Crustal structure of Guadeloupe Islands and the Lesser Antilles Arc from a new gravity and magnetic synthesis Auteur(s) : Gailler, Lydie Bouchot, Vincent Martelet, Guillaume Thinon, Isabelle Lebrun, Jean-Frédéric Münch, Philippe Auteurs secondaires : Bureau de Recherches Géologiques et Minières (BRGM) (BRGM) Laboratoire de Recherche en Géosciences et Énergies (LaRGE) ; Université des Antilles et de la Guyane (UAG) Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) Éditeur(s) : HAL CCSD Résumé : Guadeloupe Island (West French Indies) is one of the twenty islands that compose the Lesser Antilles Arc, which results from the subduction of the Atlantic Ocean plate beneath the Caribbean one. The island lies in a complex volcano-tectonic system and the need to understand its geological context has led to numerous on- and offshore geophysical investigations. This work presents the compilation and processing of available, on-land, airborne and marine, gravity and magnetic data acquired during the last 40 years on Guadeloupe Islands and at the scale of the Lesser Antilles Arc. The overall dataset provides new Bouguer and reduced to the pole magnetic anomaly maps at the highest achievable resolution. Regionally, the main central negative gravity trend of the arc allows defining two subsident areas. The first one is parallel to the arc direction (~N160°E) to the north, whereas the second unexpected southern one is oriented parallel to oceanic ridges (N130°E). Along the Outer Arc, the long wavelength positive anomaly is interpreted, at least along the Karukera Spur, as an up-rise of the volcanic basement in agreement with the seismic studies. To the NE of Guadeloupe, the detailed analysis of the geophysical anomalies outlines a series of structural discontinuities consistent with the main bathymetric morphologies, and in continuity of the main fault systems already reported in this area. Based on geophysical evidences, this large scale deformation and faulting of the Outer Arc presumably primarily affects the Atlantic subducting plate and secondarily deforms the upper Caribbean plate and the accretion prism. At the scale of Guadeloupe Island, joined gravity and magnetic modeling has been initiated based on existing interpretation of old seismic refraction profiles, with a general structure in three main layers. According to our geophysical anomalies, additional local structures are also modeled in agreement with geological observations: i) the gravity and magnetic signals confirm an up-rise of the volcanic basement below the limestone platforms outcropping on Grande-Terre Island ; ii) the ancient volcanic complexes of Basse-Terre Island are modeled with high density and reverse magnetized formations; iii) the recent volcanic centre is associated with formations consistent with the low measured density and the underlying hydrothermal system. The EW models coherently image a NNW-SSE depression structure in half-graben beneath Basse-Terre Island, its western scarp following the arc direction in agreement with bathymetric and seismic studies to the north of the island. The so-defined depressed area, and particularly its opening in half-graben toward the SW, is interpreted as the present-day front of deformation of the upper plate associated with the recent volcanic activity on and around Guadeloupe. Based on this regional deformation model, perspectives are given for further integrated investigation of key targets to address the internal structure and evolution of the Lesser Antilles Arc and Guadeloupe volcanic system. Colloque 2012 du Comité National Français de Géodésie et Géophysique (CNFGG) Clermont-Ferrand, France hal-00742653 https://hal-brgm.archives-ouvertes.fr/hal-00742653 https://hal-brgm.archives-ouvertes.fr/hal-00742653/document https://hal-brgm.archives-ouvertes.fr/hal-00742653/file/CNFGG_Caraibes.pdf | Partager |
A new starting point for the South and Equatorial Atlantic Ocean Auteur(s) : Moulin, Maryline Aslanian, Daniel Unternehr, Patrick Éditeur(s) : Elsevier Science Bv Résumé : The opening of the Equatorial and South Atlantic Oceans is still a matter of debate, particularly as concerns the locations of the intraplate deformation. We propose here a critical review of the kinematic models published since Bullard et al., 1965, based on a series of constraints: new interpretation of the magnetic anomalies, seafloor isochrons, flow lines, fracture zones, continental and oceanic homologous structures and radiometric dating of igneous rocks. All of these models present numerous unexplained misfits (gaps, overlaps and misalignments). We present here a new evolution of the Equatorial and South Atlantic Ocean from the tightest reconstruction to Chron C34. This new model confirms the hypothesis of a northward propagation of the South American deformation proposed by Eagles, but rejuvenates slightly the ages for this propagation and refines the plate reconstructions. In particular, we highlight the role of the kinematic "buffer" Santos block, located between the salty Aptian Central segment in the North and the Volcanic Hauterivian Austral segment in the South. The new initial fit presented in this study represents the tightest reconstruction that could be obtained and constitutes the base canvas on which the problem of the continental margin genesis should be addressed. Earth Science Reviews (0012-8252) (Elsevier Science Bv), 2010 , Vol. 98 , N. 1-2 , P. 1-37 Droits : 2010 Elsevier B.V. All rights reserved. http://archimer.ifremer.fr/doc/00000/11160/7883.pdf DOI:10.1016/j.earscirev.2009.08.001 http://archimer.ifremer.fr/doc/00000/11160/ | Partager |
Mesoscale variability from a high-resolution model and from altimeter data in the North Atlantic Ocean Auteur(s) : Brachet, Sidonie Le Traon, Pierre-yves Le Provost, Christine Éditeur(s) : Amer Geophysical Union Résumé : The objective of the paper is to analyze the degree of realism of the Parallel Ocean Program ( POP) model of the Los Alamos Laboratory using the combined TOPEX/Poseidon and ERS-1/2 (TPERS) sea level anomaly (SLA) data sets and to present a detailed study of mesoscale characteristics in the North Atlantic. This description spans 8 years of data from 1993 to 2000. At first, we focus on the analysis of the mean eddy kinetic energy ( EKE) and show that the major characteristics of mesoscale variability are realistically simulated despite an overestimation of the EKE model in the Gulf Stream region. We then describe the SLA space and timescales and propagation velocities at a resolution never achieved before. There is a high level of agreement between the model and altimeter values regarding spatial scales and propagation velocities. POP timescales are, however, significantly longer in the subtropical regions. The westward zonal propagation velocity of both the model and the observations are higher than the speed computed from standard Rossby wave theory. The effect of mean current advection on POP and TPERS propagation velocities is also clearly seen in the Labrador Current and in the Gulf Stream and its recirculations. Finally, a study of the seasonal and interannual variability of the high-frequency (HF) EKE is carried out. The model reproduces accurately most of the HF-EKE seasonal variations in the Caribbean Sea and at high latitudes despite a phase advance. A clear HF-EKE interannual variability is then evidenced. Our hypothesis is that a contraction of the subpolar and subtropical gyres due to the North Atlantic Oscillation (NAO) could explain a reduction of the eddy activity in the North Atlantic Current, in the Newfoundland basin, and in the Azores Current. In the Caribbean Sea, the interannual variability of the EKE for both POP and TPERS seems to be caused by an interannual variability of the wind stress. Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2004-12 , Vol. 109 , N. C1205 , P. 16 PP. Droits : 2004 AGU http://archimer.ifremer.fr/doc/00087/19841/17491.pdf DOI:10.1029/2004JC002360 http://archimer.ifremer.fr/doc/00087/19841/ | Partager |
Variabilité de la salinité de surface d'après un modèle global de couche mélangée océanique Auteur(s) : Michel, Sylvain Éditeur(s) : Université Paris 7 Denis Diderot Résumé : Sea surface salinity (SSS) influences numerous oceanic phenomena, for instance surface water ventilation, deep water formation and thermohaline circulation. SSS also controls some ocean-atmosphere coupled processes, such as the intensity of freshwater flux and the penetration of heat flux and turbulence. Salinity is more difficult to measure than temperature from in situ surveys, which results in 20 times less data being currently available. Moreover, sea surface temperature (SST) is routinely estimated from satellites, which is not possible yet for SSS. Two space missions will fill this gap soon: SMOS from the European Space Agency and Aquarius/SAC-D from NASA and CONAE. To contribute to the SMOS project, we propose a method for estimating SSS from current satellite observations and for studying the mechanisms governing its variability. We developed a simplified model of the ocean mixed layer, based on the "slab mixed layer" formulation (Frankignoul et Hasselmann, 1977). This 2D horizontal model is implemented over the global ocean, using a near 100 km resolution, and integrated during a climatological year. Air-sea fluxes are taken from the ECMWF meteorological model (ERA40 reanalysis) and the surface currents are provided by altimeter data (SSALTO-DUACS analysis). The mixed layer depth (MLD) is derived from SST observations, using an original inversion technique. The MLD fields obtained from this inversion are well correlated to in situ estimates. This effective depth represents the air-sea fluxes penetration and ensures consistency between fluxes, les currents and SST. We first validate the simulation through examination of the heat balance in north-eastern Atlantic, by comparing to measurements and models from the POMME experiment. Then we study the salinity balance in the global domain, in terms of its geographical distribution and seasonal evolution. Equilibrium between the various processes appears generally more complex than for temperature. Noteworthy, the role of atmospheric flux is less predominant (22%), while geostrophic advection (33%) and diapycnal mixing (22%) contribute more strongly. Our results indicate this model succeeds in reconstructing SSS variability over most of the oceans. Daily SSS variations are also simulated, whereas they are not represented in current observed data at a global scale. Owing to its simplicity and fast computation, the model will be useful to the SMOS mission. It can help for the measurement calibration/validation and provide a first guess estimate to the sophisticated algorithm required for SSS restitution. La salinité de surface des océans (SSS) influence de nombreux phénomènes océaniques, parmi lesquels la ventilation des eaux de surface, la formation d'eaux profondes et la circulation thermohaline. Elle détermine aussi certains processus couplés océan-atmosphère, notamment l'intensité du flux d'eau douce, la pénétration du flux de chaleur et de la turbulence. La mesure in situ de salinité est plus compliquée que celle de température, si bien qu'on dispose actuellement de 20 fois moins de données pour cette propriété. De plus, la température de surface (SST) est couramment estimée par satellite, ce qui n'est pas encore le cas de la SSS. Deux missions spatiales vont prochainement combler cette lacune : le satellite SMOS de l'Agence Spatiale Européenne et le satellite Aquarius/SAC-D de la NASA et de la CONAE. En préparation du projet SMOS, nous proposons une méthode pour estimer la SSS à partir des observations satellitaires actuelles et étudier les mécanismes de sa variabilité. Nous avons développé un modèle simplifié de couche mélangée océanique, basé sur la formulation "slab mixed layer" (Frankignoul et Hasselmann, 1977). Ce modèle 2D horizontal est implémenté sur l'océan global, avec une résolution proche de 100 km, et intégré au cours d'une année climatologique. Les flux air-mer proviennent du modèle météorologique ECMWF (réanalyse ERA40) et les courants de surface sont issus de l'altimétrie (analyse SSALTO-DUACS). La profondeur de la couche mélangée (MLD) est dérivée des observations de SST, grâce à une technique d'inversion originale. La MLD obtenue par inversion est bien corrélée aux estimations basées sur des données in situ. Cette profondeur effective représente la pénétration des flux air-mer et assure la cohérence entre les flux, les courants et la SST. La simulation est d'abord validée en examinant le bilan de chaleur dans l'Atlantique Nord-Est, par comparaison aux mesures et aux modèles de l'expérience POMME. Puis le bilan de salinité est étudié dans le domaine global, en termes de distribution géographique et d'évolution saisonnière. L'équilibre entre les différents processus est généralement plus complexe que pour la température. Notamment, le rôle du flux atmosphérique est moins prépondérant (22%), tandis que l'advection géostrophique (33%) et le mélange diapycnal (22%) contribuent fortement. Nos résultats montrent que ce modèle parvient à restituer la variabilité de la SSS sur la majeure partie des océans. Le modèle simule aussi les variations journalières de SSS, qui ne sont pas représentées à l'échelle globale dans les observations actuelles. Grâce à sa simplicité et à sa rapidité, le modèle pourra être utile dans le cadre de SMOS. Il pourra aider à la calibration/validation de la mesure et fournir une estimation a priori pour l'algorithme complexe nécessaire à la restitution de la SSS. Droits : info:eu-repo/semantics/openAccess http://archimer.ifremer.fr/doc/2006/these-2302.pdf http://archimer.ifremer.fr/doc/00000/2302/ | Partager Voir aussi SMOS SSS SST MLD heat balance Vertical entrainment Geostrophic current Air sea fluxes Satellite observations Mixed layer Télécharger |
Deux nouveaux isopodes abyssaux de l'atlantique nord appartenant au genre Janirella BONNIER, 1885 Auteur(s) : Chardy, Pierre Éditeur(s) : E.J. BRILL Leiden. Résumé : Genus Janirella Bonnier, 1885, has numerous members in the North Atlantic Ocean (J. nanseni Bonnier, 1885; J. abyssicola Richardson, 1911; J. glabra Richardson, 1911; J. spongicola Hansen, 1916; J. lobata Richardson, 1908; J. laevis Hansen, 1916; J. vemae Menzies, 1962; J. priseri Chardy, 1972) as well as in the adjoining seas (J. bonnieri Stephensen, 1915 in the Mediterranean Sea and J. carribica Menzies, 1956 in the Caribbean Sea). Two new species have been added to this list, J. bocqueti sp. n. and J. laubieri sp. n., collected during the Noratlante cruise of the R.S. "Jean Charcot". Le genre Janirella Bonnier, 1885, compte de nombreux représentants en Atlantique Nord (J. nanseni Bonnier, 1885 ; J. abyssicola Richardson, 1911 ; J. glabra Richardson, 1911 ; J. spongicola Hansen, 1916 ; J. lobata Richardson, 1908 ; J. laevis Hansen, 1916 ; J. vemae Menzies, 1962 ; J. priseri Chardy, 1972) ainsi que dans les mers adjacentes (J. bonnieri Stephensen, 1915 en Méditerranée et J. carribica Menzies, 1956 en mer des Caraïbes). A cette liste viennent s'ajouter deux espèces nouvelles, J. bocqueti sp. n. et J. laubieri sp. n., récoltées au cours de la campagne Noratlante du N.O. ,,Jean Charcot". [OCR NON CONTRÔLE] Crustaceana (E.J. BRILL Leiden.), 1974 , Vol. 26 , N. 2 , P. 129-135 Droits : E.J. BRILL Leiden. http://archimer.ifremer.fr/doc/1974/publication-5118.pdf http://archimer.ifremer.fr/doc/00000/5118/ | Partager |
L'ichthyofaune des écosystèmes associés à l'hydrothermalisme océanique : état des connaissances et résultats nouveaux Auteur(s) : Geistdoerfer, P Éditeur(s) : Gauthier-Villars Résumé : Seven new fish species have been found so far on the Pacific and Atlantic hydrothermal vents: the synaphobranchid Thermobiotes mytilogeiton; the zoarcid Thermarces cerberus and Pachycara thermophilum; the bythitid Bythites hollisi; the cyclopterid Careproctus hyaleius; one zoarcid fish; and one ophidiid fish. The characteristics of the 70 specimens collected, and their location in French and American museums, are listed. The results and observations made on vent fishes and fishes living around the periphery of the vents observed during recent dives (especially along the East Pacific Rise between 17 and 19 degrees S, the North Fiji Basin Rise and the Mid Atlantic Rise) are summarized. Previous literature on vent fishes is reviewed. Oceanologica Acta (0399-1784) (Gauthier-Villars), 1996 , Vol. 19 , N. 5 , P. 539-548 Droits : info:eu-repo/semantics/openAccess http://archimer.ifremer.fr/doc/00096/20724/18361.pdf http://archimer.ifremer.fr/doc/00096/20724/ | Partager |
A Lagrangian numerical investigation of the origins and fates of the salinity maximum water in the Atlantic - art. no. 3163 Auteur(s) : Blanke, Bruno Arhan, Michel Lazar, A Prevost, Gwenaelle Éditeur(s) : American Geophysical Union Résumé : The origins and fates of the Atlantic salinity maximum water (SMW), formed through excess evaporation in the tropics and subtropics of both hemispheres, are studied using monthly mean outputs of a numerical simulation of the world ocean climatological circulation. After defining formation domains from the surface salinity field and the vertical stratification, a Lagrangian technique is used to estimate the formation rates and main pathways in each hemisphere and the role of this water in the framework of the warm water return flow of the meridional overturning cell. Formation rates around 9 and 11 Sv are found in the Southern and Northern Hemispheres, respectively. While the export of the southern SMW from its formation area is realized by the western boundary currents, that of the northern SMW mainly results from interior subduction. Equatorward of the formation regions, a fraction of each SMW variety is entrained in the subtropical cells that connect the subtropics to the equatorial region. Poleward of them, both varieties are seen to feed the regions of subtropical mode water (STMW) formation around 35degrees of latitude in both hemispheres. The bulk of the transport associated with each variety eventually turns northward: This amounts to similar to6 Sv of southern SMW gathered in the North Brazil Undercurrent (NBUC), and similar to10 Sv of northern SMW found in the Gulf Stream at 35degreesN, of which 8 Sv have gone through the Caribbean Sea. Of the 13.4-Sv northward transport of the meridional overturning cell estimated by the model at 47degreesN, more than 50% (6.9 Sv) is found to have transited through at least one of the SMW regions. This gives an indication of the likely important role of SMW formation in the observed northward salinity increase of the upper Atlantic Ocean. Journal of Geophysical Union - Research C - Oceans (0148-0227) (American Geophysical Union), 2002-09 , Vol. 107 , N. C10 , P. NIL_610-NIL_624 Droits : 2002 by the American Geophysical Union http://archimer.ifremer.fr/doc/2002/publication-769.pdf DOI:10.1029/2002JC001318 http://archimer.ifremer.fr/doc/00000/769/ | Partager |
Impact of the winter North-Atlantic weather regimes on subtropical sea-surface height variability Auteur(s) : Barrier, Nicolas Treguier, Anne-marie Cassou, Christophe Deshayes, Julie Éditeur(s) : Springer Résumé : Interannual variability of subtropical sea-surface-height (SSH) anomalies, estimated by satellite and tide-gauge data, is investigated in relation to wintertime daily North-Atlantic weather regimes. Sea-level anomalies can be viewed as proxies for the subtropical gyre intensity because of the intrinsic baroclinic structure of the circulation. Our results show that the strongest correlation between SSH and weather regimes is found with the so-called Atlantic-Ridge (AR) while no significant values are obtained for the other regimes, including those related to the North Atlantic Oscillation (NAO), known as the primary actor of the Atlantic dynamics. Wintertime AR events are characterized by anticyclonic wind anomalies off Europe leading to a northward shift of the climatological wind-stress curl. The latter affects subtropical SSH annual variability by altered Sverdrup balance and ocean Rossby wave dynamics propagating westward from the African coast towards the Caribbean. The use of a simple linear planetary geostrophic model allows to quantify those effects and confirms the primary importance of the winter season to explain the largest part of SSH interannual variability in the Atlantic subtropical gyre. Our results open new perspectives in the comprehension of North-Atlantic Ocean variability emphasizing the role of AR as a driver of interannual variability at least of comparable importance to NAO. Climate Dynamics (0930-7575) (Springer), 2013-09 , Vol. 41 , N. 5-6 , P. 1159-1171 Droits : Springer-Verlag Berlin Heidelberg 2012 http://archimer.ifremer.fr/doc/00161/27248/25480.pdf DOI:10.1007/s00382-012-1578-7 http://archimer.ifremer.fr/doc/00161/27248/ | Partager |
SMOS salinity in the subtropical north Atlantic salinity maximum: 1. Comparison with Aquarius and in situ salinity Auteur(s) : Hernandez, Olga Boutin, Jacqueline Kolodziejczyk, Nicolas Reverdin, Gilles Martin, Nicolas Gaillard, Fabienne Reul, Nicolas Vergely, J. L. Éditeur(s) : Amer Geophysical Union Résumé : Sea surface salinity (SSS) measured from space by the Soil Moisture and Ocean Salinity (SMOS) mission is validated in the subtropical North Atlantic Ocean. 39 transects of ships of opportunity equipped with thermosalinographs (TSG) crossed that region from 2010 to 2012, providing a large database of ground truth SSS. SMOS SSS is also compared to Aquarius SSS. Large seasonal biases remain in SMOS and Aquarius SSS. In order to look at the capability of satellite SSS to monitor spatial variability, especially at scales less than 300 km (not monitored with the Argo network), we first apply a monthly bias correction derived from satellite SSS and In Situ Analysis System (ISAS) SSS differences averaged over the studied region. Ship SSS averaged over 25 km is compared with satellite and ISAS SSS. Similar statistics are obtained for SMOS, Aquarius and ISAS products (root mean square error of about 0.15 and global correlation coefficient r of about 0.92). However, in the above statistics, SSS varies due to both large scale and mesoscale (here, for scales around 100 km) variability. In order to focus on mesoscale variability, we consider SSS anomalies with respect to a monthly climatology. SMOS SSS and Aquarius SSS anomalies are more significantly correlated (r > 0.5) to TSG SSS anomaly than ISAS. We show the effective gain of resolution and coverage provided by the satellite products over the interpolated in situ data. We also show the advantage of SMOS (r=0.57) over Aquarius (r=0.52) to reproduce SSS mesoscale features. Journal Of Geophysical Research-oceans (0148-0027) (Amer Geophysical Union), 2014-12 , Vol. 119 , N. 12 , P. 8878-8896 Droits : 2014. American Geophysical Union. All Rights Reserved. http://archimer.ifremer.fr/doc/00210/32150/34082.pdf DOI:10.1002/2013JC009610 http://archimer.ifremer.fr/doc/00210/32150/ | Partager |
Crustal investigation of Guadeloupe Island and the Lesser Antilles Arc from a new potential field synthesis Auteur(s) : Gailler, Lydie Martelet, Guillaume Thinon, Isabelle Bouchot, Vincent Lebrun, Jean-frederic Munch, Philippe Auteurs secondaires : Bureau de Recherches Géologiques et Minières (BRGM) (BRGM) Université des Antilles et de la Guyane (UAG) Dynamique de la Lithosphere ; Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) - Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) Éditeur(s) : HAL CCSD Société géologique de France Résumé : International audience Guadeloupe island (West French Indies) is one of the twenty islands that compose the Lesser Antilles arc, which results from the subduction of the Atlantic ocean plate beneath the Caribbean one. The island lies in a complex volcano-tectonic system and the need to understand its geological context has led to numerous on- and offshore geophysical investigations. This work presents a compilation and the processing of available, on-land, airborne and marine, gravity and magnetic data acquired during the last 40 years on Guadeloupe islands and at the scale of the Lesser Antilles arc. The overall dataset provides new Bouguer and reduced to the pole magnetic anomaly maps at the highest achievable resolution. Regionally, the main central negative gravity trend of the arc allows defining two subsident areas. The first one is parallel to the arc direction (~N160°E) to the north, whereas the second unexpected southern one is oriented parallel to oceanic ridges (N130°E). Along the Outer arc, the long wavelength positive anomaly is interpreted, at least along the Karukera spur, as an up-rise of the volcanic basement in agreement with the seismic studies. To the NE of Guadeloupe, the detailed analysis of the geophysical anomalies outlines a series of structural discontinuities consistent with the main bathymetric morphologies, and in continuity of the main fault systems already reported in this area. Based on geophysical evidences, this large scale deformation and faulting of the Outer arc presumably primarily affects the Atlantic subducting plate and secondarily deforms the upper Caribbean plate and the accretion prism, as evidenced in bathymetry as well as on the islands. At the scale of Guadeloupe island, combined gravity and magnetic modeling has been initiated based on existing interpretation of old seismic refraction profiles, with a general structure in three main layers. According to our geophysical anomalies, additional local structures are also modeled in agreement with geological observations: i) the gravity and magnetic signals confirm an up-rise of the volcanic basement below the limestone platforms outcropping on Grande-Terre island ; ii) the ancient volcanic complexes of Basse-Terre island are modeled with high density and reverse magnetized formations; iii) the recent volcanic centre is associated with formations consistent with the low measured density and the underlying hydrothermal system. The E-W models coherently image a NNW-SSE depression structure in half-graben beneath Basse-Terre island, its western scarp following the arc direction in agreement with bathymetric and seismic studies to the north of the island. The so-defined depressed area, and particularly its opening in half-graben toward the SW, is interpreted as the present-day front of deformation of the upper plate, associated with the recent volcanic activity on and around Guadeloupe. Based on this regional deformation model, perspectives are given for further integrated investigation of key targets to address the internal structure and evolution of the Lesser Antilles arc and Guadeloupe volcanic system. EISSN: 1777-5817 hal-00853352 https://hal.archives-ouvertes.fr/hal-00853352 DOI : 10.2113/gssgfbull.184.1-2.77 | Partager |
Distribution et taxonomie des Howella (Perciformes, percichthyidae) de l'Atlantique Auteur(s) : Post, A Éditeur(s) : Société Française d'Ichtyologie Résumé : On the basis of geographical distribution and morphological analysis of the Atlantic Howella , two subspecies of H. brodiei have been established, H. brodiei brodiei for the IndoPacific and H. brodiei atlanlica for the tropical and boreal Atlantic. H. sherborni has been recognized as a separate species, probably distributed circumglobally in southern Ocean but presently recorded only from the South Atlantic, the central South Pacific and from off southern and south-eastern Australia respectively. H. b. atlanlica and H. b. brodiei are distinct by having 3 scale rows between the lateral line and the origin of the second dorsal fin, while H. sherborni has 4 scale rows there. H. sherborni is in geographical contact with the two subspecies while H. b. brodiei and H. b. atlantica are geographically isolated from each other. The new subspecies, H. b. atlantica occurs in the North Atlantic and the tropical South Atlantic. Specimens from 75 mm SL and longer, predominantly occur in the boreal areas, while specimens less than that length occur in the tropical areas respectively. A day and night bathymetric distribution and a size-depth stratification have been observed. NOT CONTROLLED OCR L'étude de la distribution et l'analyse des caractères méristiques des Howella de l'Atlantique montre la présence dans les régions tempérées nord et tropicales d'une sous-espèce nouvelle, H. brodiei atlantica, et dans la zone tempérée sud de H. sherborni. H. sherborni, caractérisé par 4 rangées d'écailles entre la ligne latérale et l'origine de la seconde dorsale, est au contact, dans l'Atlantique, de H. b. atlantica et, dans les Océans Indien et Pacifique de H. b. brodiei; ces deux sous-espèces, isolées géographiquement, possèdent 3 rangées d'écailles entre la ligne latérale et l'origine de la seconde dorsale. Les exemplaires d'H. b. atlanlica mesurant 75 mm LS ou plus ont été capturés dans la zone tempérée de l'Atlantique nord et ceux de moins de 75 mm principalement dans l'Atlantique tropical et subtropical nord. Les différences de distribution bathymétrique, le jour et la nuit et selon les tailles, sont étudiées chez H. b. atlanlica et H. sherborni. OCR NON CONTRÔLE Cybium (Société Française d'Ichtyologie), 1991-02 , Vol. 15 , N. 2 , P. 111-128 Droits : 1991 Société Française d'Ichtyologie http://archimer.ifremer.fr/doc/1991/publication-3769.pdf http://archimer.ifremer.fr/doc/00000/3769/ | Partager |
Geology of Northern Borborema Province, NE Brazil and its correlation with Nigeria, NW Africa Auteur(s) : Arthaud, M.H. Caby, Renaud Fuck, R.A. Dantas, L. Parente, C. Auteurs secondaires : Departamento de Geologia, Universidade Federal do Ceará ; Université du Québec Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) Instituto de Geociências, Universidade de Brasilia ; Universidade de Brasilia [Brasília] (UnB) R.J. Pankhurst; R.A.J. Trouw; B.B. de Brto Neves; M.J. de Wit Éditeur(s) : HAL CCSD Geological Society of London Résumé : The Borborema and Benin–Nigeria provinces of NE Brazil and NW Africa, respectively, are key areas in the amalgamation of West Gondwana by continental collision during the Brasiliano/Pan-African orogenies. Both are underlain by complex basement: Nigeria has c. 3.05 Ga Archaean crust but no known Palaeoproterozoic rocks >2.0 Ga; in NE Brazil, 2.6–3.5 Ga Archaean rocks form small cores within Palaeoproterozoic gneiss terrains affected by plutonism at c. 2.17 Ga. Both regions exhibit Late Palaeoproterozoic (c. 1.8 Ga) rift-related magmatism and metasedimentary sequences overlying the basement. The Seridó Group of NE Brazil (<0.65 Ga) is similar to the Igarra Sequence in SW Nigeria. The Ceará Group, which may date back to c. 0.85 Ga, is a passive margin deposit on crust thinned during initiation of an oceanic domain. In both provinces, basement and sedimentary cover were involved in tangential tectonics that resulted in crust-thickening by nappe-stacking associated with closure of this ocean. Frontal collision between c. 0.66 and 0.60 Ga later evolved to an oblique collision, generating north–south continental strike-slip shear zones at c. 0.59 Ga. In NE Brazil, the main Pan-African suture is probably buried beneath the Parnaíba Basin. The Transbrasiliano Lineament, interpreted as the prolongation of the Kandi–4°50 Lineament in Hoggar, may represent a cryptic suture. West Gondwana: Pre-cenozoic correlations across the south atlantic region hal-00412234 https://hal.archives-ouvertes.fr/hal-00412234 DOI : 10.1144/SP294.4 | Partager |
Submersible observations of the invertebrate fauna on the continental-slope southwest of ireland (ne atlantic-ocean) Auteur(s) : Tyler, Pa Zibrowius, H Éditeur(s) : Gauthier-Villars Résumé : Relatively little is known of the fauna found on rock substrates in the deep ocean. As a result of the Franco-British deep diving cruise Cyaporc in 1986 using the submersible Cyana we present observations of a highly diverse sponge, cnidarian and echinoderm fauna occurring between 1 800 and 3 000 m on the steep slopes to the west of the Porcupine Bank and Goban Spur. This fauna is dominated. by suspension feeders and appears to show a vertical zonation corresponding to water mass structure. The highest biomass and variety of echinoderms are found between 2 100 and 2 600 m bathed in northward flowing North East Atlantic Deep Water. We present also additional observations of species known from previous sampling programmes but rarely photographed in their natural environment. Oceanologica Acta (0399-1784) (Gauthier-Villars), 1992 , Vol. 15 , N. 2 , P. 211-226 Droits : info:eu-repo/semantics/openAccess http://archimer.ifremer.fr/doc/00100/21154/18773.pdf http://archimer.ifremer.fr/doc/00100/21154/ | Partager |
Lithosphere-asthenosphere interaction beneath Ireland from joint inversion of teleseismic P-wave delay times and GRACE gravity Auteur(s) : O'Donnell, J. P. Daly, E. Tiberi, Christel Bastow, I. D. O'Reilly, B. M. Readman, P. W. Hauser, F. Auteurs secondaires : Earth and Ocean Sciences, School of Natural Sciences, National University of Ireland, Galway ; Université du Québec Manteau et Interfaces ; Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) - Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) School of Earth Sciences [Bristol] ; University of Bristol [Bristol] Dublin Institute for Advanced Studies, Dublin ; Université du Québec UCD School of Geological Sciences, University College Dublin ; Université du Québec Éditeur(s) : HAL CCSD Oxford University Press (OUP) Résumé : International audience The nature and extent of the regional lithosphere-asthenosphere interaction beneath Ireland and Britain remains unclear. Although it has been established that ancient Caledonian signatures pervade the lithosphere, tertiary structure related to the Iceland plume has been inferred to dominate the asthenosphere. To address this apparent contradiction in the literature, we image the 3-D lithospheric and deeper upper-mantle structure beneath Ireland via non-linear, iterative joint teleseismic-gravity inversion using data from the ISLE (Irish Seismic Lithospheric Experiment), ISUME (Irish Seismic Upper Mantle Experiment) and GRACE (Gravity Recovery and Climate Experiment) experiments. The inversion combines teleseismic relative arrival time residuals with the GRACE long wavelength satellite derived gravity anomaly by assuming a depth-dependent quasilinear velocity-density relationship. We argue that anomalies imaged at lithospheric depths probably reflect compositional contrasts, either due to terrane accretion associated with Iapetus Ocean closure, frozen decompressional melt that was generated by plate stretching during the opening of the north Atlantic Ocean, frozen Iceland plume related magmatic intrusions, or a combination thereof. The continuation of the anomalous structure across the lithosphere-asthenosphere boundary is interpreted as possibly reflecting sub-lithospheric small-scale convection initiated by the lithospheric compositional contrasts. Our hypothesis thus reconciles the disparity which exists between lithospheric and asthenospheric structure beneath this region of the north Atlantic rifted margin. ISSN: 0956-540X hal-00617815 https://hal.archives-ouvertes.fr/hal-00617815 DOI : 10.1111/j.1365-246X.2011.04921.x | Partager Voir aussi Gravity anomalies Earth structure Body waves Seismic tomography Dynamics of lithosphere [SDU.STU.GP] Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph] [PHYS.PHYS.PHYS-GEO-PH] Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph] [SDE.MCG] Environmental Sciences/Global Changes |
Inter-specific and ontogenic differences in delta C-13 and delta N-15 values and Hg and Cd concentrations in cephalopods Auteur(s) : Chouvelon, Tiphaine Spitz, Jerome Cherel, Y. Caurant, Florence Sirmel, R. Mendez-fernandez, P. Bustamante, Paco Éditeur(s) : Inter-research Résumé : Chemical tracers (e. g. stable isotopes or trace metals) are increasingly used to study trophic ecology and feeding habits of marine organisms and various factors can affect their values. The aim of the present study was to provide information on ontogenic effects on stable carbon and nitrogen values (delta C-13 and delta N-15) and on cadmium (Cd) and mercury (Hg) concentrations in 5 cephalopod species from the Bay of Biscay (North-East Atlantic Ocean). To this end, individuals belonging to 3 species showing the widest range of sizes were analysed for muscle delta C-13 and delta N-15 values and muscle Hg, and digestive gland Cd concentrations. Results showed that stable isotope ratios allowed discrimination of specific feeding strategies during ontogenesis. Segregation between 5 cephalopod species in terms of trophic ecology was also evidenced (different isotopic niches). In contrast, Hg concentrations varied over the same order of magnitude in these 5 cephalopod species, despite higher levels in the benthic octopus Eledone cirrhosa. Consistently, Hg concentrations followed the same ontogenic pattern and increased with increasing body size/age of cephalopods. Finally, Cd concentrations varied over 3 orders of magnitude among the 5 species. Despite possible effects of physiology in terms of metal bioaccumulation, Cd concentrations were likely to reflect specific feeding preferences or feeding zones and ontogenic variability within a single species. Thus, ontogenic effects have to be taken into account when stable isotope ratios of carbon and nitrogen or trace metals are used as ecological tracers; the best recommendation being to focus on a given class age. Marine Ecology Progress Series (0171-8630) (Inter-research), 2011 , Vol. 433 , P. 107-120 Droits : Inter-Research 2011 · www.int-res.com http://archimer.ifremer.fr/doc/00166/27761/25938.pdf DOI:10.3354/meps09159 http://archimer.ifremer.fr/doc/00166/27761/ | Partager Voir aussi Stable isotopes Metals Trace elements Ontogenesis Prey Ecological tracer Northeastern Atlantic Télécharger |
Deep circulation in the equatorial Atlantic Ocean Auteur(s) : Gouriou, Y Andrie, C Bourles, B Freudenthal, S Arnault, S Aman, A Eldin, G Du Penhoat, Y Éditeur(s) : Amer Geophysical Union Résumé : In the Atlantic Ocean, the northward export of warm surface water is compensated by a southward flow of cold North Atlantic Deep Water (NADW). The NADW is transported southward along the American continental margin within the Deep Western Boundary Current (DWBC). Some tracer and float observations have shown that part of the DWBC water flows eastward along the equator. Here we present three meridional velocity sections which give an instantaneous image of the top-to-bottom zonal circulation along the equatorial Atlantic. They reveal the presence of Equatorial Deep Jets (EDJs) between 1 degrees 30'N and 1 degrees 30'S, alternating eastward-westward currents with short vertical scale, surrounded by columns of eastward currents (the Extra Equatorial Jets or EEJs) at 2 degreesN and 2 degreesS. In addition to direct velocity measurements, tracer distributions give indications of water-mass feeding of the EDJs and EEJs by the DWBC. Geophysical Research Letters (0094-8276) (Amer Geophysical Union), 2001-03 , Vol. 28 , N. 5 , P. 819-822 Droits : 2001 AGU http://archimer.ifremer.fr/doc/00000/10369/9567.pdf http://archimer.ifremer.fr/doc/00000/10369/ | Partager |
Seismic anisotropy in the eastern United States: Deep structure of a complex continental plate Auteur(s) : Barruol, Guilhem Silver, Paul, Vauchez, A. Auteurs secondaires : Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) Department of Terrestrial Magnetism [Carnegie Institution] ; Carnegie Institution for Science [Washington] Éditeur(s) : HAL CCSD American Geophysical Union Résumé : International audience We have analyzed shear wave splitting recorded by portable and permanent broadband and long-period stations located in the eastern United States. Teleseismic shear waves (SKS, SKKS, and PKS) were used to retrieve the splitting parameters: the orientation of the fast wave polarization plane ϕ and the delay time δt. In total, 120 seismic events were processed, allowing for more than 600 splitting measurements. Within the Appalachians, stations located in the western (external) part are characterized by δt≈1s and ϕ trending N50°– 70°E in the south and central regions and N30°–40°E in the north, closely following the trend of the orogenic belt in these areas. The transition region between north and central is characterized by δt≈1–1.3 s and by E-W trending ϕ that are at a high angle to the regional geologic trend. Measurements at two stations located in the eastern (internal) part of the belt indicate very weak anisotropy. The large-scale pattern of anisotropy is not consistent with that predicted for simple asthenospheric flow beneath the plate. Splitting along the southern and eastern margins of the continent is consistent with that expected for Grenvillian deformation, an alternative model of asthenospheric flow around the cratonic keel cannot be ruled out. Within the cratonic core, the correlation between δt and lithospheric thickness suggests a lithospheric anisotropy. Smaller-length-scale variations also argue for a significant contribution of lithospheric structures. The fabric responsible for shear wave splitting may have formed during tectonic episodes that affected the eastern United States, i.e., the Grenville and Appalachian orogenies and the subsequent rifting of the North Atlantic Ocean. Our observations in the western Appalachians suggest that the anisotropy may be preserved since the Grenvillian orogeny. The absence of detectable splitting in the two stations in the eastern Appalachians is attributed to the igneous intrusions related to the Atlantic rifting. The measurements in the transition between the northern and central southern Appalachians, constitute an intriguing anomaly, whose E-W ϕ have little obvious relation to the regional surface geology. We suggest two possible causes: (1) the local dominance of asthenospheric flow, motivated by the proximity of a pervasive low-velocity anomaly and (2) lithospheric deformation in a transcontinental strike-slip fault zone active during the Appalachian collision. ISSN: 2169-9313 hal-01388859 http://hal.univ-reunion.fr/hal-01388859 http://hal.univ-reunion.fr/hal-01388859/document http://hal.univ-reunion.fr/hal-01388859/file/Barruol_JGR_1997.pdf DOI : 10.1029/96JB03800 | Partager |
A comparison of dissolved and particulate mn and al distributions in the western north-atlantic Auteur(s) : Yeats, Pa Dalziel, Ja Moran, Sb Éditeur(s) : Gauthier-Villars Résumé : The dissolved Mn distribution on an oceanographic section along 50-degrees-W in the western North Atlantic shows decreasing concentrations in the offshore direction in the surface layer and with depth at the deep water stations. Leachable particulate Mn concentrations are low in the open ocean surface waters and elevated at intermediate depths. Dissolved Al concentrations in the surface layer are higher in the open ocean than on the shelf and the vertical distributions are characterized by surface maxima, a subsurface minimum at almost-equal-to 1 000 m and increasing concentrations in the deep waters. Leachable particulate Al concentrations are elevated on the shelf and in open ocean surface waters compared to the intermediate and deep waters. The Deep Western Boundary Current has high levels of dissolved Al and leachable particulate Mn and Al, and low levels of dissolved Mn. The distribution of dissolved Al is controlled primarily by inputs from atmospheric dust and removal onto biogenic particles. Both fluvial and atmospheric inputs affect dissolved Mn levels with removal occurring primarily by oxidation of Mn2+. The Al distribution is characterized by short residence times in shelf and surface waters and relatively constant distribution coefficients. The Mn distribution is characterized by longer surface water residence times, shorter deep water residence times, and more widely varying distribution coefficients than Al. Removal of Al by a surface adsorption mechanism and Mn by slower oxidation of Mn2+ are consistent with these observations. A model of Mn oxidation kinetics accurately predicts the intermediate depth leachable particulate Mn maximum. Oceanologica Acta (0399-1784) (Gauthier-Villars), 1992 , Vol. 15 , N. 6 , P. 609-619 Droits : info:eu-repo/semantics/openAccess http://archimer.ifremer.fr/doc/00101/21186/18803.pdf http://archimer.ifremer.fr/doc/00101/21186/ | Partager |
Geochemistry of the highly depleted peridotites drilled at ODP Sites 1272 and 1274 (Fifteen-Twenty Fracture Zone, Mid-Atlantic Ridge): Implications for mantle dynamics beneath a slow spreading ridge Auteur(s) : Godard, Marguerite Lagabrielle, Yves Alard, Olivier Harvey, J. Auteurs secondaires : Géosciences Montpellier ; Université des Antilles et de la Guyane (UAG) - Institut national des sciences de l'Univers (INSU - CNRS) - Université de Montpellier (UM) - Centre National de la Recherche Scientifique (CNRS) Éditeur(s) : HAL CCSD Elsevier Résumé : International audience During ODP Leg 209, a magma-starved area of the Mid-Atlantic Ridge (MAR) was drilled in the vicinity of the Fifteen-Twenty Fracture Zone (FZ) that offsets one of the slowest portions of the spreading ridge. We present here the results of a bulk rock multi-elemental study of 27 peridotites drilled at Sites 1272 and 1274 (to the south and the north of the FZ, respectively). The peridotites comprise mainly of harzburgites with minor dunites. Clinopyroxene (Cpx), which is interstitial and interpreted as secondary, is observed in Site 1274 peridotites. Sites 1272 and 1274 peridotites have low Al2O3 contents (<= 1 anhydrous wt.%), high Mg# (>91.5), and bulk rock trace elements compositions mostly below 0.1 x primitive mantle (PM). These peridotites, and in particular Site 1272 peridotites, represent the most depleted peridotites yet sampled at a slow spreading ridge. Their compositions indicate high degrees of partial melting and melt extraction. A single open-system melting event (melting plus percolation of melts produced within upwelling mantle) can explain their highly depleted yet linear chondrite-normalized REE patterns, characterized by a steady depletion from HREE to LREE. Late melt-rock reactions and precipitation of Cpx explains the slightly less depleted compositions of Site 1274 peridotites. Hence, the differences in composition between Sites 1272 and 1274 peridotites do not provide evidence for regional variations in the degrees of partial melting from the south to the north of the FZ. The occurrence of highly refractory peridotites in the Fifteen-Twenty area suggests we sampled a more actively convecting mantle than generally supposed below slow spreading centers. ISSN: 0012-821X hal-00412001 https://hal.archives-ouvertes.fr/hal-00412001 DOI : 10.1016/j.epsl.2007.11.058 | Partager |
Le genre Hymenaster (Astérides) dans l'océan Atlantique Auteur(s) : Sibuet, Myriam Éditeur(s) : Museum National d'Histoire Naturelle Résumé : Several species of the genus Hymenaster (Asteroidea) collected in the abyssal cruises Biaçores, Biogas and Polygas in the North East Atlantic Ocean make possible a synthesis of available data on the species known from the Atlantic Ocean. Two species H. reticulatus and H. tenuispinus are new to Science. A morphological comparative study is carried out for the 17 species reviewed and is presented in the form of a tabular key. The bathymetrical and geographical distributions are included. [NOT CONTROLLED OCR] La présence de nombreuses espèces du genre Hymenaster dans les collections d'Astérides provenant de prélèvements abyssaux effectués dans le Nord-Est Atlantique (missions Biaçores, Biogas et Polygas) a conduit à une étude synthétique de l'ensemble des espèces connues de l'océan Atlantique. Deux espèces, H. reticulatus et H. tenuispinus, sont nouvelles pour la Science et portent à 17 le nombre d'espèces connues de l'océan Atlantique. Une clef tabulaire résume les caractères distinctifs entre ces espèces dont la répartition biogéographique et bathymétrique est étudiée. [OCR NON CONTRÔLE] Bulletin du Museum National d'Histoire Naturelle (Museum National d'Histoire Naturelle), 1976 , Vol. 368 , N. 256 , P. 305-324 Droits : Museum National d'Histoire Naturelle http://archimer.ifremer.fr/doc/1976/publication-5094.pdf http://archimer.ifremer.fr/doc/00000/5094/ | Partager |