Combinaison multi-capteurs de données de couleur de l'eau (application en océanographie opérationnelle)

TOULOUSE3-BU Sciences (315552104) / SudocTOULOUSE-Observ. Midi Pyréné (315552299) / SudocSudocFranceF

Zones de minimum d'oxygène (OMZs) de l'océan moderne (une étude focalisée dans l'OMZ du Pacifique Sud Est)

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF

Variabilité spatiale et temporelle du système biologique dans la convergence subtropicale au sud de l'Afrique

Au sud de l'Afrique du sud, le système frontal des Aiguilles, formé par la juxtapositon du front des Aiguilles (AF) et du front subtropical (STF) associés respectivement, au courant de retour des Aiguilles (ARC) et à la Convergence Subtropicale (STC) et plus au sud par le front subantarctique (SAF), est le siège d'une activité mésoéchelle importante. L'interaction à mésoéchelle des processus physiques et géochimiques est donc influencée par la variabilité spatiale et temporelle du système des Aiguilles et de déterminer l'impact de la variabilité des fronts thermodynamiques AF, STF, et SAF sur la distribution phytoplanctonique et sur la production primaire à l'échelle saisonnière et interannuelle. L'analyse en ondelettes, menée conjointement sur quatre années (Octobre 1997 - Septembre 2001) d'observations spatiales multi-capteurs (couleur de l'eau SeaWiFS, altimétrie Topex/Poseïdon-ERS2, radiométrie infrarouge AVHRR) et sur les champs modélisés correspondants provenant du modèle couplé physique-biologie AGAPE-Bio en simulation interannuelle, a permis d'étudier les relations existantes entre le front biologique et les fronts thermodynamiques (AF, STF, SAF). La variabilité saisonnière et interannuelle du système frontal des Aiguilles est étudiée au travers des résultats de simulation et confrontée aux mesures in situ OISO (Océan Indien Service d'Observation) sur la période 1998-2001. Les images de couleur de l'eau SeaWiFS révèlent la sporadicité des enrichissements en chlorophylle le long de la STC. Une analyse statistique est réalisée en vue de déterminer les caractéristiques (durée de vie, extension et distribution spatiale et temporelle) de ces évènements enrichis. Une étude similaire réalisée sur les champs de chlorophylle modélisés nous a permis d'examiner les causes responsables de l'apparition et de la disparition de ces enrichissements sporadiques en chlorophylle. Dans la plupart des situations, la dynamique de la couche de mélange au sein des évènements combinée avec la disponibilité en lumière joue un rôle prépondérantSouth of South Africa, the greater Agulhas Current system, formed by the Agulhas Front (AF) in close juxtapositon with the Subtropical Front (STF), associated to the Agulhas Return Current (ARC) and the Subtropical Convergence (STC), respectively, and farther south by the Subantartic Front (SAF) is a region of intense mesoscale activity presenting enhanced levels of biological production and chlorophyll a. The spatial and temporal variability of a such frontal system influences the physical/biological interactions. The aim of this work is to examine the spatio-temporal variability of the Aguhas frontal system and to determine how the variability of the thermodynamic fronts (AF, STF, SAF) affects the chlorophyll field and the primary production at seasonal and interannual time scales. A wavelet analysis is performed on the 4-years (October 1997 - September 2001) time series of multi-sensors satellite data sets (ocean colour collected by SeaWiFS, mapped sea level anomalies from Topex/Poseïdon-ERS2 and sea surface temperature provided by the infrared radiometer AVHRR) in order to characterize the time and space variability of the front comparing the biological front with the dynamical fronts. A similar analysis is carried out on modelled fields provided by an eddy-permitting, physical-biological coupled model AGAPE-Bio using interannual forcing. Seasonal and interannual variability of the frontal system is then studied through the model results and compared with in situ observations from OISO (Océan Indien Service d'Observation) over the 1998-2001 period. Satellite remote sensing reveals localized high chlorophyll a concentrations, appearing as intermittent event-scale blooms in this region. A statistical analysis is conducted along the Subtropical Convergence to characterize these event-scale blooms in terms of lifetime, chlorophyll concentration, areal extension and spatial distribution. Our numerical model simulates this process with a fair degree of verisimilitude and is used to investigate the physico-biogeochemical requirements for bloom events to occur. We demonstrate that in most cases the limiting factor is intensity of vertical stratification combined with light availabilityTOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Influence of mesoscale physical processes on planktonic ecosystems in the regional ocean (application to the Eastern Boundary upwelling systems)

TOULOUSE3-BU Sciences (315552104) / SudocTOULOUSE-Observ. Midi Pyréné (315552299) / SudocSudocFranceF

Potentiel de la télédétection pour l'analyse des propriétés optiques du système océan-atmosphère et application à l'estimation de la photosynthèse phytoplanctonique

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Transports of the Brazil and Malvinas currents at their confluence

Geostrophic transports of the western boundary currents at the Brazil/Malvinas Confluence in the South Atlantic Ocean are estimated from the data set of the Confluence 3 cruise (February 1990) with a nonlinear inverse model which takes into consideration density, current meter and wind data, and dynamical (planetary vorticity, Ekman, mass conservation) constraints. Inversions are carried out with two initial different levels of no motion at 1500 m (Case A) and at 3000 m (Case B). Consistencies of the water volume transports provided by both inversions are analyzed and compared to previous estimates. Current meter constraints are applied in the Malvinas Current region where a total transport of 45 +/- 7 Sv (1 Sv = 10(6) m(3) s(-1)) is given by both inversions. Within the Brazil Current region, discrepancies between both inversions appear. Case A provides a total transport of 30 +/- 7 Sv while case B gives a total transport of 56 +/- 8 Sv. In the first two layers (0-1000 m; 1000-2000 m), case B (53 Sv) gives larger transport than case A (32 Sv). North of the Confluence and at the North Atlantic level, water is found to flow northward in case A at a rate of 3.4 +/- 2 Sv and southward in case B at a rate of 3 +/- 3 Sv. Case B results are more in agreement with our present knowledge of water mass circulation in the Confluence region than case A results. Eastward transports at the Brazil-Malvinas Confluence are estimated to be 20 +/- 7 Sv and 30 +/- 7 Sv for cases A and B, respectively. Compared to the total transports of the Brazil and Malvinas Currents, these estimates suggest that most of the water supplied to the Confluence area recirculates within the Brazil Current and the Malvinas Current regions

Short-term photoacclimation effects on photoinhibition of phytoplankton in the Drake Passage (Southern Ocean)

We assessed whether short-term photoacclimation responses of natural phytoplankton populations in the Drake Passage (Southern Ocean) were affecting protection from photodamage as cells are mixed up to the surface from depth. To this end, we measured phytoplankton fluorescence characteristics and their ratio of xanthophyll cycle pigment to photosynthetic pigments within the upper mixed layer (UML) and in short-term deck incubation experiments. Phytoplankton within the UML photoacclimated by increasing their ratio of xanthophyll cycle (diadinoxanthin [dd] and diatoxanthin [dt]) pigments to chlorophyll a. The photoacclimation processes observed within the UML did, however, not influence the protection of phytoplankton from photodamage during short-term near-surface irradiance experiments. Exposure to near-surface irradiance resulted in photodamage in all experiments, regardless of the phytoplankton community composition and irradiance levels. Incubating phytoplankton for six hours at either 2% or 50% of surface irradiance prior to exposure to near-surface irradiance did not alter the photodamage characteristics. This suggests that short-term photoacclimation processes within the UML are not adequate to protect phytoplankton from photodamage when cells are mixed up to the surface from depth, and that repair of damaged photosystems is crucial for maintaining photosynthesis under fluctuating irradiance conditions, even at very low mean irradiance levels. Likely, continuously operating photoacclimation processes offset to some extent the negative effects of photodamage on photosynthetic performance, albeit with increased metabolic costs.

Recent advances in understanding the effects of climate change on the world’s oceans

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A graphic novel from the 4th International Symposium on the Effects of Climate Change on the World’s Oceans

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