Éditeur(s) : HAL CCSD
Résumé : Poster
The Lesser Caucasus in Armenia is an active volcanic and tectonic zone which resulted from the collision of the Arabian and the Eurasian plates since Neogene times. The During Quaternary, Lesser Caucasus was uplifted (0.3 mm/yr; Mitchell and Westaway, 1999) and experienced extensional tectonics times. Large lakes developed in graben structures. The diatomitic sequences of the Shamb paleo-lake (South Armenia) offer a rare opportunity to give new insights of Western Asia paleo-climate. Based on macroflora analysis, Bruch and Gabrielyan (2002) proposed a cooling and drying general climate trend through Pleistocene times in relation with a general uplift of the chain. Several questions have to be answer for this poorly investigated region. Did the climate record humid glacials and arid interglacials as suggested northward in Kazakhstan? What are the vegetation and climate responses to orbital parameters and to the monsoon? Moreover the lesser Caucasus is known as the entrance way used by the first hominids in Eurasia during Pleistocene time. How was the environment at this time? We present an integrated palynological, 40Ar/39Ar isotopic and magnetostratigraphic study for the most complete section (Joannin et al., in press). 40Ar/39Ar dating of two volcaniclastic layers provided ages of 1.24 ± 0.03 and 1.16 ± 0.02 Ma (2. Magnetostratigraphic data show that the entire Shamb section is of reversed polarity which correlates with part of the Matuyama period (1.785-1.070 Ma). Pollen assemblages and macroremains diversity revealed an alternation of glacial and interglacial phases that are compared with climate changes inferred from the global isotopic curve. The Shamb section ranges from approximately 1.300 to 1.080 Ma in age (marine isotopic stages 40 to 31). The vegetation of the Lesser Caucasus developed in a mosaic pattern in a Pleistocene continental, mostly arid climate, similar to the present-day climate. The vegetation changes record a dominant climate response to the obliquity orbital parameter. The influence of precession could not be established from the Shamb data. Pollen and macroflora both indicate that glacial periods were cold and dry and that interglacials were warm with local humidity. The early Pleistocene climatic model for Western Asia is thus similar to the climatic model for the Mediterranean area. Bruch, A., Gabrielyan, I.G., 2002. Quantitative data of the Neogene climatic development in Armenia and Nakhichevan. Acta Universitatis Carolinae – Geologica 46, 41–48. Joannin, S., Cornée, J.J., Münch, P., Fornari, M., Vasiliev, J., Krijgsman, W., Nahapetyan, S., Gabrielyan, Y., Ollivier, V., Roiron, P., Chataîgnier, C. In press. Early Pleistocene climatic cycles in continental deposits of the Lesser Caucasus of Armenia inferred from palynology, magnetostratigraphy, and 40Ar/39Ar dating. Earth and Planetary Science Letters. Mitchell, J., Westaway, R., 1999. Chronology of Neogene and Quaternary uplift and magmatism in the Caucasus: constraints from K-Ar dating of volcanism in Armenia. Tectonophysics 304, 157–186.
EGU Eurasian Climate and Tectonics
Vienne, Austria

hal-00481799
https://hal.archives-ouvertes.fr/hal-00481799

Éditeur(s) : HAL CCSD
Résumé : The effects of climate change on extreme events are difficult to assess because extremes present large variability and consequently, it is difficult to identify significant trends in relation to the lack of instrumental long time series. Here we present a record of these extreme storm events in the French Mediterrannean coast over the past 7000 years based on a long sediment core from lagoonal environment in Gulf of Lions. Using a high resolution multiproxies approach on core associating grain size, faunal to reconstruct Mid to Late Holocene history of backbarrier deposits in relation to landfalling activity. Even if change in lagoon geomorphological setting over the Holocene does not allow to compare storm events in terms of intensity trough time, we have recorded six periods of increase in storm activity at 6200, 5500, 4400, 3200, 1500 yr cal B.P. and over the LIA (450 and 100 yr cal B.P.). These evidences of changes in coastal hydrodynamic, inversely correlated to periods of aridification in Western Mediterranean region, are in phase with those observed over the North Atlantic and correspond to Holocene cooling events. This increase in storm activity during Holocene cold events over Mediterranean region was probably due to thermal gradient increase leading to enhanced lower tropospheric baroclinicity over a large Central Atlantic-European domain. This study demonstrates that temperatures in North Atlantic region influence the severe storm activity and therefore the Mediterranean climate at Holocene timescale.
Les effets du changement climatique sur les événements extrêmes sont difficiles à estimer car ces phénomènes présentent une large variabilité, et par conséquent il est délicat d'identifier des tendances significatives compte tenu de l'absence de longues séries de données instrumentales. Dans cette étude, nous présentons un enregistrement de ces tempêtes extrêmes sur la côte Méditerranéenne française au cours des 7000 dernières années à partir de carottes sédimentaires prélevées dans un système lagunaire du Golfe du Lion. L'utilisation d'une approche multi-traceur à haute résolution avec des analyses granulométriques, faunistiques, géochimiques (XRF), en minéraux argileux associées à des données chronologiques de radiocarbone et de 210Pb, 137Cs ; nous a permis de reconstruire l'histoire, au cours de l'Holocène, des dépôts lagunaires en relation avec l'activité des tempêtes. Bien que les paramètres morphologiques de cet environnement lagunaire aient changé durant l'Holocène, ne permettant pas de comparer ces événements au cours du temps en terme d'intensité, nous enregistrons six périodes d'augmentation de l'activité des tempêtes datées à 6200, 5500, 4400, 3200, 1500 an cal B.P. et durant le Petit Age Glaciaire (de 450 à 100 an cal B.P.). Ces changements de l'activité hydrodynamique côtière, en antiphase avec les périodes d'aridifications en Méditerranée de l'Ouest, sont corrélées avec celles observées dans le bassin Nord Atlantique et correspondent aux événements de refroidissement Holocène. L'augmentation de l'activité des tempêtes dans la cette région de la Méditerranée durant les périodes froides, associée à une diminution des températures au pôle Nord, est probablement liée à l'augmentation du gradient thermique qui, par interaction barocline, favorise les cycles d'évolution des tempêtes dans toute l'Europe et la Méditerranée de l'Ouest. Cette étude démontre ainsi que la température dans la région Nord Atlantique influence l'activité des tempêtes extrêmes et donc du climat Méditerranéen à l'échelle de l'Holocène.
https://tel.archives-ouvertes.fr/tel-00437757

tel-00437757
https://tel.archives-ouvertes.fr/tel-00437757
https://tel.archives-ouvertes.fr/tel-00437757/document
https://tel.archives-ouvertes.fr/tel-00437757/file/Sabatier_these.pdf

Éditeur(s) : Geological Society of America
Résumé : A seismic-refraction study of the sedimentary structure of the South West African continental shelf was carried out between lat 17°S and 24°S using expendable sonobuoys. Striking differences exist both in the topography and sedimentary structure between the shelf north and south of the Walvis Ridge. South of the ridge, as far as lat 23°S, the shelf consists of a prograded series, whereas north of the ridge, at least as far as lat 17°S, east-trending canyons cut the shelf sedimentary cover. The steep northem scarp of Walvis Ridge can be traced eastward under the sediment of the continental margin. The southern flank of the ridge is buried under a thicker sedimentary cover and could only be traced eastward to long. 10°E on seismic-reflection records. This flank probably parallels the northern scarp under the continental margin. Two-dimensional structural models, built with the help of seismic-retlection and seismic-refraction results and based on the hypothesis of local isostatic equilibrium, account for the obsewed gravity profiles. A compensating root consists of light material (density 2.95 g/cm3) and reaches a depth of about 25 km. Gravity results also suggest that the Walvis Ridge does not constitute a superimposed load on the lithosphere; rather, the ridge and its underlying compensating mass were created at approximately the same time as the adjacent ocean basins. The creation of the two aseismic ridges of the South Atlantic - the Rio Grande Rise and Walvis Ridge - by a mantle hot spot and plume is accepted; this theory seems to explain most of the peculiar features of the Walvis Ridge. However, it is probable that the surface expression of the mantle hot spot was controlled by the presence of weak zones in the lithosphere such as transform faults. [NOT CONTROLLED OCR]
Geological Society of America Bulletin (Geological Society of America), 1975 , Vol. 86 , P. 1713-1724

Droits : Geological Society of America
http://archimer.ifremer.fr/doc/1975/publication-4978.pdf
http://archimer.ifremer.fr/doc/00000/4978/

Éditeur(s) : American Geophysical Union
Résumé : We present new high-resolution bathymetry and backscatter data acquired in 2006 with the ROV Victor 6000 over the Lucky Strike hydrothermal field, Mid-Atlantic Ridge. As long-term monitoring of the Lucky Strike area (MoMAR project) is being implemented, these new high-resolution data offer an unprecedented view of the distribution of hydrothermal edifices, eruptive facies, and small-scale tectonic features in the Lucky Strike vent field. We show that vents located in the NW and NE correspond with wide expanses of lumpy seafloor which we interpret as primarily made of broken chimneys and sulfide edifices. They are found above scarps with relief > 50 m or on associated mass wasting deposits. By contrast, the SE and SW vents correspond with small expanses of lumpy seafloor and are located near smaller scarps which we interpret as more recent faults. Hydrothermal edifices in the SW venting area appear very recent, postdating the emplacement and faulting of the most recent lava. We propose that this difference in the age of hydrothermal edifices does not mean that hydrothermal venting itself is more recent in the southern part of the Lucky Strike field because preexisting sulfide deposits there may have been buried by recent volcanic deposits. Instead, the older edifices in the northern part of the hydrothermal field may have been allowed more time to grow because they are set above the level of recent lava flows. The formation of a lava lake is the most recent eruptive event detected at Lucky Strike. Lava drainback is evidenced by benches and lava pillars, suggesting a close connection with an underlying magma reservoir, which probably corresponds to the melt body imaged by Singh et al. (2006). We have found no evidence that this lake was active for months to decades, as lava lakes at terrestrial volcanoes. It may instead have formed as a lava pond, with successive lava flows covering the eruptive vents, as proposed for similar features at the EPR. The horizontal surface of the lake is deformed only near its southwestern shore, along a NNE-trending set of faults and fissures, which appear to control the distribution of hydrothermal chimneys.
Geochemistry Geophysics Geosystems (1525-2027) (American Geophysical Union), 2009-02 , Vol. 10 , N. 2 , P. 1-18

Droits : 2009 American Geophysical Union
http://archimer.ifremer.fr/doc/2009/publication-6161.pdf
DOI:10.1029/2008GC002171
http://archimer.ifremer.fr/doc/00000/6161/

Éditeur(s) : HAL CCSD IWA Publishing
Résumé : International audience
This study proposes a new approach for improving resource quality management, monitoring and treatment plant management, whatever the environmental and climatic stressors. First trend analysis of water quality at a river basin scale, based on historical water quality data and multivariate exploitation (principal component analysis, PCA), led to a classification of the monitoring stations with regard to the main pressures (land use, urbanization and hydroclimatic impacts). This method was applied to the Vilaine's watershed, the largest river basin in Brittany, western France, and one which is under agricultural and urban pressure. A complementary research using a UV index was proposed for the evaluation of spatial and temporal variations of water quality. This approach may be considered as a useful and relevant tool to quickly assess the variation of water quality and the main explanatory factors. It also points out monitoring stations under specific stressors considered as outliers regarding UV parameters. Finally, PCA and UV index give complementary results. PCA allows factors influencing drinking water resource to be highlighted and the UV index allows global water quality under specific times and impacts to be reflected.
Water Science and Technology: Water Supply

hal-00878159
https://hal.archives-ouvertes.fr/hal-00878159
DOI : 10.2166/ws.2012.047

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The presence of two regional seismic networks in southeastern France provides us high-quality data to investigate upper mantle flow by measuring the splitting of teleseismic shear waves induced by seismic anisotropy. The 10 three-component and broadband stations installed in Corsica, Provence, and western Alps efficiently complete the geographic coverage of anisotropy measurements performed in southern France using temporary experiments deployed on geodynamic targets such as the Pyrenees and the Massif Central. Teleseismic shear waves (mainly SKS and SKKS) are used to determine the splitting parameters: the fast polarization direction and the delay time. Delay times ranging between 1.0 and 1.5 s have been observed at most sites, but some larger delay times, above 2.0 s, have been observed at some stations, such as in northern Alps or Corsica, suggesting the presence of high strain zones in the upper mantle. The azimuths of the fast split shear waves define a simple and smooth pattern, trending homogeneously WNW–ESE in the Nice area and progressively rotating to NW–SE and to NS for stations located further North in the Alps. This pattern is in continuity with the measurements performed in the southern Massif Central and could be related to a large asthenospheric flow induced by the rotation of the Corsica–Sardinia lithospheric block and the retreat of the Apenninic slab. We show that seismic anisotropy nicely maps the route of the slab from the initial rifting phase along the Gulf of Lion (30–22 Ma) to the drifting of the Corsica–Sardinia lithospheric block accompanied by the creation of new oceanic lithosphere in the Liguro–Provençal basin (22–17 Ma). In the external and internal Alps, the pattern of the azimuth of the fast split waves follows the bend of the alpine arc. We propose that the mantle flow beneath this area could be influenced or perhaps controlled by the Alpine deep penetrative structures and that the Alpine lithospheric roots may have deflected part of the horizontal asthenospheric flow around its southernmost tip.
ISSN: 0040-1951

hal-00109313
https://hal.archives-ouvertes.fr/hal-00109313
https://hal.archives-ouvertes.fr/hal-00109313/document
https://hal.archives-ouvertes.fr/hal-00109313/file/barruol_TGRS_Tphy2004_hal.pdf
DOI : 10.1016/j.tecto.2004.08.002

Éditeur(s) : Wiley / Blackwell
Résumé : For the first time, a deep seismic data set acquired in the frame of the Algerian-French SPIRAL program provides new insights regarding the origin of the westernmost Algerian margin and basin. We performed a tomographic inversion of traveltimes along a 100-km-long wide-angle seismic profile shot over 40 ocean bottom seismometers offshore Mostaganem (Northwestern Algeria). The resulting velocity model and multichannel seismic reflection profiles show a thin (3-4 km thick) oceanic crust. The narrow ocean-continent transition (less than 10 km wide) is bounded by vertical faults and surmounted by a narrow almost continuous basin filled with Miocene to Quaternary sediments. This fault system, as well as the faults organized in a negative-flower structure on the continent side, marks a major strike-slip fault system. The extremely sharp variation of the Moho depth (up to 45 +/- 3 degrees) beneath the continental border underscores the absence of continental extension in this area. All these features support the hypothesis that this part of the margin from Oran to Tenes, trending N65-N70 degrees E, is a fossil subduction-transform edge propagator fault, vestige of the propagation of the edge of the Gibraltar subduction zone during the westward migration of the Alboran domain.
Geophysical Journal International (0956-540X) (Wiley / Blackwell), 2015-02 , Vol. 200 , N. 2 , P. 1027-1043

Droits : The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society
http://archimer.ifremer.fr/doc/00255/36670/35278.pdf
http://archimer.ifremer.fr/doc/00255/36670/35279.pdf
DOI:10.1093/gji/ggu454
http://archimer.ifremer.fr/doc/00255/36670/

Éditeur(s) : Pêche thonière et dispositifs de concentration de poissons, Caribbean-Martinique, 15-19 Oct 1999
Résumé : This paper develops a comparative overview of the development of Fish Aggregating Devices (or fads) by the tropical purse seine fisheries in various ocean areas (Atlantic, Indian, Western and Eastern Pacific Oceans). First, a comparative review of fishery statistics is developed. Recent catches on fads by purse seiners can be estimated at a level of one million tons yearly. This comparison allows to describe the fishing zones and catch trends over time, the species composition and size taken in the various fad fisheries. Skipjack tuna is the dominant species in most fad fisheries, but significant amounts of yellowfin and bigeye are also frequently taken under fads. The paper also presents an overview of various observer data concerning the by-catches of the various fisheries using fads. This comparison allows to estimate the total worldwide yearly by-catches at about 100,000 t, and their species composition in each ocean. The fad technology used in the various oceans by purse seiners is described. The recent use of fads by purse seiners has introduced major uncertainties in most stock assessments, because analyses are hampered by changes in the fishing effort in a fad fishery, by changes in fishing zones and in sizes caught. As a last point, the management of fads presently done or in view by the various tuna bodies are introduced. It appears that the present massive use of fads worldwide is perhaps an unsafe fishing mode, which could produce serious overfishing of many stocks. There is then a consensus that the use of fads needs to be controlled and limited to sustainable biological levels.

Droits : Ifremer
http://archimer.ifremer.fr/doc/00042/15278/12664.pdf
http://archimer.ifremer.fr/doc/00042/15278/

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
We use digital elevation models and satellite imagery data completed with field observations to develop an integrated morphotectonic analysis of the anomalous topography of the Central Cordillera of Patagonia between 46 degrees S and 48 degrees S, in a region overlying subducted segments of the Chile Spreading Ridge. This region shows a number of peculiar features, not expected in a normal subduction-related belt located away from a buried spreading center. First, it is characterized by overall short-wavelength topography and highly contrasted reliefs, typical of deeply incised young mountain belts, but surprisingly, also by an average very low elevation of similar to 900 m. Second, the Cordillera lacks central high reliefs; instead, there is a central, depressed domain with average low slope gradients including the deepest point of the study area (300 m below sea level in the bottom of Lake General Carrera/Buenos Aires). This depressed area is flanked by western and eastern regions of higher elevation having opposite general slope dips. To the east, the central Patagonian Cordillera is now separated from the flat plains of the Pampean domain (representing its former piedmont) and several elevated basaltic plateaus (mesetas) by 160 degrees N-180 degrees N trending morphotectonic corridors and the western border scarps of the mesetas. These scarps correspond to neotectonic features controlled by recent vertical faults, mostly active after 3 Ma. Remnants of a former peneplain, the Avellanos surface, are widespread within the entire Cordilleran region. From geological evidence, this peneplain formed between 15 and 4 Ma and was connected originally with the mesetas domain and now is dissected by these corridors. It is shown that a negative inversion related to extensional and strike-slip faulting occurred in the frontal region of the Cordillera at 3 Ma synchronously with the emplacement of magmatic products. Timing of the extensional deformation in central Patagonia is concomitant with the migration at depth of different segments of the South Chile Ridge, which entered the trench at 6 and 3 Ma, respectively, and the consequent opening of a slab window allows asthenospheric hot mantle to reach lithospheric regions. Finally, migration of segments of the Chile Spreading Ridge since 6 Ma triggered regional uplift of the Cordillera followed by limited extension in relation with increased thermal weakening of the crust.
ISSN: 0278-7407

hal-00486334
https://hal.archives-ouvertes.fr/hal-00486334
DOI : 10.1029/2009TC002453

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
We assessed the extent of recent environmental changes on leaf morphological (stomatal density, stomatal surface, leaf mass per unit area) and physiological traits (carbon isotope composition, δ(13)C(leaf) , and discrimination, Δ(13)C(leaf) , oxygen isotope composition, δ(18)O(leaf) ) of two tropical rainforest species (Dicorynia guianensis; Humiria balsamifera) that are abundant in the Guiana shield (Northern Amazonia). Leaf samples were collected in different international herbariums to cover a 200 year time-period (1790-2004) and the whole Guiana shield. Using models describing carbon and oxygen isotope fractionations during photosynthesis, different scenarios of change in intercellular CO(2) concentrations inside the leaf (C(i)), stomatal conductance (g), and photosynthesis (A) were tested in order to understand leaf physiological response to increasing air CO(2) concentrations (C(a)). Our results confirmed that both species displayed physiological response to changing C(a) . For both species, we observed a decrease of about 1.7‰ in δ(13)C(leaf) since 1950, without significant change in Δ(13)C(leaf) and leaf morphological traits. Furthermore, there was no clear change in δ(18)O(leaf) for Humiria over this period. Our simulation approach revealed that an increase in A, rather than a decrease in g, explained the observed trends for these tropical rainforest species, allowing them to maintain a constant ratio of C(i)/C(a) .
ISSN: 0140-7791

halsde-00675165
https://hal.archives-ouvertes.fr/halsde-00675165
DOI : 10.1111/j.1365-3040.2011.02333.x
PUBMED : 21486302

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
This study examines the response of the Central Patagonian Cordillera to the subduction of the active South Chile Ridge and the development of the asthenospheric slab window beneath Patagonia since the Pliocene. We investigated the eastern part of the Cordillera where the glacio-volcanic piedmont is topographically inverted. Glacial morphology and associated deposits capping the top of these piedmonts reveal that during the Pliocene (after 3 Ma), glaciers were flowing to the east over a regional surface connecting the western Cordillera and the palaeo-piedmont. N160-trending normal faulting along the western edge of the inverted plateau disrupted the geomorphic surface after 3 Ma. At a regional scale, extensional tectonics is responsible for a relief inversion with a minimum value of 800 m. The timing of extensional tectonics is contemporaneous with the subduction of the spreading axis and the development of the slab window beneath Central Patagonia.
ISSN: 0954-4879

hal-00595547
https://hal.archives-ouvertes.fr/hal-00595547
DOI : 10.1111/j.1365-3121.2010.00981.x

Éditeur(s) : HAL CCSD Wiley
Résumé :  
Positive aboveground biomass trends have been reported from old-growth forests across the Amazon basin and hypothesized to reflect a large-scale response to exterior forcing. The result could, however, be an artefact due to a sampling bias induced by the nature of forest growth dynamics. Here, we characterize statistically the disturbance process in Amazon old-growth forests as recorded in 135 forest plots of the RAINFOR network up to 2006, and other independent research programmes, and explore the consequences of sampling artefacts using a data-based stochastic simulator. Over the observed range of annual aboveground biomass losses, standard statistical tests show that the distribution of biomass losses through mortality follow an exponential or near-identical Weibull probability distribution and not a power law as assumed by others. The simulator was parameterized using both an exponential disturbance probability distribution as well as a mixed exponential-power law distribution to account for potential large-scale blowdown events. In both cases, sampling biases turn out to be too small to explain the gains detected by the extended RAINFOR plot network. This result lends further support to the notion that currently observed biomass gains for intact forests across the Amazon are actually occurring over large scales at the current time, presumably as a response to climate change.
ISSN: 1354-1013

hal-01032162
https://hal.archives-ouvertes.fr/hal-01032162
DOI : 10.1111/j.1365-2486.2009.01891.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : Pb, Hf, Nd and Sr isotopes of basaltic lavas from the two Reunion Island volcanoes are reported in order to examine the origin of the sources feeding these volcanoes and to detect possible changes through time. Samples, chosen to cover the whole lifetime of the two volcanoes (from 2 Ma to present), yield a chemically restricted (compared to 0113 lavas) but complex distribution. Reunion plume isotopic characteristics have been defined on the basis of the composition of uncontaminated shield-building lavas from the Piton de la Fournaise volcano. The average epsilon(Nd), epsilon(Hf), Sr-87/Sr-86 and Pb-206/Pb-204, Pb-207/Pb-204, and Pb-208/Pb-204 isotope ratios calculated for this component are +4.4, +9.1, 0.70411, 18.97, 15.59 and 39.03, respectively. In Pb-Pb isotope space, each volcano defines a distinct linear trend but slight variation are also detected within the various volcanic sequences. The Piton des Neiges volcano yields a distinct and significantly more scattered isotopic distribution than Piton de la Fournaise for both Pb, Hf and Nd isotope tracers. A principal component analysis of the Pb isotope data from Piton de la Fournaise reveals a major contribution of the C and EM-1 components (with a clear Dupal flavor) as main components for the modem Reunion plume. The same components have been identified for Piton des Neiges but with a stronger participation of a depleted mantle component and a weaker EM-1 contribution. The compositional change of the lavas erupted by the Piton des Neiges and Piton de la Fournaise volcanoes is attributed to the impingement of two small-scale blobs of plume material at the base of the Reunion lithosphere. Compared to other hot-spots worldwide, in particular Hawaii and Kerguelen, magmas beneath Reunion are generated from a considerably more homogeneous, compositionally more primitive plume higher in Pb-206. Although shallow-level contamination processes have been locally detected they did not alter significantly the composition of the plume magmas. This is tentatively attributed to mantle dynamics producing small, high-velocity blobs that ascend rapidly through the lithosphere, and to the lack of a well-developed magma chamber at depth in the lithosphere.
ISSN: 0012-821X

hal-00412196
https://hal.archives-ouvertes.fr/hal-00412196
DOI : 10.1016/j.epsl.2007.11.018

Éditeur(s) : HAL CCSD
Résumé : International audience
While the impact of network properties on information spread- ing is now widely studied, in uence of network dynamics is very little known. In this paper, we study how evolution mechanisms tradition- ally observed within social networks can a ect information di usion. We present an approach that merges two models: model of informa- tion di usion through social networks and model of network evolution. Since epidemics provide a reference in application domains of information spreading, we measure the impact of basic network structure changes on epidemic peak value and timing. Then we investigate observed trends in terms of changes appearing in the network structure. Our results provide promising results on how and why network dynamics is a strong param- eter to integrate in requirements for information spreading modelling.
World Summit on the Knowledge Society
Mykonos, Greece

hal-00768405
https://hal.archives-ouvertes.fr/hal-00768405

Éditeur(s) : HAL CCSD Geological Society
Résumé : International audience
An integrated stratigraphic study was conducted on the shallow water carbonate platforms of the Guadeloupe archipelago to refine the tectonic evolution of the Lesser Antilles forearc. The carbonate platforms are now dated to the Zanclean-Calabrian interval, and their demise occurred between 1.5 and 1.07 Ma. The precise chronostratigraphy allows dating of the main extensional tectonic events since the late Miocene. An initial episode occurred during the late Miocene, related to the reactivation of inherited N130°E-trending shear zones, and led to the emergence of most parts of the forearc. Subsequently, Zanclean to early Piacenzian carbonate platforms developed in association with a general subsidence of the forearc. During the late Piacenzan, a second extensional episode occurred. At this time La Désirade underwent major uplift and emergence whereas most of the forearc remained submerged. Prior to 1.07 Ma, a third north-south extensional episode occurred and led to the final demise of the carbonate platforms. Thus the forearc was characterized by general subsidence since the early Pliocene interrupted by three main extensional episodes and related differential uplifts. This suggests that the Lesser Antilles subduction is probably erosive north of latitude 15°N since c. 5 Ma, related to aseismic ridge subduction.
ISSN: 0016-7649

hal-01053696
https://hal.archives-ouvertes.fr/hal-01053696
DOI : 10.1144/jgs2013-005

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The interpretation of high-resolution 2D marine seismic profiles together with the analysis of sea-bottom cores allowed a stratigraphic and structural framework of the Provence continental shelf to be proposed. The integration of onshore and offshore stratigraphy, structure and geomorphology provided new insights into Messinian paleotopography and paleohydrography. A geological map of the offshore Provence continental shelf, isobath map of the base Plio-Quaternary surface are presented for the first time in this area. The base Plio-Quaternary surface is a polyphased unconformity that is composed of deep canyons developed by fluvial erosion during the Messinian event, and wave-cut surfaces formed during post-Messinian transgressions. The study evidenced a deep, E-W-trending canyon (Bandol canyon) connected to the head of the Cassidaigne canyon, and filled with up to 600 m-thick Plio-Quaternary deposits. The development of canyons on the Provence margin during the Messinian event was dominantly controlled by the lithology and structure of pre-Messinian formations. A map of the Messinian paleo-drainage network is proposed to explain the presence of deep canyons in the Eastern area and the lack of incision in the Western area. An underground karst drainage scheme is proposed, linked with the current submarine Port-Miou spring.
ISSN: 0264-8172

insu-01009592
https://hal-insu.archives-ouvertes.fr/insu-01009592
https://hal-insu.archives-ouvertes.fr/insu-01009592/document
https://hal-insu.archives-ouvertes.fr/insu-01009592/file/Mar-Pet-Tassy.pdf
DOI : 10.1016/j.marpetgeo.2014.05.001

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Ecological signs of Earth's biosphere forewarn an alarming trajectory towards a global mass-extinction. Assessing species performance and susceptibilities to decline is essential to comprehend and reverse this trend. Yet it is challenging, given difficulties associated with quantifying individual and population processes that are variable across time, space, and life-stages. We describe a new approach to estimating and comparing species performances that combines empirical data, a novel theoretical consideration of population dynamics, and modern statistics. Our approach allows for a more realistic continuous representation of individual performances along development stages while taking into account non-linearity, and natural variability as captured by spatio-temporally replicated observations. We illustrate its application in a coral meta-assemblage composed of populations of the three major reef-building taxa Acropora, Pocillopora, Porites. Using a unique set of highly replicated observations of individual coral dynamics under various environmental conditions, we show how taxa differ in their investment in recruitment and size-specific aptitude for growth and survival, notably through different use of clonal shrinkage, fragmentation, fission, and fusion processes. Our results reveal contrasting life-history trade-offs among taxa which, along with differing patterns of density-dependent recruitment, modulate species responses to decline. These differences in coral life history traits reflect opposing life-strategies, imply regulation at differing life-stages, and explain divergence in species trajectories. Our findings indicate a high potential for resilience in Pocillopora and Porites populations, thanks respectively to a sustained recruitment that promotes demographic elasticity through replacement of individuals, and a steady resistance to mortality which confers persistence through lingering of individuals. Resilience in Acropora appears more arbitrary, given high susceptibility to perturbations and dependency of recruitment on presence of established local populations. We identify management actions that can complement Acropora's life history and benefit recovery of its populations following mortality events. Our regression-modelling approach to quantifying and comparing species performances in different population processes is applicable to all taxa, as illustrated even those with complex clonal life histories, and can be implemented at wide spatio-temporal and taxonomic coverage. It can promote more accurate representation of species dynamics in both descriptive and predictive modelling approaches. The semi-parametric contrast curve method we develop facilitates comparing response variables along continuous explicative metrics while accounting for multiple sources of complexity in empirical data. It should widely benefit investigations in ecology and quantitative science.
ISSN: 1476-945X

hal-01212337
https://hal-univ-perp.archives-ouvertes.fr/hal-01212337
DOI : 10.1016/j.ecocom.2015.07.003

Éditeur(s) : HAL CCSD
Résumé : Atmospheric carbon dioxide records indicate that the land surface has acted as a strong global carbon sink over recent decades, with a substantial fraction of this sink probably located in the tropics, particularly in the Amazon. Nevertheless, it is unclear how the terrestrial carbon sink will evolve as climate and atmospheric composition continue to change. Here we analyse the historical evolution of the biomass dynamics of the Amazon rainforest over three decades using a distributed network of 321 plots. While this analysis confirms that Amazon forests have acted as a long-term net biomass sink, we find a long-term decreasing trend of carbon accumulation. Rates of net increase in above-ground biomass declined by one-third during the past decade compared to the 1990s. This is a consequence of growth rate increases levelling off recently, while biomass mortality persistently increased throughout, leading to a shortening of carbon residence times. Potential drivers for the mortality increase include greater climate variability, and feedbacks of faster growth on mortality, resulting in shortened tree longevity. The observed decline of the Amazon sink diverges markedly from the recent increase in terrestrial carbon uptake at the global scale, and is contrary to expectations based on models.
ISSN: 1476-4687

hal-01204223
https://hal.archives-ouvertes.fr/hal-01204223
DOI : 10.1038/nature14283
PRODINRA : 294797
PUBMED : 25788097