Résumé : The populations of fishes dwelling near the sea bed (demersal species) on the continental shelf are usually the object of intense commercial exploitation. The Bay of Biscay shelf is no exception. Hence, populations suffer from this exploitation. Moreover, the general role played by hydro-climatic variations in the regulation of the abundance of demersal fish populations (population dynamics) is traditionally admitted. In the Bay of Biscay, a warming of the surface water has been observed over the three last decades (Koutsikopoulos et al., 1998). Climate change therefore has potential consequences on fish communities. Thus, the structure and dynamics of fish populations on the continental shelf of the Bay of Biscay are susceptible to suffer both from the effects of a human activity (fishing) and of climate change (warming). Fisheries should therefore suffer more or less from these changes depending on their adaptation capacity.
Les peuplements de poissons vivant à proximité du fond (espèces démersales) sur le plateau continental font généralement l'objet d'une exploitation commerciale intense. Le plateau du Golfe de Gascogne n'échappe pas à cette règle. Les populations y subissent donc les effets de l'exploitation. Par ailleurs, le rôle général des variations hydro-climatiques dans la régulation de l'abondance des populations démersales de poissons (la dynamique des populations) est classiquement admis. Dans le Golfe de Gascogne, un réchauffement des eaux de surface au cours des trois dernières décennies est observé (Koutsikopoulos et al., 1998). Le changement climatique a donc des conséquences potentielles sur la communauté de poissons. Ainsi, la structure et la dynamique du peuplement de poissons du plateau continental du Golfe de Gascogne sont susceptibles de répondre à la fois aux effets d'une activité humaine (la pêche) et du changement climatique (réchauffement). Les pêcheries devraient donc subir ces changements selon leur capacité d'adaptation.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/2006/rapport-6347.pdf
http://archimer.ifremer.fr/doc/00000/6347/

Résumé : L'importance des forêts tropicales dans le cycle du carbone à l'échelle planétaire est majeure, tant en terme de stock qu’en terme de flux de CO2. Plusieurs études mettent en évidence des changements au sein des forêts tropicales au cours des 20 dernières années, notamment des changements de la dynamique forestière et une augmentation de la biomasse aérienne. Les déterminants de ces variations sont aujourd’hui discutés et nous proposons ici d’apporter une contribution à ce débat. Les données utilisées dans ce travail proviennent du dispositif de suivi forestier à long terme de Paracou, Guyane Française, mis en place en 1984 et qui recouvre plus de 120 ha de forêt tropicale humide. Les données météorologiques proviennent de la tour à flux du dispositif, Guyaflux. Les mesures de diamètre proviennent de la base Guyafor pour les données annuelles et bisannuelles, et des mesures de 260 arbres à proximité de la tour à flux pour les mesures diamétriques intra-annuelles.Cette thèse se divise en deux grandes parties. La première concerne l’analyse de la biomasse du dispositif de suivi forestier de Paracou en Guyane et l’implication des changements de structure de cette forêt sur le bilan de carbone. Cette partie est constituée de deux points. (i) Quelles échelles temporelles et spatiales sont pertinentes pour analyser les composantes de structure (biomasse, aire basale et nombre de tiges) et de dynamique (croissance, recrutement et mortalité) des forêts tropicales afin de minimiser les effets d’échantillonnage ? Nous avons établi une méthodologie permettant de relier les intervalles de temps et la surface de mesure aux coefficients de variation de chacune des variables de structure et de dynamique de la forêt. (ii) Quels processus démographiques sont prépondérants dans l’explication des variations de biomasse et comment se redistribue la biomasse accumulée dans le système ? L’augmentation de la biomasse observée sur le dispositif de Paracou serait liée à la rareté des évènements de mortalité des gros arbres qui portent une part très importante de la biomasse.La deuxième partie de la thèse concerne l’analyse de l’effet du climat à moyen terme, inter et intra-annuel, et les effets directs du climat dans les changements de dynamique de la forêt. Cette partie se divise en 3 points. (i) Comment quantifier le stress hydrique en forêt tropicale humide ? Nous avons réalisé un modèle journalier de réserve en eau du sol pour les arbres en forêt tropicale. (ii) Quelles variables sont explicatives de la croissance des arbres en forêt guyanaise ? Nous avons montré que l’eau dans le sol est le facteur le plus explicatif du déterminisme climatique parmi un panel de variables climatiques. (iii) Quels traits fonctionnels sont prédicteurs de la réponse des arbres aux variations climatique ? Nous avons déterminé que des traits spécifiques, densité du bois et la hauteur maximale, ainsi que le diamètre de l'arbre au moment de la mesure, modulent la croissance des arbres en réponse au climat.
At a global scale tropical forest play a major role in term of carbon stock as well as in term of CO2 fluxes. Several studies have highlighted changes in tropical forest functioning during the last 20 years including a faster turnover and an increase of above ground biomass. The drivers of these changes are discussed and throughout this thesis we propose to contribute to this debate. We use the data from the Paracou experimental site in French Guiana established in 1984 on 120 hectares of moist tropical forest. Meteorological data come from the flux tower of the site, Guyaflux. We use annual and bisannual diameter measurements from the Guyafor database, and intra-annual diameter increments from the measurements of 260 trees near the flux tower.This thesis has two main parts. In the first part we present the biomass analysis of the Paracou permanent plots and the impact of structural changes in this forest on the carbon budget. The first part is constituted by two points. (i) Which temporal and spatial scale used to analyze the structure (biomass, basal area and stem density) and dynamics (tree growth, recruitment and mortality)components of tropical forest in order to minimized sample bias ? We establish a simple method to rely measurement interval between census and surface of measurement to the coefficient of variation of forests structure and dynamic components (ii) Which demographic process are involved in the explanation of biomass variation and how the biomass is distributed in the system ? The observed increase of biomass at Paracou could be link to the rarity of big trees mortality events. These big trees represent the larger part of the biomass. In the second part, we present the analysis of intra and inter-annual climate variation effects on forest dynamic changes. This part is divided in two points. (i) How to model drought stress in moist tropical forest ? We built a daily water balance model for tropical trees. (ii) Which climate variables explain the tree growth in guianian forests? We shown that soil water availability is the determinant factor of tree growth among a panel of climate variables. (iii) Which functional traits are involved in the tropical tree growth responses to climate? In this analysis, we determined that wood specific gravity, maximum tree height and tree diameter modulate the tree growth response to climate variations.

http://www.theses.fr/2011AGUY0481/document

Éditeur(s) : HAL CCSD Elsevier
Résumé : Vegetation phenology is the study of the timing of seasonal events that are considered to be the result of adaptive responses to climate variations on short and long time scales. In the field of remote sensing of vegetation phenology, phenological metrics are derived from time series of optical data. For that purpose, considerable effort has been specifically focused on developing noise reduction and cloud-contaminated data removal techniques to improve the quality of remotely-sensed time series. Comparative studies between time series composed of satellite data acquired under clear and cloudy conditions and from radiometric data obtained with high accuracy from ground-based measurements constitute a direct and effective way to assess the operational use and limitations of remote sensing for predicting the main plant phenological events. In the present paper, we sought to explicitly evaluate the potential use of MODerate resolution Imaging Spectroradiometer (MODIS) remote sensing data for monitoring the seasonal dynamics of different types of vegetation cover that are representative of the major terrestrial biomes, including temperate deciduous forests, evergreen forests, African savannah, and crops. After cloud screening and filtering, we compared the temporal patterns and phenological metrics derived from in situ NDVI time series and from MODIS daily and 16-composite products. We also evaluated the effects of residual noise and the influence of data gaps in MODIS NDVI time series on the identification of the most relevant metrics for vegetation phenology monitoring. The results show that the inflexion points of a model fitted to a MODIS NDVI time series allow accurate estimates of the onset of greenness in the spring and the onset of yellowing in the autumn in deciduous forests (RMSE <= one week). Phenological metrics identical to those provided with the MODIS Global Vegetation Phenology product (MDC12Q2) are less robust to data gaps, and they can be subject to large biases of approximately two weeks or more during the autumn phenological transitions. In the evergreen forests, in situ NDVI time series describe the phenology with high fidelity despite small temporal changes in the canopy foliage. However, MODIS is unable to provide consistent phenological patterns. In crops and savannah, MODIS NDVI time series reproduce the general temporal patterns of phenology, but significant discrepancies appear between MODIS and ground-based NDVI time series during very localized periods of time depending on the weather conditions and spatial heterogeneity within the MODIS pixel. In the rainforest, the temporal pattern exhibited by a MODIS 16-day composite NDVI time series is more likely due to a pattern of noise in the NDVI data structure according to both rainy and dry seasons rather than to phenological changes. More investigations are needed, but in all cases, this result leads us to conclude that MODIS time series in tropical rainforests should be interpreted with great caution. (C) 2013 Elsevier Inc. All rights reserved.
ISSN: 0034-4257

hal-01032407
https://hal.archives-ouvertes.fr/hal-01032407
DOI : 10.1016/j.rse.2013.01.010

Éditeur(s) : Elsevier Science Bv
Résumé : The present study focused on turbidite sedimentation in the Cilaos turbidite system, a volcaniclastic deep-sea fan recently recognized offshore La Réunion Island. A set of piston cores was collected in order to establish the stratigraphy of this fan and to examine the processes controlling the turbidite sedimentation off the Cilaos cirque (Piton des Neiges volcanic massif) over the last climatic cycle. Two main phases of turbidite activity were identified, during the ca 140–127 ka and 30–0 ka periods, coinciding with the two last glacial–interglacial transitions (i.e., Terminations II and I). In addition to changes in climate and eustatic sea-level, these periods coincide with a low effusive volcanic activity of the Piton des Neiges volcano. The high erosional rates identified in the Cilaos cirque during these intervals of both low effusive volcanic activity and enhanced rainfall level are probably the main driver of sediment supply to the deep‐sea depositional system. These new findings also highlight the important capacity of volcaniclastic turbidite systems to record rapid paleoenvironmental changes.
Sedimentary Geology (0037-0738) (Elsevier Science Bv), 2012-12 , Vol. 281 , P. 180-193

Droits : 2012 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00105/21659/19383.pdf
DOI:10.1016/j.sedgeo.2012.09.010
http://archimer.ifremer.fr/doc/00105/21659/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Multi-proxy analysis of two marine sediment cores (MS27PT and MD04-2726) from the Nile continental slope provides evidence of changes in Nile sediment discharge related to changes in Ethiopian African Monsoon (EAM) precipitation, and allows us to reconstruct changes in Nile River runoff, vegetation and erosion in the Nile headwaters. Sediment element composition and neodymium isotopic composition reveal significant changes in clastic sediment provenance, with sources oscillating between a Saharan aeolian contribution during the Last Glacial Maximum/deglacial transition and during the Late Holocene, and a Blue/Atbara Nile fluvial contribution during the African Humid Period (AHP). This study provides a new understanding of past environmental changes. Between 14.6 and 14.13 ka there was a major input of sediments from the Ethiopian Highlands, consistent with a stronger EAM at that time. Climate in the Nile basin was wetter between 14.8 and 8.4 ka, with a corresponding increase in Blue Nile water and sediment discharge via the main Nile into the Eastern Mediterranean. The gradual climatic transition from the AHP to the present-day dry climate was reflected in a decrease in Blue Nile sediment deposition and flood discharge between 8.4 and 3.7 ka, with aridity at a maximum between 3.7 and 2.6 ka. The onset of drier conditions in the Blue Nile basin seems to have begun before the 8.2 ka cooling event in the North Atlantic. We speculate that the climatic change from the wet AHP to the dry late Holocene may have been a result of a break in the low latitude dynamic equilibrium between climate, vegetation and erosion, which may in turn have affected the climate in higher latitudes. Reduced Nile flow may also have had an impact on Levantine Intermediate Water originating in the Eastern Mediterranean through an increase in intermediate water formation.
ISSN: 0277-3791

hal-01277950
https://hal.archives-ouvertes.fr/hal-01277950
DOI : 10.1016/j.quascirev.2015.10.030

Éditeur(s) : Elsevier Science Bv
Résumé : The Var turbiditic system located in the Ligurian Sea (SE France) is an intermediate mud/sand-rich system. The particularity of the Var deep-sea fan is its single channel with abrupt bends and its asymmetric and hyper-developed levee on the right hand side: the Var Sedimentary Ridge. Long-term sediment accumulation on the Var Sedimentary Ridge makes this an ideal target for studying the link between onshore climate change and deep-sea turbidite stratigraphy. This paper focuses on the establishment of the first detailed stratigraphy of the levee, which is used to analyze the timing of overbank deposition throughout the last deglaciation. Main results indicate that high variability in turbidite frequencies and deposition rates along the Var Sedimentary Ridge are determined by two main parameters: 1) the progressive decrease of the levee height controlling the ability of turbidity currents to spill out from the channel onto the levee, and 2) climatic variations affecting the drainage basin, in particular changes in glacial condition since late Last Glacial Maximum to early Holocene. Compared to other deep-water areas, this study confirms the ability of turbiditic systems to record past climatic events on millennial timescales, and underlines the influence of European deglaciation on the observed decrease in turbidite activity in the Var canyon. The presence of a very narrow continental shelf and a single, large channel-levee system makes the Var Sedimentary Ridge a unique example of climate-controlled turbiditic accumulations. (C) 2010 Elsevier B.V. All rights reserved.
Marine Geology (0025-3227) (Elsevier Science Bv), 2011-01 , Vol. 279 , N. 1-4 , P. 148-161

Droits : 2010 Elsevier Ltd All rights reserved.
http://archimer.ifremer.fr/doc/00030/14104/11370.pdf
DOI:10.1016/j.margeo.2010.10.021
http://archimer.ifremer.fr/doc/00030/14104/

Éditeur(s) : Elsevier
Résumé : During the Fanindien 2006 cruise of R/V 'Beautemps-Beaupre', high resolution multibeam bathymetry, sub-bottom profiling and sediment coring was carried out along the East African margin, offshore Tanzania and Mozambique (Indian Ocean). The newly acquired data reveal the presence of a giant deep-sea valley (the Tanzania channel) that is more than 10 km wide at 4000 m water depth, along the continental rise. The valley remains similar to 70 m deep and 7 km wide at 800 km from the Tanzania coast. Morphological comparison with worldwide submarine channels show that the Tanzania channel is one of the largest known submarine valleys. This discovery brings new light on development of submarine valleys that drain sediments originated from the East African Rift System (EARS) highlands (i.e. the Tanzania channel and its neighbor Zambezi channel located similar to 1000 km southward). Both of the systems have a morphology markedly different to the classical sinuous, V-shaped channels located at similar latitudes (e.g. the Zaire or Amazon channels). Their submarine drainage system consists of a downslope converging tributary canyons joining a central trunk channel in the continental rise. The presence of such giant deep-sea drainage systems is probably linked to a strong structural control on the sediment pathway, associated to a massive sediment transfer towards the Indian Ocean in relation with the tectonic activity of the East African Rift System (i.e. the uplift periods trough mid-Miocene and Plio-Pleistocene times) and its interplay with the East African equatorial climate changes.
Marine Geology (0025-3227) (Elsevier), 2008-12 , Vol. 255 , N. 3-4 , P. 179-185

Droits : 2008 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00324/43491/42958.pdf
DOI:10.1016/j.margeo.2008.09.002
http://archimer.ifremer.fr/doc/00324/43491/

Éditeur(s) : HAL CCSD
Résumé : We present high-resolution bulk sedimentary δ 15N data from the southern edge of the present-day oxygen minimum zone of the eastern South Pacific. The record is interpreted as representing changes in water column nitrogen removal during the last 70,000 years. We found significant fluctuations in the isotopic signal that suggest major reorganizations of the oxygen minimum zone at millennial timescales. These fluctuations were not related to other millennial-scale changes like the Northern Hemisphere's Dansgaard-Oeschger climate swings or local changes in primary productivity, so appear to be dictated by the Southern Hemisphere's climate rhythm. This is preliminarily corroborated by an overall agreement between our δ 15N data and the sedimentary proxy of ice sheet dynamics in Patagonia, which is in turn correlated with surface water properties at the midlatitude subduction region of the eastern South Pacific intermediate waters. Finally, potential implications on late Quaternary changes in atmospheric CO2 concentrations are discussed.
Paleoceanography / PALEOECEANOGRAPHY

hal-00407260
https://hal.archives-ouvertes.fr/hal-00407260
DOI : 10.1029/2006PA001308

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Understanding long-term variability in the frequency of intense storm activity is important for assessing whether changes are controlled by climate evolution. Understanding this variability is also important for predicting present and future community vulnerability and economic loss. Our ability to make these assessments has been limited by the short (less than 50 years) instrument record of storm activity. Storm-induced deposits preserved in the sediments of coastal lagoons offer the opportunity to study the links between climatic conditions and storm activity on longer timescales. In this study, we present a record of these extreme climatic events that have occurred in the French Mediterrannean coast over the past 1500 years. The identification of these extreme events is based on the analysis of sediment cores from Gulf of Aigues-Mortes lagoons that contain a specific sedimentary and geochemical signature associated with intense storms.;Overwash deposits do not show any evidence of intense storm landfalls in the region for several hundred years prior to the late 17th century A.D. The apparent increase in intense storms around 250 years ago occurs during the latter half of the Little Ice Age, a time of lower continental surface temperatures. Comparison of the sediment record with palaeoclimate records indicates that this variability was probably modulated by atmospheric dynamics. The apparent increase of the superstorm activity during the latter half of the Little Ice Age was probably due to the thermal gradient increase leading to enhanced lower tropospheric baroclinicity over a large Central Atlantic/European domain and leading to a modification of the occurrence of extreme wind events along the French Mediterranean coast. A complete understanding of the relationship between climate fluctuations, storm activity, and the coastal response will be crucial to predicting the impacts of future climate change.
ISSN: 0031-0182

hal-00617525
https://hal.archives-ouvertes.fr/hal-00617525
DOI : 10.1016/j.palaeo.2010.11.009

Éditeur(s) : HAL CCSD Inter-Research
Résumé : International audience
The effects of global change are particularly serious in areas where range shiftsof species are physically constrained such as the Ligurian Sea, which is one ofthe coldest sectors of the Mediterranean. In this basin, historical informationon water temperature (from the sea surface down to 75 m depth) dates backto the 1950s. Early studies also recorded warm-water species occurrence.Thanks to these data we provide the first detailed characterization of watertemperature variation from 1958 up to 2010 in the layer 0–75 m depth. Wecoupled this analysis with the available information on rocky reef epibenthiccommunities (literature review from 1955 to 1964 and field data from 1980 to2010). The analysis of water temperature revealed several patterns of variation:a cooling phase from 1958 to 1980, a phase of rapid warming from 1980 to1990 and a phase of slower warming from 1990 to 2010. Inter-annual variationin temperature increased over the entire period for the water layer down to20 m. Warm-water native and alien species richness increased during thewarming phases. Literature estimates suggest a decrease in warm-water nativespecies richness during the cooling phase. The analysis of quantitative data collectedin the early 1990s and late 2000s indicated a decrease in the cover ofwarm-water native species on shallow rocky reefs and an increase in deeperwaters. We argue that increased inter-annual variation in water temperaturemay disadvantage native warm-water species in shallow waters. Our resultsindicate that the effect of temperature rises in cold, constrained basins may bemore complex than the simple prediction of species changing their geographicalrange according to their thermal limits.
Marine Ecology Progress Series

hal-01239259
https://hal-univ-perp.archives-ouvertes.fr/hal-01239259
DOI : 10.1111/maec.12277

Éditeur(s) : HAL CCSD BioMed Central
Résumé : International audience
ABSTRACT: BACKGROUND: Climate change poses unprecedented challenges, ranging from global and local policy challenges to personal and social action. Heat-related deaths are largely preventable, but interventions for the most vulnerable populations need improvement. Therefore, the prior identification of high risk areas at the community level is required to better inform planning and prevention. We aimed to demonstrate a simple and flexible conceptual framework relying upon satellite thermal data and other digital data with the goal of easily reproducing this framework in a variety of urban configurations. RESULTS: The study area encompasses Rennes, a medium-sized French city. A Landsat ETM + image (60 m resolution) acquired during a localized heatwave (June 2001) was used to estimate land surface temperature (LST) and derive a hazard index. A land-use regression model was performed to predict the LST. Vulnerability was assessed through census data describing four dimensions (socio-economic status, extreme age, population density and building obsolescence). Then, hazard and vulnerability indices were combined to deliver a heatwave health risk index. The LST patterns were quite heterogeneous, reflecting the land cover mosaic inside the city boundary, with hotspots of elevated temperature mainly observed in the city center. A spatial error regression model was highly predictive of the spatial variation in the LST (R2 = 0.87) and was parsimonious. Three land cover descriptors (NDVI, vegetation and water fractions) were negatively linked with the LST. A sensitivity analysis (based on an image acquired on July 2000) yielded similar results. Southern areas exhibited the most vulnerability, although some pockets of higher vulnerability were observed northeast and west of the city. The heatwave health risk map showed evidence of infra-city spatial clustering, with the highest risks observed in a north--south central band. Another sensitivity analysis gave a very high correlation between 2000 and 2001 risk indices (r = 0.98, p < 10-12). CONCLUSIONS: Building on previous work, we developed a reproducible method that can provide guidance for local planners in developing more efficient climate impact adaptations. We recommend, however, using the health risk index together with hazard and vulnerability indices to implement tailored programs because exposure to heat and vulnerability do not require the same prevention strategies.
ISSN: 1476-072X

inserm-00762303
http://www.hal.inserm.fr/inserm-00762303
http://www.hal.inserm.fr/inserm-00762303/document
http://www.hal.inserm.fr/inserm-00762303/file/1476-072X-11-38.pdf
DOI : 10.1186/1476-072X-11-38

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Coarse woody debris (CWD, dead wood sections a parts per thousand yen10 cm diameter) represents a large store of carbon in tropical forests; however, estimates of the flux of carbon from CWD in these forests remain poorly constrained. The objective of this study was to resolve the dry/wet season response of respiration in CWD (R (cwd)), and investigate the importance of biotic and abiotic factors for predicting the seasonal change of R (cwd) at the ecosystem level. This study presents a 4-month time series of R (cwd) measurements conducted on 42 dead trees (26 species) at the Paracou Research Station in French Guiana. R (cwd) measurements were repeated 13 times on each CWD sample from July to November 2011, spanning the transition from wet to dry season, and then from dry season to the following wet season. Seasonal drought caused monthly R (cwd) to drop by 20.5 +/- A 5.1% over the wet-dry transition. Changes in woody tissue moisture content explained 41.9% of the measured seasonal variability in R (cwd), but 60% of the seasonal variability in mean forest R (cwd) rates could be modelled using surface soil water content. We estimate that R (cwd) is approximately 5% of annual ecosystem respiration (R (eco)) and that seasonal variations in R (cwd) contribute appreciably to seasonal variations of R (eco), and should be included in functional models simulating the response of tropical rainforest ecosystems to current and future climate.
ISSN: 1432-9840

hal-01032431
https://hal.archives-ouvertes.fr/hal-01032431
DOI : 10.1007/s10021-013-9684-x

Éditeur(s) : HAL CCSD Wiley
Résumé : Tropical forests contain an important proportion of the carbon stored in terrestrial vegetation, but estimated aboveground biomass (AGB) in tropical forests varies two-fold, with little consensus on the relative importance of climate, soil and forest structure in explaining spatial patterns. Here, we present analyses from a plot network designed to examine differences among contrasting forest habitats (terra firme, seasonally flooded, and white-sand forests) that span the gradient of climate and soil conditions of the Amazon basin. We installed 0.5-ha plots in 74 sites representing the three lowland forest habitats in both Loreto, Peru and French Guiana, and we integrated data describing climate, soil physical and chemical characteristics and stand variables, including local measures of wood specific gravity (WSG). We use a hierarchical model to separate the contributions of stand variables from climate and soil variables in explaining spatial variation in AGB. AGB differed among both habitats and regions, varying from 78 Mg ha−1 in white-sand forest in Peru to 605 Mg ha−1 in terra firme clay forest of French Guiana. Stand variables including tree size and basal area, and to a lesser extent WSG, were strong predictors of spatial variation in AGB. In contrast, soil and climate variables explained little overall variation in AGB, though they did co-vary to a limited extent with stand parameters that explained AGB. Our results suggest that positive feedbacks in forest structure and turnover control AGB in Amazonian forests, with richer soils (Peruvian terra firme and all seasonally flooded habitats) supporting smaller trees with lower wood density and moderate soils (French Guianan terra firme) supporting many larger trees with high wood density. The weak direct relationships we observed between soil and climate variables and AGB suggest that the most appropriate approaches to landscape scale modeling of AGB in the Amazon would be based on remote sensing methods to map stand structure.
ISSN: 1354-1013

hal-01374829
https://hal.archives-ouvertes.fr/hal-01374829
DOI : 10.1111/j.1365-2486.2011.02432.x
PRODINRA : 183370

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : Le bassin du fleuve Sixaola est un bassin transfrontalier partagé entre le Costa Rica et le Panama. Localisé sur la façade caraïbe de l’isthme centraméricain, il est depuis une vingtaine d’années considérées par les organismes de coopération et les organisations non gouvernementales comme un espace privilégié pour la coopération en matière environnementale. Ce bassin concentre en effet d’importantes richesses naturelles et culturelles propres à cette façade caraïbe. Dans le même temps, on y constate une importante vulnérabilité sociale et des dégradations environnementales croissantes, d’autant plus qu’on trouve autour de ce bassin des activités productives polluantes (monocultures, tourisme, etc.), ainsi que les villages les plus pauvres des deux pays.Cet article cherche à analyser comment, à côté des mécanismes d’intégration et des initiatives appuyées par les États, cet espace connaît aussi de nombreux projets et programmes de coopération menés par des organismes internationaux et des organisations non gouvernementales (ONG). Ces projets visent principalement à accroître la coopération transfrontalière pour la conservation et la gestion environnementale.En revanche, leur rôle est de plus en plus remis en cause par des acteurs locaux qui affirment que ces organismes « transnationaux » déplacent les États et imposent des projets qui ne prennent pas en compte les réalités et les besoins locaux tout en développant des discours « hégémoniques » sur la gestion intégrée des bassins transfrontaliers, le changement climatique, entre autres.
The Sixaola River basin is shared by Costa Rica and Panama. On the Caribbean side of the Central American Isthmus, it has been considered by cooperation organisms and non-governmental organizations as a privileged space for environmental cooperation for the past 20 years. This basin in fact concentrates an important amount of natural and cultural heritage that is endemic to this side of the Caribbean. At the same time, one can observe increasing social vulnerability and environmental degradation related to the presence of the poorest communities of both Panama and Costa Rica within the basin, and to polluting activities (monoculture, tourism, etc.) carried out around it.This article analyzes how this space is the locus of State integration mechanisms and other initiatives, at the same time that it harbors international organism and non-governmental cooperation programs. These latter projects claim to increase trans-border cooperation for conservation and environmental management.But their role is increasingly being contested by local stakeholders, who more and more claim that these “transnational” organisms displace States and impose projects that do not take into account local realities and needs, while developing “hegemonic” discourses on integrated management of trans-border basins and climate change, among other issues.
Amérique centrale
Costa Rica
Panama

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.5747
http://journals.openedition.org/etudescaribeennes/5747

Éditeur(s) : HAL CCSD Springer Verlag (Germany)
Résumé : International audience
Mass bleaching events resulting in coral mortality are among the greatest threats to coral reefs, and are projected to increase in frequency and intensity with global warming. Achieving a better understanding of the consistency of the response of coral assemblages to thermal stress, both spatially and temporally, is essential to determine which reefs are more able to tolerate climate change. We compared variations in spatial and taxonomic patterns between two bleaching events at the scale of an island (Moorea Island, French Polynesia). Despite similar thermal stress and light conditions, bleaching intensity was significantly lower in 2007 (approximately 37 % of colonies showed signs of bleaching) than in 2002, when 55 % of the colonies bleached. Variations in the spatial patterns of bleaching intensity were consistent between the two events. Among nine sampling stations at three locations and three depths, the stations at which the bleaching response was lowest in 2002 were those that showed the lowest levels of bleaching in 2007. The taxonomic patterns of susceptibility to bleaching were also consistent between the two events. These findings have important implications for conservation because they indicate that corals are capable of acclimatization and/or adaptation and that, even at small spatial scales, some areas are consistently more susceptible to bleaching than others.
ISSN: 0167-6369

hal-00905944
https://hal.archives-ouvertes.fr/hal-00905944
DOI : 10.1007/s10661-012-2923-3

Éditeur(s) : HAL CCSD Inter Research
Résumé : International audience
The main objective of the VULSACO (VULnerability of SAndy COasts to climate change and anthropic pressure) project was to investigate present day and potential future vulnerability of sandy coasts at the 2030 horizon, i.e. on a time scale related to climate variability. The method, based on a multidisciplinary approach bringing together geologists, geographers, physicists, social psychologists, engineers and stakeholders, was structured around 4 axes: field data analysis; numerical modelling; analysis of governance and stakeholder perceptions; and development of vulnerability indexes. This approach was designed to investigate vulnerability at a local scale and was applied to 4 contrasting beaches located in France: Sète Lido (Mediterranean Sea), Truc Vert and La Tresson beaches (Atlantic Ocean), and Dewulf (English Channel). The results focus on decadal and multi-annual beach trends at the Truc Vert beach site. There is almost no trend in beach volume at Truc Vert beach, although there is a variation in this parameter on a cycle of 2 to 3 yr, with variations related to wave energy and probably to indexes of climate variability. Numerical modelling identified the sensitivity of beach responses to changes in wave height and direction, especially in terms of subtidal morphology and the potential development of shoreline instability. Together with the observed offshore wave angle at the Biscay Buoy, these model results suggest that a potential change in wave angle due to climate variability could significantly modify the bars' morphology. The combination of data analysis and numerical modelling contributed to the development of vulnerability indexes designed for sandy coasts, which take into account climate-dependant variables such as waves. This allowed the differentiation of the sites in terms of vulnerability to erosion: Sète Lido and Truc Vert beach were the most and least vulnerable sites, respectively. These indexes help in identifying the dominant components of beach vulnerability, and provide potential for the study of how anthropogenic factors affect vulnerability. The study of stakeholder perceptions and decision-making with regard to climate-related risk also highlighted potential anthropogenic effects on beach vulnerability, and identified possible site-specific outcomes.
ISSN: 0936-577X

hal-00843946
https://hal-brgm.archives-ouvertes.fr/hal-00843946
DOI : 10.3354/cr01153

Éditeur(s) : HAL CCSD Wiley
Résumé :  
Drier periods from the late Pleistocene and early Holocene have been hypothesized to have caused the disappearance of various rainforest species over large geographical areas in South America and restricted the extant populations to mesic sites. Subsequent improvement in climatic conditions has been associated with recolonization. Changes in population size associated with these extinction-recolonization events should have affected genetic diversity within species. However, these historical hypotheses and their genetic consequences have rarely been tested in South America. Here, we examine the diversity of the chloroplast and nuclear genomes in a Neotropical rainforest tree species, Vouacapoua americana (Leguminosae, Caesalpinioideae) in French Guiana. The chloroplast diversity was analyzed using a polymerase chain reaction-restriction fragment length polymorphism method (six pairs of primers) in 29 populations distributed over most of French Guiana, and a subset of 17 populations was also analyzed at nine polymorphic microsatellite loci. To determine whether this species has experienced extinction-recolonization, we sampled populations in areas supposedly not or only slightly affected by climatic changes, where the populations would not have experienced frequent extinction, and in areas that appear to have been recently recolonized. In the putatively recolonized areas, we found patches of several thousands of hectares homogeneous for chloroplast variation that can be interpreted as the effect of recolonization processes from several geographical origins. In addition, we observed that, for both chloroplast and nuclear genomes, the populations in newly recolonized areas exhibited a significantly smaller allelic richness than others. Controlling for geographic distance, we also detected a significant correlation between chloroplast and nuclear population differentiation. This result indicates a cytonuclear disequilibrium that can be interpreted as a historical signal of a genetic divergence between fragmented populations. In conclusion, the spatial genetic structure of contemporary V. americana populations shows evidence that this species has experienced large extinction-recolonization events, which were possibly caused by past climatic change.
ISSN: 0014-3820

hal-01032194
https://hal.archives-ouvertes.fr/hal-01032194
DOI : 10.1111/j.0014-3820.2003.tb01517.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : Iron content of the bulk marine sediment from the Chilean continental margin has been used to infer millenial-scale climate changes in southeast Pacific [Lamy, F., Klump, J., Hebbeln, D., Wefer, G., 2000. Rapid climate change in northern Chile over the last 80 ka recorded in a marine sediment core. Terra Nova 12: 8–13]. Changes of iron contents have been related to a varying contribution of Andean (Fe-rich) versus Coastal Range (Fe-poor) source rocks ultimately controlled by continental rainfall changes. However, variations observed could also be produced by changes in the proportions of two components in the sediment — a detrital component with low and constant Fe content and an authigenic phase (Fe oxide, pyrite, apatite, etc.) with high Fe content. A sequential extraction has been used to partition the total iron content in the sediment of core GeoB 7101 at the continental margin of Chile. The extraction steps included five fractions: exchangeable, bound to carbonates, bound to Fe–Mn oxides, bound to organic matter, and residual. Iron appeared to be mainly present in the residual fraction, i.e. in the detrital component. Our study indicates that total Fe or Fe/Al may be used to infer millenial-scales climate changes in the southeastern Pacific.
ISSN: 0025-3227

hal-00407253
https://hal.archives-ouvertes.fr/hal-00407253
DOI : 10.1016/j.margeo.2007.03.006

Éditeur(s) : Wiley-blackwell
Résumé : The reef fauna connectivity of the West Indian Ocean (WIO) is one of the least studied globally. Here we use genetic analyses of the grouper Epinephelus merra (Bloch 1793) to determine patterns of connectivity and to identify barriers to dispersal in this WIO marine area. Phylogeographic and population-level analyses were conducted on cytochrome b sequences and microsatellites (13 loci) from 557 individuals sampled in 15 localities distributed across the West Indian Ocean. Additional samples from the Pacific Ocean were used to benchmark the WIO population structure. The high level of divergence revealed between Indian and Pacific localities (of about 4.5% in sequences) might be the signature of the major tectonic and climatic changes operating at the Plio-Pleistocene transition, congruently with numerous examples of Indo-Pacific speciation. In comparison, the E. merra sequences from the Indian Ocean constitute a monophyletic clade with a low average genetic distance (d < 0.5%). However both genetic markers indicated some structure within this ocean. The main structure revealed was the isolation of the Maldives from the WIO localities (a different group signature identified by clustering analysis, great values of differentiation). Both marker types reveal further significant structure within the WIO, mainly the isolation of the Mascarene Islands (significant AMOVA and isolation-by-distance patterns) and some patchy structure between the northernmost localities and within the Mozambique Channel. The WIO genetic structure of E. merra appeared congruent with main biogeographic boundaries and oceanographic currents.
Marine Ecology-an Evolutionary Perspective (0173-9565) (Wiley-blackwell), 2015-09 , Vol. 36 , N. 3 , P. 447-461

Droits : 2014 Blackwell Verlag GmbH
http://archimer.ifremer.fr/doc/00189/30046/28566.pdf
DOI:10.1111/maec.12153
http://archimer.ifremer.fr/doc/00189/30046/

Éditeur(s) : Université des Antilles Études caribéennes
Résumé : Au cours des vingt dernières années, l'industrie des croisières au Mexique a apporté des changements importants qui découlent des tendances mondiales actuelles, d'un meilleur positionnement sur le marché, pour l'adoption généralisée de politiques nationales de promotion du tourisme croisière et pour la réforme radicale du système portuaire national qui a permis l'entrée de la participation privée dans les investissements des infrastructures, de gestion et d'exploitation des ports. Dans ce contexte, on a redéfini l´organisation spatiale du tourisme de croisière avec de nouveaux ports d´arrivée, des itinéraires variés à partir de différents ports d´origine et d’escales plaçant le Mexique en tête des destinations mondiales de l’industrie des croisières. Ainsi, l'objectif de cet article est d'examiner les conditions qui ont conduit à la dynamique spatio-temporelle du tourisme de croisière dans le pays à travers un examen critique de la nouvelle géographie régionale du tourisme de croisière au Mexique.
The cruise industry in Mexico has had significant changes stemming from current global trends during the last two decades. This has been due to its favorable and strategic geographical position in the market, its warm climate and proximity to the United States. Hence there has been a major relevance towards adopting national tourism policies as well as reforming the national port system allowing the entrance of private investment infrastructure, cruise terminal management and operation. The spatial organization of cruise tourism destination ports in Mexico has been redefined in this context. That is to say, there are new home ports, new routes and ports of call that have placed the country as a world’s leading destination for cruise ship arrivals. Therefore, the aim of this paper is to examine the conditions which have led the spatio-temporal dynamics into a critical review of the new regional geography of cruise tourism in Mexico.
En las dos últimas décadas el sector de los cruceros turísticos en México ha presentado profundos cambios, derivados de las tendencias globales, de un mayor aprovechamiento de su favorable condición geográfica dentro del mercado, por una mayor incorporación de la actividad en las políticas turísticas nacionales y por la profunda reforma del sistema portuario nacional que posibilitó el ingreso de la participación privada en la inversión de infraestructura, gestión y operación de terminales de cruceros. En este contexto se ha redefinido la organización espacial del turismo de cruceros con nuevas rutas que articulan diferentes puertos de origen y escalas que han posicionado a México como destino líder mundial en arribo de cruceros. De esta forma, el objetivo del presente artículo es examinar las condiciones que han propiciado la dinámica espacio-temporal del turismo de cruceros en el país, que conduzca a una revisión crítica de la nueva geografía regional de los cruceros turísticos en México.
Mexique

Droits : info:eu-repo/semantics/openAccess
urn:doi:10.4000/etudescaribeennes.5077
http://journals.openedition.org/etudescaribeennes/5077