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

Joannin, Sébastien; Vannière, Boris; Galop, Didier; Peyron, Odile; Haas, Jean Nicolas; Gilli, Adrian; Chapron, Emmanuel; Wirth, Stefanie B.; Anselmetti, Flavio S.; Desmet, Marc; Magny, Michel

doi:10.5194/cp-9-913-2013

Cited by 46 publications

(51 citation statements)

References 81 publications

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“…39 • N) supports these conclusions with phases of shallower water around 5500 and 4000 cal BP. As discussed by Joannin et al (2013), if we take into account the radiocarbon age uncertainty (standard deviation), the lowering which developed between 2500 and 1800 cal BP may be equivalent to the well-known phase identified around 2700-2500 cal BP at the Subboreal-Subatlantic transition (van Geel et al, 1996). Another relevant interpretation, if we consider the relatively northern latitudinal location of Lake Trifoglietti at more than 39 • N, may be to infer a possible slight migration south to 40 • N of the boundary between the north-and the south-central Mediterranean sectors characterised by contrasting palaeohydrological patterns.…”

Section: Centennial-scale Eventsmentioning

confidence: 99%

North–south palaeohydrological contrasts in the central Mediterranean during the Holocene: tentative synthesis and working hypotheses

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Abstract. On the basis of a multi-proxy approach and a strategy combining lacustrine and marine records along a north–south transect, data collected in the central Mediterranean within the framework of a collaborative project have led to reconstruction of high-resolution and well-dated palaeohydrological records and to assessment of their spatial and temporal coherency. Contrasting patterns of palaeohydrological changes have been evidenced in the central Mediterranean: south (north) of around 40° N of latitude, the middle part of the Holocene was characterised by lake-level maxima (minima), during an interval dated to ca. 10 300–4500 cal BP to the south and 9000–4500 cal BP to the north. Available data suggest that these contrasting palaeohydrological patterns operated throughout the Holocene, both on millennial and centennial scales. Regarding precipitation seasonality, maximum humidity in the central Mediterranean during the middle part of the Holocene was characterised by humid winters and dry summers north of ca. 40° N, and humid winters and summers south of ca. 40° N. This may explain an apparent conflict between palaeoclimatic records depending on the proxies used for reconstruction as well as the synchronous expansion of tree species taxa with contrasting climatic requirements. In addition, south of ca. 40° N, the first millennium of the Holocene was characterised by very dry climatic conditions not only in the eastern, but also in the central- and the western Mediterranean zones as reflected by low lake levels and delayed reforestation. These results suggest that, in addition to the influence of the Nile discharge reinforced by the African monsoon, the deposition of Sapropel 1 has been favoured (1) by an increase in winter precipitation in the northern Mediterranean borderlands, and (2) by an increase in winter and summer precipitation in the southern Mediterranean area. The climate reversal following the Holocene climate optimum appears to have been punctuated by two major climate changes around 7500 and 4500 cal BP. In the central Mediterranean, the Holocene palaeohydrological changes developed in response to a combination of orbital, ice-sheet and solar forcing factors. The maximum humidity interval in the south-central Mediterranean started ca. 10 300 cal BP, in correlation with the decline (1) of the possible blocking effects of the North Atlantic anticyclone linked to maximum insolation, and/or (2) of the influence of the remnant ice sheets and fresh water forcing in the North Atlantic Ocean. In the north-central Mediterranean, the lake-level minimum interval began only around 9000 cal BP when the Fennoscandian ice sheet disappeared and a prevailing positive NAO-(North Atlantic Oscillation) type circulation developed in the North Atlantic area. The major palaeohydrological oscillation around 4500–4000 cal BP may be a non-linear response to the gradual decrease in insolation, with additional key seasonal and interhemispheric changes. On a centennial scale, the successive climatic events which punctuated the entire Holocene in the central Mediterranean coincided with cooling events associated with deglacial outbursts in the North Atlantic area and decreases in solar activity during the interval 11 700–7000 cal BP, and to a possible combination of NAO-type circulation and solar forcing since ca. 7000 cal BP onwards. Thus, regarding the centennial-scale climatic oscillations, the Mediterranean Basin appears to have been strongly linked to the North Atlantic area and affected by solar activity over the entire Holocene. In addition to model experiments, a better understanding of forcing factors and past atmospheric circulation patterns behind the Holocene palaeohydrological changes in the Mediterranean area will require further investigation to establish additional high-resolution and well-dated records in selected locations around the Mediterranean Basin and in adjacent regions. Special attention should be paid to greater precision in the reconstruction, on millennial and centennial timescales, of changes in the latitudinal location of the limit between the northern and southern palaeohydrological Mediterranean sectors, depending on (1) the intensity and/or characteristics of climatic periods/oscillations (e.g. Holocene thermal maximum versus Neoglacial, as well as, for instance, the 8.2 ka event versus the 4 ka event or the Little Ice Age); and (2) on varying geographical conditions from the western to the eastern Mediterranean areas (longitudinal gradients). Finally, on the basis of projects using strategically located study sites, there is a need to explore possible influences of other general atmospheric circulation patterns than NAO, such as the East Atlantic–West Russian or North Sea–Caspian patterns, in explaining the apparent complexity of palaeoclimatic (palaeohydrological) Holocene records from the Mediterranean area.

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Section: Centennial-scale Eventsmentioning

confidence: 99%

North–south palaeohydrological contrasts in the central Mediterranean during the Holocene: tentative synthesis and working hypotheses

et al. 2013

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“…During these periods, human activities seem relatively limited: the forest recovers and erosion strongly diminishes. Only a small increase in anthropogenic pollen (from 2300 to 1700 cal BP) indicates a human presence in the watershed that is most likely less marked by pastoralism than by crop cultivation, which in turn has a reduced effect on the forested area (Joannin et al, 2013). From 1700 to 1200 cal BP, the reduction of agro-pastoral activities may be associated with the massive migration period (Tinner et al, 2003;Büntgen et al, 2011).…”

Section: Four Successive Periods Of Palaeoenvironmental Changesmentioning

confidence: 99%

“…This paper presents only arboreal and non-arboreal pollen (AP/NAP) curves and an "anthropic" pollen-sum curve (Cerealia type, Secale type, Triticum type, Cannabis-humulus type, Plantago lanceolata, Rumex, Urticaceae). A related paper (Joannin et al, 2013) is dedicated to the reconstruction of detailed vegetation dynamics around Lake Ledro.…”

Section: Pollen Analysesmentioning

confidence: 99%

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

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Abstract. Two lacustrine sediment cores from Lake Ledro in northern Italy were studied to produce chronologies of flood events for the past 10 000 yr. For this purpose, we have developed an automatic method that objectively identifies the sedimentary imprint of river floods in the downstream lake basin. The method was based on colour data extracted from processed core photographs, and the count data were analysed to capture the flood signal. Flood frequency and reconstructed sedimentary dynamics were compared with lake-level changes and pollen inferred vegetation dynamics. The results suggest a record marked by low flood frequency during the early and middle Holocene (10 000–4500 cal BP). Only modest increases during short intervals are recorded at ca. 8000, 7500, and 7100 cal BP. After 4500–4000 cal BP, the record shows a shift toward increased flood frequency. With the exception of two short intervals around 2900–2500 and 1800–1400 cal BP, which show a slightly reduced number of floods, the trend of increasing flood frequency prevailed until the 20th century, reaching a maximum between the 16th and the 19th centuries. Brief-flood frequency increases recorded during the early and middle Holocene can be attributed to cold climatic oscillations. On a centennial time scale, major changes in flood frequency, such as those observed after ca. 4500/4000 and 500 cal BP, can be attributed to large-scale climatic changes such as the Neo-glacial and Little Ice Age, which are under orbital and possibly solar control. However, in the Bronze Age and during the Middle Ages and modern times, forest clearing and land use probably partially control the flood activity.

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“…This accelerates during the late Holocene (from 4100 cal yr BP onwards) through continuous records of anthropogenic pollen indicators and drops in arboreal pollen percentages. More details on the Lake Ledro pollen, vegetation and lake-level history are given in Joannin et al (2013) and in Magny et al (2009Magny et al ( , 2012a.…”

Section: Lake Ledro (Northern Italy)mentioning

confidence: 99%

“…The chronology spans the last 17 000 yr Grosseto (7 m asl) using 13 14 C dates (Table 1) and 1 date from the Ledro II littoral site (Magny et al, 2012a) aligned using stratigraphic comparison. The temporal resolution is approximately estimated to 66 yr / sample throughout the Holocene (more details are given in Joannin et al, 2013).…”

Section: Lake Ledro (Northern Italy)mentioning

confidence: 99%

Contrasting patterns of climatic changes during the Holocene across the Italian Peninsula reconstructed from pollen data

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Lake-level records from Italy suggest that patterns of precipitation in the central Mediterranean during the Holocene were divided between the north and south, but a scarcity of reliable palaeoclimatic records in the north and central-southern Mediterranean means new evidence is needed to validate this hypothesis. We provide robust quantitative estimates of Holocene climate in the Mediterranean region using four high-resolution pollen records from northern (Lakes Ledro and Accesa) and southern (Lakes Trifoglietti and Pergusa) Italy. Multiple methods are used to provide an improved assessment of the palaeoclimatic reconstruction uncertainty. The multi-method approach uses the pollenbased weighted averaging, weighted-average partial leastsquares regression, modern analogue technique, and the nonmetric multidimensional scaling/generalized additive model methods. We use independent lake-level data to validate the precipitation reconstructions. Our results support a climatic partition between northern and southern Italy during the Holocene, confirming the hypothesis of opposing mid-Holocene summer precipitation regimes in the Mediterranean. The northern sites (Ledro, Accesa) are characterized by minima for summer precipitation and lake levels during the early to midHolocene, while the southern sites (Trifoglietti, Pergusa) are marked by maxima for precipitation and lake levels at the same time. Both pollen-inferred precipitation and lake levels indicate the opposite pattern during the late Holocene, a maximum in northern Italy and a minimum in southern Italy/Sicily. Summer temperatures show the same partitioning, with warm conditions in northern Italy and cool conditions in Sicily during the early/mid-Holocene, and a reversal during the late Holocene. Comparison with marine cores from the Aegean Sea suggests that climate trends and gradients observed in Italy show strong similarities with those recognized from the Aegean Sea, and more generally speaking in the eastern Mediterranean

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

Cited by 46 publications

References 81 publications

North–south palaeohydrological contrasts in the central Mediterranean during the Holocene: tentative synthesis and working hypotheses

North–south palaeohydrological contrasts in the central Mediterranean during the Holocene: tentative synthesis and working hypotheses

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

Contrasting patterns of climatic changes during the Holocene across the Italian Peninsula reconstructed from pollen data

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