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Auteur (up) Béhagle, N.; du Buisson, L.; Josse, E.; Lebourges-Dhaussy, A.; Roudaut, G.; Ménard, F.
Titre Mesoscale features and micronekton in the Mozambique Channel: An acoustic approach Type Article scientifique
Année 2014 Publication Revue Abrégée Deep Sea Research Part II: Topical Studies in Oceanography
Volume 100 Numéro Pages 164-173
Mots-Clés Acoustics; Mesoscale eddies; micronekton; Mozambique Channel; Satellite altimetry
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ISSN 0967-0645 ISBN Médium
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Numéro d'Appel LL @ pixluser @ collection 344
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Auteur (up) Benazzouz, A.; Mordane, S.; Orbi, A.; Chagdali, M.; Hilmi, K.; Atillah, A.; Pelegri, J.L.; Demarcq, H.
Titre An improved coastal upwelling index from sea surface temperature using satellite-based approach : the case of the Canary Current upwelling system Type Article scientifique
Année 2014 Publication Revue Abrégée Continental Shelf Research
Volume 81 Numéro Pages 38-54
Mots-Clés Canary upwelling system; Coastal upwelling; Coastal upwelling index; Remote sensing; Sea surface temperature; West Africa
Résumé A new methodology to derive an SST-based upwelling index was based on a rigorous spatial analysis of satellite SST fields and their variability, by referring to previous works, from Wooster et al. (1976) to Santos et al. (2011). The data was precautiously processed by considering data quality aspects (including cloud cover) and the best way to derive accurate coastal SST and its offshore reference. The relevance of the developed index was evaluated by comparing its spatial and seasonal consistency against two wind-based indices as well as with the previous SST-based indices, largely superseding these later ones in term of overall quality and spatio-temporal dynamic. Our index adequately describes the spatio-temporal variability of the coastal upwelling intensity in the Canary Current upwelling system and has the advantage of describing complementary aspects of the coastal dynamics of the region that were not covered by Ekman-based indices. The proposed methodology is generic and can be easily applicable to various coastal upwelling systems, especially the four major eastern boundary upwelling ecosystems.
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ISSN 0278-4343 ISBN Médium
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Numéro d'Appel LL @ pixluser @ collection 351
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Auteur (up) Benazzouz, A.; Pelegri, J.L.; Demarcq, H.; Machin, F.; Mason, E.; Orbi, A.; Pena-Izquierdo, J.; Soumia, M.
Titre On the temporal memory of coastal upwelling off NW Africa Type Article scientifique
Année 2014 Publication Revue Abrégée J. Geophys. Res.-Oceans
Volume 119 Numéro 9 Pages 6356-6380
Mots-Clés atlantic; Canary Current; cape blanc region; circulation; Coastal upwelling; eastern boundary; Ekman transport; interannual variability; northwest africa; NW Africa; sea-surface temperature; SST difference; system; temporal memory; water
Résumé We use a combination of satellite, in situ, and numerical data to provide a comprehensive view of the seasonal coastal upwelling cycle off NW Africa in terms of both wind forcing and sea surface temperature (SST) response. Wind forcing is expressed in terms of both instantaneous (local) and time-integrated (nonlocal) indices, and the ocean response is expressed as the SST difference between coastal and offshore waters. The classical local index, the cross-shore Ekman transport, reproduces reasonably well the time-latitude distribution of SST differences but with significant time lags at latitudes higher than Cape Blanc. Two nonlocal indices are examined. One of them, a cumulative index calculated as the backward averaged Ekman transport that provides the highest correlation with SST differences, reproduces well the timing of the SST differences at all latitudes (except near Cape Blanc). The corresponding time lags are close to zero south of Cape Blanc and range between 2 and 4 months at latitudes between Cape Blanc and the southern Gulf of Cadiz. The results are interpreted based on calculations of spatial and temporal auto and cross correlations for wind forcing and SST differences. At temporal scales of 2-3 weeks, the alongshore advection of alongshore momentum compensates for interfacial friction, allowing the upwelling jet and associated frontal system to remain active. We conclude that the coastal jet plays a key role in maintaining the structure of coastal upwelling, even at times of relaxed winds, by introducing a seasonal memory to the system in accordance with the atmospheric-forcing annual cycle.
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Langue English Langue du Résumé Titre Original
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ISSN 2169-9275 ISBN Médium
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Numéro d'Appel MARBEC @ isabelle.vidal-ayouba @ collection 1194
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Auteur (up) Bertrand, A.; Grados, D.; Colas, F.; Bertrand, S.; Capet, X.; Chaigneau, A.; Vargas, G.; Mousseigne, A.; Fablet, R.
Titre Broad impacts of fine-scale dynamics on seascape structure from zooplankton to seabirds Type Article scientifique
Année 2014 Publication Revue Abrégée Nat Commun
Volume 5 Numéro Pages
Mots-Clés Biological sciences; Ecology; Oceanography
Résumé In marine ecosystems, like most natural systems, patchiness is the rule. A characteristic of pelagic ecosystems is that their ‘substrate’ consists of constantly moving water masses, where ocean surface turbulence creates ephemeral oases. Identifying where and when hotspots occur and how predators manage those vagaries in their preyscape is challenging because wide-ranging observations are lacking. Here we use a unique data set, gathering high-resolution and wide-range acoustic and GPS-tracking data. We show that the upper ocean dynamics at scales less than 10 km play the foremost role in shaping the seascape from zooplankton to seabirds. Short internal waves (100 m–1 km) play a major role, while submesoscale (~1–20 km) and mesoscale (~20–100 km) turbulence have a comparatively modest effect. Predicted changes in surface stratification due to global change are expected to have an impact on the number and intensity of physical structures and thus biological interactions from plankton to top predators.
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Numéro d'Appel LL @ pixluser @ collection 389
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Auteur (up) Bez, N.; Braham, C.B.
Titre Indicator variables for a robust estimation of an acoustic index of abundance Type Article scientifique
Année 2014 Publication Revue Abrégée Canadian Journal of Fisheries and Aquatic Sciences
Volume 71 Numéro 5 Pages 709-718
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Résumé In North West Africa, pelagic fisheries are an essential economic sector. However, the scientific community fails to perform satisfactory assessments of key pelagic species like sardinella, owing to a lack of relevant indices of abundance to tune the model. This paper provides an alternative acoustic index based on a semiquantitative modelisation of acoustic densities. Acoustic energy is split into binomial variables coding for null, low, medium, large, and very large densities. A multivariate geostatistical approach allows (i) mapping the spatial distribution of classes of densities and (ii) computing a new acoustic index of abundance for Sardinella aurita and Sardinella maderensis. We used the surveys of RV Fridtjof Nansen (1995-2006) and RV Al-Awam (2007-2010). Our results indicated that empirical spatial structures were highly stable over time for both between areas and surveys. Co-kriging maps also showed that sardinella had stable hot spots of distribution. The indices of abundance developed in the present study were tested in an assessment procedure and outperformed all the indices used routinely by the FAO-CECAF (Fishery Committee for the Eastern Central Atlantic) assessment working group.
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Numéro d'Appel LL @ pixluser @ collection 352
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