the history of tree species distribution. An altitudedependent progressive time delay of the first continuous occurrence of Abies (fir) and of the Larix (larch) development has been observed since the Lateglacial in the southern Alps. This pattern suggests that the mid-altitude Lake Ledro area was not a refuge and that trees originated from lowlands or hilly areas (e.g. Euganean Hills) in northern Italy. Preboreal oscillations (ca. 11 000 cal BP), Boreal oscillations (ca. 10 200, 9300 cal BP) and the 8.2 kyr cold event suggest a centennial-scale climate forcing in the studied area. Picea (spruce) expansion occurred preferentially around 10 200 and 8200 cal BP in the south-eastern Alps, and therefore reflects the long-lasting cumulative effects of successive boreal and the 8.2 kyr cold event. The extension of Abies is contemporaneous with the 8.2 kyr event, but its development in the southern Alps benefits from the wettest interval 8200-7300 cal BP evidenced in high lake levels, flood activity and pollen-based climate reconstructions. Since ca. 7500 cal BP, a weak signal of pollen-based anthropogenic activities suggest weak human impact. The period between ca. 5700 and ca. 4100 cal BP is considered as a transition period to colder and wetter conditions (particularly during summers) that favoured a dense beech (Fagus) forest development which in return caused a distinctive yew (Taxus) decline.We conclude that climate was the dominant factor controlling vegetation changes and erosion processes during the early and middle Holocene (up to ca. 4100 cal BP).

Mass-movement and flood-induced deposits in Lake Ledro, southern Alps, Italy: implications for Holocene palaeohydrology and natural hazards

High-resolution seismic profiles and sediment cores from Lake Ledro combined with soil and riverbed samples from the lake's catchment area are used to assess the recurrence of natural hazards (earthquakes and flood events) in the southern Italian Alps during the Holocene. Two well-developed deltas and a flat central basin are identified on seismic profiles in Lake Ledro. Lake sediments have been finely laminated in the basin since 9000 cal. yr BP and frequently interrupted by two types of sedimentary events (SEs): light-coloured massive layers and dark-coloured graded beds. Optical analysis (quantitative organic petrography) of the organic matter present in soil, riverbed and lacustrine samples together with lake sediment bulk density and grain-size analysis illustrate that light-coloured layers consist of a mixture of lacustrine sediments and mainly contain algal particles similar to the ones observed in background sediments. Light-coloured layers thicker than 1.5 cm in the main basin of Lake Ledro are synchronous to numerous coeval mass-wasting deposits remoulding the slopes of the basin. They are interpreted as subaquatic mass-movements triggered by historical and pre-historical regional earthquakes dated to AD2005, AD1891, AD1045 and 1260, 2545, 2595, 3350, 3815, 4740, 7190, 9185 and 11 495 cal. yr BP. Darkcoloured SEs develop high-amplitude reflections in front of the deltas and in the deep central basin. These beds are mainly made of terrestrial organic matter (soils and lignocellulosic debris) and are interpreted as resulting from intense hyperpycnal flood event. Mapping and quantifying the amount of soil material accumulated in the Holocene hyperpycnal flood deposits of the sequence allow estimating that the equivalent soil thickness eroded over the catchment area reached up to 5mm during the largest Holocene flood events. Such significant soil erosion is interpreted as resulting from the combination of heavy rainfall and snowmelt. The recurrence of flash flood events during the Holocene was, however, not high enough to affect pedogenesis processes and highlight several wet regional periods during the Holocene. The Holocene period is divided into four phases of environmental evolution. Over the first half of the Holocene, a progressive stabilization of the soils present through the catchment of Lake Ledro was associated with a progressive reforestation of the area and only interrupted during the wet 8.2 event when the soil destabilization was particularly important. Lower soil erosion was recorded during the mid-Holocene climatic optimum (8000-4200 cal. yr BP) and associated with higher algal production. Between 4200 and 3100 cal. yr BP, both wetter climate and human activities within the drainage basin drastically increased soil erosion rates. Finally, from 3100 cal. yr BP to the present-day, data suggest increasing and changing human land use.