Éditeur(s) : Université de Brest
Résumé : The channel-lobe transition zone has been studied in two turbiditic systems: the Amazon channel-mouth lobe complex at the termination of the last eight channel-levee systems and the Neochannel termination, the last active channel of the Petit-Rhone turbidite system. - In the two cases, the internal geometry and stacking pattern of the deposits show a significant control of the configuration (size and shape) of the receiving basins, their morphology (gradients and subtle gradient changes), and their degree of confinement. - The Amazon and Petit-Rhone systems, with lobes built after the Last Glacial Maximum and the ensuing sea-level rise, evidence the major impact of external forcings (climatic events and eustatic variations) that induce variations in sediment fluxes delivered to the deep basin and therefore exert a control on channel-mouth lobes construction. The channel-mouth lobes of the Amazon and Petit-Rhone systems, even if they are located at great distances from the river mouths, at the termination of the turbidite systems and in areas characterised by subtle morphological variations, are both constrained by combined internal (accommodation and compensation) and external factors (post-glacial deconnection between the fluvial system and the deep basin).
La zone de transition chenal-levées/lobes a été étudiée dans 2 systèmes turbiditiques : le complexe de lobes à la terminaison des 8 derniers chenaux de l'éventail de l'Amazone et la terminaison du Néochenal, dernier chenal de l'éventail du Petit-Rhône. - Dans les deux cas, l'agencement des dépôts et leur évolution dans l'espace et le temps révèlent un fort contrôle de la configuration des réceptacles (taille et forme), de la morphologie des fonds (pentes et taux de changement des pentes) et du degré de confinement. - Les systèmes de l'Amazone et du Petit-Rhône, dont les lobes se sont construits à partir du Dernier Maximum Glaciaire et lors de la remontée du niveau marin qui a suivi, ont en outre permis de souligner l'impact majeur, sur la mise en place des lobes terminaux, de certains forçages externes (événements climatiques et variations eustatiques), qui déterminent les variations des flux sédimentaires arrivant au bassin. Ainsi, bien que situés à des distances considérables des sources fluviatiles et dans des zones distales où les variations de relief sont très ténues, les lobes terminaux de ces deux grands systèmes turbiditiques se sont révélés contraints à la fois par des processus internes (processus de compensation) et par des processus externes (déconnexion post-glaciaire du fleuve et du bassin).

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2008/these-6796.pdf
http://archimer.ifremer.fr/doc/00000/6796/

Éditeur(s) : Elsevier Sci Ltd
Résumé : This study analyses the impact on the oceanic mean state of the evolution of the oceanic component (NEMO) of the climate model developed at Institut Pierre Simon Laplace (IPSL-CM), from the version IPSL-CM4, used for third phase of the Coupled Model Intercomparison Project (CMIP3), to IPSL-CM5A, used for CMIP5. Several modifications have been implemented between these two versions, in particular an interactive coupling with a biogeochemical module, a 3-band model for the penetration of the solar radiation, partial steps at the bottom of the ocean and a set of physical parameterisations to improve the representation of the impact of turbulent and tidal mixing. A set of forced and coupled experiments is used to single out the effect of each of these modifications and more generally the evolution of the oceanic component on the IPSL coupled models family. Major improvements are located in the Southern Ocean, where physical parameterisations such as partial steps and tidal mixing reinforce the barotropic transport of water mass, in particular in the Antarctic Circumpolar Current) and ensure a better representation of Antarctic bottom water masses. However, our analysis highlights that modifications, which substantially improve ocean dynamics in forced configuration, can yield or amplify biases in coupled configuration. In particular, the activation of radiative biophysical coupling between biogeochemical cycle and ocean dynamics results in a cooling of the ocean mean state. This illustrates the difficulty to improve and tune coupled climate models, given the large number of degrees of freedom and the potential compensating effects masking some biases.
Ocean Modelling (1463-5003) (Elsevier Sci Ltd), 2013-12 , Vol. 72 , P. 167-184

Droits : 2013 The Authors. Published by Elsevier Ltd. All rights reserved.
http://archimer.ifremer.fr/doc/00170/28102/26612.pdf
DOI:10.1016/j.ocemod.2013.09.001
http://archimer.ifremer.fr/doc/00170/28102/

Éditeur(s) : Springer
Résumé : We present the global general circulation model IPSL-CM5 developed to study the long-term response of the climate system to natural and anthropogenic forcings as part of the 5th Phase of the Coupled Model Intercomparison Project (CMIP5). This model includes an interactive carbon cycle, a representation of tropospheric and stratospheric chemistry, and a comprehensive representation of aerosols. As it represents the principal dynamical, physical, and bio-geochemical processes relevant to the climate system, it may be referred to as an Earth System Model. However, the IPSL-CM5 model may be used in a multitude of configurations associated with different boundary conditions and with a range of complexities in terms of processes and interactions. This paper presents an overview of the different model components and explains how they were coupled and used to simulate historical climate changes over the past 150 years and different scenarios of future climate change. A single version of the IPSL-CM5 model (IPSL-CM5A-LR) was used to provide climate projections associated with different socio-economic scenarios, including the different Representative Concentration Pathways considered by CMIP5 and several scenarios from the Special Report on Emission Scenarios considered by CMIP3. Results suggest that the magnitude of global warming projections primarily depends on the socio-economic scenario considered, that there is potential for an aggressive mitigation policy to limit global warming to about two degrees, and that the behavior of some components of the climate system such as the Arctic sea ice and the Atlantic Meridional Overturning Circulation may change drastically by the end of the twenty-first century in the case of a no climate policy scenario. Although the magnitude of regional temperature and precipitation changes depends fairly linearly on the magnitude of the projected global warming (and thus on the scenario considered), the geographical pattern of these changes is strikingly similar for the different scenarios. The representation of atmospheric physical processes in the model is shown to strongly influence the simulated climate variability and both the magnitude and pattern of the projected climate changes.
Climate Dynamics (0930-7575) (Springer), 2013-05 , Vol. 40 , N. 9-10 , P. 2123-2165

Droits : The Author(s) 2013. This article is published with open access at Springerlink.com
http://archimer.ifremer.fr/doc/00138/24966/23079.pdf
DOI:10.1007/s00382-012-1636-1
http://archimer.ifremer.fr/doc/00138/24966/

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : Quantitative analyses on calcareous nannofossil assemblages on high temporal resolution (600-800 years) have been carried out from Core KC01B in the Ionian Sea (Eastern Mediterranean) throughout Marine Isotope Stage (MIS) 13-9, between 500 and 300 ka. This is an interval of considerable climate changes, known as the Mid-Brunhes event, which includes MIS 11, considered as a possible analogue for future interglacial conditions. In the Mediterranean core, the interval is characterized by the dominance of Gephyrocapsa spp., as also known from ocean records. Calcareous nannofossil abundance fluctuations have been interpreted in terms of modification of sea surface primary productivity/water stratification and temperature. Specifically, the increase in abundance of Gephyrocapsa caribbeanica and small Gephyrocapsa coupled with decreases of Florisphaera profunda, Syracosphaera spp. and Rhabdosphaera spp. suggests enhanced primary productivity/mixed surface waters during interglacial stages and at the Terminations, which can be interpreted in terms of interaction between climate changes and mesoscale oceanographic circulation. On the other hand, distributions of Calciosolenia spp., Oolithotus spp. and Umbilicosphaera sibogae, which are in phase with delta O-18 curve showing higher abundances at the lighter values of the marine isotope record, are considered as warm-water indicators. Biotic proxies point to peculiar climate dynamics through the MIS 12-11 transition (i.e. Termination V). High productive, cool, low salinity and turbid surface waters characterize the early MIS 11(421-408 ka) and likely reflect enhanced continental humidity/monsoon activity over North Africa and increased runoff into the basin. A late surface water warming with respect to Termination V is established at about 403 ka, during a period of low insolation forcing, almost coeval with the deposition of sapropel S11. A climate optimum, lasting about 15 ky (403-389 ka), is then recorded during a period of low insolation forcing centred at 398 ka. The later part of MIS 11 is characterized by climate deterioration at about 389 ka. Comparison with results from subtropical to polar Atlantic records suggests a remarkable relation between Mediterranean and Atlantic climate regimes.
Quaternary International (1040-6182) (Pergamon-elsevier Science Ltd), 2013-03 , Vol. 288 , P. 97-111

Droits : 2011 Elsevier Ltd and INQUA. All rights reserved.
http://archimer.ifremer.fr/doc/00181/29194/27593.pdf
DOI:10.1016/j.quaint.2011.12.007
http://archimer.ifremer.fr/doc/00181/29194/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Experimental modelling applied to the study of orogenic wedge dynamics has been a subject of fruitful research for more than 30 years, although the technique dates back as far as the early XIXth century. On one hand, several first order parameters controlling the structural evolution of mountain belts have been intensively investigated using the classic tectonic "sandbox" models. The main parameters are the properties of the basal décollement, the deforming material, the backstop, and fluxes, kinematics and surface processes. On the other hand, the morphological evolution of a mountain relief subjected to changing tectonic or climatic forcing has been addressed using another kind of approach called "geomorphic" models. Nowadays, the literature is extremely rich, particularly for the sandbox technique, so that it becomes difficult to have an exhaustive view of the effects of the above parameters on mountain evolution. In this article, we propose a detailed review of the main results obtained using both "tectonic" and "geomorphic" approaches. Our goal is to provide an almost complete state-of-the-art in the experimental study of relief dynamics to guide present and future researchers in their understanding of mountain belt evolution.
ISSN: 0040-1951

hal-00757713
https://hal.archives-ouvertes.fr/hal-00757713
DOI : 10.1016/j.tecto.2012.01.027

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : Climate may act on the dispersal and connectivity of marine populations through changes in the oceanic circulation and temperature, and by modifying species' prey and predator distributions. As dispersal and connectivity remain difficult to assess in situ, a first step in studying the effects of climate change can be achieved using biophysical models. To date, only a few biophysical models have been used for this purpose. Here we review these studies and also include results from other recent modelling efforts. We show that increased sea temperature, a major change expected under climate warming, may impact dispersal and connectivity patterns via changes in reproductive phenology (e.g., shift in the spawning season), transport (e.g., reduced pelagic larval duration under faster development rates), mortality (e.g., changes in the exposure to lethal temperatures), and behaviour (e.g.. increased larval swimming speed). Projected changes in circulation are also shown to have large effects on the simulated dispersal and connectivity patterns. Although these biophysical modelling studies are useful preliminary approaches to project the potential effects of climate change, we highlight their current limitations and discuss the way forward, in particular the need for adequate coupled hydrodynamic-biogeochemical simulations using atmospheric forcing from realistic climate change scenarios. (C) 2010 Elsevier Ltd. All rights reserved.
Progress In Oceanography (0079-6611) (Pergamon-elsevier Science Ltd), 2010-10 , Vol. 87 , N. 1-4 , P. 106-113

Droits : 2010 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/00031/14176/11522.pdf
DOI:10.1016/j.pocean.2010.09.005
http://archimer.ifremer.fr/doc/00031/14176/

Éditeur(s) : HAL CCSD Blackwell Publishing
Résumé : International audience
Differentiating between forced regressive deposits from deglacial periods inhigh latitude domains and forced regressive deposits from the onset of glacialperiods in low latitude domains is fundamental for the accurate interpretationof glacial cycles within the geological record and then for thereconstruction of palaeogeography and palaeo-climate. A forced regressivedeglacial sequence is documented from the Lake Saint-Jean basin (Quebec,Canada). In this area, the Late Pleistocene to Holocene sediments haverecorded the Laurentide ice sheet retreat accompanied by the invasion ofmarine waters (Laflamme Gulf) from ca 129 cal kyr BP. Subsequently, fluviodeltaicand coastal prograding wedges were deposited; they followed thebase-level fall due to glacio-isostatic rebound. This succession, representinga transition from glacial to post-glacial periods within a previously glaciatedarea, was investigated through recent mapping, preserved landforms, faciesanalysis, and new optical stimulated luminescence and radiocarbon dates.Three basin-scale geological sections share a common lower part made ofisolated ice-contact fan deposits overlying bedrock. Throughout the entirebasin, ice-contact fans are capped by glacimarine muds. Above, fluvial andcoastal prograding systems were deposited and evolved through four steps:(i) deltaic systems progressively increased in width; (ii) coastal influence onsedimentation increased; (iii) hydrographic drainage systems became moreorganised; and (iv) deltas graded from steep (Gilbert delta) to low-angle foresets(mouth-bar delta). Deposited during the base-level fall from glacioisostaticrebound, the complete succession has been designated as a singlefalling stage system tract referred to as a deglacial falling stage system tract.It is representative of a deglaciation sequence in areas previously covered byice during glacial periods (i.e. medium to high latitude domains). Diagnosticcriteria are provided to identify such a deglacial falling stage system tract inthe geological record, which may aid identification of previously unknownglacial cycles.
ISSN: 1469-3496

insu-01184731
https://hal-insu.archives-ouvertes.fr/insu-01184731
DOI : 10.1111/sed.12196

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Seasonal climate forecasts mainly rely on the atmospheric sensitivity to its lower boundary conditions and on their own predictability. Besides sea surface temperature (SST), soil moisture (SM) may be an additional source of climate predictability particularly during boreal summer in the mid-latitudes. In this work, we investigate the role of SM initial conditions on near-surface climate predictability during ten boreal summer seasons using three complementary ensembles of AMIP-type simulations performed with the Arpège-Climat atmospheric general circulation model. First we have conducted an assessment of the SM predictability itself through a comparison of simple empirical SM models with Arpège-Climat. The statistical and dynamical models reveal similar SM prediction skill patterns but the Arpège-Climat reaches higher scores suggesting that it is at least suitable to explore the influence of SM initialization on atmospheric predictability. Then we evaluate the relationships between SM predictability and some near surface atmospheric predictability. While SM initialization obviously improves the predictability of land surface evaporation, it has no systematic influence on the precipitation and near surface temperature skills. Nevertheless, the summer hindcast skill is clearly improved during specific years and over certain regions (mainly north America and eastern Europe in the Arpège-Climat model), when and where the SM forcing is sufficiently widespread and strong. In this case, a significant impact is also found on the occurrence of heat waves and heavy rains, whose predictability at the seasonal timescale is a crucial challenge for years to come.
ISSN: 0930-7575

meteo-00346948
https://hal-meteofrance.archives-ouvertes.fr/meteo-00346948
DOI : 10.1007/s00382-008-0375-9

Éditeur(s) : The National Academy of Sciences of the USA
Résumé : The patterns of variations in fisheries time series are known to result from a complex combination of species and fisheries dynamics all coupled with environmental forcing (including climate, trophic interactions, etc.). Disentangling the relative effects of these factors has been a major goal of fisheries science for both conceptual and management reasons. By examining the variability of 169 tuna and billfish time series of catch and catch per unit effort (CPUE) throughout the Atlantic as well as their linkage to the North Atlantic Oscillation (NAO), we find that the importance of these factors differed according to the spatial scale. At the scale of the entire Atlantic the patterns of variations are primarily spatially structured, whereas at a more regional scale the patterns of variations were primarily related to the fishing gear. Furthermore, the NAO appeared to also structure the patterns of variations of tuna time series, especially over the North Atlantic. We conclude that the patterns of variations in fisheries time series of tuna and billfish only poorly reflect the underlying dynamics of these fish populations; they appear to be shaped by several successive embedded processes, each interacting with each other. Our results emphasize the necessity for scientific data when investigating the population dynamics of large pelagic fishes, because CPUE fluctuations are not directly attributable to change in species' abundance.
Proceedings of the National Academy of Sciences of the United States of America (0027-8424) (The National Academy of Sciences of the USA), 2008-04 , Vol. 105 , N. 14 , P. 5420-5425

Droits : 2008 by The National Academy of Sciences of the USA
http://archimer.ifremer.fr/doc/2008/publication-3984.pdf
DOI:10.1073/pnas.0709034105
http://archimer.ifremer.fr/doc/00000/3984/

Éditeur(s) : HAL CCSD
Résumé : 38 pages
Rapport
The Chicxulub impact crater, México, is unique. It is the only known terrestrial impact structure that has been directly linked to a mass extinction event and the only terrestrial impact with a global ejecta layer. Of the three largest impact structures on Earth, Chicxulub is the best preserved. Chicxulub is also the only known terrestrial impact structure with an intact, unequivocal topographic peak ring. Chicxulub’s role in the Cretaceous/Paleogene (K-Pg) mass extinction and its exceptional state of preservation make it an important natural laboratory for the study of both large impact crater formation on Earth and other planets and the effects of large impacts on the Earth’s environment and ecology. Our understanding of the impact process is far from complete, and despite more than 30 years of intense debate, we are still striving to answer the question as to why this impact was so catastrophic.During International Ocean Discovery Program (IODP) Expedition 364, Paleogene sediments and lithologies that make up the Chicxulub peak ring were cored to investigate (1) the nature and formational mechanism of peak rings, (2) how rocks are weakened during large impacts, (3) the nature and extent of post-impact hydrothermal circulation, (4) the deep biosphere and habitability of the peak ring, and (5) the recovery of life in a sterile zone. Other key targets included sampling the transition through a rare midlatitude section that might include Eocene and Paleocene hyperthermals and/or the Paleocene/Eocene Thermal Maximum (PETM); the composition and character of the impact breccias, melt rocks, and peak-ring rocks; the sedimentology and stratigraphy of the Paleocene–Eocene Chicxulub impact basin infill; the chronology of the peak-ring rocks; and any observations from the core that may help us constrain the volume of dust and climatically active gases released into the stratosphere by this impact. Petrophysical property measurements on the core and wireline logs acquired during Expedition 364 will be used to calibrate geophysical models, including seismic reflection and potential field data, and the integration of all the data will calibrate impact crater models for crater formation and environmental effects. The proposed drilling directly contributes to IODP Science Plan goals:Climate and Ocean Change: How resilient is the ocean to chemical perturbations? The Chicxulub impact represents an external forcing event that caused a 75% level mass extinction. The impact basin may also record key hyperthermals within the Paleogene.Biosphere Frontiers: What are the origin, composition, and global significance of subseafloor communities? What are the limits of life in the subseafloor? How sensitive are ecosystems and biodiversity to environmental change? Impact craters can create habitats for subsurface life, and Chicxulub may provide information on potential habitats for life, including extremophiles, on the early Earth and other planetary bodies. Paleontological and geochemical studies at ground zero will document how large impacts affect ecosystems and effects on biodiversity.Earth Connections/Earth in Motion: What are the composition, structure and dynamics of Earth’s upper mantle? What mechanisms control the occurrence of destructive earthquakes, landslides, and tsunami? Mantle uplift in response to impacts provides insight into dynamics that differ between Earth and other rocky planets. Impacts generate earthquakes, landslides, and tsunami, and scales that generally exceed plate tectonic processes yield insight into effects, the geologic record, and potential hazards.IODP Expedition 364 was a Mission Specific Platform expedition to obtain subseabed samples and downhole logging measurements from the sedimentary cover sequence and peak ring of the Chicxulub impact crater. A single borehole was drilled into the Chicxulub impact crater on the Yucatán continental shelf, recovering core from 505.7 to 1334.73 m below seafloor with ~99% core recovery and acquiring downhole logs for the entire depth.
International Ocean Discovery Program

hal-01639520
https://hal.archives-ouvertes.fr/hal-01639520
DOI : 10.14379/iodp.pr.364.2017

Éditeur(s) : Pergamon-elsevier Science Ltd
Résumé : Catch data of large pelagic fish such as tuna, swordfish and billfish are highly variable ranging from short to long term. Based on fisheries data, these time series are noisy and reflect mixed information on exploitation (targeting, strategy, fishing power), population dynamics (recruitment, growth, mortality, migration, etc.), and environmental forcing (local conditions or dominant climate patterns). In this work, we investigated patterns of variation of large pelagic fish (i.e. yellowfin tuna, bigeye tuna, swordfish and blue marlin) in Japanese longliners catch data from 1960 to 2004. We performed wavelet analyses on the yearly time series of each fish species in each biogeographic province of the tropical Indian and Atlantic Oceans. In addition, we carried out cross-wavelet analyses between these biological time series and a large-scale climatic index, i.e. the Southern Oscillation Index (Sol). Results showed that the biogeographic province was the most important factor structuring the patterns of variability of Japanese catch time series. Relationships between the SOI and the fish catches in the Indian and Atlantic Oceans also pointed out the role of climatic variability for structuring patterns of variation of catch time series. This work finally confirmed that Japanese longline CPUE data poorly reflect the underlying population dynamics of tunas. (C) 2010 Elsevier Ltd. All rights reserved.
Progress In Oceanography (0079-6611) (Pergamon-elsevier Science Ltd), 2010-07 , Vol. 86 , N. 1-2 , P. 276-282

Droits : 2010 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00011/12231/9029.pdf
DOI:10.1016/j.pocean.2010.04.019
http://archimer.ifremer.fr/doc/00011/12231/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Big storm events represent a major risk for populations and infrastructures settled on coastal lowlands. In the Western Mediterranean, where human societies colonized and occupied the coastal areas since the Ancient times, the variability of storm activity for the past three millennia was investigated with a multi-proxy sedimentological and geochemical study from a lagoonal sequence. Mappings of the geochemistry and magnetic susceptibility of detrital sources in the watershed of the lagoon and from the coastal barriers were undertaken in order to track the terrestrial or coastal/marine origin of sediments deposited into the lagoon. The multi-proxy analysis shows that coarser material, low magnetic susceptibility, and high strontium content characterize the sedimentological signature of the paleostorm levels identified in the lagoonal sequence. A comparison with North Atlantic and Western Mediterranean paleoclimate proxies shows that the phases of high storm activity occurred during cold periods, suggesting a climatically-controlled mechanism for the occurrence of these storm periods. Besides, an in-phase storm activity pattern is found between the Western Mediterranean and Northern Europe. Spectral analyses performed on the Sr content revealed a new 270-year solar-driven pattern of storm cyclicity. For the last 3000 years, this 270-year cycle defines a succession of ten major storm periods (SP) with a mean duration of 96 ± 54 yr. Periods of higher storm activity are recorded from >680 to 560 cal yr BC (SP10, end of the Iron Age Cold Period), from 140 to 820 cal yr AD (SP7 to SP5) with a climax of storminess between 400 and 800 cal yr AD (Dark Ages Cold Period), and from 1230 to >1800 cal yr AD (SP3 to SP1, Little Ice Age). Periods of low storm activity occurred from 560 cal yr BC to 140 cal yr AD (SP9 and SP8, Roman Warm Period) and from 820 to 1230 cal yr AD (SP4, Medieval Warm Period).
ISSN: 0277-3791

hal-01277796
https://hal.archives-ouvertes.fr/hal-01277796
DOI : 10.1016/j.quascirev.2015.10.009

Éditeur(s) : HAL CCSD Editions Paralia CFL
Résumé : Les lagunes du Golfe du Lion constituent un patrimoine naturel reconnu ainsi qu'un enjeu essentiel pour les activités économiques locales. Leur évolution morphologique est donc une question importante dans le contexte actuel de changements climatiques et environnementaux. L'analyse de données topo-bathymétriques du système des étangs Palavasiens a permis de mieux cerner son évolution depuis le XVIIIème siècle. Les actions anthropiques et les apports du bassin versant apparaissent comme les facteurs principaux de l'évolution du système. Au cours des 40 dernières années, le système montre une tendance à se combler lentement avec une accumulation moyenne de 1,3 mm/an. Des différences de fonctionnement sur chacun des étangs sont mises en lumière en fonction des forçages naturels et anthropiques locaux. Lagoons of the Gulf of Lion, recognized for their natural heritage, are a key challenge for local economic activities. Their morphological evolution is an important issue in the current context of climate and environmental changes. Analysis of topo-bathymetric data of the Palavasian lakes system has helped to clarify its evolution since the XVIII th century. Human impacts and contributions from the watershed appear to be the main drivers governing the evolutionof the system. Over the past40 years, the system shows a tendency to slowly fill at an accumulation rate of 1.3 mm/year. Differences between lagoons are highlighted according to local natural and anthropogenic forcings.
ISSN: 1760-8716

hal-00854075
https://hal.archives-ouvertes.fr/hal-00854075
DOI : 10.5150/revue-paralia.2011.007

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The morphogenetic evolution of the Lesser Caucasus has been strongly influenced by Plio-Quaternary volcanic and tectonic events and Pleistocene glaciations. Fluvio-lacustrine environments, indicated by diatomaceous deposits, prevailed in the Syunik region of southern Armenia during the Pliocene and Pleistocene. The Pleistocene diatomaceous deposits studied contain leaf impressions and pollen, allowing local palaeoclimatic reconstructions. The chronology of morphogenetic events has been determined by 17 radiometric dates (K/Ar, Ar/Ar, U/Th), palaeomagnetic investigations and is placed in a spatial context by a detailed geomorphological map and a 24-km geological transect of the Vorotan valley, the main area studied. Before 1.21 Ma, tectonic movements (antecedents of the lower part of the Vorotan valley) generated extensive lake formations with diatomaceous deposits. From 993 ka, volcanic eruptions produced lava flows that covered the fluvio-lacustrine accumulations. During Marine Isotopic Stages 12, 6 and 4, glaciers and fluvio-glacial deposits were probably present overall the principal uplands and valleys of southern Armenia. At 53.68 ka (MIS 3), 12.6 ka, 10.78 ka and 4.14 ka (MIS 1), the development of travertines on some slopes and in some valleys highlights temperate and humid climatic phases. Palaeobotanical studies of leaf and pollen floras show that the vegetation changed several times from forested to steppic phases in response to the climate oscillations of the Lower Pleistocene. This work proposes a first morphogenic and palaeoclimatic reconstruction from the lower Pleistocene to the Postglacial period, when the first settlements of the population in the Lesser Caucasus were influenced by tectono-volcanic events, lake level changes and glacialeinterglacial oscillations forced by the obliquity orbital parameter (41 ky cycles).
ISSN: 1040-6182

hal-00481939
https://hal.archives-ouvertes.fr/hal-00481939
DOI : 10.1016/j.quaint.2010.02.008

Éditeur(s) : HAL CCSD Société géologique de France
Résumé : A study combining very high resolution seismic and sediment core data has been carried out on the Thau lagoon (Mediterranean coast, microtidal setting, SE France) in order to understand more clearly the dynamics and Holocene chronology of its closure through the different stages of its filling. One main seismic unit (U2) has been defined into the infill, above the rocky basement (U0) and a composite unit U1, which is interpreted as remnants of Pleistocene fluvial terraces or/and to early marine Holocene deposits. Unit U2, that reaches locally 9 m in thickness, rests conformably on U1 in the central part of the lagoon and onlaps U0 or U1 close to the edge of the lagoon. It is divided in two sub-units, U2-1 and U2-2. U2-2 rests paraconformably on U2-1 in the central part of the lagoon where the infill is the thickest, while a marked erosional unconformity is observed between U2-1 and U2-2 on topographic highs of the basement and on the seaward edge of the lagoon. A total of seven elementary sequences have been observed in U2-1 and U2-2.;According to core data, U2 consists in a series of mud-dominated sequences, with shell fragments dispersed at the base. The vertical distribution of the fauna into U2-1 and U2-2 reveals a lagoonal environment. However in U2-1, marine species are more abundant in the south of the lagoon. C-14 AMS dating provides three ages: similar to 6000 cal yr B.P. in the lower part of U2-1 on CAL1, 5400 cal yr B.P. just above the boundary between U2-1 and U2-2 on CAL4, similar to 3000 cal yr B.P. in the middle of U2-2 on CAL4.;A scenario to explain the lagoon infill stratigraphy and geometry is proposed. The beginning of the lagoon infill occurred with the initiation of the barrier construction, as soon as the sea-level rise slowed down significantly, i.e. between 7000-6000 yr B.P. The sediment-fill began into the back-barrier system, with a high rate of sedimentation for U2-1, according to the radiocarbon data. At 5400 yr B.P., the barrier is assumed to be totally closed leading to the deposition of the fully lagoonal U2-2 succession. The unconformity between U2-1 and U2-2 is interpreted as the result of a rapid landward retreat of the barrier. This severe retreat could be related to climate forcing and/or brutal change in sediment discharge driven by the Rhone River, which is the main sediment source of the longshore drift. In this scenario, the last sub-unit, U2-2, represents most of the late Holocene infill. In this framework, the elementary sequences observed in U2-2 could be related to high frequency climate changes of about 1000-1500 years periodicity according to C-14 dates.
EISSN: 1777-5817

hal-00486386
https://hal.archives-ouvertes.fr/hal-00486386
DOI : 10.2113/gssgfbull.181.2.197

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
A temporary network of 10 broad-band seismic stations has been installed in French Polynesia for the Polynesian Lithosphere and Upper Mantle Experiment (PLUME). All the seismic stations were installed either on volcanic islands or on atolls of the various archipelagos of French Polynesia in a manner which complements the geographic coverage provided by the regional permanent stations. The primary aim of PLUME is to image the upper mantle structures related to plate motion and hotspot activity. However, because of its proximity to all sites, the ocean is responsible for a high level of noise in the seismic data and we show that these data can also be used to analyse ocean wave activity. The power spectral density (PSD) analyses of the seismic data recorded in French Polynesia show clear peaks in the 0.05– 0.10 Hz band (periods between 10 and 20 s), which corresponds to swell frequencies. Clear peaks in this frequency band are also observed in infrasonic data recorded on Tahiti. Ground motion analysis shows that the swell-related seismic noise (SRSN) is linearly polarized in the horizontal plane and its amplitude decreases rapidly with the distance from the shore. The microseismic and the infrasonic 'noise' amplitudes show very similar variations from station to station and both are strongly correlated with the swell amplitudes predicted by the National Oceanic and Atmospheric Administration (NOAA), wind-forced, 'WaveWatch' models. The swell direction can be estimated from SRSN polarization analysis but this has to be done with care since, for some cases, the ground motions are strongly controlled by the islands' anisometric shapes and by swell refraction processes. We find cases, however, such as Tahiti or roughly circular Tuamotu atolls, where the azimuth of the swell is in good agreement with the seismic estimates. We, therefore, demonstrate that the SRSN and the infrasonic signal observed in French Polynesia can be used in such cases as a proxy for swell amplitude and azimuth. From the continuous analysis of the data recorded in 2003 at the permanent seismic station PPTL in Tahiti, transfer functions have been obtained. This could provide a way to quantify the swell activity during the last two decades and, therefore, assist in the investigation of climate changes.
ISSN: 0956-540X

hal-01388809
http://hal.univ-reunion.fr/hal-01388809
http://hal.univ-reunion.fr/hal-01388809/document
http://hal.univ-reunion.fr/hal-01388809/file/Barruol_swell_GJI2006.pdf
DOI : 10.1111/j.1365-246X.2006.02871.x

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
A temporary network of 10 broad-band seismic stations has been installed in French Polynesia for the Polynesian Lithosphere and Upper Mantle Experiment (PLUME). All the seismic stations were installed either on volcanic islands or on atolls of the various archipelagos of French Polynesia in a manner which complements the geographic coverage provided by the regional permanent stations. The primary aim of PLUME is to image the upper mantle structures related to plate motion and hotspot activity. However, because of its proximity to all sites, the ocean is responsible for a high level of noise in the seismic data and we show that these data can also be used to analyse ocean wave activity. The power spectral density (PSD) analyses of the seismic data recorded in French Polynesia show clear peaks in the 0.05– 0.10 Hz band (periods between 10 and 20 s), which corresponds to swell frequencies. Clear peaks in this frequency band are also observed in infrasonic data recorded on Tahiti. Ground motion analysis shows that the swell-related seismic noise (SRSN) is linearly polarized in the horizontal plane and its amplitude decreases rapidly with the distance from the shore. The microseismic and the infrasonic 'noise' amplitudes show very similar variations from station to station and both are strongly correlated with the swell amplitudes predicted by the National Oceanic and Atmospheric Administration (NOAA), wind-forced, 'WaveWatch' models. The swell direction can be estimated from SRSN polarization analysis but this has to be done with care since, for some cases, the ground motions are strongly controlled by the islands' anisometric shapes and by swell refraction processes. We find cases, however, such as Tahiti or roughly circular Tuamotu atolls, where the azimuth of the swell is in good agreement with the seismic estimates. We, therefore, demonstrate that the SRSN and the infrasonic signal observed in French Polynesia can be used in such cases as a proxy for swell amplitude and azimuth. From the continuous analysis of the data recorded in 2003 at the permanent seismic station PPTL in Tahiti, transfer functions have been obtained. This could provide a way to quantify the swell activity during the last two decades and, therefore, assist in the investigation of climate changes.
ISSN: 0956-540X

hal-01323691
http://hal.univ-reunion.fr/hal-01323691
http://hal.univ-reunion.fr/hal-01323691/document
http://hal.univ-reunion.fr/hal-01323691/file/Barruol_et_al_2006.pdf
DOI : 10.1111/j.1365-246X.2006.02871.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) : American Geophysical Union
Résumé : Thick forced regressive units on the wide continental shelf of the Gulf of Lions (western Mediterranean) recorded the composite effect of sea level changes during the Quaternary. They are mostly composed of coastal siliciclastic and bioclastic wedges showing clinoform geometry. These deposits have been intensively explored through high-resolution seismic investigations, but only recently it was possible to ground truth seismic interpretations, based on a long (100 m) borehole that crossed the succession and recovered a large part of the mainly sandy deposits (similar to 84% recovery). A multiproxy analysis of the sedimentary succession shows that (1) the stratal architecture of the shelf margin is defined by major bounding surfaces that are polygenic erosion surfaces associated with coarse-grained material incorporating abundant and diverse shells, including cold-water fauna (presently absent from the Mediterranean Sea). Between each surface, coarsening upward units with steep (up to 5 degrees) foresets are made of massive (more than 20 m thick) sands with possible swaley and hummocky cross-stratification, passing seaward to sands with muddy intervals and, further offshore, alternating highly boiturbated sands and silts. Each prograding wedge corresponds to a forced-regressive shoreface (or delta front/prodelta), deposited during the overall sea level falls occurring at (relatively slow) interglacial/glacial transition and therefore represents the record of 100 ka cyclicity. Higher-frequency Milankovitch cyclicities are also probably represented by distinct shoreface/delta front wedges; (2) detailed examination of the architecture and chronostratigraphy of the most recent sequence shows that minor bounding surfaces, corresponding to abrupt shallowing of sedimentary facies, separate downward stepping parasequences within the last 100 ka sequence. These events are in phase with millennial-scale glacial climatic and sea level variability, the downward shift surfaces corresponding to the falls during the coldest stadials. These deposits provide a comprehensive and well-constrained Pleistocene analog to the numerous shoreface deposits attributed to falling-stage systems tracts recognized in ancient stratigraphic records, studied at the outcrop scale.
Geochemistry Geophysics Geosystems - G3 (1525-2027) (American Geophysical Union), 2008-11 , Vol. 9 , N. Q11R05 , P. NIL_40-NIL_66

Droits : 2008 American Geophysical Union
http://archimer.ifremer.fr/doc/2008/publication-4929.pdf
DOI:10.1029/2007GC001854
http://archimer.ifremer.fr/doc/00000/4929/

Résumé : Ce travail est l'expression d'une volonté de chercheurs, de la Carabe d'améliorer les connaissances scientifiques méso- et micro-météorologiques appliquées aux milieux insulaires sous influence des alizés et de développer la recherche dans ces domaines.On sait que le phénomène météorologique le plus remarquable impactant les îles de la Caraïbe reste le cyclone tropical. Mais d'autres phénomènes, a des échelles inferieures, telles que les pluies intenses, les houles, la dégradation de la qualité de l'air ont une importance aigüe en termes de risques naturels ou de risques sur la sante. Ces exemples attestent la nécessité d'utiliser des méthodes de descente d'échelle pour exploiter l'information météorologique et/ou climatique de grande échelle et dériver des scenarios locaux et régionaux appliques aux territoires insulaires. Ce défi est important car l'attente d'analyses scientifiques pertinentes dans ces domaines est grande.Les travaux présentés dans ce mémoire ont pour principaux objectifs la simulation numérique puis l'analyse des mécanismes méso- et micro-échelles qui induisent des circulations locales diurnes et nocturnes sur l'archipel de la Guadeloupe à l'aide de codes numériques météorologiques éprouves car largement utilises en recherche et en prévision opérationnelle.Ils constituent donc la première étude de modélisation numérique à haute résolution en basse atmosphère, par descente d'échelle dynamique, pour des intervalles d'espace compris entre 1 km et 111 m sur cet archipel.Le modelé atmosphérique Weather Research and Forecasting ARW V3.4 (WRF ARW), non-hydrostatique, a été utilise pour l'ensemble des simulations pour modéliser la troposphère depuis l'échelle globale à l'échelle de la turbulence.Trois situations météorologiques classiques réelles d'une durée de 48 heures, correspondant à 80 % des situations météorologiques observées dans la zone, alizes soutenus (AS), alizes moyens (AM), alizes faibles (AF) ont été examinées. Ces situations sont caractérisées par les valeurs du nombre de Froude local suivantes : 0,82 (AS), 0,41 (AM) et 0,21 (AF). Six domaines de modélisation ont été sélectionnés pour effectuer les descentes d'échelle dynamiques : D01 (maille de 27 km), D02 (maille de 9 km), D03 (maille de 3 km), D04 (maille de 1 km), D05 (maille de 333 m) et D06 (maille de 111 m) avec soixante-dix niveaux verticaux. Les quatre premiers domaines (D01 à D04) couvrent l'archipel de la Guadeloupe et sont utilisés en mode méso-échelle à l'aide d'un schéma d'ensemble de couche limite planétaire YSU. Les domaines D05 (couvrant l'île de la Basse-Terre et le centre de l'archipel) et D06 (couvrant la zone littorale et rurale du Petit Cul-de-Sac Marin et la zone urbaine de l'agglomération pointoise) sont utilisés en mode Large Eddy Simulation avec une fermeture de la turbulence 1,5 TKE 3D. Le modèle WRF a été forcé toutes les six heures par l'assimilation des champs d'analyses globales du modèle NCEP FNL (1° de résolution). Les simulations effectuées ont permis d'obtenir des champs de variables météorologiques 10-minutes à très hautes résolutions spatiales.Les résultats des simulations méso- et micro-échelles ont été confrontés aux valeurs expérimentales obtenues à l'aide de capteurs places sur des mâts météorologiques (campagne Atmo-Mangrov et réseau de mesure Météo-France). Il s'agissait d'optimiser l'utilisation des couplages de codes numériques tout en conservant la possibilité de les confronter aux observations expérimentales.Les résultats des simulations numériques micro-échelles, des différents cas (AS, AM, AF) sont utilisées pour forcer (c'est-à-dire définir les conditions limites) un modèle lagrangien de dispersion de particules : FLEXPART. Le système couple FLEXPART-WRF a été employé dans le domaine D06 pour étudier la dispersion du panache d'oxydes d'azote émis par la principale usine de production d'électricité de l'île.
The present work expresses the will of Caribbean researchers to improve the meso- and micro-meteorological scientific knowledge of the trade winds influenced island areas, and to develop research in these domains.It is well known that tropical hurricanes remain the most remarkable meteorological phenomena that affect the Caribbean islands. But some other phenomena, of smaller scale, such as intense rainfall events, swells, or air quality degradation, are of extreme importance for natural or health hazards. These examples show the need to use downscaling methods to exploit large scale meteorological or climatic information, and to obtain local and regional scenarios for the island areas. This is an important challenge, as sound scientific studies in these matters are eagerly expected. The aim of the research works exposed in the present dissertation is numerical simulation and analysis of the meso- and microscale mechanisms that induce diurnal and nocturnal local circulations in the Guadeloupe archipelago, using numerical meteorological models that are widely used in research and in operational forecasting.These works represent the first high-resolution (1 km to 111 m) numerical study of the lower atmosphere over the Guadeloupe archipelago. The Weather Research and Forecasting ARW 3.4 (WRF-ARW) model is used to simulate the troposphere from global scale to turbulence scale. Real cases of three typical weather types (80% of cases during a year) are examined during 48 hours : strong trade winds (STW), medium trade winds (MTW) and weak trade winds (WTW). These weather types are characterized by values of the local Froude number : 0.82 (STW), 0.41 (MTW) and 0.21 (WTW). Six domains have been selected for the dynamical downscaling : D01 (grid spacing of 27 km), D02 (grid spacing of 9 km), D03 (grid spacing of 3 km), D04 (grid spacing of 1 km), D05 (grid spacing of 333 m) and D06 (grid spacing of 111 m), including 70 vertical levels. The first four domains (D01 to D04) cover the Guadeloupe archipelago and are used in the meso-scale simulations with the planetary boundary layer scheme YSU (ensemble mean). Domain D05 (covering the Basse-Terre island and the middle of the archipelago) and domain D06 (covering the coastal and rural area of Le Petit Cul-de-Sac Marin and the urban area of Pointe-à-Pitre), are employed in the micro-scale simulation (LES) with the 3D TKE 1.5 order closure scheme. WRF has been 6 hourly reinitialized with the NCEP FNL global analyses (resolution of 1°). These simulations permitted to obtain 10-minutes meteorological variable fields with a very high resolution (111 m).Meso-scale and micro-scale model results have been evaluated with observational data from meteorological stations (field campaign Atmo-Mangrov, French Met Office).Once validated, the micro-scale model outputs have been used for the assimilation of the lagrangian particle dispersion model : FLEXPART. The coupling FLEXPART-WRF has been employed in domain D06, in order to analyze the dispersion of the nitrogen oxide plume emitted by the main power plant of the archipelago.

http://www.theses.fr/2014AGUY0735/document