The Pollen Sequence of Les Échets (France): A New Element for the Chronology of the Upper Pleistocene

Les Échets mire (near Lyon, France) is one of the very few European sites showing an almost continuous record from the glaciation that preceded the Eemian up to now. The pollen diagram can easily be correlated with those from Grande Pile (Vosges). On the basis of a comparison between the two sequences, the age of three clearly temperate post-Eemian episodes (Saint-Germain Ia, Ic and Il at Grande Pile) is discussed. The authors correlate these episodes with the Early Würm Interstadials of Amersfoort, Brorup and Odderade described in Northern Europe and accept the chronology of Grande Pile that dates Saint-Germain I and Saint-Germain Il between ca 115 000 and 70 000 BP, thus making them equivalents of deep sea isotopic stages 5c and 5a. This leads to refute the 14C chronology admitted up to now that places the Early Würm between 75 000 and 55 000 BP. Considering the predominant temperate episodes during this period, the authors propose to use the term "Pre-Würm" instead of "Early Würm". During the Middle Würm, three not well-marked interstadials can be recognized. No interstadial is found during the late Pleni-Würm.Le marais des Échets (près de Lyon, France) constitue l'un des rares sites européens qui présente un remplissage à peu près continu depuis la glaciation qui a précédé l'Éémien jusqu'à nos jours. Le diagramme pollinique peut aisément être mis en corrélation avec ceux de La Grande Pile (Vosges). À partir de comparaisons entre ces deux séquences, la position chronostratigraphique des trois épisodes très nettement tempérés post-éémiens (Saint-Germain la, Ic et II à La Grande Pile) est discutée. Les auteurs mettent en corrélation ces épisodes avec les interstades du Würm ancien, Amersfoort, Brorup et Odderade, décrits en Europe du Nord et acceptent la chronologie de La Grande Pile qui situe Saint-Germain I et II entre environ 115 000 et 70 000 BP et qui en font les équivalents des étages isotopiques océaniques 5c et 5a. Ceci implique que la chronologie 14C admise jusqu'ici et plaçant le Würm ancien entre environ 75 000 et 55 000 BP est totalement erronée. Compte tenu de la prépondérance des épisodes tempérés durant cette période, les auteurs proposent le remplacement de la dénomination "Würm ancien" par celle de "Pré-Würm ". Durant le Würm moyen, trois interstades de faible amplitude ont été reconnus aux Échets, alors qu'aucune variation climatique positive n'est décelable durant le Pléni-Würm final.Das Moor von Les Échets (in der Nàhe von Lyon, Frankreich) ist eines der wenigen europàischen Gelànde, das ein fast kontinuierliches Zeugnis ablegt von der dem Eemian vorausgehenden Eiszeit bis heute. Das Pollendiagramm kann sehr leicht mit denen von Grande Pile (Vogesen) in Zusammenhang gebracht werden. Ausgehend von dem Vergleich zwischen diesen zwei Sequenzen wird das Alter von drei auf das Eemian folgenden und eindeutig gemàpigten Stadien diskutiert (Saint-Germain la, Ic und Il in Grande Pile). Die Autoren setzen dièse Episoden in Beziehung zu den Interstadialen von Amersfoort, Brerup und Odderade, die in Nord Europa beschrieben werden und akzeptieren die Chronologie von Grande Pile, die Saint-Germain I und Saint-Germain II zwischen etwa 115 000 und 70 000 v.u.Z. datiert, und sie so zu Àquivalenten der iso-topischen Tiefsee-Stadien 5c und 5a macht. Das fùhrt zu einer Ablehnung der 14C Chronologie, die bisher galt, und das frühe Würm zwischen 75 000 und 55 000 v.u.Z. ansetzte. Unter Beachtung der dominierenden gemàssigten Episoden wàhrend dieser Zeit schlagen die Autoren vor, den Terminus "Prâ-Würm" an Stelle von "Frùhes Würm" zu benutzen. Wàhrend des Mittel-Würms kônnen drei nicht gut voneinander abgegrenzte Interstadiaie erkannt werden. Während des spàteren Pleni-Würms kann kein Interstadial festgestellt werden

Interdisciplinary characterisation and environmental imprints of mining and forestry in the upper Durance valley (France) during the Holocene

International audienceThe upper Durance valley contains the largest silverelead mines of the French Southern Alps. We investigated the characterisation and impact of these mining activities and associated forestry in the Argentière (L'Argentière-La Bessée) and Faravel (Freissinières) districts using a multidisciplinary approach that includes archaeological, palynological, geochemical, anthracological and dendrochrono-logical studies applied to mining remnants and a peat bog (Fangeas, in the Faravel district). More specifically , we studied the occurrence of lead contamination episodes, the chronology of mining activities and their link to the evolution in woodland cover. Our chronology is based on mining archaeology, radiocarbon dating of about thirty charcoal samples and the dendrochronological analysis of more than 170 specimens of exhumed waterlogged wood. The anthracological analysis was established with more than 10,000 charcoals from firesetting. The main geochemical approach was based on the analysis of lead and its stable isotopes in sediment fractions from a peat core. The combination of palynological records and lead isotope imprints were used to characterise (i) a Roman contamination episode unknown to archaeology, (ii) the development of medieval mining activities and (iii) the reactivation of mining during the Modern period and the Industrial Revolution. Medieval mining coincides with an extension of the high mountain agropastoral areas. The in situ continuous human activities in the same industrial territory led to rational communal management of subalpine forests, but also to their parcelling that reached its peak in the High Middle Ages. Mining during the Modern period coincides with significant stress on woodland areas that also appears to be related to lumber and fuel timber production for shipyards (French Royal Navy) as well as the functioning of several military fortresses. The mining reactivation during the 19th c. matched public measures of forest protection that took shape in the afforestation programme of the uplands

Pollen-based reconstruction of Holocene vegetation and climate in Southern Italy: the case of Lago di Trifoglietti

International audienceA high-resolution pollen record from Lago Trifoglietti in Calabria (southern Italy) provides new insights into the paleoenvironmental and palaeoclimatic changes which characterise the Holocene period in the southern Italy. The chronology is based on 11 AMS radiocarbon dates from terrestrial organic material. The Holocene history of the vegetation cover shows the persistence of an important and relatively stable Fagus forest present over that entire period, offering a rare example of a beech woodstand able to withstand climate changes for more than 11 000 yr. Probably in relation with early Holocene dry climate conditions which affected southern Italy, the Trifoglietti pollen record supports a southward delay in thermophyllous forest expansion dated to ca. 13 500 cal BP at Monticchio, ca. 11 000 cal BP at Trifoglietti, and finally ca. 9800 cal BP in Sicily. Regarding the human impact history, the Trifoglietti pollen record shows only poor imprints of agricultural activities and anthopogenic indicators, apart from those indicating pastoralism activities beneath forest cover. The selective exploitation of Abies appears to have been the strongest human impact on the Trifoglietti surroundings. On the basis of (1) a specific ratio between hygrophilous and terrestrial taxa, and (2) the Modern Analogue Technique, the pollen data collected at Lago Trifoglietti led to the establishment of two palaeoclimatic records tracing changes in (1) lake depth and (2) annual precipitation. On a millennial scale, these records give evidence of increasing moisture from ca. 11 000 to ca. 9400 cal BP and maximum humidity from ca. 9400 to ca. 6200 cal BP, prior to a general trend towards the drier climate conditions that have prevailed up to the present. In addition, several successive centennial-scale oscillations appear to have punctuated the entire Holocene. The identification of a cold dry event around 11 300 cal BP, responsible for a marked decline in timberline altitude and possibly equivalent to the PBO, remains to be confirmed by further investigations verifying both chronology and magnitude. Two cold and possibly drier Boreal oscillations developed at ca. 9800 and 9200 cal BP. At Trifoglietti, the 8.2 kyr event corresponds to the onset of cooler and drier climatic conditions which persisted until ca. 7500 cal BP. Finally, the second half of the Holocene was characterised by dry phases at ca. 6100–5200, 4400–3500, and 2500–1800 cal BP, alternating with more humid phases at ca. 5200–4400 and ca. 3500–2500 cal BP. Considered as a whole, these millennial-scale trends and centennial-scale climatic oscillations support contrasting patterns of palaeohydrological changes recognised between the north- and south-central Mediterranean

Authenticated DNA from Ancient Wood Remains

• Background The reconstruction of biological processes and human activities during the last glacial cycle relies mainly on data from biological remains. Highly abundant tissues, such as wood, are candidates for a genetic analysis of past populations. While well-authenticated DNA has now been recovered from various fossil remains, the final ‘proof' is still missing for wood, despite some promising studies. • Scope The goal of this study was to determine if ancient wood can be analysed routinely in studies of archaeology and palaeogenetics. An experiment was designed which included blind testing, independent replicates, extensive contamination controls and rigorous statistical tests. Ten samples of ancient wood from major European forest tree genera were analysed with plastid DNA markers. • Conclusions Authentic DNA was retrieved from wood samples up to 1000 years of age. A new tool for real-time vegetation history and archaeology is ready to us

Sensibilité de la sédimentation organique aux variations climatiques du Tardi-Wuerm et de l'Holocène; le lac du Bouchet (Haute-Loire, France)

Deux carottes de sédiments superficiels (2 à 3 m) prélevées dans le lac du Bouchet (Haute Loire, France) ont été étudiées du point de vue de leur composition minérale et organique. Les corrélations établies à partir des données concernant lamatière organique ainsi que celles de la palynologie, ont permis de replacer les deux premiers mètres de la série sédimentaire dans la logique climato-stratigraphique du passage Tardi-Würm-Holocène. Nous montrons ici que des variations climatiques de faible amplitude comme celles de l'Holocène, engendrent des changements importants dans la nature, la quantité et le mode de préservation des constituants organiques sédimentés

An integrated palaeoenvironmental investigation of a 6200 year old peat sequence from Ile de la Possession, Iles Crozet, sub-Antarctica

International audienceA 6200 year old peat sequence, cored in a volcanic crater on the sub-Antarctic Ile de la Possession (Iles Crozet), has been investigated, based on a multi-proxy approach. The methods applied are macrobotanical (mosses, seeds and fruits) and diatom analyses, complemented by geochemical (Rock-Eval6) and rock magnetic measurements. The chronology of the core is based on 5 radiocarbon dates. When combining all the proxy data the following changes could be inferred. From the onset of the peat formation (6200 cal yr BP) until ca. 5550 cal yr BP, biological production was high and climatic conditions must have been relatively warm. At ca. 5550 cal yr BP a shift to low biological production occurred, lasting until ca. 4600 cal yr BP. During this period the organic matter is well preserved, pointing to a cold and/or wet environment. At ca. 4600 cal yr BP, biological production increased again. From ca. 4600 cal yr BP until ca. 4100 cal yr BP a “hollow and hummock” micro topography developed at the peat surface, resulting in the presence of a mixture of wetter and drier species in the macrobotanical record. After ca. 4100 cal yr BP, the wet species disappear and a generally drier, acidic bog came into existence. A major shift in all the proxy data is observed at ca. 2800 cal yr BP, pointing to wetter and especially windier climatic conditions on the island probably caused by an intensification and/or latitudinal shift of the southern westerly belt. Caused by a stronger wind regime, erosion of the peat surface occurred at that time and a lake was formed in the peat deposits of the crater, which is still present today

VARIATIONS DEPUIS 10000 ANS DE LA REPARTITION ET DE LA PRODUCTIVITE DES FORETS D'ALTITUDE DANS LES ALPES ET LE JURA ET SIMULATION DES CHANGEMENTS FUTURS

Ce travail repose sur les charbons de bois enfouis dans les sols et les autres macrorestes ont été datés par 14C et identifiés botaniquement, et pour un site particulier (lac Cristol), sur les analyses de pollens, d'insectes, de macro-restes végétaux, charbons de bois et tronc d'arbres ont été combinés en une « approche multi-proxy » afin de mieux comprendre les variations de la forêt de montagne en réponse aux changements climatiques globaux et à l'activité anthropique. Les variations de la limite de la forêt sont de plus de 500 m durant l'Holocène. La période la plus chaude semble avoir été 9000-8000 ans cal B.P. (années calendaires avant le présent). Les hauts niveaux lacustres du début et de la fin de l'Holocène sont de natures en fait assez différentes. Au début de l'Holocène ils sont principalement dus à une évapotranspiration plus faible, et à la fin de l'Holocène à des précipitations plus élevées. L'ensemble de ces informations a permis de tester un modèle de végétation (Biome3) par une utilisation en mode inverse et à essayer de prédire l'évolution de la végétation. Un doublement de CO2 permet à la végétation d'évoluer vers des conditions plus tempérées. Une « forêt mixte tempérée », pourra devenir une forêt décidue tempérée grâce à des hivers nettement plus doux et à une meilleure efficacité dans l'utilisation de l'eau en été. Ces sites d'altitude ont connu une telle végétation entre 9000 et 8000 ans cal B.P