ArchiMer - Institutional Archive of Ifremer

    Avis de l'Ifremer. Enquête administrative n° SB20/01

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    Qualité bactériologique des coquillages sur les zones de culture et les gisements naturels d'Ille-et-Vilaine et des Côtes d'Armor (années 1989 et 1990)

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    La qualité bactériologique des coquillages d'Ille-et-Vilaine et des Côtes d'Armor est présentée pour les années 1989 et 1990. Un classement est proposé prenant pour référence l'arrêté du 16.10.1976 et les directives CEE du 30.10.1979 et du 15.07.1991. D'une manière générale les secteurs conchylicoles sont d'une qualité satisfaisante en regard des règles nationales en vigueur (arrêté du 16.10.1976) ou à venir (directive CEE du 15.07.91), à l'exception des baies de Morieux et de la Fresnaye. Par contre la qualité bactériologique des gisements naturels de coquillage est très variable, ce qui pose des problèmes sanitaires aigus dans le cas de la pêche de loisir

    Etude des hémocytes et d'une néoplasie hémocytaire chez les moules Mytilus edulis et Mytilus trossulus (Mollusca, Bivalvia)

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    La transmissibilité d'une néoplasie hémocytaire de moules M. trossulus du Puget Sound, Etat de Washington (USA) à des moules M. edulis a été montrée bien que la prévalence semble faible. L'étiologie n'a cependant pas pu être déterminée.  La caractérisation antigénique des hémocytes normaux de M. edulis et des hémocytes néoplasiques de M. trossulus, a été réalisée à l'aide d'anticorps monoclonaux (AcMs). Quatre classes d'AcMs spécifiques des hémocytes normaux ont été obtenus. L'AcM de classe I reconnaît spécifiquement les granulocytes basophiles alors que les autres classes d'anticorps réagissent avec les deux types de granulocytes. Les AcMs de classe IV semblent associés à la différenciation des granulocytes. Les AcMs spécifiques des hémocytes néoplasiques semblent reconnaître des protéines différemment exprimées, d'un point de vue quantitatif, sur les hémocytes 4n ou sur les hémocytes 5n. Des immunodosages de type ELISA et· lIF ont été développés pour le diagnostic de la néoplasie hémocytaire. La caractérisation fonctionnelle des hémocytes de M. edulis a été entreprise par là mise en évidence d'une activité métabolique respiratoire associée à la phagocytose de particules de zymosan. Ce métabolisme oxydatif ainsi que trois activités enzymatiques (β-glucuronidase, alpha-glucosidase et N-acétyl-β-glucosaminidase) sont absents chez les hémocytes néoplasiques. La mise au point de primocultures d'hémocytes a permis d'étudier les interactions in vitro et de mettre ainsi en évidence la phagocytose des cellules néoplasiques de M. trossulus par les hémocytes de M. edulis. Les images de cytocidies observées ne semblent pas associées à un mécanisme de type "burst" respiratoire. La recherche de proto-oncogènes a conduit au clonage et au séquençage d'une portion de la séquence du proto-oncogène rho chez M. edulis. Ces résultats correspondent àu premier proto-oncogène décrit chez un Mollusque bivalve

    Instability of a two-step Rankine vortex in a reduced gravity QG model

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    We investigate the stability of a steplike Rankine vortex in a one-active-layer, reduced gravity, quasi-geostrophic model. After calculating the linear stability with a normal mode analysis, the singular modes are determined as a function of the vortex shape to investigate short-time stability. Finally we determine the position of the critical layer and show its influence when it lies inside the vortex

    African monsoon enhancement during the penultimate glacial period (MIS 6.5 similar to 170 ka) and its atmospheric impact

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    A reconstruction of northwest African summer monsoon strength during the cold marine isotopic stage (MIS) 6 indicates a link to the seasonal migration of the Intertropical Convergence Zone (ITCZ). High-resolution studies of eolian dust supply and sea surface temperature recorded in marine core MD03-2705, on the Mauritanian margin, provide a better understanding about the penultimate glacial history of northwestern African aridity/humidity and upwelling coastal activity. Today, site MD03-2705 experiences increased upwelling and dust flux during the winter months, when the ITCZ is in a southerly position. Analyses of foraminifera isotopic composition suggest that during MIS 6.5 (180 - 168 ka) the average position of the ITCZ migrated north, marked by an increase in the strength of the summer monsoon, which decreased eolian dust transport and the coastal upwelling activity. The northward migration is in phase with a specific orbital combination of a low precessional index with a high obliquity signal. High-resolution analysis of stable isotopes (delta(18)O and delta(13)C) and microscale resolution geochemical (Ti/Al and quartz grain counts) determinations reveal that the transition between monsoonal humid (MIS 6.5) and dry (MIS 6.4) conditions has occurred in less than 1.3 ka. Such rapid changes suggest a nonlinear link between the African monsoonal rainfall system and environmental changes over the continent. This study provides new insights about the influence of vegetation and oceanic temperature feedbacks on the onset of African summer monsoon and demonstrates that, during the penultimate glacial period, changes in tropical dynamics had regional and global impacts

    Monsoon hydrography and productivity changes in the East China Sea during the past 100,000 years: Okinawa Trough evidence (MD012404)

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    We analyzed the high-resolution foraminifer isotope records, total organic carbon (TOC), and opal content from an Okinawa Trough core MD012404 in order to estimate the monsoon hydrography and productivity changes in the East China Sea (ECS) of the tropical western Pacific over the past 100,000 years. The variability shown in the records on orbital time scales indicates that high TOC intervals coincide with the increases of boreal May-September insolation driven by precession cycles (similar to 21 ka), implying a strong connection to the variations in monsoons. We also observed possibly nearly synchronous, millennial-scale changes of the ECS surface hydrography (mainly driven by salinity changes but also by temperature effects) and productivity coincident with monsoon events in the Hulu/Dongge stalagmite isotope records. We found that increased freshening and high productivity correlate with high monsoon intensity in interstadials. This study suggests that the millennial-scale changes in monsoon hydrography and productivity in the ECS are remarkable and persistent features over the past 100,000 years

    Magnetic properties and geochemistry of the active oxidation front and the youngest sapropel in the eastern Mediterranean Sea

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    Magnetic properties (IRM, ARM, chi (in), S-ratio at 0.3 T, room temperature (RT) hysteresis and thermomagnetic curves) and geochemical data (Fe, S, Mn, Al, Ti, organic C) were studied in two eastern Mediterranean boxcores (ABC26 and BC19) at a resolution of 3-5 mm. The boxcores contain sapropel S1 (9-6 kyr BP) at a few decimetres below seafloor. The magnetic fraction consists predominantly of single-domain (SD) to pseudo-single-domain (PSD) magnetite in the entire cores. The original input of magnetic grains comes from two sources: aeolian dust (both cores) and volcanic ash from the Minoan eruption of Santorini (core BC19 only). Non-steady-state diagenesis has changed the magnetic mineralogy considerably in these alternating organic-rich /organic-poor sediments. During deposition of sapropel S1, reductive diagenesis and pyritization in and just below the sapropel caused lower magnetic intensities, coarser magnetic grain sizes and partial maghemitization. In thermomagnetic curves two types of pyrite can be identified: one oxidizes below 450 degreesC and the other above 450 degreesC. The higher oxidation temperature is predominantly found below the sapropel. This may be related to the microtexture of pyrite, which is euhedral below sapropels and mainly framboidal within sapropels. Since the end of sapropel deposition a downward moving oxidation front has oxidized the upper half(c. 5 cm) of the sapropel. The oxidized part of the sapropel is enriched in diagenetically formed Fe oxides with relatively high coercivity and ARM. The maximum coercivity is found in a distinct layer between the present-day Mn- and Fe-redox boundaries at the top of the unoxidized sapropel. The freshly precipitated Fe oxides in this centimetre-thick layer contain a mixture of superparamagnetic (SP) grains and high-coercivity SD magnetite. Higher in the oxidized zone the freshly precipitated Fe oxides have aged into generally slightly lower-coercivity SD grains, with relatively high ARM. In addition to the diagenetic formation of Fe oxides at the top of the sapropel, formation of a ferrimagnetic Fe monosulphide may have occurred within the sapropel during later stages of diagenesis, which may have enhanced the ARM signal in the organic-rich interval in particular

    Assessing the internal consistency of the CARINA data base in the Pacific sector of the Southern Ocean

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    The CARINA project is aimed at gathering and providing secondary quality control checks on carbon and carbon-relevant hydrographic and geochemical data from cruises all across the Atlantic, Arctic and Southern Ocean. In total the project gathered 188 cruises that were not previously available to the public. Of these 188 cruises, 37 are part of the Southern Ocean. Parameters from the Southern Ocean cruises, including total carbon dioxide (TCO2), total alkalinity, oxygen, nitrate, phosphate and silicate, were examined for cruise-to-cruise consistency. pH and chlorofluorocarbons (CFCs) are also part of the data base, but are not discussed here. This paper focuses on the quality control of the Southern Ocean data from the Pacific sector which consisted of 29 cruises of which 17 were included in a previous synthesis called GLODAP, 11 were new cruises from the CARINA dataset, and one cruise was included in GLODAP but was updated with new data and therefore also included in CARINA. The Pacific sector quality control procedures included crossover analysis between stations and inversion analysis of all crossover data. The GLODAP data were included into the analysis as reference cruises but without applying the GLODAP recommended adjustments so the corrections could be independently verified. The outcome of this effort is an internally consistent, high-quality carbon data set for all cruises, including the reference cruises

    Metabolomic Profiles of Dinophysis acuminata and Dinophysis acuta Using Non-Targeted High-Resolution Mass Spectrometry: Effect of Nutritional Status and Prey

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    Photosynthetic species of the genus Dinophysis are obligate mixotrophs with temporary plastids (kleptoplastids) that are acquired from the ciliate Mesodinium rubrum, which feeds on cryptophytes of the Teleaulax-Plagioselmis-Geminigera clade. A metabolomic study of the three-species food chain Dinophysis-Mesodinium-Teleaulax was carried out using mass spectrometric analysis of extracts of batch-cultured cells of each level of that food chain. The main goal was to compare the metabolomic expression of Galician strains of Dinophysis acuminata and D. acuta that were subjected to different feeding regimes (well-fed and prey-limited) and feeding on two Mesodinium (Spanish and Danish) strains. Both Dinophysis species were able to grow while feeding on both Mesodinium strains, although differences in growth rates were observed. Toxin and metabolomic profiles of the two Dinophysis species were significantly different, and also varied between different feeding regimes and different prey organisms. Furthermore, significantly different metabolomes were expressed by a strain of D. acuminata that was feeding on different strains of the ciliate Mesodinium rubrum. Both species-specific metabolites and those common to D. acuminata and D. acuta were tentatively identified by screening of METLIN and Marine Natural Products Dictionary databases. This first metabolomic study applied to Dinophysis acuminata and D.acuta in culture establishes a basis for the chemical inventory of these specie

    Histology of Tritia mutabilis gonads: using reproductive biology to support sustainable fishery management

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    The mutable nassa, Tritia mutabilis, a marine gastropod that is widely exploited on the Adriatic coast is an important source of income for small-scale fishermen in the Mediterranean Sea, particularly in the Gulf of Lion. However, the lack of knowledge on the ecology and biology of this species limits our capacities to propose and produce an effective management plan. As a result, stocks are currently declining, especially in Italy. In order to optimize a management plan for this fishery, we designed a study to better characterize the reproductive biology of T. mutabilis, using gonad histology and performing a regular monitoring of population size frequency. The average shell height of individuals during the breeding period was 24 ± 2.7mm for males and 30 ± 3.7mm for females. The presence of small females (10 mm) and large males (32 mm) in the whole sample challenged previous assumptions regarding protandry (sex change from male to female). The size at first maturity was estimated for males and females at 17.5mmand 24.4mmshell height, respectively. In Italy, current management measures include a minimum conservation reference size of 20mmin shell height. Therefore, it is likely that many individuals that did not reproduce are being caught, which could partly explain the decline observed, despite conservation measures introduced more than ten years ago. Overall, our study provides some baseline information to establish, in consultation with fishermen, management measures for this small-scale fishery in Franc
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