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Registros recuperados: 17
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A biophysical model of S. aurita early life history in the northern Gulf of Guinea ArchiMer
Kone, Vamara; Lett, Christophe; Penven, Pierrick; Bourles, Bernard; Djakoure, Sandrine.
S. aurita is the most abundant small pelagic fish in the northern Gulf of Guinea. Its reproduction and recruitment depend crucially on environmental conditions. We developed a biophysical model of S. aurita early life history by coupling offline an individual-based model with the regional oceanic modeling system (ROMS). We used this model to investigate the main factors driving variability in eggs and larval dispersal and survival in the northern Gulf of Guinea. Precisely, individuals were released from different spawning areas along the coast and tracked for a period of 28 days corresponding to their planktonic phase. Individuals that remained in the coastal recruitment areas at an age more than 7 days, at which they can supposedly actively retain...
Tipo: Text Palavras-chave: Hydrodynamic model; Individual-based model; S. aurita early life stage; Recruitment; Upwelling; Northern Gulf of Guinea.
Ano: 2017 URL: http://archimer.ifremer.fr/doc/00357/46790/46656.pdf
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A new definition of the South-East Madagascar Bloom and analysis of its variability ArchiMer
Dilmahamod, Ahmad Fehmi; Penven, Pierrick; Aguiar gonzalez, B.; Reason, C. J. C.; Hermes, J. C..
The South‐East Madagascar Bloom occurs in an oligotrophic region of the South‐West Indian Ocean. Phase‐locked to austral summer, this sporadic feature exhibits substantial temporal and spatial variability. Several studies, with different hypotheses, have focused on the initiation mechanism triggering the bloom but none has been as yet clearly substantiated. With 19‐years of ocean colour dataset available as well as in‐situ measurements (Argo profiles), the time is ripe to review this feature. The bloom is characterized in a novel manner and a new bloom index is suggested, yielding 11 bloom years, including 3 major bloom years (1999, 2006 and 2008). Spatially, the bloom varies from a mean structure (22° S‐32° S; 50° E‐∼70°E) both zonally and meridionally. A...
Tipo: Text Palavras-chave: South-East Madagascar Bloom; South-East Madagascar Current; La Nina; Cyanobacterial bloom.
Ano: 2019 URL: https://archimer.ifremer.fr/doc/00482/59338/62118.pdf
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Agulhas Leakage Predominantly Responds to the Southern Hemisphere Westerlies ArchiMer
Durgadoo, Jonathan V.; Loveday, Benjamin R.; Reason, Chris J. C.; Penven, Pierrick; Biastoch, Arne.
The Agulhas Current plays a crucial role in the thermohaline circulation through its leakage into the South Atlantic Ocean. Under both past and present climates, the trade winds and westerlies could have the ability to modulate the amount of Indian-Atlantic inflow. Compelling arguments have been put forward suggesting that trade winds alone have little impact on the magnitude of Agulhas leakage. Here, employing three ocean models for robust analysisa global coarse-resolution, a regional eddy-permitting, and a nested high-resolution eddy-resolving configurationand systematically altering the position and intensity of the westerly wind belt in a series of sensitivity experiments, it is shown that the westerlies, in particular their intensity, control the...
Tipo: Text Palavras-chave: Boundary currents; Meridional overturning circulation; Wind stress; Mesoscale models; Numerical analysis; Modeling.
Ano: 2013 URL: http://archimer.ifremer.fr/doc/00161/27247/25452.pdf
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Circulation around La Reunion and Mauritius islands in the south-western Indian Ocean: A modeling perspective ArchiMer
Pous, Stephane; Lazure, Pascal; Andre, Gael; Dumas, Franck; Halo, Issufo; Penven, Pierrick.
Circulation around both islands is dominated by westward propagating features The predominant time scale of variability of currents and SSH is 60 days There is local generation of eddies in the lee of the islands due to topography
Tipo: Text Palavras-chave: Ocean circulation; Hydrodynamic model; La Reunion; Eddies; Rossby waves.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00195/30624/29073.pdf
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Cyclogeostrophic balance in the Mozambique Channel ArchiMer
Penven, Pierrick; Halo, Issufo; Pous, Stephane; Marie, Louis.
Three methods are proposed for the inclusion of inertia when deriving currents from sea surface height (SSH) in the Mozambique Channel: gradient wind, perturbation expansion, and an iterative method. They are tested in a model and applied to satellite altimetry. For an eddy of 25 cm amplitude and 100 km radius, typical of Mozambique Channel rings at 18°S, the error made with geostrophy is 40% for the anticyclones and 20% for the cyclones. Inertia could reach one third of the pressure gradient. Geostrophy underestimates subsurface currents by up to 50 cm s−1, resulting in errors of 30–40%. The iterative method results in errors of <5% for the most part of the structure. The error RMS in velocities based on 8 years of model SSH is in excess of 30 cm s−1...
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Ano: 2014 URL: http://archimer.ifremer.fr/doc/00175/28617/27045.pdf
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Energetics of the Tropical Atlantic Zonal Mode ArchiMer
Burls, N. J.; Reason, C. J. C.; Penven, Pierrick; Philander, S. G..
Sea surface temperature in the central-eastern equatorial Atlantic has a seasonal cycle far bigger than that of the Pacific, but interannual anomalies smaller than those of the Pacific. Given the amplitude of seasonal SST variability, one wonders whether the seasonal cycle in the Atlantic is so dominant that it is able to strongly influence the evolution of its interannual variability. In this study, interannual upper-ocean variability within the tropical Atlantic is viewed from an energetics perspective, and the role of ocean dynamics, in particular the role of ocean memory, within zonal mode events is investigated. Unlike in the Pacific where seasonal and interannual variability involve distinctly different processes, the results suggest that the latter...
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Ano: 2012 URL: http://archimer.ifremer.fr/doc/00130/24169/22260.pdf
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High-resolution regional ocean dynamics simulation in the southwestern tropical Atlantic IRD
Silva, M.; Araujo, M.; Servain, Jacques; Penven, Pierrick; Lentini, C.A.D..
Tipo: Text Palavras-chave: CIRCULATION OCEANIQUE; COURANT MARIN; FLUX THERMIQUE; TEMPERATURE DE SURFACE; VARIATION SAISONNIERE; VARIATION INTERANNUELLE; MODELE.
Ano: 2010 URL: http://www.documentation.ird.fr/hor/fdi:010050933
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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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Linking wind and interannual upwelling variability in a regional model of the southern Benguela - art. no. 2188 ArchiMer
Blanke, Bruno; Roy, Claude; Penven, Pierrick; Speich, Sabrina; Mcwilliams, James; Nelson, Greville.
We quantify the wind contribution to the development of interannual sea surface temperature (SST) anomalies along the shelf of southern Africa. We compare numerical simulations that differ only in the amount of variability kept in the ERS1/2-derived surface wind forcing. Surprisingly, most of the cold and warm episodes over the Agulhas Bank are strictly related to local fluctuations of the forcing, whereas the shelf of the west coast extending 400 km north of Cape Columbine is equally sensitive to open-sea wind fluctuations. We diagnose the respective role of mesoscale eddy activity and of low frequency and intra-monthly wind fluctuations in generating interannual SST variability. The fair degree of correlation obtained at a few locations between the model...
Tipo: Text Palavras-chave: Numerical simulation; Wind fluctuation; Sea surface temperature; Upwelling.
Ano: 2002 URL: https://archimer.ifremer.fr/doc/2002/publication-770.pdf
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Mesoscale eddy variability in the southern extension of the East Madagascar Current: Seasonal cycle, energy conversion terms, and eddy mean properties ArchiMer
Halo, Issufo; Penven, Pierrick; Backeberg, Bjoern; Ansorge, Isabelle; Shillington, Frank; Roman, Raymond.
In this study, we used more than 17 years of satellite altimetry observations and output from an ocean model to investigate the mesoscale eddy variability and forcing mechanisms to the south of Madagascar. Analysis of energy conversion terms in the model has shown seasonality on eddy formation, both by barotropic and baroclinic instabilities: maximum in winter (JJA) and minimum in summer (DJF). The eddies were mainly formed in the upper ocean (0–300 m) and at intermediate depths (800–2000 m) by barotropic and baroclinic instabilities, respectively. The former dominated in the southeastern margin of Madagascar, and the latter to the southwest, where the South-East Madagascar Current (SEMC) separates from the continental shelf. Seasonality of the eddy...
Tipo: Text Palavras-chave: Mesoscale eddies; Barotropic; Baroclinic instabilities; Seasonality; Eddy properties; Variability.
Ano: 2014 URL: http://archimer.ifremer.fr/doc/00222/33348/31749.pdf
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Modelling the tides and their impacts on the vertical stratification over the Sofala Bank, Mozambique ArchiMer
Chevane, C. M.; Penven, Pierrick; Nehama, F. P. J.; Reason, C. J. C..
The Sofala Bank, a wide shelf located along the central coast of Mozambique, hosts tides with high amplitudes. The Regional Ocean Modelling System (ROMS) was used to analyse the tidal currents on the bank and to investigate their effects on the stratification and generation of tidal fronts. During spring tides, barotropic tidal currents with maximum values ranging from 40 cm s–1 to 70 cm s–1 are found on the central bank. The major axis of the tidal ellipses for M2 and S2 follow a cross-shelf direction with mainly anticlockwise rotation. Similar to observations, three distinct regimes occur: (i) a warm well-mixed region on the inner shelf where the depths are <30 m; (ii) a wellmixed colder region above the shelf edge; and (iii) a stratified region...
Tipo: Text Palavras-chave: Barotropic tidal currents; ROMS; Sea surface temperature; Shallow seas; Tidal front.
Ano: 2016 URL: http://archimer.ifremer.fr/doc/00362/47276/47852.pdf
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Modulation of the Agulhas Current Retroflection and Leakage by Oceanic Current Interaction with the Atmosphere in Coupled Simulations ArchiMer
Renault, Lionel; Mcwilliams, James C.; Penven, Pierrick.
Coupled ocean-atmosphere simulations are carried out for the Mozambique Channel, the Agulhas Current System, and the Benguela Upwelling System to assess the ocean surface current feedback to the atmosphere and its impact on the Agulhas Current (AC) retroflection and leakage. Consistent with previous studies, we show that the current feedback slows down the oceanic mean circulation and acts as an oceanic eddy killer by modulating the energy transfer between the atmosphere and the ocean, reducing by 25% the mesoscale energy and inducing a pathway of energy transfer from the ocean to the atmosphere. The current feedback, by dampening the Eddy Kinetic Energy (EKE), shifts westward the distribution of the AC retroflection location, reducing the presence of...
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Ano: 2017 URL: http://archimer.ifremer.fr/doc/00389/50077/50670.pdf
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Ocean variability over the Agulhas Bank and its dynamical connection with the southern Benguela upwelling system ArchiMer
Blanke, Bruno; Penven, Pierrick; Roy, Claude; Chang, Nicolette; Kokoszka, Florian.
This study analyzes the oceanic pathway connecting the Agulhas Bank to the southern Benguela upwelling system by means of a quantitative Lagrangian interpretation of the velocity field calculated by a high-resolution numerical simulation of the ocean around the southwestern tip of Africa. The regional ocean model is forced with National Centers for Environmental Prediction surface winds over 1993-2006 and offers a relevant numerical platform for the investigation of the variability of the water transferred between both regions, both on seasonal and intraseasonal time scales. We show that the intensity of the connection fluctuates in response to seasonal wind variability in the west coast upwelling system, whereas intraseasonal anomalies are mostly related...
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Ano: 2009 URL: http://archimer.ifremer.fr/doc/2009/publication-7388.pdf
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Physical speciation of iron in the Atlantic sector of the Southern Ocean along a transect from the subtropical domain to the Weddell Sea Gyre ArchiMer
Chever, Fanny; Bucciarelli, Eva; Sarthou, G.; Speich, Sabrina; Arhan, Michel; Penven, Pierrick; Tagliabue, A..
[1] Distributions of total dissolvable iron (TDFe; unfiltered), dissolved iron (DFe; 0.2 mu m filtered), and soluble iron (SFe; 0.02 mu m filtered) were investigated during the BONUS-GoodHope cruise in the Atlantic sector of the Southern Ocean (34 degrees S/17 degrees E-57 degrees S/0 degrees, February-March 2008). In the mixed layer, mean values of 0.43 +/- 0.28 and 0.22 +/- 0.18 nmol L-1 were measured for TDFe and DFe, respectively. In deeper waters, TDFe and DFe concentrations were 1.07 +/- 0.68 and 0.52 +/- 0.30 nmol L-1, respectively. DFe concentrations decreased from the north (subtropical waters) to the south (Weddell Sea Gyre). In the subtropical domain, dusts coming from Patagonia and southern Africa and inputs from the African continental margin...
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Ano: 2010 URL: http://archimer.ifremer.fr/doc/00017/12808/9763.pdf
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Seasonal phasing of Agulhas Current transport tied to a baroclinic adjustment of near-field winds ArchiMer
Hutchinson, Katherine; Beal, Lisa M.; Penven, Pierrick; Ansorge, Isabelle; Hermes, Juliet.
The Agulhas Current plays a significant role in both local and global ocean circulation and climate regulation, yet the mechanisms that determine the seasonal cycle of the current remain unclear, with discrepancies between ocean models and observations. Observations from moorings across the current and a 22 year proxy of Agulhas Current volume transport reveal that the current is over 25% stronger in austral summer than in winter. We hypothesize that winds over the Southern Indian Ocean play a critical role in determining this seasonal phasing through barotropic and first baroclinic mode adjustments and communication to the western boundary via Rossby waves. Our hypothesis is explored using single layer and one‐and‐a‐half layer models. We find that the...
Tipo: Text Palavras-chave: Agulhas Current; Seasonal cycle; Wind stress curl; Rossby waves; Indian Ocean; Reduced gravity model.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00454/56607/58300.pdf
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Shelf-edge jet currents in the southern Benguela: a modelling approach ArchiMer
Veitch, Jennifer; Hermes, Juliet; Lamont, Tarron; Penven, Pierrick; Dufois, Francois.
The dynamics and seasonal variability of jet currents on the southern Benguela shelf-edge are investigated using a climatologically forced ROMS model. The jet is primarily forced by the intense horizontal gradients that exist across the southern Benguela shelf. These gradients are set up by nearshore cooling via the strongly seasonal upwelling regime and variable offshore warming by the advection of Agulhas waters. While the nearshore cooling is prevalent only during the spring and summer upwelling season, the offshore warming exists throughout the year. As a result intensified geostrophically adjusted currents exist throughout the year, particularly off the Cape Peninsula and Cape Columbine. However, the distinct shelf-edge jet features are most intense...
Tipo: Text Palavras-chave: Southern Benguela; Shelf-edge jet; Numerical model.
Ano: 2018 URL: https://archimer.ifremer.fr/doc/00403/51401/51976.pdf
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Simulation of a coastal jet retention process using a barotropic model ArchiMer
Penven, Pierrick; Roy, Claude; Colin De Verdiere, Alain; Largier, John.
In the southern Benguela, sardine and anchovy spawn on the Western Agulhas Bank. Eggs and larvae are transported to the West coast nursery ground by a! coastal current. Once the larvae reach the West coast, retention within the favorable coastal domain is key to larvae survival and recruitment. The Cape Columbine-St Helena Bay area is the main nursery ground along the West Coast. In this area, the interaction between upwelling and topography results in the formation of an upwelling plume. The plume, and the associated circulation patterns, is thought to be the mechanism providing retention within the coastal domain. The dynamics of the plume are studied using a set of:numerical experiments. It is shown that an equatorward wind forcing produces a cyclonic...
Tipo: Text Palavras-chave: Benguela; Effets de cap; Modélisation; Rétention; Recrutement; Benguela; Cape effects; Modeling; Retention; Recruitment.
Ano: 2000 URL: http://archimer.ifremer.fr/doc/00323/43385/42826.pdf
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