International audienceA high-resolution sedimentological and geochemical study was performed on a 20 m long core from the alpine Lake Anterne (2063 m a.s.l., NW French Alps) spanning the last 10 ka. Sedimentation is mainly of minerogenic origin. The organic matter quantity (TOC%) as well as its quality (hydrogen (HI) and oxygen (OI) indices) both indicate the progressive onset and subsequent stabilization of vegetation cover in the catchment from 9950 to 5550 cal. BP. During this phase, the pedogenic process of carbonate dissolution is marked by a decrease in the calcium content in the sediment record. Between 7850 and 5550 cal. BP, very low manganese concentrations suggest anoxic conditions in the bottom-water of Lake Anterne. These are caused by a relatively high organic matter (terrestrial and lacustrine) content, a low flood frequency and longer summer stratification triggered by warmer conditions. From 5550 cal. BP, a decrease in TOC, stabilization of HI and higher sedimentation rates together reflect increased erosion rates of leptosols and developed soils, probably due to a colder and wetter climate. Then, three periods of important soil destabilization are marked by an increased frequency and thickness of flood deposits during the Bronze Age and by increases in topsoil erosion relative to leptosols (HI increases) during the late Iron Age/Roman period and the Medieval periods. These periods are also characterized by higher sedimentation rates. According to palynological data, human impact (deforestation and/or pasturing activity) probably triggered these periods of increased soil erosion

International audienceInvestigation of Lake Allos sediments revealed ~ 160 graded layers, interpreted as flood deposits, over the last 1400 yr. Comparisons with records of historic floods support the interpretation of flood deposits and suggest that most recorded flood events are the result of intense meso-scale precipitation events. As there is no evidence for any major changes in erosion processes in the catchment since the Medieval Warm Period (MWP), we interpret the Allos record in terms of repeated intense precipitation events over the last millennium, with a low flood frequency during the MWP and more frequent and more intense events during the Little Ice Age. This interpretation is consistent with the pattern of increasingly humid conditions in the northwestern Mediterranean region. This long-term trend is superimposed on high frequency oscillations that correlate with solar activity and autumnal North Atlantic Oscillation (NAO). Finally, a comparison of flood records across the northwestern Mediterranean region showed that intense precipitation events in Allos (east of the Rhône Valley) were out of phase with events in the Cévennes (west of the Rhône) but in phase with events in eastern Spain. Supported by meteorological analyses, this suggests an oscillation in atmospheric circulation patterns over the northwestern Mediterranean

International audienceA high-resolution sedimentological and geochemical study of a high-altitude proglacial lake (Lake Blanc, Aiguilles Rouges, 2352m a.s.l.) revealed 195 turbidites, 190 of which are related to flood events over the last 1400 years. We used the coarsest sediment fraction of each turbidite as a proxy for the intensity of each flood event. Because most flood events at this locality are triggered by localized summer convective precipitation events, the reconstructed sedimentary record reveals changes in the frequency and intensity of such events over the last millennium. Comparisons with other temperature, palaeohydrological and glacier reconstructions in the region suggest that the most intense events occurred during the warmest periods, i.e. during the Medieval Climate Anomaly (AD 800-1300) and the current period of global warming. On a multi-decadal time scale, almost all the flood frequency peaks seem to correspond to warmer periods, whereas multi-centennial variations in flood frequency appear to follow the regional precipitation pattern. Consequently, this new Alpine flood record provides further evidence of a link between climate warming and an increase in the frequency and intensity of flooding on a multidecadal time scale, whereas the centennial variability in flood frequencies is related to regional precipitation patterns

In central Western Europe, several studies have shown that colder Holocene periods, such as the Little Ice Age, also correspond to wet periods. However, in mountain areas which are highly sensitive to erosion processes and where precipitation events can be localized, past evolution of hydrological activity might be more complicated. To assess these past hydrological changes, a paleolimnological approach was applied on a 13.4-m-long sediment core taken in alpine Lake Anterne (2063 m asl) and representing the last 3.5 ka. Lake sedimentation is mainly composed of flood deposits triggered by precipitation events. Sedimentological and geochemical analyses show that floods were more frequent during cold periods while high-intensity flood events occurred preferentially during warmer periods. In mild temperature conditions, both flood patterns are present. This underlines the complex relationship between flood hazards and climatic change in mountain areas. During the warmer and/or dryer times of the end of Iron Age and the Roman Period, both the frequency and intensity of floods increased. This is interpreted as an effect of human-induced clearing for grazing activities and reveals that anthropogenic interferences must be taken into account when reconstructing climatic signals from natural archives.

Radiocarbon dates for the ancient drawings in the Chauvet-Pont d'Arc Cave revealed ages much older than expected. These early ages and nature of this Paleolithic art make this United Nations Educational, Scientific and Cultural Organization (UNESCO) site indisputably unique. A large, multidisciplinary dating program has recently mapped the anthropological evolution associated with the cave. More than 350 dates (by 14 C, U-Th, TL and 36 Cl) were obtained over the last 15 y. They include 259 radiocarbon dates, mainly related to the rock art and human activity in the cave. We present here more than 80 previously unpublished dates. All of the dates were integrated into a high-precision Bayesian model based on archaeological evidence to securely reconstruct the complete history of the Chauvet-Pont d'Arc Cave on an absolute timescale. It shows that there were two distinct periods of human activity in the cave, one from 37 to 33,500 y ago, and the other from 31 to 28,000 y ago. Cave bears also took refuge in the cave until 33,000 y ago. . Based on stylistic considerations, this art was first attributed to the Solutrean period (∼22,000-18,000 B.P.). Surprisingly, however, the first 14 C dates of black drawings (the only depictions datable by this method) indicated a much older age (∼32,000-30,000 B.P.) (6-9). These dates had a significant impact on commonly accepted theories of the evolution of prehistoric art (10) and thus emphasized the need to obtain a thorough understanding of the occupation history of the cave. A clear chronological framework would reveal the age not only of the art, but also of the periods of human and animal occupation and their relationship to the geomorphological evolution of the cave.Chronologies can be relative or absolute. In this context, relative dating refers to the ordering of the art works and natural or animal related events within a relative temporal sequence, commonly based on patterns of superimposition of the different occurrences: for example, a painting that is overlain by another in a "stratigraphic sequence" is the oldest of the two, and a bear scratch on top of a drawing indicates that humans no longer occupied the cave when the scratch was made. Based on this information alone, however, we do not know how much older the underlying event is: thus the need to obtain absolute dates of parietal art works.In the chronology presented here, we use all of the absolute dates obtained from the art works, as well as other data associated with the parietal art, and animal and human occupations. Our earlier sampling methods and 14 C methodology were criticized (11-13). Before publishing further rock art dating results, we therefore initiated a broad, international intercomparison program of 14 C dating, followed by a holistic chronological model based on an extensive corpus of dates obtained by several different methods.A set of 259 radiocarbon dates is currently available (Fig. 1 and SI Appendix, Fig. S1 and Table S1). They were compiled over the last 15 y and include analyses performed ...

Since its discovery, the Chauvet cave elaborate artwork called into question our understanding of Palaeolithic art evolution and challenged traditional chronological benchmarks [Valladas H et al. (2001) Nature 413:419-479]. Chronological approaches revealing human presences in the cavity during the Aurignacian and the Gravettian are indeed still debated on the basis of stylistic criteria [Pettitt P (2008) J Hum Evol 55:908-917]. The presented 36 Cl Cosmic Ray Exposure ages demonstrate that the cliff overhanging the Chauvet cave has collapsed several times since 29 ka until the sealing of the cavity entrance prohibited access to the cave at least 21 ka ago. Remarkably agreeing with the radiocarbon dates of the human and animal occupancy, this study confirms that the Chauvet cave paintings are the oldest and the most elaborate ever discovered, challenging our current knowledge of human cognitive evolution.absolute dating | cosmonuclide | remote sensing | rockart | rockfall C hauvet cave, in Vallon Pont d'Arc, Ardèche, France, is a site of exceptional scientific interest for a number of reasons: (i) the variety of its majestic parietal; (ii) very good conservation of the floor and wall ornamentations, exhibiting human and animal imprints; (iii) revelations of unknown techniques in Palaeolithic rock art (such as stump drawing); (iv) predominance of rare themes such as felines and rhinoceroses; and (v) unequalled aesthetic delivery (1). On the basis of stylistic comparison with known elements, the Chauvet cave rock ornamentations were initially estimated as being Solutrean (22-17 ka BP) and Magdalenian (17-10 ka BP) (2). The first radiocarbon dates ranging from approximately 30 to approximately 32 14 C ka BP (3, 4) thus disagreed with stylistic analyses such as formalized by Leroi-Gouran (5). Although currently confirmed by 82 radiocarbon dating (6, 7), by crossing dating methods (8,9), and supported by the recent discovery of manifestations of sophisticated Aurignacian prehistoric art (40-28 ka BP) in the Swabian Jura (10), it still remains unclear whether the current stylistic framework should be abandoned in favor of radiocarbon chronologies. Additional robust chronological constraints are therefore critical in establishing Chauvet cave as a reliable benchmark in the absence of comparable equivalent (1,11,12). If corroborated by an independent method, the absolute chronological framework of the Chauvet drawings will indeed establish them as the oldest and most elaborate Aurignacian paintings ever discovered. This will furthermore confirm the existence of an already extremely mature art at that time period during which only few elaborate engraving are known (10), but no other paintings (13,14). To fill this knowledge gap, a geomorphological study combined with 36 Cl dating of rockslide surfaces overhanging the cave entrance was conducted. The Chauvet Cave ClosureGeomorphological studies carried out at Chauvet cave during the last 10 y have unambiguously demonstrated that only one entrance to the cave existed at t...

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