Résumé : Ce travail fait suite à la publication du premier volume « Etude de la crise de la pêche de la crevette en Guyane » (Lampert, 2011). Dans ce premier volume nous avons répondu à la première question qui se posait : « la crise de la crevette est-elle due à la pêche elle-même ? ». Nous avons pu répondre par la négative, laissant la porte ouverte à des hypothèses environnementales et trophiques. Facteurs environnementaux La piste des facteurs environnementaux est liée aux changements climatiques, pérennes ou cycliques. L’augmentation de la température de surface de la mer, les changements dans le régime des vents, de la houle et la salinité, la relation qu’il peut y avoir entre le recrutement et les précipitations locales, les débits des fleuves guyanais ou de l’Amazone. Sans oublier les indicateurs climatiques à grande échelle tels que la Southern Ocillation Index (SOI) et la Northern Oscillation Index (NOI) (Santamaría-del-Ángel et al. 2011 ; Aragon-Noriega et Alcántara-Razo 2005 ; Parsons et Lear 2001 ; Serge Garcia et Le Reste 1981 ; S. Garcia 1988 ; Saoud et Davis 2003 ; Rivierre 2007 ; Leal-Gaxiola et al. 2001 ; Li et Clarke 2005 ; Lee 2004 ; Ouellet, Savard, et Larouche 2007). Facteurs trophiques La crevette étant l’une des proies préférées des poissons de Guyane, nous avons avancé dans le premier volume l’hypothèse d’un impact trophique suite à la pression de la pêche au vivaneau. De l’autre coté du réseau trophique, il reste à explorer la piste des changements dans l’abondance phytoplanctonique, qui constitue l’essentiel de l’alimentation des larves de crevette. Un changement significatif dans leur source de nourriture pourrait avoir des conséquences dans leur recrutement. Il en va de même pour l’évolution de la mangrove en biomasse, qui fournit matière organique et refuge pour les larves (Anderson 2000 ; Fuentes-Yaco et al. 2007 ; D. G. Parsons et Colburne 2000 ; Santamaría-Miranda et al. 2005). Les données collectées sont présentées dans la première partie de ce document avec une étude de chaque paramètre et le choix du meilleur indicateur. Dans la deuxième partie nous abordons un premier traitement de ces données afin d’évaluer leur pertinence dans les relations qui peuvent exister avec les valeurs des recrutements de crevettes. Une étude plus exhaustive sera menée dans un prochain volume où seront ajoutés des paramètres tels que les concentrations en chlorophylle, en matières en suspension ou des matières organiques dissoutes. Ce deuxième volume est réalisé dans le cadre du marché ouvert par la Direction des Pêches Maritimes et de l’Agriculture (DPMA) « Marché DPMA 2012-021 », intitulé : Etude portant sur l’effet du changement climatique et/ou du réseau trophique sur le stock guyanais des crevettes pénéïdes. Il constitue le rapport intermédiaire du marché. Dans le troisième volume pourra être abordé l’étude liée au réseau trophique par les analyses des contenus stomacaux des vivaneaux, par les séries de données de biomasse phytoplanctonique (images satellite) et de son paramètre « chlorophylle » et par l’évolution temporelle de la biomasse de la mangrove. La piste de la dérive des oeufs et larves de crevettes depuis les côtes brésiliennes pourra également être explorée si le modèle de courants de surface venait à être opérationnel en 2013. Il permettrait d’avoir des cartes de courants et vitesses de surface permettant de valider l’hypothèse émise dans le volume 1.

Droits : 2013 Ifremer
http://archimer.ifremer.fr/doc/00137/24844/22928.pdf
http://archimer.ifremer.fr/doc/00137/24844/

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

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

Éditeur(s) : Elsevier
Résumé : High-resolution sedimentological and micropaleontological studies of several deep-sea cores retrieved from the levees of the Celtic and Armorican turbidite systems (Bay of Biscay - North Atlantic Ocean) allow the detection of the major oscillations of the British-Irish Ice Sheet (BIIS) and 'Fleuve Manche' palaeoriver discharges over the last 30,000 years, which were mainly triggered by climate changes. Between 30 and 20 cal ka, the turbiditic activity on the Celtic-Annorican margin was weak, contrasting with previous stratigraphic models which predicted a substantial increase of sediment supply during low sea-level stands. This low turbidite deposit frequency was most likely the result of a weak activity of the 'Fleuve Manche' palaeoriver and/or of a reduced seaward transfer of sediments from the shelf to the margin. However, two episodes of turbiditic activity increase were detected in the Celtic-Armorican margin, during Heinrich events (HE) 3 and 2. This strengthening of the turbiditic activity was triggered by the meltwater releases from European ice sheets and glaciers favouring the seaward transfer of subglacial material, at least via 'Fleuve Manche' palaeoriver. At around 20 cal ka, a significant increase of turbidite deposit frequency occurred as a response to the onset of the last deglaciation. The retreat of the European ice sheets and glaciers induced a substantial increase of the 'Fleuve Manche' palaeoriver discharges and seaward transfer of continentally-derived material into the Armorican turbidite system. The intensification of the turbiditic activity on the Celtic system was directly sustained by the widespread transport of subglacial sediments from the British-Irish Ice Sheet (BIIS) to the Celtic Sea via the Irish Sea Basin. A sudden reduction of turbiditic activity in the Armorican system, between ca. 19 and 18.3 cal ka, could have been triggered by the first well known abrupt sea-level rise ('meltwater pulse', at around 19 cal ka) favouring the trapping of sediment in the 'Fleuve Manche' palaeoriver valleys and the decrease of the seaward transfer of continentally-derived material. The maximum of turbiditic activity strengthening in the Celtic-Armorican margin, between ca. 18.3 and 17 cal ka, was induced by the decay of European ice sheets and glaciers producing the most extreme episode of the 'Fleuve Manche' palaeoriver runoff and a great seaward transfer of subglacial material into the Bay of Biscay, Between ca. 17.5 and 16 cal ka, the turbiditic activity significantly decreased in both Celtic and Armorican turbidite systems in response to a global re-advance of glaciers and ice sheets in Europe. The last episode of ice sheet retreat, between ca. 16 and 14 cal ka, is well expressed in the Celtic system by a new increase of the turbiditic activity. The major episode of sea-level rise at around 14 cal ka ('Meltwater Pulse 1A'), precluding the seaward transfer of sediments, induced the end of turbiditic activity in both the Celtic and the Armorican system. Although two main phases of global sea-level rise seem to have had an effect on the Celtic-Armorican margin, this work proposes the BUS retreat and associated riverine discharges as the main trigger mechanisms of the turbiditic activity in this region during the last 30,000 years.
Marine Geology (0025-3227) (Elsevier), 2008 , Vol. 247 , N. 1-2 , P. 84-103

Droits : 2008 Elsevier B.V. All rights reserved
http://archimer.ifremer.fr/doc/2008/publication-3729.pdf
DOI:10.1016/j.margeo.2007.08.006
http://archimer.ifremer.fr/doc/00000/3729/

Résumé : Partie intégrante de la République Française, les collectivités d’outre-mer oscillent entre identité institutionnelle avec la métropole et quête d'une certaine forme d'autonomie identitaire. Cette particularité trouve sa traduction dans les différentes réformes constitutionnelles depuis leur inscription dans les constitutions de 1946 et 1958. Avec la révision constitutionnelle de 28 mars 2003 sur l'organisation décentralisée de la République, une nouvelle donne institutionnelle s'ouvre pour ces collectivités d'Outre-Mer. Les consultations référendaires sur le statut de la Martinique organisées le 7 décembre 2003, puis les 10 et 24 janvier 2010 s'inscrivaient dans cette logique là.C’est dans ce contexte de mise en place d’une collectivité unique dotée d’une assemblée unique qu’il convient d'aborder les problématiques d’aménagement du territoire. Une telle approche passe par l’analyse des principaux textes relatifs à l’aménagement du territoire ainsi que des évolutions législatives dans ce domaine. Il est important de souligner la volonté sans cesse exprimée par les élus locaux pour l’exercice de plus de responsabilité notamment au regard des politiques d’aménagement du territoire. Pourtant, à ce niveau, le rôle de l’État demeure toujours aussi prépondérant et ce, en dépit des lois de décentralisation. D’où la nécessité d'approfondir l'étude des rapports entre collectivités territoriales et l’État. L’approche comparative des statuts juridiques de Martinique, Guadeloupe, Guyane, Saint-Martin, Polynésie française, s’impose dès lors comme une étape incontournable dans une telle analyse.
Integral part of the French Republic, communities overseas range from corporate identity with the city and looking for some form of self-identity . This feature is its translation into the various constitutional reforms since their inscription in the constitutions of 1946 and 1958. With the constitutional revision of 28 March 2003 on the decentralized organization of the Republic, a new institutional opens for these overseas communities. The referendums on the status of Martinique held December 7, 2003 , then on 10 and 24 January 2010 were part of this logic is in this context of establishing a unique community with a meeting only appropriate to address land issues. Such an approach requires an analysis of key texts relating to planning and legislative developments in this area. It is important to note the willingness constantly expressed by local elected officials to exercise more responsibility especially with regard to land use policies. However, at this level, the role of the state remains as dominant and , despite the decentralization laws. Hence the need for further study of the relationship between local authorities and the state. The comparative approach to legal status of Martinique , Guadeloupe , Guyana, Saint- Martin, French Polynesia , is therefore needed as an essential step in such an analysis.

http://www.theses.fr/2012AGUY0593

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/

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
In this paper, the generalized Stokes problem αu−νΔu+∇p=f, ∇u=0, is considered, where ν denotes the kinematic viscosity, α is a positive parameter proportional to the inverse of the time-step, and the source term f gathers the external forcing, the nonlinear term, and the explicit part of the linear term. The system is derived from a time discretization for the Navier-Stokes equation governing the motion of a two-dimensional incompressible fluid. A domain decomposition numerical method is developed for solving the system. The original domain is divided into several nonoverlapping subdomains, and in each subdomain the concerned equations are discretized by certain finite element methods. A new feature of the method is that the pressure p is required to be piecewise linear rather than piecewise constant, so that the nonphysical oscillations in the solution using piecewise linear pressure are eliminated. However, a difficulty in using piecewise linear pressure is that the Stokes problem in each subdomain involves Dirichlet boundary conditions on pressure at the interface, which is not a real Stokes problem. To avoid the difficulty, a modification is proposed which removes the continuity conditions on the pressure across the interface. In this way, the Stokes problem in each subdomain has only Dirichlet boundary conditions on the velocity. Formulations and discussions for both the methods are presented, which shows that the modified method is simpler than the original one. Numerical experiments are displayed to show the efficiency of the methods, especially that the modified method has the same accuracy as the original one.
ISSN: 0749-159X

hal-00730200
https://hal.archives-ouvertes.fr/hal-00730200

Éditeur(s) : HAL CCSD
Résumé : International audience
The results of the Shubnikov-De Haas (SDH) oscillation measurements on CuInSe2-doped (CIS) crystals are presented for the first time. The measurements were performed in the temperature range from 1.9 to 40 K in pulsed magnetic fields up to 40 T. It was found that the Fermi surface of electrons consisted of one sphere. The values of the cyclotron effective mass at the bottom of the conduction band, the inter-band momentum matrix element and the g* factor were calculated.
Applied Physic Letters

hal-00808595
https://hal.univ-antilles.fr/hal-00808595
DOI : 10.1063/1.107741

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The dating of alluvial landforms by cosmogenic nuclides requires distinguishing the pre-deposition inheritance from the post-deposition history of the clasts in the studied marker. Moreover, estimating catchment-scale erosion rates from the concentrations of cosmogenic nuclides in active alluvia requires a good knowledge of the local/regional relationships between rock exhumation and transport through space and time. This is still poorly known for timescales of tens of thousand years. In order to document the evolution of clast exhumation and transport rates through time, we analyze in situ 10Be concentrations in boulders and cobbles from hillslopes to outlet of an arid mountainous catchment located in Gobi-Altay, Mongolia, strongly affected by global climatic changes during the Pleistocene-Holocene period. Samples were collected on bedrock, abandoned alluvial deposits, active colluvia and alluvia. Our results show a large 10Be scattering in the active river bed, consistent with a low and discontinuous catchment erosion rate dominated by mass wasting and fluvial incision. On the contrary, pre-exposure signal within abandoned terraces is much more homogeneous, consistent with climatic pulses responsible of strong erosional events on hillslopes and rapid fluvial transport. These results show that exhumation/transport processes at the catchment scale vary in style and intensity through time as a consequence of climatic oscillations. The occurrence of abrupt climatic changes during short periods of time recorded by 10Be concentrations in abandoned alluvia raise questions about the temporal applicability of catchment erosion rates derived from cosmogenic nuclide concentrations measured in sediments of active rivers. On the other hand, strong and short erosion events limit and homogenize the pre-exposure 10Be signal in associated deposits like debris-flows, making them particularly suitable markers for dating in active tectonic and paleoclimatic studies.
ISSN: 0169-555X

hal-00626702
https://hal.archives-ouvertes.fr/hal-00626702
https://hal.archives-ouvertes.fr/hal-00626702/document
https://hal.archives-ouvertes.fr/hal-00626702/file/GEOMOR-2485R1_corrected.pdf
DOI : 10.1016/j.geomorph.2011.07.023

Éditeur(s) : Gauthier-Villars
Résumé : Marine muds deposited on the French Guiana coast mostly originate in the Amazon. Recent sediments are composed of (a) illite (33 %) and chlorite (13 %) of Andean mountain origin; and (b) kaolinite (28 %) and smectite (26 %), principally from the Amazonian lowlands but also from the Guiana Shield. In the coastal mud prism, high-resolution seismic profiles, together with sedimentological, micropaleontological and soil engineering studies, supplemented by C-14 dates, permitted a stratigraphic interpretation of eight cores. Three episodes have been determined on the basis of clay-mineral variations related to Amazonian lowland, Andean and Guiana shield sources. The older episodes 3 (3000-1700 y BP) and 2 (1700-1000 y BP) are predominantly characterized by lowland-derived clays (smectite = 43 %, kaolinite = 26 %) from Amazonian and local sources. The most important event is a reduction of the Andean source, due to successive dry phases which occurred in western Amazonia about 2200 and 1200 y BP, confirming that regional decreases in rainfall, water discharge and erosion were associated with climatic fluctuations. It is suggested that these dry phases (within the last 3000 years) are the consequence of several protracted (10-100 years) periods, during which atmospheric conditions mimicked the present-day ''El Nino Southern Oscillation'' (ENSO) phenomenon. As a result, particulate flux from the ocean decreased, leading to reduced silting of the Guiana coast, In the past 1000 years (episode 1), illite and chlorite have increased, indicating a stronger Andean contribution to the Amazonian continental flux that reaches the ocean. This is the first demonstration that the nature of the coastal marine muds of northern South America reflects climatic changes in the Amazon basin.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1996 , Vol. 19 , N. 5 , P. 477-487

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00094/20506/18175.pdf
http://archimer.ifremer.fr/doc/00094/20506/

Éditeur(s) : American Geophysical Union
Résumé : [1] A multiproxy integrated chronological framework, based on oxygen and carbon stable isotope stratigraphy, biostratigraphy (foraminifera and nannoplankton bioevents and foraminifer assemblage-based climate cyclicity), magnetostratigraphy, sapropel stratigraphy, and C-14 AMS radiometric dates, has been achieved for borehole PRAD1-2, collected in 185.5 m water depth in the central Adriatic. This work was carried out within the European Community project Profiles across Mediterranean Sedimentary Systems (PROMESS1). The 71.2 m long borehole spans a time interval between late MIS 11 and MIS 1 (the last 370 ka), showing a chronological resolution of 500 and 250 years per cm during interglacial and glacial intervals, respectively. At present, this record is the most expanded and continuous marine record available for the Adriatic Basin. Several orbital cycles can be recognized in the PRAD1-2 record: the 100 ka glacial-interglacial fluctuations and the 23 ka precession-related cycles, which in turn control the deposition of sapropel layers. An integrated analysis of short-term oscillations within the Last Glaciation interval (MIS 4-MIS 2) allowed the identification of the Adriatic signature of Dansgaard-Oeschger events, showing the potential to achieve a more refined chronostratigraphic framework for the top part of the PRAD1-2 record. Finally, the age model obtained by this study allowed the chronological integration of the main foraminifera bioevents detected in the borehole as well as of the volcanoclastic layers present in the upper part of the record. Despite its proximal location, PRAD1-2 presents a continuous record and shows the potential to be consistently correlated both with deep-sea and continental records in the Mediterranean region and beyond.
Geochemistry Geophysics Geosystems (1525-2027) (American Geophysical Union), 2008 , Vol. 9 , P. NIL_107-NIL_127

Droits : 2008 American Geophysical Union
http://archimer.ifremer.fr/doc/2008/publication-3605.pdf
DOI:10.1029/2007GC001713
http://archimer.ifremer.fr/doc/00000/3605/

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/