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| Registros recuperados: 23 | |
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| Dilmahamod, A. F.; Penven, Pierrick; Aguiar‐gonzález, B.; Reason, C. J. C.; Hermes, J. C.. |
| The South‐East Madagascar Bloom, one of the most compelling biogeochemical features of the Indian Ocean, occurs sporadically during austral summer in the oligotrophic waters south‐east of Madagascar, where it can cover up to 1% of the global ocean surface area. Its spatial extension and its timing are highly variable. A high‐resolution biophysical model is used to investigate a previous hypothesis that the onset of a particular circulation of the South‐East Madagascar Current advects fresher and nutrient‐rich waters eastward, feeding the bloom. The model is able to reproduce an intermittent phytoplankton bloom with large spatial variability but in the subsurface layers, as well as the presence of an irregular retroflection of the South‐East Madagascar... |
| Tipo: Text |
Palavras-chave: South-East Madagascar Bloom; South-West Indian Ocean; Phytoplankton Bloom; Biogeochemical Modeling; South-East Madagascar Current. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00631/74325/73965.pdf |
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| 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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| 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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| Couvelard, Xavier; Messager, Christophe; Penven, Pierrick; Smet, Sébastien; Lattes, Philippe. |
| The oceanic circulation south of Africa is characterised by a complex dynamics with a strong variability due to the presence of the Agulhas current and numerous eddies. This area of interest is also the location of several natural gas fields under seafloor which are targeted for drilling and exploitation. The complex and powerful ocean currents induces significant issues for ship operations at the surface as well as under the surface for deep sea operations. Therefore, the knowledge of the state of the currents and the ability to forecast them in a realistic manners could greatly enforce the safety of various marine operation. Following this objective, an array of HF radar systems were deployed to allow a detailed knowledge of the Agulhas currents and its... |
| Tipo: Text |
Palavras-chave: 4DVAR; Agulhas current; HF radar; ROMS; Forecast. |
| Ano: 2021 |
URL: https://archimer.ifremer.fr/doc/00677/78929/81299.pdf |
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| Thiéblemont, Antoine; Hernández-molina, F. Javier; Miramontes, Elda; Raisson, François; Penven, Pierrick. |
| We present a combined study of the geomorphology, sedimentology, and physical oceanography of the Mozambique Channel to evaluate the role of bottom currents in shaping the Mozambican continental margin and adjacent Durban basin. Analysis of 2D multichannel seismic reflection profiles and bathymetric features revealed major contourite deposits with erosive (abraded surfaces, contourite channels, moats, furrows and scours), depositional (plastered and elongated-mounded drifts, sedimentary waves), and mixed (terraces) features, which were then used to construct a morpho-sedimentary map of the study area. Hydrographic data and hydrodynamic modelling provide new insights into the distribution of water masses, bottom current circulation and associated processes... |
| Tipo: Text |
Palavras-chave: Contourites; Bottom currents; Sedimentary processes; Water mass interfaces; Continental margin; Mozambique channel. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00488/60002/63238.pdf |
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| 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... |
| Tipo: Text |
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| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00175/28617/27045.pdf |
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| 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... |
| Tipo: Text |
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| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00130/24169/22260.pdf |
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| 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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| 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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| 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... |
| Tipo: Text |
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| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00389/50077/50670.pdf |
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| 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... |
| Tipo: Text |
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| Ano: 2009 |
URL: http://archimer.ifremer.fr/doc/2009/publication-7388.pdf |
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| 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... |
| Tipo: Text |
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| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00017/12808/9763.pdf |
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| Djakoure, S.; Penven, Pierrick; Bourles, Bernard; Kone, V.; Veitch, J.. |
| The northern Gulf of Guinea is a part of the eastern tropical Atlantic where oceanic conditions due to the presence of coastal upwelling may influence the regional climate and fisheries. The dynamics of this coastal upwelling is still poorly understood. A sensitivity experiment based on the Regional Oceanic Modeling System (ROMS) is carried out to assess the role of the detachment of the Guinea Current as a potential mechanism for coastal upwelling. This idealized experiment is performed by canceling the inertia terms responsible for the advection of momentum in the equations and comparing with a realistic experiment. The results exhibit two major differences. First, the Guinea Current is found to be highly sensitive to inertia, as it is no longer detached... |
| Tipo: Text |
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| Ano: 2017 |
URL: https://archimer.ifremer.fr/doc/00391/50248/69638.pdf |
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| 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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| Registros recuperados: 23 | |
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