Academic literature on the topic 'Écosystèmes – Pacifique (océan ; ouest)'
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Dissertations / Theses on the topic "Écosystèmes – Pacifique (océan ; ouest)"
Barbin, Laure. "Distribution du micronecton dans le Pacifique tropical ouest : caractérisation de la structuration des écosystèmes par méthodes acoustiques." Electronic Thesis or Diss., Sorbonne université, 2024. http://www.theses.fr/2024SORUS139.
Full textPelagic ecosystems are key elements of the global oceans, hosting numerous exchanges between the euphotic surface and mesopelagic depths. This zone exhibits a high biodiversity and a complex trophic network, with micronekton as a central component. This compartment comprises organisms measuring between 2 and 20 cm and encompasses a wide variety of species, including fish, crustaceans, molluscs, and gelatinous organisms (such as jellyfish, pyrosomes, salps). Micronekton serves as the primary food source for top predators like tuna, marine mammals, and seabirds and is predominantly feeding on zooplankton, thus occupying a central position in the trophic network. Additionally, some micronekton species undertake a diel migration between surface and depths, known as the nycthemeral migration, occurring with each solar cycle: organisms residing in deep mesopelagic layers during the day (>300m) ascend to the surface at sunset and vice versa at dawn. This vertical migration, observed in all oceans, is one of the largest global migrations. Its substantial biomass on a global scale, central role in the trophic network, and migratory behavior contributing to oceanic biogeochemical fluxes make micronekton an indispensable element in the study of pelagic ecosystems. This thesis investigates micronekton in the tropical Pacific through three main axes: 1) observation methods and abundance estimation, 2) improvement through recent technologies, particularly broadband acoustic profilers, and 3) characterization of micronekton distribution at the Pacific scale by defining ecosystems linked to environmental variables. Axis 1) initially examines micronekton observation methods, their respective biases, and their complementary nature. By focusing on acoustic-trawl measurements in the southwest tropical Pacific, we compare micronekton abundance estimates obtained through trawling and acoustics to estimate the difference of abundance obtained by one and the other method at different depths. In axis 2), we explore the contribution of a broadband profiler to micronekton abundance and distribution studies, developing an echo-counting algorithm to estimate organism density by depth. The final axis 3) utilizes acoustic data collected during three WARMALIS campaigns in the western tropical Pacific to describe it at large scale. Five different ecosystems could be characterized. The spatio-temporal distribution of micronekton appears different in each of them, in relation with environmental variables (temperature, oxygen, salinity, currents, etc.). This division highlights the presence of the Warm Pool, the equatorial upwelling, and oligotrophic zones, each characterized by different vertical structuring and micronekton density. This thesis emphasizes the various biases of micronekton study methods and the utility of combining them to obtain more robust estimates. By then applying these methods to the tropical Pacific, it demonstrates the considerable variability of ecosystems on a Pacific scale. Including this spatial variability in global predictions of micronekton abundance and biomass is essential for refining estimates and understanding the link between the environment and biology. Finally, it reaffirms the need to consider micronekton for the sustainable preservation and management of oceanic ecosystems
Receveur, Aurore. "Ecologie spatiale du micronecton : distribution, diversité et importance dans la structuration de l'écosystème pélagique du Pacifique sud-ouest." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0401.
Full textThe New Caledonian pelagic ecosystem in the southwest Pacific contains a high diversity of predators, such as seabirds and cetaceans. The recent creation of the Natural Park of the Coral Sea created a need for solid information on the functioning of this remarkable ecosystem, particularly on the dynamics of the micronecton (organisms between 1 and 20 cm constituting food of top predators) and its central role in food webs, especially since is the most poorly understood. In this context, this PhD showed a strong influence of environment on its spatial and seasonal distribution with on average more micronekton in the south than in the north, and more in winter than in summer. The species composing the micronecton are riche in crustaceans in the north and in cephalopods and fish in the south. The micronecton abundance would tend to decrease under the influence of climate change. Finally, we showed that the spatial distribution of this group influenced the presence of six groups of predators: yellowfin tuna, albacore tuna, dolphin, dolphin, shearwater and red-footed body
Garidel-Thoron, Thibault de. "Dynamique climatique de l'Océan Pacifique ouest équatorial au cours du Pléistocène récent." Aix-Marseille 3, 2002. https://tel.archives-ouvertes.fr/tel-00008934.
Full textUsing planktonic foraminifera and coccolithophorids, we investigated past climate dynamics of the western equatorial Pacific warm pool (WPWP)during the Late Pleistocene. We developped a new planktonic foraminifera transfer function, not biased by the ecosystem structure. Using this method, the last 185 kyrs SSTs in the WPWP oscillated between 27 and 29. 5ʿC, in agreement with alkenones estimates. The "deep" atmospheric convection over the WPWP was thus a stable feature of the Late Pleistocene climate. As revealed by nannoflora, the precession cycles appear to force a rocking of the Indo-Pacific thermocline, following an "El Niño-Southern Oscillation-like" mechanism. At millenial time-scale, the Dansgaard-Oeschger cycles were find in past changes in East Asian winter monsoon. A 1500 yrs cycle imprints this 200 kyrs monsoon record. A high-resolution record of carbon isotopic changes in the WPWP, exhibits the occurrence of large methane gas-hydrates releases during the last glacial stage
Le, Bec Nolwenn. "Reconstitution des salinités et des températures des eaux de surface dans l'océan Pacifique tropical sud-ouest au cours du dernier siècle : étude multi-traceurs d'un corail scléractiniaire massif (Porites sp.) des îles Fidji." Paris 11, 2001. http://www.theses.fr/2001PA112102.
Full textDeschamps, Anne. "Contribution à l'étude de la formation du bassin ouest philippin : nouvelles données sur la bordure ouest et la dorsale fossile." Montpellier 2, 2001. http://www.theses.fr/2001MON20058.
Full textBrunel, Jean-Pierre. "L'évaporation sous différents climats du sud-ouest Pacifique : études énergétique et isotopique." Paris 11, 1992. http://www.theses.fr/1992PA112475.
Full textLafoy, Yves. "Evolution géodynamique des bassins marginaux Nord-Fidjien et de Lau (Sud-Ouest Pacifique)." Brest, 1989. http://www.theses.fr/1989BRES2024.
Full textDurand, Pascale. "Taxonomie des bactéries oxydant les composés soufrés réduits en milieu hydrothermal profond : cas du sud-ouest Pacifique." Brest, 1992. http://www.theses.fr/1992BRES2008.
Full textRigolot, Patrick. "Origine et évolution du "système" ride de Nouvelle-Calédonie/Norfolk (sud-ouest pacifique) : synthèse des données de géologie et de géophysique marine : étude des marges et bassins associés." Brest, 1989. http://www.theses.fr/1989BRES2018.
Full textCillaurren, Espérance. "La pêche à la traîne autour des dispositifs de concentration de poissons mouillés à Vanuatu : un exemple dans le Pacifique sud-ouest." Brest, 1987. http://www.theses.fr/1987BRES2034.
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