La dynamique superficielle du panache du Rhône d'après l'imagerie infrarouge satellitaire

International audienceL'examen systématique d'environ 150 thermographies du Golfe du Lion permet de déterminer les limites superficielles du panache thermique en mer et, grâce à l'apport de données météorologiques et hydrauliques concourantes, de décrire son évolution. Le vent a une action prépondérante et rapide sur la forme de la nappe, nettement déviée vers la droite du vent d'environ 50°. Le temps de réponse de la nappe à cette action croît avec le débit du fleuve, et est de l'ordre de 5 heures

Redressements NOAA AVHRR

Ce texte décrit les algorithmes utilisés par le logiciel de redressement NOAA developpé au laboratoire de télédétection du Centre de Recherche Océanographique de Dakar Thiaroye (CRODT). Il est opérationnel depuis septembre 1986. Il insiste sur les problèmes d'implantation de ce type de programme sur un petit calculateur et indique les performances obtenues. (Résumé d'auteur

The dynamics of the Mediterranean Sea from space: some techniques and their applications

This paper presents some remote sensing techniques and their applications to the understanding of the marine dynamics of the Mediterranean Sea. We emphasize the usefulness of the data provided by meteorological satellites in the visible, near-infrared and infrared ranges. Two techniques are discussed, the first dealing with estimations of wind magnitude at the sea surface, and the second with the prediction of the surface current field. Since the solar light reflected by the surface of the sea depends strongly on the sea state which is driven by the wind, observations of glitter pattern in the near infrared range allow measurements of the wind magnitude. On the other hand, estimations of surface current can be made either when considering patches observed in visible or infrared as passive tracers, or when solving the equation of the heat conservation using a couple of infrared images

Ocean currents and gradients of surface layer properties in the vicinity of the Madagascar Ridge (including seamounts) in the South West Indian Ocean

This work is part of the MADRidge Project special issue which aims to describe pelagic ecosystems in the vicinity of three prominent shallow seamounts in the South West Indian Ocean: one here named MAD-Ridge (240 m below the surface) plus Walters Shoal (18 m) on the Madagascar Ridge, and La Pérouse (60 m) on the abyssal plain east of Madagascar. The three span latitudes 20°S and 33°S, some 1500 km. The study provides the background oceanography for the once-off, multidisciplinary snapshot cruise studies around the seamounts. As life on seamounts is determined by factors such as summit depth, proximity to the light layers of the ocean, and the ambient circulation, a first description of regional spatial-field climatologies (16–22 years) and monthly along-ridge gradients of surface wind (driving force), water column properties of sea surface temperature, mixed layer depth, chlorophyll-a and eddy kinetic energy, plus ocean currents is provided. Being relevant to many applications in the study domain, these properties in particular reveal contrasting environments along the Madagascar Ridge and between the three seamounts that should drive biological differences. Relative to the other two seamounts, MAD-Ridge is in the more extreme situation, being at the end of the East Madagascar Current, where it experiences sturdy, albeit variable, currents and the frequent passing of mesoscale eddies

Phytoplankton functional groups in the Northern Humboldt Current Ecosystem (NHCE)

El Norte del ecosistema de la Corriente de Humboldt, localizado a lo largo del Sudeste del Océano Pacífico, frente a Perú, es considerado uno de los más productivos sistemas naturales en el mundo, siendo de gran relevancia el estudio del fitoplancton como base de la trama trófica marina. Tomando en cuenta las relaciones entre la superficie celular, biovolumen y máxima dimensión lineal de las células de las especies del fitoplancton, se encontraron 140 especies en el grupo funcional ‘R‘ (especies ruderales, adaptables a condiciones altas de mezcla); 133 especies en el grupo funcional ‘S’ (especies Stress-tolerantes, predominantes en condiciones oligotróficas y de alta luz) y 19 en el grupo funcional ‘C’ (especies colonizadoras, oportunistas, predominantes en condiciones mesotróficas y de alta luz). En el grupo funcional R destacaron las diatomeas elongadas, pennadas, dispuestas en cadenas; en el grupo funcional S se encontraron dinoflagelados, diatomeas centrales grandes y silicoflagelados; mientras que, en el grupo funcional C destacaron cocolitofóridos, algunos dinoflagelados mixotróficos y fitoflagelados. Los porcentajes de coincidencia entre la clasificación morfométrica de grupos funcionales del presente estudio y la clasificación ecológica, estuvieron entre 52 y 90%. Se propone el uso de estos grupos para evaluar las variaciones espacio-temporales del fitoplancton y su relación con las condiciones ambientales en el Norte del ecosistema de la Corriente de Humboldt, cuyos niveles de turbulencia son menores al de los fiordos chilenos.ABSTRACT: The Northern Humboldt Current ecosystem (NHCE), located in the southeastern Pacific off Peru, is one of the most productive natural systems worldwide. This area is of great relevance for the study of phytoplankton as the basis of the marine trophic web. Based on the relationships between the cell surface area, biovolume, and maximum linear dimension of the cells of the phytoplankton species, we found 140 species in the functional group ‘R’ (ruderal species, which are adaptable to high mixing conditions); 133 species in functional group ‘S’ (Stress-tolerant species, predominant in oligotrophic and high light conditions), and 19 species in functional group ‘C’ (colonizing, opportunistic species, predominant in mesotrophic and high light conditions). These three functional groups (FGs) are respectively formed by elongated, pennate, and chain-forming diatoms (group R); dinoflagellates, large central diatoms, and silicoflagellates (group S), and coccolithophores, some mixotrophic dinoflagellates, and phytoflagellates (group C). The percentages of coincidence between the morphometric classification of the FGs of this study and the ecological classification were between 52% and 90%. We propose the use of FGs to evaluate the spatio-temporal variations of phytoplankton and its relation with environmental conditions in the NHCE, whose turbulence levels are lower than those recorded in Chilean fjords

Microphytoplankton Dynamics and Diversity Patterns in the Southern Alboran Sea: Insights into Climate-Induced Changes

1 page, figuresThe Mediterranean Sea is a hotspot of biodiversity 1 Marine Plankton Ecology Laboratory, National Institute of Fisheries Research, Casablanca, Morocco 2 Health and Environment laboratory, Faculty of Sciences Ain Chock, Hassan II University, Casablanca, Morocco 3 Department of Marine Biology and Oceanography, Institute of Marine Sciences (CSIC), Barcelona, Spain 4 MARBEC, Montpellier University, CNRS, Ifremer, IRD, Sète, France 5 MARBEC, Montpellier University, CNRS, Ifremer, IRD, Montpellier, France Hajar Idmoussi1, 2 , Francesc Peters3 , Mohamed Laabir5, Hervé Demarcq4 , Marta Estrada3 , Laura Arin3 , Ahmed Makaoui1 , Omar Ettahiri1 ,Tarik Baibai1, Said Charib1, Karim Hilmi1, Ahmed Errhif and Laila Somoue1 2 Microphytoplankton Dynamics and Diversity Patterns in the Southern Alboran Sea: Insights into Climate-­‐Induced Changes The Mediterranean Sea is a hotspot of biodiversity. The concept of diversity provide an interesting indicator of phytoplankton community properties. Irigoien et al., 2004 using a marine phytoplankton global dataset, found a diversity peak at intermediate levels of phytoplankton biomass. No work has been done on biomass and diversity patterns of the microphytoplankton fraction in the Southern Alboran Sea (Moroccan case)Peer reviewe