Dissertations / Theses on the topic 'Océanographie – Atlantique (océan ; nord)'
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Karleskind, Pierre. "Bilan en carbone, oxygène et nutriments dans l'Atlantique nord-est : influence de la petite et de la moyenne échelle." Brest, 2008. http://www.theses.fr/2008BRES2053.
Full textColas, François. "Circulation et dispersion lagrangiennes en Atlantique nord-est." Brest, 2003. http://www.theses.fr/2003BRES2010.
Full textThe North-Eastern Atlantic circulation, complex and not well-known, is studied with an intensive use of lagrangian data collected during the ARCANE program, at North-Atlantic Central Waters (NACW) and Mediterranean Water (MW) depths. The study is conducted from the basin-scale to the meso-scale. The first part of the thesis describes new mean circulation solutions over the basin and in the west IberiaBay of Biscay region with also seasonal solutions. The influence of meso-scale eddies on the dynamics is underlined. A more specific study of the continental slope current system, with lagrangian and eulerian data and with' numerical solution from POP model, shows seasonal variations of the poleward slope current notably at the MW level. These variations are, at least partially, thought to be driven by the annual wind variations. It suggests a possible seasonality of the eddy formation. The second part of this work consists in studying the turbulent field by its dispersive processes, which are of importance in such a weak mean circulation field. The absolute dispersion reveals an anomalous superdiffusive behaviour at intermediate times. This behaviour is caused by the meso-scale eddies influence and an explanation in terra of Levy Flights is suggested. The relative dispersion study shows two distinct regimes, not often observed in the ocean, and we discuss their origin and significance: an exponential separation ai initial times followed by a Richardson regime at intermediate times. These two complementary visions allow us to get a more precise insight in the dispersive processes in the region
Paillet, Jérôme. "Eau modale et ventilation océanique en Atlantique nord-est." Brest, 1996. http://www.theses.fr/1996BRES2004.
Full textPailler, Delphine. "Paléoproductivité océanique au cours des derniers cycles glaciaires : implications climatiques et préservation de la matière organique." Aix-Marseille 3, 2000. http://www.theses.fr/2000AIX30012.
Full textOrganic carbon, carbonate and alkenones (special biomolecules produced by the coccolithophorids algae) contents of sediment cores from the Iberian margin provide a semi-quantitative estimate for marine productivity during the last 140 000 years. During glacialperiods and terminations, increased productivity and colder alkenone-estimates of sea surface temperature suggest an intensification of the coastal upwelling. Following the changes in atmospheric and oceanic circulation in the North Atlantic, the upwelling is weaker during interglacial periods. During the last glaciation, these changes are frequently interrupted by brief, cold and poorly productive events probably related to the Heinrich events, the coldest periods of the Dansgaard-Oeschger cycles and the most extensive glacial conditions. Close to the Maldives, in the eastern part of the equatorial Arabian Sea, the concentrations of marine organic matter and redox sensitive trace elements (uranium, cadmium, molybdenum) display simultaneous increases every 23 000 years, during low summer insolation of the northern hemisphere. .
Louarn, Essyllt. "Étude de la variabilité de la circulation des masses d'eau profondes en Atlantique Nord en relation avec le climat : utilisation des traceurs transitoires halocarbonés." Brest, 2008. http://www.theses.fr/2008BRES2035.
Full textThe North Atlantic deep circulation variability is studied regarding global change. The variability is assessed using halocarbonated tracers (CFC-11, CFC-1 2, CFC-113 and CC14) and studying hydrographic cruises spanning from 1991 to 2006. In this work, water mass formation (Mediterranean Sea Water and Labrador Sea Water) and North Atlantic deep water masses properties and transport variability are studied. First, in the Gulf of Cadiz, the presence of a old and high-silicate water, caracterized as Antarctic lntermediate Water, is observed. That water is seen as participating to the lower Mediterranean Sea Water out of the Gulf. The formation site of the upper Labrador Sea Water is observed wider than formerly considered. It forms every year in the central Labrador Sea, that zone, under certain conditions, extends to the north South of Greenland (2005). Under severe wintertime, deep convection can occur in the Imminger Sea as observed in this study in 1997 and 2002. Second, the variability of the Labrador Sea Water is high since the 90’s. A reduction of the maximal convection depth is observed, at the same time the CFC-1 1 transport decreased at the level of the LSW. The Denmark Strait Overflow Water variability observed in the lmminger Sea is linked to a change in proportion of different waters composing it, in particular the presence of Polar Surface Water. Finally the CFC-11 fluxes north of the North Atlantic show a diminution of the air-sea exchange above that area especially in 2006 due to a decrease of the winter mixed layer depth, supporting a decrease of the uptake of anthropogenic carbon in that area
Manthé, Sandrine. "Variabilité de la circulation thermohaline glaciaire et interglaciaire en Atlantique Nord tracée par les foraminifères planctoniques et la microfaune benthique." Bordeaux 1, 1998. http://www.theses.fr/1998BOR10659.
Full textBouinot, Thomas. "Variabilité de la circulation méridienne dans l’Océan Atlantique Nord au cours des 2000 dernières années." Thesis, Paris 11, 2011. http://www.theses.fr/2011PA112322/document.
Full textThe purpose of this thesis was to study the surface oceanic circulation in the North Atlantic Ocean during the last 2,000 years, and its link with the intensity of the subpolar and the subtropical gyres. To fulfill these objectives, I studied sediment cores with a high sedimentation rate to reconstruct the multidecadal variability of the temperature and the water column stratification, controlled by the dynamic of oceanic gyres. To improve the marine paleoclimatic signal recorded from planktonic foraminifera, I constrained their growing season and their calcification depth by analyzing the oxygen isotopic composition of their calcitic shells. I also established calibrations between Mg/Ca ratio and temperature for the main species used.I applied these calibrations to reconstruct the hydrological conditions in key areas of the North Atlantic Ocean. I constructed an index of the subpolar gyre that traduces the dynamic intensity of the subpolar gyre and the subtropical gyre. I also studied the variability of the upper water column based on the analysis of deep-dwelling foraminifera. I interpret past changes in the water column stratification as resulting from changes in the intensity of Westerly winds. The similarities between the wind forcing evolution and the index of the subpolar gyre dynamics led me to propose a coupling between the ocean and the atmosphere on the multidecadal time scale. The consequences of the gyres dynamic on heat transport and the impacts of the change in westerly wind strength on European climate are studied in the last part of the manuscript
Jiang, Weimin. "Centennial AMOC variability : mechanism and impacts." Electronic Thesis or Diss., Sorbonne université, 2022. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2022SORUS193.pdf.
Full textThe Atlantic Meridional Overturning Circulation (AMOC) consists of a warm northward current on the surface and a cold southward branch in the deep. It brings tremendous heat into the mid-latitudes in the Northern Hemisphere and thus plays an important role in governing the climate of the North Atlantic region and beyond. This thesis investigates the driving mechanism and climate impacts of a centennial to multi-centennial variability of the AMOC. The AMOC intensity is modulated by the delayed freshwater exchanges through the Fram Strait between the Arctic Ocean and the North Atlantic. The thesis also investigates the climate impacts of this low-frequency AMOC variability and associated energy transport changes. The impacts of a strong AMOC mainly include a wide warming in the Northern Hemisphere, a northward displacement of the intertropical convergence zone and more precipitations in the Northern mid-latitudes. The enhanced northward oceanic energy transport induced by intensified AMOC is compensated by the anomalous southward energy transport in the atmosphere, which leads to climate variations. This response in the atmosphere is damped by the Indo-Pacific Ocean
Resplandy, Laure. "Impacts biogéochimiques des processus de haute fréquence à l'échelle régionale et saisonnière." Paris 6, 2010. http://www.theses.fr/2010PA066089.
Full textCharria, Guillaume. "Influence des ondes de Rossby sur le système biogéochimique de l'Océan Atlantique Nord : utilisation des données couleur de l'eau et d'un modèle couplé physique/biogéochimie." Toulouse 3, 2005. http://www.theses.fr/2005TOU30268.
Full textThe marine phytoplankton in the ocean represents only less than 1% of global biomass. Phytoplankton performs half of all photosynthesis. This autotrophic biomass in ocean is then an essential element in the climate regulation through processes as carbon dioxide absorption during the photosynthesis. Therefore, we need to estimate precisely this biomass as well as the processes which affect it. Using remotely sensed data (altimetry and ocean colour) and a coupled physical/biogeochemical model (MERCATOR-OPA/NPZDDON), Rossby waves and their influence on phytoplankton biomass are specifically studied in the North Atlantic Ocean. Their features and their influences on surface chlorophyll concentrations were analysed. Through the different mechanisms identified, we estimated that these waves can induce local increases from 60% to 150% of the estimated primary production
Guihou, Abel. "Reconstitution des variations de la dynamique de la Circulation Méridienne Atlantique lors de la Dernière Entrée en Glaciation par le rapport (Pa-231/Th-230) des sédiments marins." Versailles-St Quentin en Yvelines, 2009. http://www.theses.fr/2009VERS0058.
Full textThe Atlantic Meridional Overturning Circulation (AMOC) is a key feature of the climate system. However, its dynamical evolution during an Interglacial / Glacial transition is still poorly constrained. This study aims at better understanding this evolution by focusing on the Last Glacial Inception (130,000 to 60,000 yr) and at studying the links between the AMOC and ice-sheet growth in response to Northern Hemisphere summer insolation. This study is based on the firsts (231Pa/230Th) data – a proxy for AMOC export – covering this period of time. The (231Pa/230Th) have been measured in 5 sedimentary cores chosen in the depth range between 2200 m and 3650 m in the North Atlantic Ocean. We show that the AMOC export in-depth structure varied significantly in between MIS 5. 5 and MIS 4. These variations are associated with changes in deep water chemistry. The evolution of the AMOC export in decoupled between intermediate (above 2500 m) and deep (around 3500 m) water depth. The intermediate water export is mainly driven by shifts of the Polar Front, itself driven by changes in Northern Hemisphere summer insolation amplified through high latitudes climate system. The deep-water export lags by several thousand years changes in Northern Hemisphere summer insolation and appears to respond to the ice-sheets dynamics. During the transitions towards cold MIS 5 substages, the decoupling implies a stronger heat transport by surface circulation that feeds Northern high latitude ice-sheet growth
Sommer, Anna. "Salinité de surface dans le gyre subtropical de l'Atlantique Nord (SPURS/SMOS/Mercator)." Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066436.
Full textThe focus of this work is on sea surface salinity (SSS) variability in the North Atlantic subtropical gyre. We study seasonal SSS variability and its link to the atmospheric freshwater flux at the ocean surface and to ocean dynamics at meso-scales for the period August 2012 – December 2014. The products from the soil moisture and ocean salinity (SMOS) satellite mission corrected from large scale systematic errors are tested and used to retrieve meso-scale salinity features. Furthermore, the PSY2V4R2-R4 simulation produced by Mercator with a high spatial resolution is also used. The comparison of corrected SMOS SSS data and Mercator simulation with drifter's in situ and TSG measurements from the SPURS experiment shows a reasonable agreement with RMS differences on the order of 0.15 pss.The freshwater seasonal flux is the leading term in the SSS seasonal budget. To balance its effect the ocean dynamics strongly contribute. The entrainment of deeper water is strong during the winter time. It usually acts to lower SSS, except in the south of the SSS–max region where it contributes to increase salinity. Advection is the second important component responsible for the SSS variability. It transfers further north the salty water from the evaporation maximum region. The contribution of advertion term is strongly dependent on the type of data used and their spatial resolution
Narinc, Olivier. "Variabilité interannuelle de l'eau modale à dix-huit degrés de l'Atlantique nord : contributions apportées par une simulation océanique ensembliste réaliste." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALU022.
Full textThe Eighteen Degree Water (EDW) is a mode water located in the western NorthAtlantic subtropical gyre, south of the Gulf Stream. It is typically described asformed in the winter mixed layer through air-sea exchanges, before being sub-ducted and partly eroded over the rest of the year. The EDW plays a signif-icant role in the air-sea exchanges of the North Atlantic basin, and interactswith the Atlantic meridional overturning circulation (AMOC). Previous stud-ies have shown that in eddy-permitting simulations (resolution of 1/4° or finer),a significant part of the interannual variability of the subtropical gyre and ofthe AMOC is intrinsic to the ocean, meaning that it is independent from atmo-spheric variability and is driven by oceanic processes. The present study usesa realistically forced 20 year, 1/4°, 50-member regional ocean/sea-ice ensemblesimulation with identical air-sea fluxes for all ensemble members. By employingestablished methods that take advantage of the ensemble dimension we are ableto characterise the relative roles of intrinsic and atmospherically forced variabil-ity in the interannual variability of the EDW. Our simulation is shown to be ingood agreement with an observation-based 1/4°, 3-dimensional gridded analy-sis. Investigating average properties of the EDW, we show that while nearly allEDW variability is atmospherically forced at annual and subannual timescales,the intrinsic variability becomes significant at interannual timescales. Resultsobtained in the ensemble simulation are shown to be compatible with observedvariability, suggesting that EDW observations are affected by a significant anddifficult to quantify intrinsic variability. By separating the EDW volume intoa ventilated volume (below the area where EDW is in contact with the atmop-shere) and a subducted volume (the rest of the total volume), we were also ableto describe the yearly cycle of EDW volume change. We found that on averageover the 20 years of the simulation and over the 50 ensemble members, EDW for-mation is in near equilibrium with EDW destruction, and that forced variabilityis dominant in both processes although intrinsic variability plays a greater rolein EDW destruction. In addition, a 12-year timescale is apparent in the intrin-sic variability of EDW volume. The subducted volume carries this 12-year modeof intrinsic variability, modulated by the yearly addition of new EDW volumethrough ventilation. Overall, the results presented in this thesis show that thetypical description of EDW variability as atmospherically-driven is incomplete,and that intrinsic variability is also significant at interannual timescales, moreimportantly in the destruction of EDW
Dale, Alizée. "Contributions des processus physiques à la variabilité récente (1980-2015) des concentrations en nutriments dans le gyre subpolaire en Atlantique Nord." Electronic Thesis or Diss., université Paris-Saclay, 2023. http://www.theses.fr/2023UPASJ024.
Full textThe Subpolar Gyre (SPG) of the North Atlantic plays a key role in the carbon cycle and climate variability. It is the site of a vigorous spring phytoplankton bloom, maintained by the seasonal transport of nutrients in association with light. Macro-nutrients (NO3, PO4, DSi) are supplied predominantly to the mixed layer by lateral transport from high latitudes (mainly through the Davis and Hudson Straits), from lower latitudes by the North Atlantic Current, or by vertical transport from below the mixed layer where higher concentrations are present. These supply processes have been suggested to vary in response to the North Atlantic Oscillation, a major mode of natural climate variability. When the NAO index is negative, as it was the case from the mid-1990s to the end of the 2000s, physical conditions are similar to those projected under climate change (i.e. , warming and freshening, weakening of deep convection, slowing down of the Atlantic Meridional Overturning Circulation, increasing straatification. During the same period, a decline in macro-nutrient concentrations was observed throughout the region leading to the hypothesis that underlying processes could be similar to those acting under global warming to reduce mixed layer nutrient levels. The main objective of this thesis was to analyze and quantify the contributions of dynamic processes (i.e., lateral and vertical transport) to the observed variability in macro-nutrient mixed layer concentrations over the SPG between 1980 and 2015. The analysis used a coupled physical-biogeochemical model (NEMO-PISCES) discretized on a quarter-degree grid. An assessment of the model's representation of the spatial and temporal variability of macro-nutrient concentrations and the main physical processes, such as deep convection in the Labrador Sea, and the lateral transport of water and nutrients, was carried out in comparison with data from observations. An initial focus was on the Labrador Sea, which is a region characterized by deep, intense, and variable winter convection, making it an ideal laboratory for distinguishing the role of variability in deep winter convection from that of the Subpolar Gyre circulation and inputs from the Arctic Ocean. Despite some weakening, the contribution of changes of Arctic DSi transport through the Davis and Hudson Straits to observed nutrient variability was shown to be negligible (= 3%). Deep convection was identified as the main driver of the decline in pre-bloom DSi concentrations in the Labrador Sea. The study was extended next to the broader SPG, with assessment of the recent variability of macro-nutrient concentrations in the mixed layer through analysis of the variability of lateral and vertical transports between a period of strong positive NAO, a period of negative NAO, and the period following. In addition to the temporal variability of concentrations in response to atmospheric forcing, regional differences emerge, with a contribution dominated by vertical transport in the Labrador and Irminger Seas, led by variations in the depth of the mixed layer. Zonally-integrated nutrient transport east and north of the SPG are coherent with the variability of nutrient within the SPG but decoupled from nutrient transported by the Gulf stream via the North Atlantic Current west of 38°N. In this thesis, I highlighted the predominance of vertical mixing in the contemporary variability of nutrient concentrations compared with lateral inputs. I show that a slowing of the general circulation associated with stratification of the water column leading to the weakening of vertical nutrient fluxes, as is the case under projected climate change conditions, would lead to a reduction in macronutrient concentrations and potential future primary production in the SPG
Riso, Ricardo. "Evolution spatio-temporelle de quelques métaux traces dans les systèmes frontaux de l'Atlantique nord-est (côtes de Bretagne)." Brest, 1991. http://www.theses.fr/1991BRES2004.
Full textBrivoal, Théo. "Une modélisation alternative haute résolution du couplage air-mer et de ses effets sur la dynamique océanique dans l'Atlantique Nord-Est." Thesis, Toulouse 3, 2021. http://www.theses.fr/2021TOU30211.
Full textSmall - scale ocean - atmosphere interactions have a significant impact on ocean dynamics, but their representation requires coupled ocean - atmosphere models, which are complex and expensive. This thesis supports the idea that it is possible to represent these interactions through a coupling of an ocean model and a stand-alone one-dimensional atmospheric boundary layer model. In this thesis we show that this simplified approach represents a realistic atmospheric boundary layer, as well as dynamical and thermal couplings in the North-East Atlantic. We show that the dynamical coupling at fine scales significantly modifies the ocean kinetic energy down to 1500 meters depth. Finally, the processes responsible for this change are detailed
Henry, Françoise. "Étude du rôle du néodyme comme traceur de source et de processus dans l'océan." Toulouse 3, 1993. http://www.theses.fr/1993TOU30282.
Full textSommer, Anna. "Salinité de surface dans le gyre subtropical de l'Atlantique Nord (SPURS/SMOS/Mercator)." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066436/document.
Full textThe focus of this work is on sea surface salinity (SSS) variability in the North Atlantic subtropical gyre. We study seasonal SSS variability and its link to the atmospheric freshwater flux at the ocean surface and to ocean dynamics at meso-scales for the period August 2012 – December 2014. The products from the soil moisture and ocean salinity (SMOS) satellite mission corrected from large scale systematic errors are tested and used to retrieve meso-scale salinity features. Furthermore, the PSY2V4R2-R4 simulation produced by Mercator with a high spatial resolution is also used. The comparison of corrected SMOS SSS data and Mercator simulation with drifter's in situ and TSG measurements from the SPURS experiment shows a reasonable agreement with RMS differences on the order of 0.15 pss.The freshwater seasonal flux is the leading term in the SSS seasonal budget. To balance its effect the ocean dynamics strongly contribute. The entrainment of deeper water is strong during the winter time. It usually acts to lower SSS, except in the south of the SSS–max region where it contributes to increase salinity. Advection is the second important component responsible for the SSS variability. It transfers further north the salty water from the evaporation maximum region. The contribution of advertion term is strongly dependent on the type of data used and their spatial resolution
Bonfardeci, Alessandro. "Paleoclimatic and Paleoceanographic reconstruction of the Pleistocene‐ Holocene through the study of planktonic foraminifera of two sedimentary cores collected in North Atlantic Ocean, southwest of the Azores Islands." Thesis, Paris, Muséum national d'histoire naturelle, 2017. http://www.theses.fr/2017MNHN0027.
Full textIn the global climatic system, the North Atlantic Ocean is considered as a highly sensitive region, which plays a crucial role in the Northern Hemisphere dynamics through the so‐called Atlantic Meridional Overturning Circulation (AMOC) system, of which the Azores Front/Current System represents an important part. The main aim of the thesis is to reconstruct the complex hydrographic and climatic interactions in such a climatically‐sensitive area during middle Pleistocene to Holocene through the analysis of the planktonic foraminifera from two cores collected in the OH1 segment of the Mid‐Atlantic Ridge (MAR) south‐westward of the Azores archipelago during the Oceanograflu 2013 cruise. The manuscript is structured in three chapters presenting the major results and their interpretation (...)
Missiaen, Lise. "Quantification des changements de la circulation océanique profonde de l'Atlantique au cours des changements climatiques rapides des derniers 40 ka." Electronic Thesis or Diss., Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLV004.
Full textThe last 40 ky, have been characterized by abrupt and high amplitude temperature changes (8 to 15 °C in less than 300 years) in Greenland and in the North Atlantic region, associated with drastic ocean and atmospheric circulation changes. The mechanisms behind these abrupt climate changes are still debated. The objective of this thesis is to quantify the ocean circulation changes associated with these abrupt climate changes. In the first part of this thesis, I combined the information of three geochemical proxies in order to overcome the limitations of each proxy taken separately. The carbon isotopic ratios of the benthic foraminifers (δ13C and Δ14C), as well as the sedimentary Pa/Th ratio, have been measured in the North Atlantic sediment core SU90-08 (43°N, 30°W, 3080m). The proxies depict an apparently inconsistent situation over the last glacial maximum: the carbon isotopes indicate that the deep water mass was poorly ventilated while the Pa/Th evidence an active overturning cell. These observations question the type of signal recorded by each proxy. Besides, in order to quantify the circulation changes, a modeling approach is required. In the second part of this thesis, I have implemented the calculation of the Pa/Th in the climate model of intermediate complexity iLOVECLIM. The model is able to simulate the simultaneous evolution of the three proxies and has been used to decipher the multi-proxy response to abrupt circulation changes. The results show that the proxy response varies in the three main Atlantic water masses. In the deep (>2000m) western North Atlantic, the carbon isotopes response lags the Pa/Th response by a few hundreds of years, exemplifying/illustrating a possible decoupling between the different proxies
Assenbaum, Michel. "Etude de la Circulation Océanique à Moyenne échelle à partir des Données Lagrangiennes sur la Zone des Campagnes POMME." Phd thesis, Université Paul Sabatier - Toulouse III, 2006. http://tel.archives-ouvertes.fr/tel-00012200.
Full textun an une région de l'Océan Atlantique Nord-Est situé entre les Açores et la Péninsule
Ibérique afin de comprendre les processus qui font de cette région l'un des principaux puits de
dioxyde de carbone atmosphérique. Ce travail décrit la circulation océanique à méso-échelle dans
POMME. Des trajectoires de flotteurs lagrangiens de subsurface et de flotteurs ARGO sont utilis
ées pour identifier des structures tourbillonnaires et déterminer leur évolution. Combinées à
d'autres observations par analyse objective multi-données, elles fournissent des champs synoptiques
de la circulation horizontale, dans lesquels les transports turbulents sont estimés par diagnostics
lagrangiens. Une configuration régionale du modèle MICOM a été mise en place pour
produire une réanalyse de la circulation dans POMME en assimilant les trajectoires des flotteurs
lagrangiens. Des méthodes spécifiques ont été développées pour tenir compte du caractère lagrangien des observations dans des techniques d'assimilation séquentielle et variationnelle
Missiaen, Lise. "Quantification des changements de la circulation océanique profonde de l'Atlantique au cours des changements climatiques rapides des derniers 40 ka." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLV004/document.
Full textThe last 40 ky, have been characterized by abrupt and high amplitude temperature changes (8 to 15 °C in less than 300 years) in Greenland and in the North Atlantic region, associated with drastic ocean and atmospheric circulation changes. The mechanisms behind these abrupt climate changes are still debated. The objective of this thesis is to quantify the ocean circulation changes associated with these abrupt climate changes. In the first part of this thesis, I combined the information of three geochemical proxies in order to overcome the limitations of each proxy taken separately. The carbon isotopic ratios of the benthic foraminifers (δ13C and Δ14C), as well as the sedimentary Pa/Th ratio, have been measured in the North Atlantic sediment core SU90-08 (43°N, 30°W, 3080m). The proxies depict an apparently inconsistent situation over the last glacial maximum: the carbon isotopes indicate that the deep water mass was poorly ventilated while the Pa/Th evidence an active overturning cell. These observations question the type of signal recorded by each proxy. Besides, in order to quantify the circulation changes, a modeling approach is required. In the second part of this thesis, I have implemented the calculation of the Pa/Th in the climate model of intermediate complexity iLOVECLIM. The model is able to simulate the simultaneous evolution of the three proxies and has been used to decipher the multi-proxy response to abrupt circulation changes. The results show that the proxy response varies in the three main Atlantic water masses. In the deep (>2000m) western North Atlantic, the carbon isotopes response lags the Pa/Th response by a few hundreds of years, exemplifying/illustrating a possible decoupling between the different proxies
Hisard, Philippe. "Etat moyen et variabilité des courants équatoriaux et des structures thermiques associées dans l'Océan Pacifique et l'Océan Atlantique." Paris 6, 1986. http://www.theses.fr/1986PA066111.
Full textPommier, Alexis. "Analyse objective de la dynamique aerologique de basses couches dans l'espace Atlantique Nord : mécanismes et évolution de 1950 à 2000." Lyon 3, 2005. https://scd-resnum.univ-lyon3.fr/out/theses/2005_out_pommier_a.pdf.
Full textThe synoptic activity analysis at surface layer (after reconstruction by algorithm), during the period 1950-2000, on the North Atlantic region permits to justify the hypothesis according to which the climatic variability can be to explain by Highs and Lows behavior evolutions. The exams of the two data bases (Highs and Lows) allow: to have a better knowledge of the evolution of the different features of the Highs and Lows for every time scales, to set up a winter (JFM) general circulation scheme at surface layer showing the oscillation during the period between two patterns. Weak pattern from 1950 to 1970 and Strong pattern from 1970 to 2000. To create an index: North Atlantic Aerological Dynamic Index (NADI) summarizing the atmospheric intensity for every time scales. This index is able to avoid some limits of the reference index (e. G. NAO) and so permits to improve the understanding of the internal mechanisms of the atmospheric dynamic, to clarify the parameters involved in the occurrence of the deep Lows. Therefore, this work improves the knowledge of the atmospheric dynamic at surface layer (mechanisms and evolution) over the North Atlantic region from 1950 to 2000
Mémery, Laurent. "Traceurs transitoires et circulation generale : etude du tritium dans l'atlantique nord." Paris 6, 1989. http://www.theses.fr/1989PA066346.
Full textFidalgo, González Luis. "La cinématique de l'Atlantique nord : la question de la déformation intraplaque." Brest, 2001. http://www.theses.fr/2001BRES2035.
Full textThe kinematic reconstructions of the North Atlantic present the problem of the fit north and south of the Faeroe-Iceland-Greenland Ridge. The reconstructions obtained using fracture zones as the primary structure for tectonic reconstructions, confirm the existence of discontinuities at several scales on kinematic fits. Geological data allow these discontinuities to be interpreted in terms of intraplate deformation. The model presented offers a chronology for this deformation and tries to quantify it. In addition to well known compressional intraplate deformation, this model proposes significant extensional deformation in the oceanic lithosphere west of Iberia. It confirms the abrupt deceleration of African plate motion towards Europe between anomalies C31 and C24. Finally, this model proposes a mixed crustal affinity (oceanic and continental) for the Rockall Plateau, similar to oceanic plateaus in the Indian Ocean
Forget, Gaël. "Profils ARGO et assimilation 4DVAR pour le suivi climatique de l'Océan Nord Atlantique." Brest, 2005. http://www.theses.fr/2005BRES2005.
Full textDeployed in recent years, the autonomous profilers ARGO array aims to monitor the global ocean climatic variability. We here consider the temperature and salinity profiles provided by ARGO during 2002/2003 in the North Atlantic Ocean, which is of major importance for the thermohaline circulation and the climate. Using (4DVAR) assimilation in a general circulation model, we show that the ARGO profiles can actually improve our knowledge of the climatic state (hydrography and circulation) of the ocean. Through assimilation experiments with model simulated profiles, we assess the skills of such a data set and validate the method. With a large simulated representativity error and a realistic number of profiles, we show that the assimilation captures the large scale anomalies of the hydrography and the circulation. We discuss the results regarding the data spatial sampling. Then we move confidently to the assimilation of the real data. Even though the model and the error sources are respectively imperfect and uncertain in this case, the estimation system behaves as in the idealized experiments. Using independant validations, we prove that the assimilation of actual ARGO profiles provides an estimate of the 2002/2003 hydrography that is more precise than a climatology. Moreover, replacing the ARGO profiles by climatological ones, we show that the assimilation system is able to reproduce the variability of a front position or of water mass properties. The assimilation of the actual ARGO profiles clearly improves the one year model circulation too, even, though we do not modify the wind forcing. Assimilating climatological information only in parts of the domain, we analyse the hydrographic constraint on the circulation
Garnier, Valérie. "Variabilité mésoéchelle de l'Atlantique Nord à partir des données altimétriques topex-poseidon : étude de l'influence du vent ers1." Brest, 1997. http://www.theses.fr/1997BRES2038.
Full textFernández, Ibáñez Camila. "Cycle de l'azote et production primaire dans l'Atlantique Nord-Est : suivi saisonnier et influence de la méso échelle." Aix-Marseille 2, 2003. http://www.theses.fr/2003AIX22096.
Full textCosson, Nathalie. "Structure et diversité des peuplements benthiques profonds en réponse à des situations trophiques contrastées dans l'océan Atlantique nord-est tropical et tempéré." Brest, 1996. http://www.theses.fr/1996BRES2045.
Full textCayre, Olivia. "Reconstitutions paléocéanographiques au quaternaire récent à partir de l'analyse quantitative des foraminifères planctoniques dans l'Océan Indien et dans l'Atlantique du Nord-Est." Aix-Marseille 3, 1997. http://www.theses.fr/1997AIX30110.
Full textDeltel, Charles. "Estimation de la circulation dans l'Océan Atlantique Sud par assimilation variationnelle de données in situ : Impact du contrôle optimal des forçages et de l'hydrologie aux frontières ouvertes." Brest, 2002. http://www.theses.fr/2002BRES2036.
Full textObservations show that state-of-the-art numerical ocean models often fail to accurately represent reality. This is partly due to a lack of accuracy in initial and boundary conditions. Also, air-sea fluxes are known to have large uncertainties, and their estimation via advanced estimation methods remains poorly explored. Here, systematic twin data experiments were performed to assess how well such forcings, initial conditions (IC) and open boundary conditions (OB) may be improved via 4D-Var assimilation of profile data in an ocean model. The system is based on the OPA8. 1 model and its adjoint code. The model resolves the seasonal circulation of the South Atlantic Ocean. The assimilated data are either the Reynaud et al. [1998] climatological seasonal hydrological data. In part I, the South Atlantic configuration is described. A spin-up simulation of several years is validated and gives the idealized data needed later. In part II, we describe how the estimation of the OBs anf forcings in the assimilation scheme is implemented, in addition to the previously existing ICs estimation. In part III, idealized experiments during austral summer show that our data are appropriate in identifying the seasonal mean heat and freshwater fluxes, but not their intraseasonal variability. In addition, the wind stress estimation proves an ill-posed problem, in particular in the westerly winds region. A stronger result is that the system can erroneously modify perfect wind data to balance a heat flux error. Limitations of the results due to our configuration are discussed. In part IV, we move to real data and cycle four climatological seasons, estimating all unknowns but the wind. Optimal trajectories prove compatible with the data, but exhibit systematic biases for which solutions are discussed. The parameters controlled in this study show a positive impact on observational fit
Dubus, Laurent. "Instabilité barocline des courants méridiens de la zone intergyre en Atlantique nord-est : impacts sur la circulation de grande échelle et mélange de traceur associé." Brest, 1999. http://www.theses.fr/1999BRES2043.
Full textAllain, Valérie. "Écologie, biologie et exploitation des populations de poissons profonds de l'Atlantique du nord-est." Brest, 1999. http://www.theses.fr/1999BRES2023.
Full textThomas, Bertrand. "Etude des terres rares associées aux particules et sédiments marins, cas de la marge continentale du Golfe de Gascogne (Atlantique N. -E. ) et de la dorsale médio-Atlantique (37o-38o)." Pau, 1998. http://www.theses.fr/1998PAUU3019.
Full textPenduff, Thierry. "Etude de la dynamique de l'Atlantique nord-est à l'aide d'un modèle numérique régional." Brest, 1998. http://www.theses.fr/1998BRES2031.
Full textCzaja, Arnaud. "Sur les interactions ocean atmosphere dans l'atlantique nord et la variabilite de la thermocline." Paris 6, 1998. http://www.theses.fr/1998PA066454.
Full textGrelaud, Michaël. "Variabilité climatique multi-échelles depuis le pléistocène terminal jusqu'à l'actuel, sur la marge pacifique nord américaine." Aix-Marseille 3, 2008. http://www.theses.fr/2008AIX30059.
Full textThe North American Pacific margin surface hydrography is characterized by the California Current System (CCS) whose intensity seasonally responds to the dynamic of northeastern Pacific atmospheric cells. On longer time scales, CCS's intensity depends on climatic oscillators: the El Nino Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). The fossil assemblages of coccolithophores in two oceanic sedimentary basins (Santa Barbara and Soledad) were used to reconstruct the dynamics of these climate oscillations over the last 28,000 years. The ENSO and PDO have persisted throughout this period and have strengthened over time, their cyclicity responding to the precession. The maxima of their intensity are observed during the middle Holocene and during the 20th century. The morphometry of coccoliths shows that calcification is mainly controlled by sea surface temperature
Moreno, Eva. "Propriétés magnétiques des sédiments de la marge du Portugal : traceurs des variations climatiques et océanographiques en Atlantique Nord depuis 340 000 ans." Aix-Marseille 3, 2000. http://www.theses.fr/2000AIX30050.
Full textMagnetic properties of sediments cored along the Portugal Margin have been analyzed and compared to other paleoenviromental indicators in order to reconstruct the climatic variations and oceanic regimes in the North Atlantic during the past 340 000 years. Three mechanisms of mineral transport have been identified : 1) iceberg rafting responsible for IRD (Ice Rafted Detritus) deposition , 2) eolian transport of dust and 3) deep water currents responsible for the transport of fine-grained magnetic minerals. The IRD contain a magnetic fraction (Ti-magnetite) associated with quartz and silicate grains. Their rhythmicity determined by the collapse of Northern ice caps, varies between 5 000 and 11 000 years. The precisely dated IRD layers identified by peaks Sl to S4 are contemporaneous with the Heinrich events HI to H4. IRD layers have also been identified during stages 5, 6 and 7, showing the existence of Heinrich-like events
Drévillon, Marie. "Interaction océan-atmosphère à l'échelle saisonnière sur la région Atlantique-Nord-Europe : rôle des routes dépressionnaires et mécansimes associés sur la variabilité climatique." Toulouse 3, 2002. http://www.theses.fr/2002TOU30224.
Full textObservational studies reveal a lagged relationship between mid latitude North Atlantic summer Sea Surface Temperatures (SST) and next winter atmospheric circulation over the North Atlantic Europe (NAE) region. Another interaction is found between autumn tropical Atlantic SST and next winter atmospheric circulation in the NAE region. A model study with a hierarchy of models, complexifying towards a more realistic ocean, together with a set of storm track activity diagnostics, are used to show the central role played by the storm track in the ocean-atmosphere interaction processes inducing those lagged relationships. Long coupled atmosphere-ocean experiments (150 years) show that these mechanisms have an impact on longer time scales variability (decadal to centenary)
Louvel, Véronique. "Les marges conjuguées de l'Atlantique Nord : structure et modélisation de l'ouverture océanique." Université Louis Pasteur (Strasbourg) (1971-2008), 1995. http://www.theses.fr/1995STR13017.
Full textConil, Sébastien. "Modélisation de l'influence océanique sur la variablilité atmosphérique dans la région Atlantique Nord Europe." Paris 6, 2003. http://www.theses.fr/2003PA066068.
Full textLaurent, Carine. "Variabilité climatique basse-fréquence simulée en Atlantique Nord par un modèle couplé océan-atmosphère." Paris 6, 2000. http://www.theses.fr/2000PA066524.
Full textBeaugrand, Grégory. "Biodiversité pélagique et changements hydroclimatiques dans l'océan Atlantique Nord." Paris 6, 2001. http://www.theses.fr/2001PA066390.
Full textDrouineau, Hilaire. "Développement et ajustement d’un modèle de dynamique des populations structuré en longueur et spatialisé appliqué au stock Nord de merlu (Merluccius merluccius)." Rennes, Agrocampus Ouest, 2008. http://www.theses.fr/2008NSARH073.
Full textLegeleux, Françoise. "Relations entre particules marines et message sédimentaire : flux de matière dans la colonne d'eau et transformations à l'interface eau-sédiments dans l'océan atlantique tropical de Nord-Est." Paris 6, 1994. http://www.theses.fr/1994PA066397.
Full textPiron, Anne. "Observation de la convection profonde en mer d'Irminger sur la période 2002-2015 par les flotteurs Argo." Thesis, Brest, 2015. http://www.theses.fr/2015BRES0059/document.
Full textThe deep convection events are important because they form the intermediate and deep water masses feeding the global circulation. The Labrador Sea is the main site of deep convection in the North Atlantic Ocean and produces the intermediate Labrador Sea Water (LSW). The lrminger Sea was also cited but was forgotten during decades because of the lack of direct observations. This thesis provides the first description of the lrminger Sea deep convection at basin scale, thanks to the Argo data. Three convective events occurred in the lrminger Sea since 2010. During the 2011-2012 winter, the convection reached 1000 m and is explained by the sequence of the Greenland tip jets. The event of the 2O13-2O14 winter, reaching 130O m, is characterized by a strong preconditioning and a weak forcings by the Greenland tip jets.The convection event of the 2O14-2015 winter, reaching 1700 m, shows many of persistant tip jets. The advection of LSW from the Labrador Sea explains the deepest mixed layers observed during the last two winters. The results show that deep convection in the lrminger Sea is not a rare isolated event and plays a significant role on the climate balance
Boisséson, Éric de. "Les eaux modales du gyre subpolaire de l’Atlantique Nord : origine, formation, variabilité." Brest, 2010. http://www.theses.fr/2010BRES2001.
Full textThe subpolar mode waters of the North Atlantic ocean play a key role in the general oceanic surface circulation. Their life cycle bas only been described from an average of observations collected during several decades. This description avoids the real time scale of the life cycle of the mode waters and smooths their variability. This thesis work deals with these two parameters by analysing both the ORCA025-G70 model fields and the observations. The lagrangian analysis of the ORCAO25-G70 fields highlights the key role of the North Atlantic current in the life cycle of the mode waters. The time scales of this cycle are very short. The surface atmospheric fluxes and the mixing are the formation processes of the mode waters. These ones are rapidly advected by the North Atlantic Current toward the areas of deep convection. If the mode water formation is driven by the atmospheric fluxes, the mode Water variability le driven by the advection. This variability is linked to the variable intensity of the main branches of the North Atlantic current in the subpolar gyre. These variations are linked to the variable influence of the subpolar and subtropical contributions to the mode water feeding. This relative influence is responsible for the great changes in the subpolar mode water properties observed in the past decades. The processes describes by the model are close to the observations. Therefore, we consider from a heat budget calculation that the Argo array should be able to provide a precise description of the mode water formation and variability on a pentadal to decadal time scale
Royer, Juliette. "Modélisation des stocks de céphalopodes de Manche." Caen, 2002. http://www.theses.fr/2002CAEN2048.
Full textIppolito, Pascale. "Contribution de l'analyse de la microfaune planctonique et benthique à la paléo-océanographie de l'Océan Austral (Atlantique S-E et Océan Indien S-O)." Bordeaux 1, 1985. http://www.theses.fr/1985BOR10505.
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