Carole Bégeot

Contrasting patterns of hydrological changes in Europe in response to Holocene climate cooling phases.

The quantitative reconstruction of climatic parameters from pollen and lake-level data obtained at Saint-Jorioz, Lake Annecy (eastern France), gives evidence for cooler and wetter conditions during the 8.2 ka cold event. A comparison of these regional data with other hydrological records reconstructed in Europe for the same period suggests, as a working hypothesis, that mid-latitudes between ca 50° and 43° underwent wetter conditions in response to the cooling, whereas northern and southern Europe were marked by drier climate, in the latter case leading to an interruption of the sapropel 1 formation in the Mediterranean. A similar hydrological tri-partition of Europe can be observed during other Holocene cooling phases associated with North Atlantic IRD events. Data indicate, that the middle zone characterised by wetter climate conditions could have had a more extended latitudinal amplitude during phases of climate cooling weaker than the 8.2 ka event. The differences in expansion of the wet mid-European zone depending on Holocene climate cooling phases could reflect variations in the strength of the Atlantic Westerly Jet in relation with the thermal gradient between high and low latitudes.

Le Tardiglaciaire du massif Jurassien : bilan et perspectives de recherches [The Lateglacial injurassian massif : state and research perspectives]

During a long time the pollinic zonation in the Jura Lateglacial was divided in five zones i.e. the Oldest Dryas, the Belling, the Older Dryas, the Allerod and the Younger Dryas. Then this zonation became more simple: between the Oldest Dryas and the Younger Dryas is inserted a climaticly unstable period, the « Bolling-Allerod Interstade». Now, hight resolution pollen analyses from Jurassian non-anthropized wetlands reveal a very detailed vegetation history. The succession of the different vegetations from the Lateglacial period is particularly well marked by loge range and sometimes short time climatic fluctuations. New micro-analyses show swift variations of the vegetation which could be correlated with cold oscillations recorded in ice and marine cores, specially the Intra Bolling Cold Period (IBCP), the Older Dryas and the Intra-Allerod Cold Period (IACP or Gerzensee/Killarney oscillation). This current research reveals also a bipartition of the Oldest Dryas and a tripartition of the Younger Dryas. But many problems are not yet solved like the period between the deglaciation and the outset of the Oldest Dryas.

Le comportement pollinique du Noisetier (Corylus avellana), son rôle comme indicateur d'impacts anthropiques ? L'exemple d'un transect dans le sud du Jura

Summary In an area with agricultural activities decrease, we study relationships between the pollen rain and the modern vegetation. Also we report the pollen behavior of hazelnut (Corylus avellana). Althought this taxa does not take part directly in the reconquest of land cleared and after abandoned, it reveals an high pollen production in small open areas. These results are compared to the interpretation of fossil pollen spectra especially for the beginning of agricultural practices. At this period the small cleared areas were probably limited to clearing in the middle of thick and diversified forests. So an high pollen production of hazelnut could reveal old cleared areas in pollen spectra.

Quantitative reconstruction of mid-Holocene climatic variations in the northern Alpine foreland based on Lake Morat (Swiss Plateau) and Lake Annecy (French Pre-Alps) data

Vegetation and lake-level data from the sites of Lake Morat (Switzerland) and Lake Annecy (eastern France) are used to provide quantitative estimates of climatic variables over the period 6600-5500 cal.yr BP in the nor-them Subalpine zone, and to test the method of climate reconstruction based on modern pollen analogues constrained by lake-level data. The results obtained from both sites suggest: (1) that phases of higher lake level coincided with a cooling and a shortening of the growing season and an increase in annual precipitation, and (2) that during climatic reversals summer was more affected than winter. They also provide evidence of a sensitive method of reconstruction of climatic variables capable of capturing minor climatic oscillations such as reflected by weakly pronounced lake-level fluctuations. However, comparison of results obtained at Lake Morat and Lake Annecy, with each other and with results from other sites in central Europe, also clearly indicates that either anthropogenic disturbances of the vegetation cover or an overrepresentation of taxa due to particular site exposition can bias the reconstruction of variations in climatic parameters. In addition to pluri-centennial climatic oscillations, both the Lake Morat and Lake Annecy records show a general trend toward temperature cooling over the period considered. This may be related to a reduction in summer insolation induced by orbital factors. Finally, the quantitative estimates of climatic parameters reconstructed at Lake Morat and Lake Annecy help to increase our understanding of the possible impact of climatic oscillations on ancient agricultural communities.

Past mining activities in the Vosges Mountains (eastern France): Impact on vegetation and metal contamination over the past millennium:

Coring was carried out in a soligenous marsh in the Vosges Mountains in the past mining district of Sainte-Marie-aux-Mines (eastern France). High-resolution palynological, non-pollen-palynomorph, and geochemical analyses were performed along the core. Correlations between the herbal composition of the landscape and trace metals in the core reveal a specific palynological pattern during mining activities. Two main periods of anthropogenic impacts on vegetation and trace metal contamination are shown: during the 16th–17th centuries, for mining and smelting activities, and the beginning of the 20th century, for smelting and the Industrial Revolution. No drastic deforestations occurred near the study site, contrary to historical descriptions and prints of the valley. Controlled forest practices were implemented from the beginning of the record, that is, since cal. AD 1000, so the impact of mining activities seems to be less significant than expected near mining sites. We demonstrate that the minerotrophic characteristics of the record closest to past mining sites allows for (1) the description of the landscape associated with anthropogenic activities and (2) the recording of past trace metal emissions without post-depositional mobility.

L'origine récente des peuplements de Pin à crochets (Pinus uncinata Miller ex Mirbel) sur la tourbière de Frasne et exploitation de la tourbe dans le Jura

Summary From pollen analyses, M. Reille (1989 and 1991) shows the recent development of the Pinus uncinate Miller ex Mirbel in the peat bog of Frasne (Jura). A research in forested records effectively shows that many plantings were tried in this peat bog, but never with Pinus uncinata. Actually, from the middle of the 19th century, Pinus uncinata was considered useless and was excluded out of the peat bog. In fact, the recent origin of the Pinus uncinata seems associated with the over-peat cutting since the middle of the 17th century. The peat cutting creates exploitation holes where wet zones are favourable to the germination of Pinus uncinata. This tree has been unintentionally favoured to human action, at least on the Frasne peat bog.

Tracking past mining activity using trace metals, lead isotopes and compositional data analysis of a sediment core from Longemer Lake, Vosges Mountains, France

A 157-cm-long sediment core from Longemer Lake in the Vosges Mountains of France spans the past two millennia and was analyzed for trace metal content and lead isotope composition. Trace metal accumulation rates highlight three main input phases: Roman Times (cal. 100 BC–AD 400), the Middle Ages (cal. AD 1000–1500), and the twentieth century. Atmospheric contamination displays a pattern that is similar to that seen in peat bogs from the region, at least until the eighteenth century. Thereafter, the lake sediment record is more precise than peat records. Some regional mining activity, such as that in archaeologically identified eighteenth-century mining districts, was detected from the lead isotope composition of sediment samples. Compositional data analysis, using six trace metals (silver, arsenic, cadmium, copper, lead and zinc), enabled us to distinguish between background conditions, periods of mining, and of other anthropogenic trace metal emissions, such as the recent use of leaded gasoline.

Lead Highly Available in Soils Centuries after Metallurgical Activities

Lead (Pb)-contaminated sites that resulted from past mining and smelting activities still pose toxicological and ecotoxicological issues worldwide. A large body of research has been dedicated to evaluating the contamination and proposing mitigation strategies for recently contaminated sites (from the 19th century until the present). The possible impact of older contaminations has been much less investigated. The present study focuses on soils affected by Pb-silver mining and smelting activities during the 15th to 18th centuries. A combination of sequential extractions and X-ray absorption spectroscopy was used to determine the Pb fractionation and speciation in these soils. Despite the long passage of time, Pb was still highly available (1 and 6% of Pb present in the exchangeable fraction and 46 to 71% in the reducible fraction) and mostly present as Pb sorbed on iron (oxyhydr)oxides. Galena (lead sulfide, PbS) was observed in a soil sample from a kitchen garden, suggesting the recent use of smelter slags as soil amendments. This study shows that Pb is still highly available on this site after almost five centuries, probably because of the acidic character of the soil and the soil composition.

High-temporal resolution landscape changes related to anthropogenic activities over the past millennium in the Vosges Mountains (France)

Iron mining activities in the Bruche valley (Vosges Mountains, France) date historically from the Roman period to the mid-nineteenth century. The geochemical and palynological study of a core from the peat bog of Le Champ du Feu allows highlighting impacts of these activities over the past millennium. Trace metal contamination is recorded for lead (Pb), arsenic, zinc, and antimony during the Middle Ages, the sixteenth century, and from cal. ad 1750–1900, with several sources distinguished by Pb isotope analyses. Forest exploitation is attested by the palynological analysis of the core, with exploitation of Fagus for smelting processes and cutting of Abies for agro-pastoralism. This approach highlights several patterns of contamination, corresponding to the mixing sources and the contamination intensity, which can be linked to the pollen assemblage zones. Hence, anthropogenic activities such as mining and farming led to long-term modification of the landscape composition in this mountainous area.