Fabien Arnaud | Savoie University (original) (raw)

Papers by Fabien Arnaud

Quaternary Science …, 2012

Two well-dated ca. Holocene-long sedimentary sequences from deepest parts of Lake Bourget provide... more Two well-dated ca. Holocene-long sedimentary sequences from deepest parts of Lake Bourget provide new insights onto the evolution of erosion patterns at a regional scale in NW European Alps. The combination of high resolution geochemistry -XRF core scanning, calibrated by 150 punctual measurementsand isotope geochemistry (Nd) of the terrigenous fraction permitted the reconstruction not only of the intensity, but also the type (physical erosion vs. chemical weathering) and the location (Prealpine massifs vs. High Crystalline massifs) of dominant erosion processes. Those data point the persistency of weak erosion fluxes from 9600 to 5500 cal. BP due both to a dry climate and the growing sheltering effect of soils that rapidly progressed between 9600 and 8000 cal. BP. Soils then reached a steady state before being destabilised around 4400 cal. BP, probably in response to human impact. The human impact then reached a sufficient intensity to change erosion patterns at a regional scale, but did not result in a significant increase of the regional terrigenous flux. The following enhancement of erosion processes occurred around 2700 cal. BP. It was first paced by changing climatic conditions, but probably reinforced by human impact during Late Iron Age -Antiquity period. Over the long-term trend, the Lake Bourget record pinpoints an evolution of paleohydrological conditions in the Alps dominated by dry conditions from 9500 to 4400 cal. BP and a subsequent drift toward wetter conditions that culminated during the so-called Little Ice Age (ca. 1350-1900 AD). In such a context the current dry conditions in European Alps appear out-of-trend. At Arnaud et al., Holocene alpine erosion patterns subaquatiques et sous-marines: Bilan Scientifique 2000. Ministère de la culture et de la communication. Paris. pp. 117 -137. . Holocene climate variability. Quaternary Research, 62, 243-255.

Climatic change, 2012

Flood hazard is expected to increase in the context of global warming. However, long time-series ... more Flood hazard is expected to increase in the context of global warming. However, long time-series of climate and gauge data at high-elevation are too sparse to assess reliably the rate of recurrence of such events in mountain areas. Here paleolimnological techniques were used to assess the evolution of frequency and magnitude of flash flood events in the North-western European Alps since the Little Ice Age (LIA). The aim was to document a possible effect of the post-19 th century global warming on torrential floods frequency and magnitude. Altogether 56 flood deposits were detected from grain size and geochemical measurements performed on gravity cores taken in the proglacial Lake Blanc (2170 m a.s.l., Belledonne Massif, NW French Alps). The age model relies on radiometric dating ( 137 Cs and 241 Am), historic lead contamination and the correlation of major flood-and earthquake-triggered deposits, with recognized occurrences in historical written archives. The resulting flood calendar spans the last ca 270 years (AD 1740-AD 2007. The magnitude of flood events was inferred from the accumulated sediment mass per flood event and compared with reconstructed or homogenized datasets of precipitation, temperature and glacier variations. Whereas the decennial flood frequency seems to be independent of seasonal precipitation, a relationship with summer temperature fluctuations can be observed at decadal timescales. Most of the extreme flood events took place since the beginning of the 20 th century with the strongest occurring in 2005. Our record thus suggests climate warming is favouring the occurrence of high magnitude torrential flood events in high-altitude catchments.

Quaternary …, 2012

NICE M e d i t e r r a n e an S e a NICE NICE NICE NICE NICE NICE NICE Var V e r d o n V e r d o ... more NICE M e d i t e r r a n e an S e a NICE NICE NICE NICE NICE NICE NICE Var V e r d o n V e r d o n 30 km N 1. Vidourle and Herault Rivers (France) 2. Barcelona county (Spain) 3. Estanya Lake (Spain) 4. Taravilla Lake (Spain) Lake Allos A lp s Pyr ene es U b a y e 1 3 D u r a n c e 2 Screes Carbonated conglomerate Planktonic calcareous Massive calcareous Coarse sandstone Glacier deposits underground out ow 23 50 2 3 5 0 2 5 0 0 2 5 0 0 Tête du Lac 2672 To u r s d u L a c S o u r c e t o r r e n t 500m N L a u s t o r r e n t L a c t o r r e n t

Journal of Paleolimnology

Spores of coprophilous fungi, especially Sporormiella, are often well preserved in lake sediment ... more Spores of coprophilous fungi, especially Sporormiella, are often well preserved in lake sediment cores. It has been hypothesized that such spores can be used to quantify past livestock abundance. The quantitative relationship between fungal spore abundance and livestock populations, however, is not well established, nor are the mechanisms of spore transport and deposition in lacustrine systems. Multiple cores from Lake Allos, a large high-elevation lake in the French Alps, were used to map the modern abundance of Sordaria and Sporormiella spores throughout the lake. We observed high spatial heterogeneity with respect to spore numbers. No correlation with the distance from shoreline was found. There was, however, a relation with distance from the two main lake inlets. These results were used to select two fungirich sediment cores to investigate grazing pressure over the last two centuries. Comparisons were made between spore influx and historic data on livestock densities in the catchment. A sharp decrease in Sporormiella influx ca. 1894-1895 was associated with a reported reduction in sheep in the Allos catchment at that time. Mean influx of Sporormiella decreased by a factor of three between the nineteenth and twentieth centuries, reflecting a reduction in the reported number of animals in the Lake Allos catchment, from 6,000 to 2,000. This study confirmed that Sporormiella spore abundance in lake sediments can be used as a proxy for catchment herbivore numbers in paleoecological reconstructions. Nevertheless, our data indicate that before spore accumulation can be used to infer past domestic herbivore density, one must understand the processes of coprophilous spore transfer from the catchment to the lake and the influence of core location on spore numbers in the sediment. Fig. 6 Sporormiella concentrations (number cm -3 ) and accumulation rates (number cm -2 yr -1 ) for the last 170 years in cores ALO09P3 and ALO09P13. Sediments deposited from 1868 to 1886 were not analysed because of evidence for strong flood events J Paleolimnol (2013) 49:117-127 125

Antarctic Science

Lac d'Armor (49827'S, 69842'E) is a medium-sized, fjord-type lake located on the 'Grande Terre' i... more Lac d'Armor (49827'S, 69842'E) is a medium-sized, fjord-type lake located on the 'Grande Terre' island of the Kerguelen archipelago. A dense grid of high-resolution reflection seismic profiles was collected from this lake basin. The seismic stratigraphic facies reveal a last deglaciation to Holocene infill comparable to the seismic facies found in other glacigenic lakes all over the world. Remarkable features in the seismic stratigraphy are mounded structures found at the southern edge of both sub-basins. The sediment mounds can be interpreted as sediment drifts created by wind-induced bottom currents. The onset of the build-up of these drifts initiated at some point in the Holocene and indicates a strengthening of the southern Westerlies, which are currently the dominant winds on this island.

Water Science and Technology, 2008

In order to evaluate the historical impact of urban stormwater runoff on a lacustrine environment... more In order to evaluate the historical impact of urban stormwater runoff on a lacustrine environment, eight sediment cores were collected in October 2006 in Lake Bourget (Savoie, France). Sediment samples were analysed for polycyclic aromatic hydrocarbons (PAH) and polychlorobyphenyls (PCB) in order to correlate the vertical profiles of contamination and the evolution of the urbanisation on the watershed for the last 100 years. Overall, we observe that vertical profiles of PCB and PAH concentrations in Lake Bourget are showing a downward trend, probably resulting from the pollution control measures. Concentrations of PCB and PAH measured in surface sediments are approximately 5 -10 fold less than maximal concentrations found in the cores. Maximal PAH concentrations were found at the bottom of the cores (,40 cm) which approximately correspond to the beginning of the 20th century. Maximal PCB concentrations measured in cores L5 and L6 are respectively 850 and 790 mg/g dw (dryweight). The peak of PCB corresponds to the maximum of PCB production and consumption in the 1970s. In surface sediments total PCB concentrations range between 47 and 79 mg/kg dw. Those concentrations are particularly high compared to other values measured in lake sediments and highlight the problem of a local source of PCB contamination in the watershed. General trends were observed, yet the part of urban stormwater runoff in the total contamination could not be determined.

Marine Geology, 2011

The aim of this study is to unravel the respective influence of land use and high-frequency clima... more The aim of this study is to unravel the respective influence of land use and high-frequency climate changes on the siltation of a river-influenced coastal environment. An 8.4m long sediment core was recovered in the Pertuis Charentais (western France). An accurate 14C Bayesian age model was developed to perform a depth to time conversion of high-resolution sedimentological data obtained on

… de Physique IV ( …, 2003

Quaternary …, 2011

In central Western Europe, several studies have shown that colder Holocene periods, such as the L... more 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.

Chemical …, 2005

Geochemical methods (major elements and Sr, Nd isotopes) have been used to (1) characterize Lake ... more Geochemical methods (major elements and Sr, Nd isotopes) have been used to (1) characterize Lake Le Bourget sediments in the French Alps,(2) identify the current sources of the clastic sediments and estimate the source variability over the last 600 years. Major ...

Holocene, 2009

In order to better understand the evolution of past climate-human-environment interactions in the... more In order to better understand the evolution of past climate-human-environment interactions in the North-western Alps during the Holocene, we have analysed the lipid content of two cores taken from the sediments of Lake le Bourget (French Alps). By using a specific molecular biomarker of Panicum miliaceum (broomcorn millet) previously defined and a new molecular marker of soil erosion, we demonstrate that the onset of millet cultivation coincides with the onset of major soils erosion in the catchment during the Middle Bronze Age. Although archaeological and archaeobotanical investigations indicate a discrete human occupation of the lakeshores at this period, they also point to a regional change in agricultural practices that deeply affected soils. The evolution of millet cultivation appears in strong connection with climatic variations, estimated in the same cores from the variations in titanium, a proxy of hydrological changes in the region. Social and cultural triggers cannot be discarded at this stage. Such an approach applied to more sedimentary archives shows high potential to unravel the temporal and spatial dynamics of human land-use.

Journal of Quaternary …, 2012

On the basis of sedimentological analysis of two cores taken at Chatillon, Lake Le Bourget (north... more On the basis of sedimentological analysis of two cores taken at Chatillon, Lake Le Bourget (northern French Pre-Alps), and well dated by radiocarbon dates in addition to tree ring dates obtained from an archaeological layer, this paper presents a high-resolution lake-level record for the period 4500-3500 cal. a BP. The collected data provide evidence of a complex palaeohydrological (climatic) oscillation spanning the ca. 4300-3850 cal. BP time interval, with major lake-level maxima at ca. 4200 and 4050-3850 cal. a BP separated by a lowering episode around 4100 cal. a BP. The lake-level highstands observed at Chatillon between 4300 and 3850 cal. BP appear to be synchronous with (i) a major flooding period recorded in deep cores from the large lakes Le Bourget and Bodensee, and (ii) glacier advance and tree line decline in the Alps. Such wetter and cooler climatic conditions in west-central Europe around 4000 cal. a BP may have been a nonlinear response to decrease and seasonal changes in insolation. They may also provide a possible explanation for the general abandonment of prehistoric lake dwellings north of the Alps between 4360 and 3750 cal. a BP.

AGU Fall Meeting Abstracts, 2004

Abstract Puyehue Lake is located in the Southern Volcanic Zone of Chile (Southern Lake District, ... more Abstract Puyehue Lake is located in the Southern Volcanic Zone of Chile (Southern Lake District, 40 S). This monomictic lake is under the influence of the oceanic winter polar front (WPF) and constitutes a powerful sedimentary archive for paleoenvironmental ...

Comptes Rendus Geoscience, 2006

In Lake Anterne (NW French Alps), the Roman period is characterised by a lead contamination more ... more In Lake Anterne (NW French Alps), the Roman period is characterised by a lead contamination more important than that of the 1970s, due to the use of leaded gasoline. The maximum of this contamination period has been varve-dated 220 AD, i.e., during the optimum of Roman civilization in the Alps. Crossing palaeoenvironmental and archaeological evidences points out the economic importance

Applied and …, 2011

The variability of spatial distribution and the determinism of cyanobacterial blooms, as well as ... more The variability of spatial distribution and the determinism of cyanobacterial blooms, as well as their impact at the lake scale, are still not understood, partly due to the lack of long-term climatic and environmental monitoring data. The paucity of these data can be alleviated by the use of proxy data from high-resolution sampling of sediments. Coupling paleolimnological and molecular tools and using biomarkers such as preserved DNA are promising approaches, although they have not been performed often enough so far. In our study, a quantitative PCR (qPCR) technique was applied to enumerate total cyanobacterial and total and toxic Planktothrix communities in preserved DNA derived from sediments of three lakes located in the French Alps (Lake Geneva, Lake Bourget, and Lake Annecy), containing a wide range of cyanobacterial species. Preserved DNA from lake sediments was analyzed to assess its quality, quantity, and integrity, with further application for qPCR. We applied the qPCR assay to enumerate the total cyanobacterial community, and multiplex qPCR assays were applied to quantify total and microcystin-producing Planktothrix populations in a single reaction tube. These methods were optimized, calibrated, and applied to sediment samples, and the specificity and reproducibility of qPCR enumeration were tested. Accurate estimation of potential inhibition within sediment samples was performed to assess the sensitivity of such enumeration by qPCR. Some precautions needed for interpreting qPCR results in the context of paleolimnological approaches are discussed. We concluded that the qPCR assay can be used successfully for the analysis of lake sediments when DNA is well preserved in order to assess the presence and dominance of cyanobacterial and Planktothrix communities.

Journal of Paleolimnology, 2005

... Discriminating the fingerprints of bio-induced and detrital sedimentary processes in particle... more ... Discriminating the fingerprints of bio-induced and detrital sedimentary processes in particle size distribution spectra of hard water lake sediments. Fabien Arnaud 1, 2, 3. (2005). ... oai:hal.archives-ouvertes.fr:hal-00195486. Contributeur : Fabien Arnaud <>. ...

Earth-science Reviews, 2011

Colour is a fundamental property of sediment and is often used for lithographic description to de... more Colour is a fundamental property of sediment and is often used for lithographic description to determine sedimentological structures, facies etc. However, the information contained in this parameter is difficult to extract because it is difficult to quantify. Colour can be quantified by spectrocolorimetry which provides very high resolution data quickly and non-destructively.

Quaternary Science …, 2012

Climatic change, 2012

Quaternary …, 2012

Journal of Paleolimnology

Antarctic Science

Water Science and Technology, 2008

Marine Geology, 2011

… de Physique IV ( …, 2003

Quaternary …, 2011

Chemical …, 2005

Holocene, 2009

Journal of Quaternary …, 2012

AGU Fall Meeting Abstracts, 2004

Comptes Rendus Geoscience, 2006

Applied and …, 2011

Journal of Paleolimnology, 2005

Earth-science Reviews, 2011

EGU General …, 2009

During the last decades, mountain areas have been subjected to a number of environmental changes ... more During the last decades, mountain areas have been subjected to a number of environmental changes such as glacier retreat, permafrost degradation and a higher frequency of extreme events. All of these changes affect sediment production and flux within alpine catchments, potentially generating destructive torrential floods. Lakes represent a natural trap for the mobilized sediments during such events and thus offer the possibility to reconstruct the response of geomorphologic processes to past climate changes. Such data are urgently needed to better predict the effects of future climate scenarios in alpine areas. However, to understand and calibrate the data obtained from lacustrine sediment archives it is crucial to include studies of actual processes within the catchments of these lakes. We present monitoring data obtained at Lake Anterne (2061 m asl), north-western French Alps. Considerable parts of the catchment area consist of barely vegetated scree slopes formed by easily erodible calcareous schists. Consequently, the sediments deposited in the lake basin are highly minerogenic and contain information of past erosion events. The monitoring program includes sediment traps, thermistors and a turbidity sensor within the lake, a weather station, soil temperature and humidity sensors at different slopes, automatic time-lapse cameras and a hydrological station recording water level and turbidity of the main tributary. Our data cover the last two years and show considerable variation in sediment transfer and deposition processes. On July 17th, 2007, a thunderstorm occurred and initiated numerous debris flows within the catchment and caused the deposition of a several centimetres thick, graded deposit in the lake. This event was particularly violent and generated torrential floods in the Giffre valley downstream of Lake Anterne, causing considerable damage. In particular, the destruction of a medieval bridge indicates that such an intense event was not observed in recent historical times. Two other rainfall events are subsequently visible in the breakdown of the thermocline of Lake Anterne as well as in the precipitation data. In 2008, no such conspicuous deposition events were recorded in the lake or at the weather station. The meteorological data indicate that the average summer precipitation was only 30 % lower than in 2007, but rainfall intensities reached similar values in both years. One possible explanation for the observed differences in sediment transfer is sediment exhaustion within the river channels or the passing of a threshold value in precipitation in connection with water saturated soils. Regardless of the actual factors responsible for sediment mobilization during extreme events in the summer months, such events seem to be the main mode of sediment transfer whereas snowmelt appears to be negligible. Our results show that even in small catchments the response of geomorphologic processes to (climatic) forcings is complex and several years of monitoring data are needed to fully understand the factors controlling the sediment transfer.

Among the global expressions of climatic changes over the Holocene period, changes in hydrologica... more Among the global expressions of climatic changes over the Holocene period, changes in hydrological patterns have been particularly important. Indeed, reconstructed changes of past lake levels, flood/droughts frequency or glacier position revealed high magnitude variability at various timescales. In this paper we present a synthesis of such reconstructions in NW French Alps from various natural archives (lake and river sediment sequences, glacier position evidences), all of them being located in a restricted geographic area. All of the studied sequences yield a common history at a secular to millennial timescale. In particular the Late Holocene was marked in the studied region by wet periods around 5.6, 4.2, 3.2, 2.7-2.4; 1.5-1.3; 6.5-0.5 ka cal. BP interrupted by relatively dryer periods. At a millennial to pluri-millennial timescale, we show that the Early Holocene was a period of reduced hydrological activity. The first important wet period occurred around 5.6 ka cal. BP, and a threshold seems to have been reached around 2.7 ka cal. BP. Since then, the alpine glaciers occupied a Little Ice Age-like position more than 50 % of time, whereas the inverse situation prevailed in the Early to Mid-Holocene times. This climatic change also resulted in a dramatic rise of flood frequency and a reorganisation of river Rhône geomorphology. In terms of climate forcing our results tend to demonstrate a complex interplay, at different time-scales, between long-term orbital-forced changes in insolation and the - still not yet well-understood - effect of solar activity. Indeed, the long-term trend toward more frequent and intense wet periods along the Holocene seems to be forced by the northward shift of westerlies winds in response to precession forcing, whereas the secular to pluri-secular periods of enhanced hydrological activity are synchronous to solar minima. Regarding those conclusions, the present-day warm and dry climate situation over NW Alps seems anomalous compared to the natural climate evolution and is thus likely caused by human-triggered greenhouse gases emissions.

AGU Fall Meeting Abstracts, 2004

9th International …, 2003

Université de Savoie.

EGU General …, 2010

Abstract Small lakes with little catchment areas, and high resolution Holocene sediment infilling... more Abstract Small lakes with little catchment areas, and high resolution Holocene sediment infilling, offer the interest to record mainly local perturbation and to study the switch from climatic to anthropogenic forcing. Two cores were extracted from Lake Antre in the Jura ...

Soil is a natural body occurring at the interface between the lithosphere, atmosphere and biosphe... more Soil is a natural body occurring at the interface between the lithosphere, atmosphere and biosphere. As a result, the physical and chemical properties of soils evolve with time, and the reconstruction of their history represents a key to understand past environmental changes. Palaeolimnological techniques such as sediment geochemistry can be used to investigate changes in catchment history by providing information about soil development. However, due to the lack of conservative pedosignatures (soil proxies), only few paleoecological studies have attempted to reconstruct the history of soil genesis using geochemical analyses of lacustrine sediments. Here we present a multidisciplinary study which aims to use pedosignatures, defined by a previous soil study, in order to characterize the history of soil genesis, podzolization and chemical weathering processes in two sediment sequences. Moreover, we aim to compare the timing of soil evolution with other paleoenvironmental markers (macroremains, charcoals…) in order to infer the role of climate, vegetation and possible human activities as forcing factors. In a first step, the geochemical investigation of eight subalpine soil profiles from the inner Alps allowed to define relevant proxies of two major soil processes. Parent material normalized REE patterns provide a precise tracer of chemical weathering whereas the proportions of secondary Al- and Fe-bearing phases provide a tracer of the podzolisation process. Then, the same tracers were assessed on two lacustrine and peat sediment sequences (Loup and Thyl lakes) from the subalpine domain. The proxy records, spanning ca. 4.500 yr at the Thyl lake and ca. 13.500 yr at the Loup lake, indicate that both progressive and regressive pedogenesis occurred after the deglaciation. The Thyl record is highly contrasted: the progressive setting of the mixed cembra pine ecosystem is associated to the podzolisation process (secondary Al- and Fe-bearing phases are maximal) and the increase of chemical weathering (enrichments of specific REE's fractions) that lasted totally ca. 1500 to 2000 years. Then, these progressive pathways are followed by abrupt and rapid secondary processes that could result from drastic transformation of the plant cover. The flat normalized REE patterns associated with low secondary Al and Fe values suggest a decrease of chemical weathering and podzolization. Moreover, the higher variability in cembra pine and the enrichment in sedge and other herbs remains in the lake suggest the setting of semi-open vegetation associated to the evidence of regressive soil processes. On the other hand, Loup environment and soil history are characterized by a progressive and stable evolution leading to present day old growing forests and Podzol soil type. Whereas the major sedimentological changes are sensitive to climate, the soil proxy records may be more triggered by the natural dynamic of the plant cover. At this site, human disturbances seem to have lower importance than at the Thyl site.

Simposio de cambio …, 2003

IRD - Institut de recherche pour le développement.

Geophysical …, 2007

The uppermost sediments of Lake Bourget consist of organic-rich rhythmites which have been previo... more The uppermost sediments of Lake Bourget consist of organic-rich rhythmites which have been previously related to the recent onset of persistent anoxia in the hypolimnion. Radionuclide dating (137Cs and 241Am) confirms that these laminations are biochemical ...

European …, 2010

... Combining historical and sedimentary archives to reconstruct a calendar of extreme flood even... more ... Combining historical and sedimentary archives to reconstruct a calendar of extreme flood events in high alpine areas. Bruno Wilhelm 1 , Fabien Arnaud 1 , Amaya Legaz 1 , Françoise Allignol 1 , Alain Melo, Charline Giguet-Covex 1. (2010). ...

Proceedings of the …, 2005

Université de Savoie.

EGU General …, 2010

Estuaries are the downstream end-member of fluvial systems. They are experiencing high sedimentat... more Estuaries are the downstream end-member of fluvial systems. They are experiencing high sedimentation rates, thus providing good opportunities for high resolution studies of Holocene environmental changes at the land/ocean interface. From a thorough literature survey, it appears that a rapid siltation and/or an increase in sedimentation rate were recorded in many estuarine environments, concomitantly to major migrations of human population throughout the world, both in time and space. It has been clearly related to an increase in sediment supply to estuaries in Minor Asia (Bronze Age, e.g. and in North America and Southwest Pacific (18th and 19th centuries, e.g. , in response to deforestation on catchment areas. However, this relationship is less obvious in Europe , because deforestation occurred concomitantly to climate changes of the last millennium (climate instability at the end of Medieval Warm Period, Little Ice Age) that can also explain an increase in soil erosion. Indeed, these hypotheses have been proposed to explain a similar change in Marennes-Oléron Bay (Atlantic coast of France), which consists in the sudden deposition of a few meters-thick mud drape on basal mixed mud and sand bodies . The methods used to investigate this estuarine bay so far (very high resolution seismic stratigraphy, grain size analysis and radiocarbon dating) provided relevant information about recent environmental changes, but new data are now needed for further investigation. In the present study, we provide a multi-proxy analysis of the Marennes-Oléron Bay mud drape. A new 8 m-long core (M7UC01) was sampled on an intertidal flat, its location being determined on the basis of seismic stratigraphy. Core processing included visual description, physical measurements, grain size analysis every 2.5 to 5 cm, AMS radiocarbon dating, XRF core scanning, clay mineralogy and Rock Eval analysis. Fossil molluscs and foraminifers were also recovered to provide paleoenvironmental reconstructions. Clay mineralogy of the mud drape is similar to that of the turbid plume of the Charente River, which is an important source of terrestrial sediment in the bay, and to surrounding marsh soils. Examination of sediment smear slides shows that the sediment contains abundant plant debris. The very low values of Hydrogen Index determined by Rock-Eval analysis (mean HI: 150 ± 25 mg HC.g-1 TOC) are typical of organic matter derived from land higher plants. These three results strongly suggest that the Marennes-Oléron Bay mud drape is composed of soil relicts derived from the watershed. The mud drape started to deposit at 1400 AD, which coincides with the start of the Spörer minimum. Fossil mollusc and foraminifer assemblages provide evidences of another environmental change dated to 1670 AD, which corresponds to the Maunder minimum. These data suggest a strong impact of Little Ice Age climate changes, superimposed to land reclamation and deforestation, on the increase of sediment supply in the study area. These results, compared with the detailed literature survey performed meanwhile, would provide new insights into the impact of simultaneous land use and climate changes on the sediment deposition in estuaries during the last centuries.

Subantarctic Indian Ocean, above 50°S, is one the places in the world where past atmospheric circ... more Subantarctic Indian Ocean, above 50°S, is one the places in the world where past atmospheric circulation patterns remain completely unknown. This is an important lack in scientific knowledge of past climate changes as this region is one of the key places of the climate machine. In particular, we do not know the impact of Holocene climate variability on extreme south cyclonic circulation. Lake Armor is a fjord-type lake, 98m maximum depth, located on the eastern edge of Kerguelen mainland central plateau. A first reconnaissance survey, including seismic imaging and short cores retrieving, was led here in November 2006. Seismic and bathymetric data reveal the existence of two depocentres submitted to river inputs (Heirman et al., 2007 ; Arnaud et al., 2007). The southern one is submitted to strong underwater currents and is not suited for paleoclimate reconstruction. On the contrary, the northern one exhibits finely stratified Holocene deposits which were cored in the aim of reconstructing the evolution of river floods on Kerguelen archipelago. We led on the retrieved short cores a high resolution sedimentological study, including micro-grainsize, colour, physical properties (Geotek multi-track sensor), and geochemistry (XRF core scanning, major and trace elemental composition, infrared spectrometry). In the case of lake sediments in which detrital inputs are diluted by an autochthonous biogenic fraction, such an approach permits a high resolution reconstruction of flood history (Arnaud et al., 2005; Arnaud, 2005), taking account of both sediment source and river activity evolutions. Using an XRF core scanner, we established high resolution geochemical profiles on a short 14C-dated core, spanning the last 1200 years. We here interpret the Si/Rb ratio as an indicator of biogenic silica abundance, in opposition to Rubidium-bearing detrital inputs. We hence evidenced a series of high and low terrigenous inputs, corresponding to high and low flooding activity, respectively. Our results were compared with the only available climate-related information for Late Holocene on Kerguelen archipelago: a series of two 14C ages interpreted as evidences of glacier retreat (Frénot et al., 1997). Both records match together, as the 1100-1350 AD minima of flood activity corresponds to the younger age of glacier retreat. We hence evidence three periods of wetter conditions at ca. 800-1100, 1350-1750, 1880-1940 AD, which are interpreted as periods of enhanced cyclonic circulation, compared to the present-day situation. Those results show the potential of Lake Armor sediments to establish the first Holocene palaeohydrological record in southern Indian Ocean. References Arnaud et al., 2005, The Holocene 15, 420-428 Arnaud, 2005, Jour. Of Palaeolim. 34, 519-52 Arnaud et al., 2007, ILIC congress Frénot et al., 1997, CRAS 320, 567-573. Heirman et al., 2007, ILIC congress

International …, 2011

... Bruno Wilhelm 1 , Fabien Arnaud 1 , Pierre Sabatier 1 , Elodie Brisset 2 , Frédéric Guiter 2 ... more ... Bruno Wilhelm 1 , Fabien Arnaud 1 , Pierre Sabatier 1 , Elodie Brisset 2 , Frédéric Guiter 2 , Jean-Louis Reyss 3 , Eric Chaumillon 4 , Claire Delhon 5 , Emmanuel Malet 1 , Charline Giguet-Covex 1 , Jean-Jacques Delannoy 1. (2011). ...

Torrential flood hazard is expected to increase in the context of global warming. However, long t... more Torrential flood hazard is expected to increase in the context of global warming. However, long time-series of climate and gauge data at high-elevation sites are too sparse to assess reliably recurrence times of such events in high mountain areas. Historical documents are an alternative which provide valuable information. However, historic archives are by nature subjective and variable in quality owing to hazard perception and vulnerability according to the banks land-use throughout time. To overcome these limits, natural archives may be used as complementary records. Among the various natural archives lake sediments have the advantage to be continuous records in which particular events are preserved such as earthquakes and especially flood events. Furthermore an objective magnitude of these events can be assessed from the thickness of noteworthy event-triggered deposits. However if the recognition of major event-triggered deposits can be simple, a high-resolution dating of these events is more difficult over the historical period due to a lack of chronological markers. In this paper, we present a sediment record study of a French high alpine lake where an important effort was undertaken to date precisely 56 flood events over the last three centuries from the use of historical archives. The caesium and the lead were measured to detect the fallouts of the Chernobyl accident (1986), the atmospheric nuclear weapons tests (1955-1963) and the use of leaded gasoline which culminated in the 70's. In parallel local and regional historical archives were going through in order to correlate the thickest sediment deposits triggered by major floods and earthquakes with their potential triggering historic events. Thus we were able to associate 12 historic flood and 4 earthquake dates to particular sediment deposits. The resulting flood calendar is very well-constrained thanks to 19 chronological marks over the last 270 years, i.e. one mark by 14 years. This method permitted so to reconstruct a high-resolution flood calendar to assess a reliable frequency of extreme flood events which can be compared with precise climatic parameters as the instrumental and reconstructed temperature. Finally it was equally possible to compare the recorded intensity of flood events between the both archives and thus estimate the hazard perception and vulnerability of local people throughout the last three centuries.

EGU …, 2009

... Differentiating floods and floods : apparent paradox between flood intensity reconstructi... more ... Differentiating floods and floods : apparent paradox between flood intensity reconstructions at high and low elevation sites in NW Alps over the last 2 millennia. Fabien Arnaud 1 , Charline Giguet-Covex 1 , Dirk Enters 1 , Bruno Wilhelm 1. (2009). ...

European Meteorology …, 2010

... Occurrence of extreme flood events in high and low altitude mountain areas : A spatial and te... more ... Occurrence of extreme flood events in high and low altitude mountain areas : A spatial and temporal difference of processes throughout the last 2 Millennia in NW Alps. Charline Giguet-Covex 1 , Fabien Arnaud 1 , Dirk Enters 2 , Bruno Wilhelm 1. (2010). ...

... Fiche détaillée, Récupérer au format: BibTeX -. EndNote -. TEI -. RefWorks -. Le changement c... more ... Fiche détaillée, Récupérer au format: BibTeX -. EndNote -. TEI -. RefWorks -. Le changement climatique : une contrainte incontournable pour les sociétés alpines. Fabien Arnaud 1. (2008). 1 : Environnements, Dynamiques et Territoires de la Montagne (EDYTEM). ...

Du climat à l'homme. …, 2008

Université Pierre et Marie Curie.

Du climat à l' …, 2008

Sciences de l'Homme et de la Société.

Colloque'Autour du Lac du Bourget', 2006

... Colloque "Autour du Lac du Bourget", Le Bourget du Lac : France (2006). 10 000 ans ... more ... Colloque "Autour du Lac du Bourget", Le Bourget du Lac : France (2006). 10 000 ans de crues du Rhône dans le Lac du Bourget. Fabien Arnaud 1. (04/2006). 1 : Environnements, Dynamiques et Territoires de la Montagne (EDYTEM). CNRS : UMR5204 Université de Savoie. ...

Du climat à l' …, 2008

... Variations du climat au cours des deux derniers millénaires : deux cas d&amp;amp;amp;... more ... Variations du climat au cours des deux derniers millénaires : deux cas d&amp;amp;amp;amp;amp;amp;amp;#x27;étude dans le Jura et las Alpes du Nord. Michel Magny 1 , Laurent Millet 1 , Fabien Arnaud 2 , Marc Desmet 2 , Emilie Gauthier 1 , Oliver Heiri 3 , Boris Vannière 1 , Valérie Verneaux 1. (2008). ...

'Le peuplement de l' …, 2007

9500 years of Rhône floods recorded in Lake Bourget: a comparison in the alpine chrono-climatic c... more 9500 years of Rhône floods recorded in Lake Bourget: a comparison in the alpine chrono-climatic context Two sediment cores were taken from the deep northern basin of Lake Bourget in 2001 and 2004. The length of these cores was 9 and 13.5 m, whereas the ...

Le peuplement de l' …, 2008

L'étude de trois analyses polliniques effectuées sur les sites archéologiques de Chindrieux (... more L'étude de trois analyses polliniques effectuées sur les sites archéologiques de Chindrieux (Châtillon) et de Tresserve (Le Saut de la Pucelle), sur la rive est du lac du Bourget (Savoie, France) permet de reconstituer l'histoire de la végétation et des impacts anthropiques au ...

The Holocene, 2009

Pollen analyses were undertaken on three small peatbogs, located on the Anterne mountain (Upper-A... more Pollen analyses were undertaken on three small peatbogs, located on the Anterne mountain (Upper-Arve Valley, French north-western Alps) at different altitudes-1855, 2060 and 2235 m asl, respectively. Their comparative study allowed for the detremination of the role played ...

IGBP, 2003

... E. Chapron 1 , M. De Batist, N. Fagel, M. Pino, R. Urrutia, F. Charlet 1 , R. Brümmer, W. San... more ... E. Chapron 1 , M. De Batist, N. Fagel, M. Pino, R. Urrutia, F. Charlet 1 , R. Brümmer, W. San Martin, A. Mora, K. De Rycker, S. Bertrand 2 , X. Boës 2 , L. Vargas, C. Beck, Fabien Arnaud 3 , Vincent Lignier 3 , F. Devleeschouwer, O. Magand 4 , M.-L. Loutre, V. Renson, Marc Tardy ...

Assemblée des …, 2009

... Enregistrement sédimentaire du lac Blanc (Belledonne, Alpes). Bruno Wilhelm 1 ,Fabien Arnaud ... more ... Enregistrement sédimentaire du lac Blanc (Belledonne, Alpes). Bruno Wilhelm 1 ,Fabien Arnaud 1 , Dirk Enters 2 , Françoise Allignol 1 , Amaya Legaz 1 , Olivier Magand 3 , Sidonie Révillon 4 , Charline Giguet-Covex 1. (2009). ...

... Françoise Allignol 1 , Fabien Arnaud 1 , Jean-Daniel Champagnac 2 , Jean-Jacques Delannoy 1 ,... more ... Françoise Allignol 1 , Fabien Arnaud 1 , Jean-Daniel Champagnac 2 , Jean-Jacques Delannoy 1 , Philip Deline 1 , Serge Fudral 1 , Dominique Gasquet 1 , Amaya Legaz 1 , André Paillet 1 , Estelle Ployon 1 , Ludovic Ravanel 1 , Georges-Marie Saulnier 3. (12/2008). ...

Bon, ça fait un moment que Marc me poursuit avec ça, cette fois il faut y aller, je me jette dans... more Bon, ça fait un moment que Marc me poursuit avec ça, cette fois il faut y aller, je me jette dans les remerciements. Etape difficile, non qu'il me soit désagréable de remercier ceux qui m'ont permis de tant apprendre ces trois dernières années, bien au contraire, mais c'est le symbole ultime d'une page qui se tourne. Et aussi, et peut-être avant tout, l'occasion de regarder une dernière fois derrière soi avant le grand saut qu'est « l'accouchement » du manuscrit haïchéri de thèse.