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Registros recuperados: 17
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A numerical modeling study of the Southern Senegal upwelling shelf: Circulation and upwelling source waters ArchiMer
Ndoye, S; Capet, Xavier; Estrade, Philippe; Machu, Eric; Kounta, L; Sow, B; Diakhate, M; Gayet, At.
The regional ocean circulation along the Southern Senegal shelf is studied using a numerical model for varying forcing fields during the upwelling season (November-May). The main objective is to study the shelf circulation of the marine environment in the Southern Senegal Upwelling Shelf (SSUS), the Lagrangian pathways by which waters are transported to the surface in the upwelling tongue and the fate of these waters. Model results are compared with hydrographic measurements during UPSEN2-ECOAO survey and satellite images datasets. The upwelling source waters and also the warm nearshore waters are analyzed, from a Lagrangian point of view, by computing the paths of particles that are passively advected by the regional ocean model velocity field (ROMS). It...
Tipo: Text Palavras-chave: Upwelling; Ocean circulation; Modeling; Coastal dynamics; Shelf; ROMS..
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00472/58346/60900.pdf
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Biomass changes and trophic amplification of plankton in a warmer ocean ArchiMer
Chust, Guillem; Allen, J. Icarus; Bopp, Laurent; Schrum, Corinna; Holt, Jason; Tsiaras, Kostas; Zavatarelli, Marco; Chifflet, Marina; Cannaby, Heather; Dadou, Isabelle; Daewel, Ute; Wakelin, Sarah L.; Machu, Eric; Pushpadas, Dhanya; Butenschon, Momme; Artioli, Yuri; Petihakis, Georges; Smith, Chris; Garcon, Veronique; Goubanova, Katerina; Le Vu, Briac; Fach, Bettina A.; Salihoglu, Baris; Clementi, Emanuela; Irigoien, Xabier.
Ocean warming can modify the ecophysiology and distribution of marine organisms, and relationships between species, with nonlinear interactions between ecosystem components potentially resulting in trophic amplification. Trophic amplification (or attenuation) describe the propagation of a hydroclimatic signal up the food web, causing magnification (or depression) of biomass values along one or more trophic pathways. We have employed 3-D coupled physical-biogeochemical models to explore ecosystem responses to climate change with a focus on trophic amplification. The response of phytoplankton and zooplankton to global climate-change projections, carried out with the IPSL Earth System Model by the end of the century, is analysed at global and regional basis,...
Tipo: Text Palavras-chave: Ecosystem model; Food web; Plankton; Primary production; Sea warming; Trophic amplification.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00188/29966/28481.pdf
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Comparative study of potential transfer of natural and anthropogenic cadmium to plankton communities in the North-West African upwelling ArchiMer
Auger, Pierre-amael; Machu, Eric; Gorgues, Thomas; Grima, Nicolas; Waeles, Mathieu.
A Lagrangian approach based on a physical-biogeochemical modeling was used to compare the potential transfer of cadmium (Cd) from natural and anthropogenic sources to plankton communities (Cd-uptake) in the NorthWest African upwelling. In this region, coastal upwelling was estimated to be the main natural source of Cd while the most significant anthropogenic source for marine ecosystem is provided by phosphate industry. In our model experiment, Cd-uptake (natural or anthropogenic) in the North-West African upwelling is the result of an interplay between the Cd dispersion (by advection processes) and the simulated biological productivity. In the Moroccan waters, advection processes limit the residence time of water masses resulting in a low natural...
Tipo: Text Palavras-chave: Cadmium; North-West African upwelling; Phosphate industry; Dispersion; Bioaccumulation; Plankton ecosystem.
Ano: 2015 URL: https://archimer.ifremer.fr/doc/00252/36310/35200.pdf
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Complex small pelagic fish population patterns arising from individual behavioral responses to their environment ArchiMer
Brochier, Timothee; Auger, Pierre-amael; Pecquerie, Laure; Machu, Eric; Capet, Xavier; Thiaw, Modou; Mbaye, Baye Cheikh; Braham, Cheikh-baye; Ettahiri, Omar; Charouki, Najib; Sene, Ousseynou Ndaw; Werner, Francisco; Brehmer, Patrice.
Small pelagic fish (SPF) species are heavily exploited in eastern boundary upwelling systems (EBUS) as their transformation products are increasingly used in the world food chain. Management relies on regular monitoring, but there is a lack of robust theories for the emergence of the populations’ traits and their evolution in highly variable environments. This work aims to address existing knowledge gaps by combining physical and biogeochemical modelling with an individual life-cycle based model applied to round sardinella (Sardinella aurita) off northwest Africa, a key species for regional food security. Our approach focused on the processes responsible for seasonal migrations, spatio-temporal size-structure, and interannual biomass fluctuations....
Tipo: Text Palavras-chave: Small pelagic fish; Sardinella aurita; Fish migration; Eastern boundary upwelling system; Individual based biophysical models; Dynamic energy budget.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00433/54433/56088.pdf
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Coupled physical/biogeochemical modeling including O-2-dependent processes in the Eastern Boundary Upwelling Systems: application in the Benguela ArchiMer
Gutknecht, E.; Dadou, Isabelle; Le Vu, B.; Cambon, Gildas; Sudre, J.; Garcon, V.; Machu, Eric; Rixen, T.; Kock, A.; Flohr, A.; Paulmier, A.; Lavik, G..
The Eastern Boundary Upwelling Systems (EBUS) contribute to one fifth of the global catches in the ocean. Often associated with Oxygen Minimum Zones (OMZs), EBUS represent key regions for the oceanic nitrogen (N) cycle. Important bioavailable N loss due to denitrification and anammox processes as well as greenhouse gas emissions (e. g, N2O) occur also in these EBUS. However, their dynamics are currently crudely represented in global models. In the climate change context, improving our capability to properly represent these areas is crucial due to anticipated changes in the winds, productivity, and oxygen content. We developed a biogeochemical model (BioEBUS) taking into account the main processes linked with EBUS and associated OMZs. We implemented this...
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Ano: 2013 URL: http://archimer.ifremer.fr/doc/00152/26314/24376.pdf
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Do Sardinella aurita spawning seasons match local retention patterns in the Senegalese-Mauritanian upwelling region? ArchiMer
Mbaye, Baye Cheikh; Brochier, Timothee; Echevin, Vincent; Lazar, Alban; Levy, Marina; Mason, Evan; Gaye, Amadou Thierno; Machu, Eric.
Sardinella aurita is the most abundant small pelagic fish in the Senegalese-Mauritanian region. The success of its reproduction crucially depends on the local circulation as this determines whether larvae reach coastal nursery areas favorable to their survival or are dispersed into the open ocean. As a first step towards evaluating sardinella vulnerability to climate-driven hydrodynamical changes, this study aims at underpinning how transport pathways drive optimal spatial and seasonal patterns for sardinella reproduction. We have used two estimates of the Senegalese-Mauritanian coastal seasonal circulation simulated by two hydrodynamical model configurations that differ in their forcing and topography. Nursery areas are determined by evaluating coastal...
Tipo: Text Palavras-chave: Bio-physical model; Canary current system; Connectivity; Larval retention; Recruitment; Sardinella aurita; Senegalese-Mauritanian upwelling; Spawning.
Ano: 2015 URL: https://archimer.ifremer.fr/doc/00254/36524/36733.pdf
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Fine-scale recognition and use of mesoscale fronts by foraging Cape gannets in the Benguela upwelling region ArchiMer
Sabarros, Philippe S.; Gremillet, David; Demarcq, Herve; Moseley, Christina; Pichegru, Lorien; Mullers, Ralf H. E.; Stenseth, Nils C.; Machu, Eric.
Oceanic structures such as mesoscale fronts may become hotspots of biological activity through concentration and enrichment processes. These fronts generally attract fish and may therefore be targeted by marine top-predators. In the southern Benguela upwelling system, such fronts might be used as environmental cues by foraging seabirds. In this study we analyzed high-frequency foraging tracks (GPS, 1 s sampling) of Cape gannets Morus capensis from two colonies located on the west and east coast of South Africa in relation to mesoscale fronts detected on daily high-resolution chlorophyll-a maps (MODIS, 1 km). We tested the association of (i) searching behavior and (ii) diving activity of foraging birds with mesoscale fronts. We found that Cape gannets shift...
Tipo: Text Palavras-chave: Seabird; Environmental cue; Behavioral shift; Area-restricted search; Feeding activity; Fractal landscape; Oceanographic fronts; Morus capensis; Southern Benguela; South Africa.
Ano: 2014 URL: https://archimer.ifremer.fr/doc/00236/34756/34575.pdf
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First Evidence of Anoxia and Nitrogen Loss in the Southern Canary Upwelling System ArchiMer
Machu, Eric; Capet, Xavier; Estrade, Philippe; Ndoye, S.; Brajard, J.; Baurand, Francois; Auger, P.-a.; Lazar, A.; Brehmer, Patrice.
The northeastern Atlantic hosts the most ventilated subsurface waters of any eastern boundary upwelling system, while coastal upwelling source waters are slightly above hypoxic levels. Anoxic conditions have previously been found offshore inside mesoscale eddies whose core waters undergo oxygen consumption for many months. Based on circumstantial in situ observations this study demonstrates that the Senegalese coastal ocean is subjected to episodic occurrence of zero dissolved oxygen concentration at depth along with elevated nitrite concentration (11 mmol/m3) and nitrate/nitrite deficit to phosphate, thereby indicating severe anoxia and intense nitrogen loss. The anoxic event was associated with a prolonged upwelling relaxation episode in March 2012 and a...
Tipo: Text Palavras-chave: Oxygen; Canary upwelling system; Anoxia; Denitrification; Shallow continental shelf.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00479/59020/61640.pdf
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Influence of mesoscale eddies on biological production in the Mozambique Channel: Several contrasted examples from a coupled ocean-biogeochemistry model ArchiMer
Jose, Yonss; Aumont, Olivier; Machu, Eric; Penven, Pierrick; Moloney, C. L.; Maury, Olivier.
The impact of mesoscale activity on phytoplankton and nutrient distribution in the Mozambique Channel was simulated by coupling a biogeochemical model (PISCES) with a regional oceanic model (ROMS). Examples of the effects of eddies on the biogeochemistry of the Mozambique Channel are presented to illustrate the complexity of the system. In the model, several cyclonic eddies were found with low concentrations of chlorophyll at their cores, which contrasts with previous studies in the open ocean. In addition, several anticyclonic eddies were simulated with high concentrations of chlorophyll at their cores. Phytoplankton growth within these mesoscale features (both cyclonic and anticyclonic eddies) occurred in response to nutrient injection into the euphotic...
Tipo: Text Palavras-chave: Ocean physical-biogeochemical coupling; Cyclonic and anticyclonic eddies; Chlorophyll; Nutrients; Mozambique Channel.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00162/27320/25549.pdf
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Inverse Estuaries in West Africa: Evidence of the Rainfall Recovery? ArchiMer
Descroix, Luc; Sané, Yancouba; Thior, Mamadou; Manga, Sylvie-paméla; Ba, Boubacar Demba; Mingou, Joseph; Mendy, Victor; Coly, Saloum; Dièye, Arame; Badiane, Alexandre; Senghor, Marie-jeanne; Diedhiou, Ange-bouramanding; Sow, Djiby; Bouaita, Yasmin; Soumaré, Safietou; Diop, Awa; Faty, Bakary; Sow, Bamol Ali; Machu, Eric; Montoroi, Jean-pierre; Andrieu, Julien; Vandervaere, Jean-pierre.
In West Africa, as in many other estuaries, enormous volumes of marine water are entering the continent. Fresh water discharge is very low, and it is commonly strongly linked to rainfall level. Some of these estuaries are inverse estuaries. During the Great Sahelian Drought (1968–1993), their hyperhaline feature was exacerbated. This paper aims to describe the evolution of the two main West African inverse estuaries, those of the Saloum River and the Casamance River, since the end of the drought. Water salinity measurements were carried out over three to five years according to the sites in order to document this evolution and to compare data with the historical ones collected during the long dry period at the end of 20th century. The results show that in...
Tipo: Text Palavras-chave: Water salinity; Inverse estuaries; West Africa; Drought; Mangrove.
Ano: 2020 URL: https://archimer.ifremer.fr/doc/00612/72434/71381.pdf
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Nitrogen transfers off Walvis Bay: a 3-D coupled physical/biogeochemical modeling approach in the Namibian upwelling system ArchiMer
Gutknecht, E.; Dadou, Isabelle; Marchesiello, P.; Cambon, Gildas; Le Vu, B.; Sudre, J.; Garcon, V.; Machu, Eric; Rixen, T.; Kock, A.; Flohr, A.; Paulmier, A.; Lavik, G..
Eastern boundary upwelling systems (EBUS) are regions of high primary production often associated with oxygen minimum zones (OMZs). They represent key regions for the oceanic nitrogen (N) cycle. By exporting organic matter (OM) and nutrients produced in the coastal region to the open ocean, EBUS can play an important role in sustaining primary production in subtropical gyres. However, losses of fixed inorganic N through denitrification and anammox processes take place in oxygen depleted environments such as EBUS, and can potentially mitigate the role of these regions as a source of N to the open ocean. EBUS can also represent a considerable source of nitrous oxide (N2O) to the atmosphere, affecting the atmospheric budget of N2O. In this paper a 3-D coupled...
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Ano: 2013 URL: http://archimer.ifremer.fr/doc/00152/26316/24373.pdf
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On the Dynamics of the Southern Senegal Upwelling Center: Observed Variability from Synoptic to Superinertial Scales ArchiMer
Capet, Xavier; Estrade, Philippe; Machu, Eric; Ndoye, Siny; Grelet, Jacques; Lazar, Alban; Marie, Louis; Dausse, Denis; Brehmer, Patrice.
Upwelling off southern Senegal and Gambia takes place over a wide shelf with a large area where depths are shallower than 20 m. This results in typical upwelling patterns that are distinct (e.g., more persistent in time and aligned alongshore) from those of other better known systems, including Oregon and Peru where inner shelves are comparatively narrow. Synoptic to superinertial variability of this upwelling center is captured through a 4-week intensive field campaign, representing the most comprehensive measurements of this region to date. The influence of mesoscale activity extends across the shelf break and far over the shelf where it impacts the midshelf upwelling (e.g., strength of the upwelling front and circulation), possibly in concert with wind...
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Ano: 2017 URL: http://archimer.ifremer.fr/doc/00374/48541/48842.pdf
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Seasonal cycle of desert aerosols in western Africa: analysis of the coastal transition with passive and active sensors ArchiMer
Senghor, Habib; Machu, Eric; Hourdin, Frederic; Gaye, Amadou Thierno.
The impact of desert aerosols on climate, atmospheric processes, and the environment is still debated in the scientific community. The extent of their influence remains to be determined and particularly requires a better understanding of the variability of their distribution. In this work, we studied the variability of these aerosols in western Africa using different types of satellite observations. Sea-WiFS (Sea-Viewing Wide Field-of-View Sensor) and OMI (Ozone Monitoring Instrument) data have been used to characterize the spatial distribution of mineral aerosols from their optical and physical properties over the period 2005-2010. In particular, we focused on the variability of the transition between continental western African and the eastern Atlantic...
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Ano: 2017 URL: https://archimer.ifremer.fr/doc/00393/50442/69636.pdf
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SST subseasonal variability in the central Benguela upwelling system as inferred from satellite observations (1999-2009) ArchiMer
Goubanova, Katerina; Illig, Serena; Machu, Eric; Garcon, Veronique; Dewitte, Boris.
Subseasonal variability of Sea Surface Temperature (SST) in the central Benguela upwelling system is investigated using TMI satellite-derived data over the period 1999-2009. Spatial patterns and time-frequency characteristics of subseasonal variability are documented based on Empirical Orthogonal Functions (EOF) decomposition and wavelet analysis. Despite the land contamination of the TMI satellite data within approximately 100 km off the coast the first EOF of SST anomalies allows characterizing the coastal upwelling variability at the subseasonal scale. Two regimes of variability are evidenced: a submonthly (2-30 days) regime with a dominant 11 days oscillation and a lower frequency intraseasonal (30-90 days) regime with a dominant 61 days oscillation....
Tipo: Text Palavras-chave: Benguela upwelling; Satellite observations; Intraseasonal variability; Wind-SST relationship; Mean vertical stratification; Antarctic oscillation.
Ano: 2013 URL: http://archimer.ifremer.fr/doc/00164/27565/25928.pdf
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Stable isotope analyses revealed the influence of foraging habitat on mercury accumulation in tropical coastal marine fish ArchiMer
Le Croizier, Gael; Schaal, Gauthier; Point, David; Le Loc'H, Francois; Machu, Eric; Fall, Massal; Munaron, Jean-marie; Boye, Aurelien; Walter, Pierre; Lae, Raymond; De Morais, Luis Tito.
Bioaccumulation of toxic metal elements including mercury (Hg) can be highly variable in marine fish species. Metal concentration is influenced by various species-specific physiological and ecological traits, including individual diet composition and foraging habitat. The impact of trophic ecology and habitat preference on Hg accumulation was analyzed through total Hg concentration and stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) analyses in the muscle of 132 fish belonging to 23 different species from the Senegalese coast (West Africa), where the marine ecosystem is submitted to nutrients inputs from various sources such as upwelling or rivers. Species-specific ecological traits were first investigated and results showed that vertical (i.e....
Tipo: Text Palavras-chave: Methylmercury sources; Trophic ecology; Feeding habitat; Metal bioaccumulation; Chemical tracers; Isotopic niche.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00458/57013/58912.pdf
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Trophic ecology influence on metal bioaccumulation in marine fish: Inference from stable isotope and fatty acid analyses ArchiMer
Le Croizier, Gael; Schaal, Gauthier; Gallon, Regis; Fall, Massal; Le Grand, Fabienne; Munaron, Jean-marie; Rouget, Marie-laure; Machu, Eric; Le Loc'H, Francois; Lae, Raymond; De Morais, Luis Tito.
The link between trophic ecology and metal accumulation in marine fish species was investigated through a multi-tracers approach combining fatty acid (FA) and stable isotope (SI) analyses on fish from two contrasted sites on the coast of Senegal, one subjected to anthropogenic metal effluents and another one less impacted. The concentrations of thirteen trace metal elements (As, Cd, Co, Cr, Cu, Fe, Li, Mn, Ni, Pb, Sn, U, and Zn) were measured in fish liver. Individuals from each site were classified into three distinct groups according to their liver FA and muscle SI compositions. Trace element concentrations were tested between groups revealing that bioaccumulation of several metals was clearly dependent on the trophic guild of fish. Furthermore,...
Tipo: Text Palavras-chave: Trace elements; Biochemical tracers; Diet; Contamination; Senegal; Tropical fish.
Ano: 2016 URL: https://archimer.ifremer.fr/doc/00348/45908/45707.pdf
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What drives the spatial variability of primary productivity and matter fluxes in the north-west African upwelling system? A modelling approach ArchiMer
Auger, Pierre-amael; Gorgues, Thomas; Machu, Eric; Aumont, Olivier; Brehmer, Patrice.
A comparative box analysis based on a multi-decadal physical-biogeochemical hindcast simulation (1980-2009) was conducted to characterize the drivers of the spatial distribution of phytoplankton biomass and production in the north-west (NW) African upwelling system. Alongshore geostrophic flow related to large-scale circulation patterns associated with the influence of coastal topography is suggested to modulate the coastal divergence, and then the response of nutrient upwelling to wind forcing. In our simulation, this translates into a coastal upwelling of nitrate being significant in all regions but the Cape Blanc (CB) area. However, upwelling is found to be the dominant supplier of nitrate only in the northern Saharan Bank (NSB) and the...
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Ano: 2016 URL: https://archimer.ifremer.fr/doc/00363/47458/69565.pdf
Registros recuperados: 17
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