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Le but de ce travail est d'analyser le comportement de la couche limite de l'écoulement au sein de coraux noirs et d'observer ou non la présence d'un effet canopée, représenté par une atténuation du courant ainsi qu'une augmentation de la turbulence. A l'aide d'un courantomètre hydroacoustique (ADCP), des données de vitesses ont été prélevées sur différents sites à Lanzarote. Des ajustements linéaires ont été effectués sur les profils de vitesse horizontale afin de déterminer la hauteur de déplacement de la couche limite au contact de corail noir. La deuxième méthode utilisée se base sur les profils d'énergie cinétique de turbulence afin de quantifier cette hauteur de déplacement. Enfin, les profils de vitesse verticale ont été étudiés pour déterminer les différentes zones d'atténuation du courant dans les forêts de corail noir. Les résultats indiquent que la couche limite de l'écoulement est déplacée et que le courant au sein des coraux noirs est atténué, signe de la présence d'un effet canopée. Les ajustements et les profils d'énergie cinétique de turbulence nous ont aussi permis de revoir et améliorer la technique d'échantillonnage utilisée à Lanzarote. The aim of this work is to analyse the behaviour of the boundary layer of the flow within black corals and to observe or not the presence of a canopy effect, represented by an attenuation of the current as well as an increase in turbulence. Using an acoustic Doppler current profiler (ADCP), velocity data were collected from different sites in Lanzarote. Linear adjustments were made to the horizontal velocity profiles in order to determine the displacement height of the boundary layer in contact with black coral. The second method used is based on the turbulence kinetic energy (tke) profiles to quantify this displacement height. Finally, vertical velocity profiles were studied to determine the different regions of current attenuation in the black coral forests. The results indicate that the flow boundary layer is displaced and the current within the black corals is attenuated, indicating the presence of a canopy effect. The adjustments and turbulence kinetic energy profiles also allowed us to review and improve the sampling technique used in Lanzarote.
couche limite --- corail noir --- effet canopée --- boundary layer --- black coral --- canopy effect --- Sciences du vivant > Sciences aquatiques & océanologie
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"The little-known history of how the Sahara was transformed from a green and fertile land into the largest hot desert in the world. The Sahara is the largest hot desert in the world, equal in size to China or the United States. Yet, this arid expanse was once a verdant, pleasant land, fed by rivers and lakes. The Sahara sustained abundant plant and animal life, such as Nile perch, turtles, crocodiles, and hippos, and attracted prehistoric hunters and herders. What transformed this land of lakes into a sea of sands? When the Sahara Was Green describes the remarkable history of Earth's greatest desert-including why its climate changed, the impact this had on human populations, and how scientists uncovered the evidence for these extraordinary events. From the Sahara's origins as savanna woodland and grassland to its current arid incarnation, Martin Williams takes us on a vivid journey through time. He describes how the desert's ancient rocks were first fashioned, how dinosaurs roamed freely across the land, and how it was later covered in tall trees. Along the way, Williams addresses many questions: Why was the Sahara previously much wetter, and will it be so again? Did humans contribute to its desertification? What was the impact of extreme climatic episodes-such as prolonged droughts-upon the Sahara's geology, ecology, and inhabitants? Williams also shows how plants, animals, and humans have adapted to the Sahara and what lessons we might learn for living in harmony with the harshest, driest conditions in an ever-changing global environment. A valuable look at how an iconic region has changed over millions of years, When the Sahara Was Green reveals the desert's surprising past to reflect on its present, as well as its possible future"--
Climatic changes --- Desertification --- Aeolian processes. --- Algae. --- Algeria. --- Alluvium. --- Americas. --- Andes. --- Anthozoa. --- Arid. --- Atlantic Ocean. --- Black coral. --- Bolivia. --- Carbon dioxide. --- Chad Basin. --- Chile. --- Climate change. --- Cnidaria. --- Cnidocyte. --- Coal. --- Coral reef. --- Date palm. --- Dendrochronology. --- Deriba Caldera. --- Desert climate. --- Desert. --- Desertification. --- Drought. --- Dry lake. --- Dry valley. --- Dune. --- Earth materials. --- Earth science. --- Earth's orbit. --- East Africa. --- Ecosystem. --- Ecuadorians. --- El Niño-Southern Oscillation. --- Emblem book. --- Erosion. --- Exploration. --- Far North (South Australia). --- Feather. --- Fertilizer. --- Fire coral. --- Goatskin (material). --- Google Earth. --- Grassland. --- Grazing. --- Great Sand Sea. --- Green development. --- Groundwater. --- Herbicide. --- Herder. --- Hippos. --- Iferouane. --- Inca Empire. --- Indo-Pacific. --- Kufra. --- Lake Chad. --- Land snail. --- Libyan Desert. --- Mauritania. --- Mediterranean Sea. --- Mesa. --- Microclimate. --- Monsoon. --- Neolithic. --- Nile. --- North Africa. --- North America. --- Overgrazing. --- Pastoralism. --- Perennial water. --- Pesticide. --- Photosynthesis. --- Plankton. --- Planula. --- Plate tectonics. --- Pollution. --- Polyp. --- Sahara. --- Sand. --- Savanna. --- Sediment. --- Semi-arid climate. --- Silt. --- Soil. --- Solar energy. --- Stolon. --- Stone tool. --- Surface layer. --- Temperate climate. --- Tentacle. --- The Natural Step. --- Tropics. --- Tunisia. --- Vegetation. --- Weathering. --- West Africa. --- Westerlies. --- Year. --- Sahara --- Climate --- History. --- Aeolian processes. --- Algae. --- Algeria. --- Alluvium. --- Americas. --- Andes. --- Anthozoa. --- Arid. --- Atlantic Ocean. --- Black coral. --- Bolivia. --- Carbon dioxide. --- Chad Basin. --- Chile. --- Climate change. --- Cnidaria. --- Cnidocyte. --- Coal. --- Coral reef. --- Date palm. --- Dendrochronology. --- Deriba Caldera. --- Desert climate. --- Desert. --- Desertification. --- Drought. --- Dry lake. --- Dry valley. --- Dune. --- Earth materials. --- Earth science. --- Earth's orbit. --- East Africa. --- Ecosystem. --- Ecuadorians. --- El Niño-Southern Oscillation. --- Emblem book. --- Erosion. --- Exploration. --- Far North (South Australia). --- Feather. --- Fertilizer. --- Fire coral. --- Goatskin (material). --- Google Earth. --- Grassland. --- Grazing. --- Great Sand Sea. --- Green development. --- Groundwater. --- Herbicide. --- Herder. --- Hippos. --- Iferouane. --- Inca Empire. --- Indo-Pacific. --- Kufra. --- Lake Chad. --- Land snail. --- Libyan Desert. --- Mauritania. --- Mediterranean Sea. --- Mesa. --- Microclimate. --- Monsoon. --- Neolithic. --- Nile. --- North Africa. --- North America. --- Overgrazing. --- Pastoralism. --- Perennial water. --- Pesticide. --- Photosynthesis. --- Plankton. --- Planula. --- Plate tectonics. --- Pollution. --- Polyp. --- Sahara. --- Sand. --- Savanna. --- Sediment. --- Semi-arid climate. --- Silt. --- Soil. --- Solar energy. --- Stolon. --- Stone tool. --- Surface layer. --- Temperate climate. --- Tentacle. --- The Natural Step. --- Tropics. --- Tunisia. --- Vegetation. --- Weathering. --- West Africa. --- Westerlies. --- Year.
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