Éditeur(s) : Elsevier
Résumé : A study of organic carbon mineralization from the Congo continental shelf to the abyssal plain through the Congo submarine channel and Angola Margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling. Two measurement techniques were coupled on a single autonomous platform: in situ benthic chambers and microelectrodes, which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters. In addition, sediment trap fluxes, sediment composition (Org-C, Tot-N, CaCO3, porosity) and radionuclide profiles provided measurements of, respectively input fluxes and burial rate of organic and inorganic compounds. The in situ results show that the oxygen consumption on this margin close to the Congo River is high with values of total oxygen uptake (TOU) of 4 +/- 0.6, 3.6 +/- 0.5 mmol m(-2) d(-1) at 1300 and 3100m depth, respectively, and between 1.9 +/- 0.3 and 2.4 +/- 0.2 mmol m(-2) d(-1) at 4000 m depth. Diffusive oxygen uptakes (DOU) were 2.8 +/- 1.1, 2.3 +/- 0.8, 0.8 +/- 0.3 and 1.2 +/- 0.1 mmol m(-2) d(-1), respectively at the same depths. The magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel-levee system, which indicates that cross-slope transport processes are active over the entire margin. Comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5-8 times larger than the vertical flux recorded in traps. Transfer of material from the Congo River occurs through turbidity currents channelled in the Congo valley, which are subsequently deposited in the Lobe zone in the Congo fan below 4800 m. Ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone, which agrees with the high organic carbon content (3%) and the large sedimentation rate (19 mm y(-1)) found on this site. The Lobe region could receive as high as 19 mol C m(-2) y(-1), 1/3 being mineralized and 2/3 being buried and could constitute the largest depocenter of organic carbon in the South Atlantic.
Deep Sea Research Part II: Topical Studies in Oceanography (0967-0645) (Elsevier), 2009-11 , Vol. 56 , N. 23 , P. 2223-2238

Droits : 2009 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/2009/publication-7316.pdf
DOI:10.1016/j.dsr2.2009.04.005
http://archimer.ifremer.fr/doc/00000/7316/

Éditeur(s) : HAL CCSD
Résumé : The sandy coasts of Languedoc-Roussillon are a zone vulnerable to erosion and flooding. These hazards are generally associated with a combination of natural factors such as waves, wind, rising sea levels and the importance of sediment supply, and are therefore worsened during storms. For the management of such risks, a better knowledge of the hydrodynamic phenomena occuring from the surf zone through to the coastal scale is essential. This need led to the development of a numerical modelling platform consisting of the 3D ocean circulation model Symphonie, usually dedicated to regional and coastal scales, which was modified to include the wave forcing, modeled by the WaveWatch III or Swan models. Using this platform the entire littoral and coastal regions can be accurately represented. The model was tested in several academic cases. Measurements on the barred beach of Sète during the winter of 2008-2009 served to refine the model, which is able to successfully reproduce the characteristics of the currents in coastal areas, drifts or rip currents over more complex bathymetries and also the vertical profiles of currents. To validate the model on the inner-shelf, we compared the simulations with measurements taken during a winter storm in 2004 around the mouth of the Têt river, as well as during storms in 2007 and 2008 in the Gulf of Aigues-Mortes. Currents are generally well reproduced. However, the scope of wave action seems limited to a depth of 30m. The characteristics of our model allow a good reproduction of the currents at all scales and the 3D nature of the model permits a more precise calculation of the shear stress and bottom current responsible, respectively, for the suspension and advection of sediments.
Le littoral sableux du Languedoc-Roussillon est un système vulnérable aux risques d'érosion et de submersion. Ces aléas sont liés à la conjonction des facteurs naturels que sont les vagues, vent, élévation du niveau de la mer et apports sédimentaires et sont donc aggravés en période de tempête. En vue d'une gestion des risques, une meilleure connaissance des phénomènes hydrodynamiques de l'échelle littorale à l'échelle côtière est essentielle. Ce travail a conduit à la réalisation d'une plateforme de modélisation numérique composée du modèle de circulation océanique 3D Symphonie, traditionnellement dédié aux échelles régionales et côtières, qui a été modifié pour inclure le forçage par les vagues, modélisées par les modèles Wavewatch III ou Swan, et ainsi étendre sa validité au littoral. Le modèle a été testé sur des cas académiques littoraux. Des mesures sur la plage à double barres de Sète pendant l'hiver 2008-2009, ont également servi à parfaire le modèle qui reproduit ainsi avec succès les caractéristiques des courants en zone littorale : la dérive, les courants sagittaux sur des bathymétries plus complexes et les profils verticaux des courants. Pour valider le modèle à des échelles plus côtières, nous avons confronté ses résultats à des mesures réalisées pendant une tempête hivernale en 2004 aux alentours de l'embouchure de la Têt, mais également sur des tempêtes de 2007 et 2008 dans le Golfe d'Aigues-Mortes. Les courants sont globalement bien reproduits. Les zones d'action des vagues semblent limitées aux zones de profondeur inférieure à 30 m. Notre modèle autorise une reproduction correcte des courants à toutes les échelles et sa nature 3D permet un calcul plus précis de la tension de cisaillement de fond et du courant près du fond, responsables respectivement de la mise en suspension et de l'advection des sédiments.
https://tel.archives-ouvertes.fr/tel-00680405

tel-00680405
https://tel.archives-ouvertes.fr/tel-00680405
https://tel.archives-ouvertes.fr/tel-00680405v2/document
https://tel.archives-ouvertes.fr/tel-00680405/file/2011_MICHAUD.pdf

Éditeur(s) : Institut de Ciències del Mar de Barcelona, CSIC
Résumé : Acoustic and core data have recently been collected on the shelf break and the upper part of the slope of the south Aquitaine continental margin. They reveal the major role played by mass-flow gravity processes in deposit erosion and redistribution, modelling of the sea-bed, and transfer of sediment toward the deep-sea. The study region is bounded in the south by the Capbreton canyon. The northern area, which shows a smooth morphology, is characterised by small-scale deformations due to sediment creep or low-amplitude slide processes. The deformations are associated with mini listric-like faults that bound packets of sediments in which the deposit geometry is typical of constructional sediment waves. These sediment waves result from the interaction of depositional and gravity deformation processes. In the southern area, closer to the canyon, wave-like structures are still present but mostly of smaller size. They only result from gravity deformation processes without any evidence of constructional processes. In the vicinity of the Capbreton canyon, the shelf break and upper slope have a much more uneven morphology with sedimentary reliefs, escarpments and depressions directed toward the canyon thalweg. The depressions look like slide scars, and could be the result of regressive slides initiated at the top of the canyon flank. The age of the sliding event responsible for the formation of the depression observed today could be middle to upper Quaternary. Since their formation, these depressions act as conduits that channel the transfer of shelf sediment into the canyon, as demonstrated by the occurrence of a meandering channel on the sea-floor of one depression.
Scientia Marina (0214-8358) (Institut de Ciències del Mar de Barcelona, CSIC), 2006-06 , Vol. 70 , N. 1 , P. 89-100

Droits : 2006 Institut de Ciències del Mar de Barcelona
http://archimer.ifremer.fr/doc/2006/publication-3960.pdf
http://archimer.ifremer.fr/doc/00000/3960/

Éditeur(s) : Inter-research
Résumé : Ecosystem-based management (EBM) requires more extensive information than single-species management. Active underwater acoustic methods provide a means of collecting a wealth of ecosystem information with high space-time resolution. Worldwide fisheries institutes and agencies are carrying out regular acoustic surveys covering many marine shelf ecosystems, but these data are underutilized. In addition, more and more acoustic data collected by vessels of opportunity are becoming available. To encourage their use for EBM, we provide a brief introduction to acoustic and complementary data collection methods in the water column, and review current and potential contributions to monitoring population abundance and biomass, spatial distributions, and predator-prey relationships. Further development of acoustics-derived indicators is needed. We review and propose indicators for assessing and monitoring zooplankton, population dynamics of fish and other nekton, and changes in diversity and food-web functioning. Acoustic methods have the potential to make a strong contribution to EBM. Evaluation of new indicators and suitable reference points in different ecosystems are the current challenges.
Marine Ecology-progress Series (0171-8630) (Inter-research), 2011 , Vol. 442 , P. 285-301

Droits : 2011 Inter-research
http://archimer.ifremer.fr/doc/00073/18445/15972.pdf
DOI:10.3354/meps09425
http://archimer.ifremer.fr/doc/00073/18445/

Éditeur(s) : Wiley / Blackwell
Résumé : P>New seismic reflection data from the Grand Banks of Newfoundland and the Newfoundland Basin add to the growing knowledge of the composition, structure and history of this non-volcanic margin. Geophysical imaging is now approaching the extent of that done previously on the conjugate margin along Iberia, providing a valuable database for the development of rifting models. Two parallel profiles over the shelf platform image deep crustal fabric representing Precambrian or possibly Appalachian deformation as well as Mesozoic extension. Progressively more intense extension of continental crust is imaged oceanwards without the highly reflective detachments frequently seen on profiles off Galicia. A landward-dipping event 'L' is imaged sporadically and appears to be analogous to a similar event on the Iberian IAM9 profile. The transition zone is probably exposed serpentinized mantle as interpreted off the Iberian margin although there appears to be a difference in the character of ridge development and reflectivity. The distinctive 'U' reflection identified previously at the base of the Newfoundland Basin deep water sedimentary section and recently identified as one or more thin basalt sills is imaged on newly presented profiles that connect previously published profiles SCR3 and SCR2 showing that 'U' is highly regular and continuous except where interrupted by basement highs. 'U' is also seen to have a major impact on the ability to image underlying basement. A full transect beginning over completely unextended continental crust through to oceanic crust has provided a data set from which estimates of extension and the pre-rifting location of the present continental edge can be made. Two estimates were obtained; 85 km based on faulting and 120 km based on crustal thickness.
Geophysical Journal International (0956-540X) (Wiley / Blackwell), 2009-08 , Vol. 178 , N. 2 , P. 1004-1020

Droits : 2009 Wiley / Blackwell
http://archimer.ifremer.fr/doc/2009/publication-6919.pdf
DOI:10.1111/j.1365-246X.2009.04162.x
http://archimer.ifremer.fr/doc/00000/6919/

Éditeur(s) : HAL CCSD Blackwell Publishing
Résumé : International audience
In the Causses platform (south-east France), Late Hettangian to Sinemurian deposits were interpreted previously as shallow-water carbonate ramp deposits. A new look at these deposits has shown a fault-controlled mosaic carbonate platform that is different from the carbonate ramp models. Within the platform mosaic, 15 lithofacies have been recognized, which are organized in four facies associations, including peritidal, restricted shallow sub-tidal, sand dunes and sub-tidal shelf facies associations. The rapid lateral and vertical facies changes, and the lack of consistent landward or seaward direction indicated by the pattern of facies changes, question the existence of a shoreline suggested by the traditional models for this region. Instead, the facies organization and cycle stacking pattern suggest deposition in a mosaic of intertidal islands between which sub-tidal restricted or open conditions could coexist in very close proximity. Such a platform mosaic would have been defined by tectonic activities along normal faults which segmented the shallow-water Causses platform. The facies and facies associations are arranged into metre-scale, peritidal and sub-tidal cycles that are also variable. Certain cycles show the same stacking pattern in all the sections and seem to be traceable over tens of kilometres. On the contrary, other cycles cannot be correlated; they are present only in specific sections and have a maximum lateral extension of 1 or 2 km. These metre-scale cycles stack to form four medium-scale cycles bounded by surfaces that display sub-aerial exposure features. Medium-scale cycles stack into two larger-scale cycles (tens of metres thick) and are bounded by well-defined karstic surfaces. Based on their lateral continuity and their stacking pattern, the metre-scale cycles are controlled probably by high frequency eustatic variations overprinting the topographic irregularities formed by differential subsidence of fault-bounded blocks. Episodic fault activities may reorganize the topography so that, even if eustatic changes may still be the major control of cycles, the expression and number of cycles could be different. Cycles of medium and large-scale are interpreted as being allogenic, controlled by changes in eustasy and/or subsidence rates as evidenced by their lateral continuity and the correlations of the large-scale cycles with third-order depositional sequences.
ISSN: 1469-3496

hal-00411940
https://hal.archives-ouvertes.fr/hal-00411940
DOI : 10.1111/j.1365-3091.2007.00896.x

Éditeur(s) : Elsevier
Résumé : In biological modelling of the coastal phytoplankton dynamics, the light attenuation coefficient is often expressed as a function of the concentrations of chlorophyll and mineral suspended particulate matter (SPM). In order to estimate the relationship between these parameters over the continental shelf of the northern Bay of Biscay, a set of in situ data has been gathered for the period 1998-2003 when SeaWiFS imagery is available. These data comprise surface measurements of the concentrations of total SPM, chlorophyll, and irradiance profiles from which is derived the attenuation coefficient of the photosynthetically available radiation, K-PAR. The performance of the IFREMER look-up table used to retrieve the chlorophyll concentration from the SeaWiFS radiance is evaluated on this new set of data. The quality of the estimated chlorophyll concentration is assessed from a comparison of the variograms of the in situ and satellite-derived chlorophyll concentrations. Once the chlorophyll concentration is determined, the non living SPM, which is defined as the SPM not related to the dead or alive endogenous phytoplankton, is estimated from the radiance at 555 nm by inverting a semi-analytic model. This method provides realistic estimations of concentrations of chlorophyll and SPM over the continental shelf all over the year. Finally, a relationship, based on non living SPM and chlorophyll, is proposed to estimate K-PAR on the continental shelf of the Bay of Biscay. The same formula is applied to non living SPM and chlorophyll concentrations, observed in situ or derived from SeaWiFS radiance.
Remote Sensing of Environment (0034-4257) (Elsevier), 2005-03 , Vol. 95 , N. 1 , P. 29-46

Droits : 2004 Elsevier Inc. All rights reserved
http://archimer.ifremer.fr/doc/2005/publication-1172.pdf
DOI:10.1016/j.rse.2004.11.007
http://archimer.ifremer.fr/doc/00000/1172/

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/

Éditeur(s) : ISTPM
Résumé : From a sedimentological point of view, the continental shelf of the French Guyana can be divided in three parts, parallel to the littoral: (1) the coastal zone where a very fluid mud is found; (2) a large band of sands which covers the rest of the continental shelf; (3) the zone of pelagic muds which corresponds to the lower part of the continental slope. The passage between the sands of the shelf and the littoral or pelagic muds is obtained by the intermediary of the muddy sands.
Revue des Travaux de l'Institut des Pêches Maritimes (0035-2276) (ISTPM), 1977-12 , Vol. 41 , N. 4 , P. 389-402

Droits : Ifremer
http://archimer.ifremer.fr/doc/1977/publication-1991.pdf
http://archimer.ifremer.fr/doc/00000/1991/

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
This study constitutes one of the few works conducted on the colonization of recent lava flows by fish communities in coral reef environment. It attempted to describe the mechanisms of colonization and environmental variables infuencing the structure of communities on the lava flows of the Piton de la Fournaise volcano at Reunion Island. It also proposed some hypotheses on the mechanisms of selection and speciation of endemic species of thesouthwestern Indian Ocean region, particularly diversified on the most recent lava flows of the Piton de la Fournaise, and provided a model of distribution of environmental and fish assemblage variables in four homogeneous patterns of colonization (landscapes) retained within the study area. The results showed fish community structure strongly related to measured environmental variables, of which depth, width of the island shelf, age of the lava flow and distance to the most recent lava flow were the most influential. It also appeared that the maximum endemic species richness was measured on the shallower stations, with narrow insular shelf, located on recent lava flows, near the lava flow from the eruption of 2007 (latest volcanic event). These characteristics define a harsh environment, to which endemic species seem well-adapted due in particular to their strong demographic and dietary flexibility. Finally, the patterns of colonization were characterized by significantly different environmental variables. The four homogeneous areas, defined by two geomorphological features, basalt blocks and drop-offs, nested within two locations, inside and outside the volcanic enclosure (current caldera), hosted fish communities whose dominant diets mainly depend on the nature, the abundance and the accessibility of available food resources. Overall, the study highlights that during early stages of ecological succession, site selection by fish communities is highly dependent on environmental constraints, specially of volcanic origin, but the physical habitat selection (geomorphology, substrate rugosity, percentage of soft substrate) seems to have littleimportance, while at least on the trophic structure and the distribution of endemic species.
ISSN: 0022-0981

hal-01253768
https://hal.archives-ouvertes.fr/hal-01253768
https://hal.archives-ouvertes.fr/hal-01253768/document
https://hal.archives-ouvertes.fr/hal-01253768/file/Pinault%20et%20al.%20-%202014%20-%20Fish%20community%20structure%20in%20relation%20to%20environmen_hal.pdf
DOI : 10.1016/j.jembe.2014.06.005

Éditeur(s) : Elsevier Science Bv
Résumé : Mechanisms controlling the transfer and retention of silicon (Si) along continental margins are poorly understood, but play a major role in the functioning of coastal ecosystems and the oceanic biological pump of carbon. Deep-sea fans are well recognized as carbon sink spots, but we lack knowledge about the importance of the fans in the global Si cycle. Here, we provide a first estimate of the role played by the Congo deep-sea fan, one of the biggest in the world, in the Si cycle. Sediment cores sampled in the deep-sea fan were analyzed to build a Si mass balance. An exceptionally high accumulation rate of amorphous silica aSiO(2) (2.29 +/- 0.58 mol Si m(-2) y(-1)) was found, due to a high sedimentation rate and the presence of aluminum in the sediments. Although favored by bioirrigation, recycling fluxes remained low (0.3 mol Si m(-2) y(-1)) and reconstructed input fluxes could only be explained by lateral inputs coming from the canyon. Preliminary calculations show that the rapid transport of aSiO(2) through the canyon and the excellent preservation efficiency in the sediments imply that 50% of aSiO(2) river inputs from the Congo River accumulate annually in the deep-sea fan. Si:C ratios in deep-sea fan sediments were very low (0.2) and only three times as high as those measured in the river itself, which suggests that material from the river and the continental shelf was delivered directly through the canyon, with very little time for Si and C cycle decoupling to take place.
Journal Of Marine Systems (0924-7963) (Elsevier Science Bv), 2015-01 , Vol. 141 , P. 71-79

Droits : 2014 Elsevier B.V. All rights reserved.
http://archimer.ifremer.fr/doc/00251/36242/35797.pdf
DOI:10.1016/j.jmarsys.2014.07.010
http://archimer.ifremer.fr/doc/00251/36242/

Éditeur(s) : Observatoire Océanologique de Banyuls sur mer
Résumé : A new species of a polychaetous annelid belonging to the genus Polydora is described. It was collected on the continental shelf of the western Mediterranean sea. Some morphological features are not consistent with the generic diagnosis. [NOT CONTROLLED OCR]
Vie et Milieu (Observatoire Océanologique de Banyuls sur mer), 1974 , Vol. 24 , N. 3A , P. 479-486

Droits : Observatoire Océanologique de Banyuls sur mer
http://archimer.ifremer.fr/doc/1974/publication-4981.pdf
http://archimer.ifremer.fr/doc/00000/4981/

Éditeur(s) : Gauthier-Villars
Résumé : Pegasus current measurements carried out along a section located off French Guiana are presented; the section was repeated five times from September 1989 to June 1991 during the NOE (region Nord-Ouest equatoriale)/STACS (Sub Tropical Atlantic Climate Studies) cruises on board the NOAA (National Oceanographic and Atmospheric Administration) research vessels. The data (vertical and horizontal distributions) show, as suggested by earliest observations, the presence of different currents. At the surface, and in winter, the North Brazil Current (NBC) flows northwestward (positive), is strong (120 cm/s), confined in the first 250 m, coastally trapped (within 250 km) and fed by offshore waters; in summer the NBC strengthens (the velocity increases to 150 cm/s), vertically extends (down to 800 m) and veers offshore; the mean NBC mass flux computed from all the sections available is 34 +/- 9 Sv with absolute maximum and minimum respectively in September 1989 (81 +/- 4 Sv) and February 1990 (13 +/- 1 Sv). Subsurface, a southeastward (negative) undercurrent (herein after named Western Boundary UnderCurrent) is present in winter-spring and located in the layer 250-800 m with similar velocities in February 1990 (- 33 cm/s) and June 1991 (- 29 cm/s) but with largest vertical and horizontal extensions in the latter case; in summer (September 1989 and September 1990) this undercurrent is absent; the mean mTBUC mass flux is - 9 +/- 3 Sv; the maximum is observed in June 1991 (- 19 +/- 2 Sv) and the minimum in February 1990 (- 3 +/- 0.4 Sv) and January 1991 (- 5 +/- I Sv). Deeper, the equatorward Deep Western Boundary Current is trapped against the continental shelf (within 100 km of the shelf break), extends downward from 1 200 to 3 000 m depth with the velocity core centred in the 1 700-2 000 m layer, is maximum (- 50 cm/s) in spring-summer and minimum (- 23 cm/s) in winter; the absolute velocity (- 92 cm/s) has been recorded at 2 000 m depth in September 1989 suggesting a strong variability at this level; the mean equatorward DWBC mass flux is - 30 +/- 14 Sv with absolute maximum and minimum respectively in September 1989 (- 59 +/- 6 Sv) and September 1990 (- 7 +/- 1 Sv). The Integrated Mass, Temperature and Salt Fluxes (IMF, ITF and ISF) with the cumulated errors, computed across the whole section and down to 3 000 m depth for the September 1990, January 1991 and June 1991 cruises, are all positive in September 1990 (respectively 1.9 +/- 19 Sv, 3.1 +/- 30.1 PW and 74 +/- 1 845 Tt/s) but all negative both in January 1991 (- 13.3 +/- 17.0 Sv, - 15.6 +/- 26.5 PW and - 478 +/- 1594 Tt/s) and June 1991 (- 3.8 +/- 10.1 Sv, - 4.0 +/- 16.3 PW, - 130 +/- 989 Tt/s) showing a strong variability between the summer and winter periods. The mean IMF, ITF and ISF values (respectively - 5.1 +/- 46.4 Sv, - 5.2 +/- 73 PW and - 178 +/- 4428 Tt/s) are high and negative, indicating the large influence of the DWBC and the associated North Atlantic Deep Water (upper part) off French Guiana at 5 degrees N.
Oceanologica Acta (0399-1784) (Gauthier-Villars), 1994 , Vol. 17 , N. 2 , P. 143-157

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00098/20881/18495.pdf
http://archimer.ifremer.fr/doc/00098/20881/

Éditeur(s) : HAL CCSD Geological Society of America
Résumé : International audience
In this study, a novel application of a statistical approach is utilized for analysis of downhole logging data from Miocene-aged siliciclastic shelf sediments on the New Jersey Margin (eastern USA). A multivariate iterative nonhierarchical cluster analysis (INCA) of spectral gamma-ray logs from Integrated Ocean Drilling Program (IODP) Expedition 313 enables lithology within this siliciclastic succession to be inferred and, through comparison with the 1311 m of recovered core, a continuous assessment of depositional sequences is constructed. Signifi cant changes in INCA clusters corroborate most key stratigraphic surfaces interpreted from the core, and this result has particular value for surface recognition in intervals of poor core recovery. This analysis contributes to the evaluation of sequence stratigraphic models of large-scale clinoform complexes that predict depositional environments, sediment composition, and stratal geometries in response to sea-level changes. The novel approach of combining statistical analysis with detailed lithostratigraphic and seismic refl ection data sets will be of interest to any scientists working with downhole logs, especially spectral gamma-ray data, and also provides a reference for the strengths and weaknesses of multi component analysis applied to continental margin lithofacies. The method presented here is appropriate for evaluating successions elsewhere and also has value for hydrocarbon exploration where sequence stratigraphy is a fundamental tool.
EISSN: 1553-040X

insu-00858238
https://hal-insu.archives-ouvertes.fr/insu-00858238
DOI : 10.1130/GES00913.1

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/

Éditeur(s) : Université de Bretagne Occidentale
Résumé : The negative impact of the man on the environment unquestionably increases. The coastal environment as a whole is the maritime environment which is the most exposed to man-made eutrophication. For instance, nitrate loads to coastal waters off Brittany (France) have increased 10 times (from 3 to s 30mg L-1NO3) during the four last decades. Eutrophication of this coastal zone is now a recurrent problem, more and more worrying. This eutrophication exhibits two main forms : " green tides ", which are caused by local proliferations and stranding of green macro-algae (particularly the Ulva species) in nitrogen-enriched areas ; phytoplanktonic blooms, which are responsible for coloured water events, toxic species can be present (Pseudo-Nitzschia, Alexandrium, Dinophysis), and induce banning of shellfish consumption. The objectives of this study are to assess the respective role of various rivers (especially the Loire and the Vilaine) in the eutrophication of the Brittany shelf ecosystem and test the impact of nitrogen enrichment in the triggering of Pseudo-Nitzchia toxicity. For these purposes, a coupled hydrodynamical/ biogeochemical 3D model has been developed and validated against past measured time-series and satellite images. After a brief analysis of primary production over the Brittany shelf under different conditions, we show a description of the real time adaptation of this model. Daily results are currently presented in real time on www.previmer.org web site. The inability of the model to correctly simulate near shore phytoplankton is worsened in this model by the fact that the turbidity field used is a climatological one, made by satellite images averaged on a decadal basis. First, near shore pixels of satellite images are scarcely reliable, secondly a climatological mean cannot represent the sudden bursts or drops of the real turbidity, highly dependent on the actual sea-state : this can explain also why the model at this moment fails to reproduce a sudden bloom occurring in a short period of sunny and calm weather. The simulated Pseudo-Nitzschia biomass and induced risk of toxicity in the water column cannot really be validated offshore, because monitoring measurements are available only near the coast, and deal only with toxicity in benthic filter feeders. To get temporarily rid of that problem, an interesting improvement would be to add to the operational model the bio-accumulation of toxin in the shellfishes : simulated concentrations in shellfish fresh would become directly comparable with usual measurements of the monitoring networks. Our model points out the important impact of Loire river loads on the primary production on the western and southern Brittany. This result is crucial for administrations in charge of reducing the terrestrial loadings responsible for eutrophication, because it can delay reduction programs on small tributaries until the main input from the Loire has been significantly reduced. A question arises, about the reliability of the haline stratification in the model, because the horizontal extent of the Loire plume will be enhanced by a stronger stratification.
L'eutrophisation des milieux marins côtiers, de plus en plus importante, représente un des impacts majeurs des activités humaines sur l'environnement. Les phénomènes d'eutrophisation sont en constante augmentation ; ces dernières décennies ont vu le nombre de sites touchés augmenter de par le monde. La bande côtière bretonne est particulièrement concernée par ce phénomène. L'eutrophisation s'y manifeste de deux façons : "Des phénomènes de marée vertes, très localisées, qui sont provoqués par la croissance excessive et l'échouage de macro-algues du genre Ulva dans ces zones riches en azote ; Des blooms de phytoplancton à l'origine des phénomènes d'eaux colorées, qui peuvent aussi provoquer des interdictions de consommation de coquillages lorsque les espèces mises en jeu sont toxiques (Pseudo-Nitzschia, Alexandrium, Dinophysis). L'objectif de ce travail est multiple : il vise à mettre en évidence et à comprendre l'impact et le rôle des apports en nutriments sur la production primaire et l'eutrophisation des milieux côtiers. Ce travail a aussi pour ambition l'identification et la compréhension des causes des phénomènes d'eutrophisation et permettre ainsi d'apporter des solutions ou des pistes d'amélioration. En n, il a aussi un objectif de prévision à court terme de l'état biologique sur la zone. Pour atteindre ces objectifs, un modèle en temps réel a été mis en oeuvre. Les résultats de simulations numériques et de mesures satellitaires sont présentés sur internet : www.previmer.org. L'outil principal de ce travail est un modèle couplé physique/biogéochimie. La partie hydrodynamique est fournie par le code Mars3D (3D hydrodynamical Model for Application at Regional Scale) développé à IFREMER. Au code hydrodynamique Mars3D est couplé le modèle des cycles de l'azote, du phosphore et du silicium d'IFREMER. Le modèle couplé permet de simuler en 3 dimensions et de manière dynamique les courants, le brassage horizontal et vertical, les champs de température et de salinité, mais aussi les principaux cycles de nutriments, reproduisant ainsi les conditions déterminantes de la production primaire. La croissance des algues est modélisée, et nous permet de voir l'influence des panaches de dilution des principales rivières bretonnes sur leur croissance. Les diffcultés du modèle à correctement simuler les concentrations en phytoplancton près des zones côtières, sont probablement dues à l'utilisation d'une climatologie de concentration en matière en suspension fondée sur des données satellitaires. Tout d'abord, les pixels côtiers des images satellitaires sont entachés d'erreurs, ensuite une climatologie n'est pas capable de représenter les apports soudains des fleuves lors des crues. Cela peut expliquer l'incapacité du modèle a représenter certains blooms liés à des périodes ensoleilées et calmes. A ce modèle de base nous avons ajouté un genre spécifique de phytoplancton : le genre Pseudo-Nitzschia. Certaines espèces de Pseudo-Nitzschia sont réputées toxiques. En effet, ce phytoplancton a la capacité de synthétiser une toxine : l'acide domoïque. Cette toxine est responsable du syndrome ASP (Amnesic Shellfish Poisoning). Le modèle reproduit globalement les mêmes zones de toxicité que les mesures du REPHY, et donne des résultats encourageants. L'étude montre que la Loire influence une large partie de la bande côtière bretonne ; son panache remonte jusqu'au nord de la mer d'Iroise, et contribue pour une grande part à l'enrichissement du sud et de l'ouest de la Bretagne. Le traçage de l'azote en provenance de la Loire au sein des cycles biogéochimiques nous a permis de quantifier cet enrichissement.

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00015/12603/9481.pdf
http://archimer.ifremer.fr/doc/00015/12603/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
The New Jersey continental shelf extends 150 km off the shoreline. During IODP Expedition 313, siliciclastic deposits of late Eocene to late Pleistocene age were drilled down to 631, 669 and 755 m below seafloor at sites 27A, 28A and 29A respectively in very shallow waters (33.5 to 36 m depth). Pore water salinities display multilayered brackish-salty-brine units 10 to 170 m thick, where low-salinity water is preferentially stored in fine-grained sediments. The sharp boundaries of these buried aquifers are often marked by cemented layers a few centimetres thick. The mineralogy and scanning electron microscope observations of these layers show two phases of cementation by authigenic minerals: (1) the early carbonate cement is frequently associated with pyrite, and (2) the late silicate cement infills the residual porosity. The isotopic compositions of the carbonate cements vary widely: −2.4 < δ¹⁸O ‰ VPDB < +2.8; −15.1 < δ¹³C ‰ VPDB < +15.6. The δ¹⁸O values indicate that the carbonate cements precipitated with pore waters comprising variable mixtures of seawater and ¹⁸O-depleted fresh water originating from submarine groundwater discharge. The δ¹³C values of the carbonate cements are related to organic matter diagenesis, providing ¹³C-depleted dissolved inorganic carbon during bacterial sulphate reduction and anaerobic oxidation of methane, and ¹³C-rich dissolved inorganic carbon during methanogenesis. The diagenetic cementation processes included chemical weathering of reactive silicate minerals by the CO²-rich pore waters issued from organic matter diagenesis that released bicarbonate, cations and dissolved silica, which were further precipitated as carbonate and silicate cements. The estimated range of temperature (18±4 °C) during carbonate precipitation is consistent with carbonate cementation at moderate burial depths; however, silicate cementation occurred later during diagenesis at deeper burial depths.
ISSN: 0276-0460

hal-01559985
https://hal.archives-ouvertes.fr/hal-01559985
DOI : 10.1007/s00367-017-0506-6

Éditeur(s) : HAL CCSD
Résumé : In the bay of Aigues-Mortes, the managers of the co astal cities try to preserve the socio-economic and patrimonial stakes against the coastal hazards, such as contamination, storm surge and erosion. In this context, a massive beach nourishment of sand (1 million of m3 for 10km of coastline) was made at the beginning of year 2008 to reduce erosion. The REPBAM project (REchargements et Panaches sédiment aires dans la Baie d'Aigues-Mortes) aims to qualify and quantify by in-situ measurements and numerical modelling: 1. the geomorphological evolution of this modified coast and 2. the impact of the sediment's resuspension on the coastal ecosystems, in particular the one of the Posidonia oceanica seagrass. A numerical modelling "wave/current/sediment" is first implemented for December 2008. Nested and curvilinear grids allow a very high resolution for the beach area but also include the inner shelf where the seagrasses are located. Hydrodynamic and topo-bathymetric measurements were acquired from January to May 2012. Model and measurements results show the same trends during storms: strong currents, seaward migrationof the innerbar, sediment resuspension and turbid on the inner shelf.
Coastal Dynamics 2013
Arcachon, France

hal-00908082
https://hal.archives-ouvertes.fr/hal-00908082

Éditeur(s) : Elsevier
Résumé : Emplacement of post-glacial turbidites is commonly controlled by rapid changes in sea level or by seismicity. On the continental rise of the Gulf of Lions (Western Mediterranean), an aseismic area, we identified turbiditic beds deposited during the rising stage and highstand of sea level. Swath bathymetry, sediment cores, in situ Cone Penetrating Tests (CPTU), heavy mineral associations and radiocarbon dating determined the source, composition, distribution and age of the turbiditic beds. Turbidites are composed of homogeneous to positively graded silts to medium sand with quartz (up to 90%), shell debris and shelfal benthic faunas. Their distribution on the sea floor is very patchy and controlled by abundant inherited erosional bedforms. Their source is found in relict regressive sands at the outershelf. Their deposition occurred just after the onset of the post-glacial sea level rise and the concomitant sediment starvation of the Rhone deep sea turbiditic system until recently. Whilst canyons are fed with sand by strong seasonal hydro-sedimentary dynamics on the outershelf, the emplacement of post-glacial turbidites is not controlled by sea level changes but probably by the periodic flushing of the canyons. Our study revealed that this low energy aseismic margin undergoes significant transport of sand, down to the base of slope, during the sea-level rise and the Holocene highstand.
Marine Geology (0025-3227) (Elsevier), 2009-02 , Vol. 257 , N. 1-4 , P. 65-86

Droits : 2009 Published by Elsevier Ltd.
http://archimer.ifremer.fr/doc/2009/publication-6316.pdf
DOI:10.1016/j.margeo.2008.10.013
http://archimer.ifremer.fr/doc/00000/6316/

Éditeur(s) : John Wiley & Sons
Résumé : Based on all available seismic refraction data, the seismic structure of the Western Approaches to the English Channel and the South Armorican continental shelf has been established. The correlation of seismic velocities showed a three-fold structure, related to geological layers as follows: 1. High-velocity, deep sequence (4.4-6.6km/sec): metamorphic basement and Lower to Middle Palaeozoic. 2. Intermediate sequence (3.6-4.3km/sec): Permo-Triassic (and Jurassic?) and possibly also Lower Cretaceous on the margin of the Western Approaches. 3. Upper sequence (1.9-3.6km/sec): Cretaceous and Cenozoic sediments. An acoustic unconformity appears to be present between the Upper sequence and the High velocity and Intermediate sequences. Different geomorphology characterizes these layers: the Palaeozoic is tectonized and generally follows the Hercynian structural trends; mainly Permo-Triassic sediments fill the depressions of the Palaeozoic floor, but only in the Western Approaches; eastwards-transgressive Cretaceous and Cenozoic sediments cover discordantly the preceding layers. [NOT CONTROLLED OCR]
Petroleum and the continental shelf of North-west Europe (John Wiley & Sons), 1975 , P. 29-43

Droits : John Wiley & Sons
http://archimer.ifremer.fr/doc/1975/publication-5465.pdf
http://archimer.ifremer.fr/doc/00000/5465/