Basé sur l'analyse conjointe et complémentaire de ~10 ans de données altimétriques et de profils verticaux de température et de salinité acquis par les profileurs Argo, l'objectif principal de cette thèse est d'étudier en détail les caractéristiques de surface et la structure verticale des tourbillons dans les 4 grands systèmes d'upwelling mondiaux (EBUS Pérou-Chili, Californie, Canaries et Benguela), qui partagent une dynamique à grande échelle relativement similaire. Les résultats principaux montrent que l'ensemble des tourbillons détectés sur les cartes altimétriques dans les 4 EBUS ont des propriétés physiques relativement proches, avec une forte proportion de tourbillons de faibles dimensions ayant une durée de vie relativement courte. Au contraire, la faible partie des tourbillons échantillonnés par les profileurs Argo montre des dimensions bien plus grandes pour des durées de vie plus longues. La sur-représentation de ces grandes échelles dans le jeu des tourbillons échantillonnés par les profileurs Argo est donc le biais majeur des résultats obtenus sur la structure verticale des tourbillons. L'analyse des profils moyens d'anomalies de température et de salinité acquis par les profileurs Argo dans les tourbillons révèle une forte hétérogénéité entre les 4 EBUS, mais également au sein de chacun de ces systèmes d'upwelling. Les structures verticales des tourbillons sont fortement liées à l'hydrologie et à la dynamique locale. Par exemple, les tourbillons de subsurface du PCUS occupent plutôt la partie Sud du système, alors que les tourbillons intensifiés en surface sont présents à la limite Nord de la gyre subtropicale. Dans le CALUS, la présence de Cuddies se devine à la côte, les autres sous-régions contenant des tourbillons dont les anomalies sont majoritairement intensifiées à la base de la pycnocline, avec comme particularité un changement de signe lié à la salinité des couches superficielles. Le CANUS est peuplé de tourbillons très différents en fonction de leur position par rapport à la zone frontale du Cap Vert : au Nord, des tourbillons intenses en subsurface, avec la présence de quelques Meddies ; au Sud, des tourbillons très superficiels. De même dans le BENUS, la partie au Nord de 15°S contient plutôt des tourbillons intensifiés dans les couches de surface, alors qu'au Sud du front d'Angola-Benguela, les tourbillons présentent des anomalies fortes sur une grande partie de la colonne d'eau. L'extrême Sud de cet EBUS est également le lieu de passage des Anneaux des Aiguilles. Les contributions de l'advection isopycnale et du déplacement de la colonne d'eau sur la verticale nous permettent d'affiner la description de ces différentes structures. La présence de grands types de tourbillons, à la morphologie bien distincte (cœur de surface, de subsurface, grande extension verticale, tourbillons fortement intensifiés, etc.), est confirmée par l'étude des tourbillons spécifiquement générés dans la bande côtière. L'analyse Lagrangienne de ces tourbillons nous permet également de décrire l'évolution temporelle de leur structure verticale, qui montre une homogénéité temporelle inattendue. Cette thèse présente donc plusieurs outils facilement applicables dans différentes régions océaniques pour caractériser la structure thermohaline des tourbillons et fournit pour la première fois une description des grands types de tourbillons peuplant les EBUS, soulignant la grande diversité de la mésoéchelle. / Merging ~10 years of altimetry maps and vertical profiles provided by Argo floats, we aim to study in details the eddy's surface characteristics and vertical structure in the 4 major Eastern Boundary Upwelling Systems (EBUS : Peru-Chile, California, Canaries and Benguela), sharing similar large-scale dynamics. Our main results show that the eddies detected on altimetry maps in the 4 EBUS have close physical properties, with a lot of small-scale structures (radius < 40km, amplitude < 1cm and lifetime < 30 days). In contrast, the few eddies sampled by Argo floats have larger dimensions (radius of ~90-140 km, amplitude of ~3-7 cm) and longer lifetimes (6-10 months). The major bias with the analyzed vertical structure is the over representation of these large-scale eddies. The temperature and salinity anomaly mean profiles acquired by Argo floats surfacing within eddies reveals a strong heterogeneity between each of the 4 EBUS, but also within them. The eddies' vertical structure is strongly influence by the local hydrology and dynamics. For example, the subsurface-intensified eddies of the PCUS tend to be located in the Southern part of this EBUS, while the surface-intensified eddies are preferentially located near the Northern boundary of the subtropical gyre. In the CALUS, we can identify Cuddies in some coastal sub-regions, but in this EBUS, most of the eddies are intensified at the base of the pycnocline, with a reversal of the salinity anomaly compared to the surface layers. In the CANUS, the Cape Verde frontal zone separates distinct subsurface-intensified eddies and some Meddies in the North, from the Southern part, where eddies are surface-intensified. In the same way, the Angola-Benguela Front of the BENUS separates the surface-intensified eddies in the North from strong, deep-reaching anomalies in the South. The Southern-most part of the BENUS is also a preferential pathway for the large Agulhas Rings and their associated cyclones. The respective contributions of isopycnal advection and vertical displacement improve the description of these very diverse structures. The presence of several eddy-types, with distinct thermohaline properties (surface or subsurface-intensified, deep vertical extend, intense or not, etc.) is confirmed by the study of eddies generated in the coastal area of each EBUS. Their Lagrangian analysis allows us to describe the temporal evolution of their vertical structure, which shows an unexpected temporal homogeneity. This manuscript presents different efficient tools used to analyze the surface characteristics, the thermohaline properties and the temporal evolution of mesoscale eddies in the 4 major EBUS, highlighting their diversity.

Les travaux ont été effectués sur le golfe du Lion. Ils présentent des résultats combinés de l'interprétation d'images de satellites, obtenues dans l'infrarouge thermique (capteur AVHRR) et dans le domaine visible (capteur CZCS) avec des connaissances historiques et des mesures recueillies simultanément en mer. Ils permettent, d'une part, d'estimer la forte variabilité spatio-temporelle de la zone de dilution rhodanienne, en particulier sous l'influence du vent local et du débit du fleuve, et, d'autre part, d'observer la formation hivernale d'eau profonde dans le golfe du Lion. L'évolution saisonnière des zones de production dans le golfe du Lion est suivie à l'aide d'images de la concentration relative en pigments chlorophylliens et de la température de la mer. Le traitement d'images du spectre visible du satellite METEOSAT II permet l'estimation mensuelle de l'éclairement solaire global au niveau de la mer.

Current meter records from a long term mooring site on the continental slope off the west coast of Vancouver Island, British Columbia, Canada are used to investigate the scales of variability of the subsurface California Undercurrent and its relation to possible driving mechanisms. Observed along the west coast of North America from Baja California to Vancouver Island, the California Undercurrent is part of the California Current System, a typical basin-scale eastern boundary circulation system. Of the four instruments at nominal depths of 35, 100, 175, and 400 m, the upper two show seasonally reversing flow, while the 175 m instrument registers a year-round poleward flow. The deepest current meter, located approximately 100 m above the bottom, reflects the influence of a nearby submarine canyon. The flow at 100 and 175 m depths, as well as the water properties sampled in the region with CTD casts, are characteristic of the temporal and spatial variability of the California Undercurrent over the continental slope off central and southern Vancouver Island. The correlation of the 175 m flow with local atmospheric forcing (wind stress) in the low-frequency band (periods of months) is higher than with ocean-wide climatic indices, suggesting that regional processes play a key role in the forcing of the subsurface flow.

The Great Australian Bight (GAB) was for many years thought to be an area of limited biological productivity due to a perceived lack of nutrient enrichment processes. These conclusions, however, were based on data from few studies in the western GAB which were assumed to reflect conditions throughout the entire GAB. More recent studies have reported the occurrence of coastal upwelling in the eastern GAB (EGAB) during summer/autumn (November-April), characterized by low sea surface temperatures and elevated concentrations of chlorophyll α, which suggests that certain areas of the GAB may be highly productive during certain times of the year. The eastern Great Australian Bight (EGAB) forms part of the Southern and Indian Oceans and is an area of high ecological and economic importance. Although it supports the largest fishery in Australia (the South Australian Sardine fishery, annual catches since 2004 ~ 25,000 to 42,500 t), quantitative estimates of the primary productivity underlying this industry are open to debate. Estimates range from < 100 mg C m⁻² day⁻¹ to > 500 mg C m⁻² day⁻¹. Part of this variation may be due to the unique upwelling circulation of shelf waters in summer/autumn (November-April), which shares some similarities with highly productive eastern boundary current upwelling systems, but differs due to the influence of a northern boundary current, the Flinders current, and a wide continental shelf. Shelf waters encompass an area of ~115,000 km², and the diverse coastal topography forms part of one of the longest stretches of southward facing coastline in the world. In summer-autumn, winds are upwelling favourable, and the Flinders current running along the continental slope causes the upwelling of the deep permanent thermocline from around 600 m depth (dynamic uplift), allowing nutrient rich cold water to entrain onto the shelf. In winterspring, the EGAB is dominated by westerly downwelling-favourable winds, and upwelling via the Flinders current is suppressed. Thus, the area is highly dynamic, with significant spatial and temporal variations in meteorology and oceanography which may drive variations in nutrient enrichment and productivity. This study represents the first intensive investigation of the primary and secondary productivity of the EGAB, and was designed to evaluate the general hypothesis that spatial and temporal variations in meteorology and oceanography in the EGAB will drive spatial and temporal variations in phytoplankton size structure, and primary and secondary productivity. It examines variations in primary and secondary productivity in the EGAB during the upwelling and downwelling seasons of 2004, and the upwelling seasons of 2005 and 2006. Daily integral productivity calculated using the vertically generalised production model (VGPM) showed a high degree of spatial variation. Productivity was low (<800 mg C m⁻² day⁻¹) in offshore central and western regions of the EGAB. High productivities (1600-3900 mg C m⁻² day⁻¹) were restricted to hotspots in the east that were influenced by the upwelled water mass. There was a strong correlation between the depth of the euphotic zone and the depth of the mixed layer that suggested that ~50% of the euphotic zone lay below the mixed layer depth. As a result, high rates of primary productivity did not require upwelled water to reach the surface. A significant proportion of total productivity in the euphotic zone (57% in 2005 and 65% in 2006) occurred in the upwelled water mass below the surface mixed layer. This result has implications for daily integral productivities modelled with the VGPM, which uses surface measures of phytoplankton biomass to calculate productivity. Macro nutrient concentrations could not be used to explain the difference in the low and high productivities (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). Mixing patterns or micro-nutrient concentrations are possible explanations for spatial variations in primary productivity in the EGAB. On a global scale, daily rates of primary productivity of the EGAB lie between the highly productive eastern boundary current upwelling systems, and less productive coastal regions of western and south eastern Australia, and the oligotrophic ocean. However, daily productivity rates in the upwelling hotspots of the EGAB rival productivities in Benguela and Humbolt currents. Temporal variation in mixing and primary productivity was examined in upwelling influenced nearshore waters off south western Eyre Peninsula (SWEP) in the EGAB. Mixing/stratification in the region was highly temporally variable due to the unique upwelling circulation in summer/autumn, and downwelling through winter/spring. Highest productivity was associated with pwelled/stratified water (up to 2958 mg C m⁻² d⁻¹), with low productivity during periods of downwelling and mixing (~300-550 mg C m⁻² d⁻¹), yet no major variations in macro-nutrient concentrations were detected between upwelling and downwelling events (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). We hypothesise that upwelling enriches the region with micro-nutrients. High productivity off SWEP appears to be driven by a shallowing of mixed layer depth due to the injection of upwelled waters above Z[subscript]cr. Low productivity follows the suppression of enrichment during downwelling/mixing events, and is exacerbated in winter/spring by low irradiances and short daylengths. Phytoplankton abundance and community composition was also examined in the shelf waters of the EGAB. Phytoplankton abundances were generally higher in near shore waters compared with offshore waters, and during the summer/autumn upwelling season compared with the winter/spring downwelling season. Three distinctly different phytoplankton communities were present in the region during the upwelling and downwelling seasons of 2004, and the upwelling season of 2005, with distinctions manifest in variations in the abundance of dominant types of phytoplankton, and differences in average cell sizes. In summer/autumn, waters influenced by upwelling were characterised by high phytoplankton abundances (particularly diatoms) and larger average cell sizes, while the warmer high-nutrientlow- chlorophyll (HNLC) waters in the region had lower phytoplankton abundances and smaller average cell sizes. The winter/spring community was made up of low abundances of relatively large cells. Diatoms always dominated, but evidence of Si limitation of further diatom growth suggests there may be an upper limit to diatom productivity in the region. The maximum observed diatom concentration of ~164,000 cells L⁻¹ occurred in February/March 2004, in an area influenced by the upwelled water mass. Variations in phytoplankton biodiversity in the shelf waters of southern Australia appear to be related to variations in the influence of upwelling in the region. Meso-zooplankton abundance and community composition was examined in the coastal upwelling system of the EGAB. Spatial and temporal variations were influenced by variations in primary productivity and phytoplankton abundance and community composition, which were driven by variations in the influence of upwelling in the region. Peak meso-zooplankton abundances and biomass occurred in the highly productive upwelling influenced nearshore waters of the EGAB. However, abundances were highly variable between regions and years, reflecting the high spatial and temporal variations in primary productivity and phytoplankton abundance that characterise the shelf waters of the region. Spatial and temporal variations in community composition were driven by changes in the abundance of classes of meso zooplankton common to all regions in both years of this study. Meroplanktonic larvae and opportunistic colonizers dominated the community through the upwelling season, in response to increased primary productivity and phytoplankton blooms. Differences in community composition between upwelling influenced waters and the more HNLC regions appear to be reflected in the relative abundances of cladocera and appendicularia, with cladocera more abundant in productive upwelling influenced areas, and appendicularia thriving in the more HNLC regions of the EGAB. Highest potential grazing rates in the EGAB occurred in nearshore regions with highest mesozooplankton biomass, most likely in response to the high phytoplankton biomass that occurs in the same regions. Peak meso-zooplankton grazing rates in the EGAB were ~80% less than those measured in south west Spencer Gulf in March 2007, and ~35% greater than grazing rates in the Huon Estuary in February 2005. Productivity in the EGAB shows significant spatial and temporal variation, with changes reflecting regional and seasonal variation in meteorology and oceanography, and the water masses present in the region. The overall productivity of a summer/autumn upwelling season was highly dependent on within-season variations in wind strength and direction, which dictate the number, intensity, and duration of upwelling events. Rates of primary productivity measured in the EGAB at a given time depended on the meteorological and oceanographic conditions in the region in the lead up to, and during, the sampling event. We hypothesise that during upwelling events, high productivity in the EGAB is driven by the enrichment of waters above Z[subscript]cr, but below the surface mixed layer, with micro-nutrients. Low productivity within summer/autumn upwelling seasons follows the suppression of this enrichment during downwelling/mixing events, and the overall productivity of the upwelling season will depend on the number, duration and intensity of these downwelling/mixing events. Low productivity during winter/spring is driven by the absence of upwelling, low irradiances and short daylengths. / Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2009

The Great Australian Bight (GAB) was for many years thought to be an area of limited biological productivity due to a perceived lack of nutrient enrichment processes. These conclusions, however, were based on data from few studies in the western GAB which were assumed to reflect conditions throughout the entire GAB. More recent studies have reported the occurrence of coastal upwelling in the eastern GAB (EGAB) during summer/autumn (November-April), characterized by low sea surface temperatures and elevated concentrations of chlorophyll α, which suggests that certain areas of the GAB may be highly productive during certain times of the year. The eastern Great Australian Bight (EGAB) forms part of the Southern and Indian Oceans and is an area of high ecological and economic importance. Although it supports the largest fishery in Australia (the South Australian Sardine fishery, annual catches since 2004 ~ 25,000 to 42,500 t), quantitative estimates of the primary productivity underlying this industry are open to debate. Estimates range from < 100 mg C m⁻² day⁻¹ to > 500 mg C m⁻² day⁻¹. Part of this variation may be due to the unique upwelling circulation of shelf waters in summer/autumn (November-April), which shares some similarities with highly productive eastern boundary current upwelling systems, but differs due to the influence of a northern boundary current, the Flinders current, and a wide continental shelf. Shelf waters encompass an area of ~115,000 km², and the diverse coastal topography forms part of one of the longest stretches of southward facing coastline in the world. In summer-autumn, winds are upwelling favourable, and the Flinders current running along the continental slope causes the upwelling of the deep permanent thermocline from around 600 m depth (dynamic uplift), allowing nutrient rich cold water to entrain onto the shelf. In winterspring, the EGAB is dominated by westerly downwelling-favourable winds, and upwelling via the Flinders current is suppressed. Thus, the area is highly dynamic, with significant spatial and temporal variations in meteorology and oceanography which may drive variations in nutrient enrichment and productivity. This study represents the first intensive investigation of the primary and secondary productivity of the EGAB, and was designed to evaluate the general hypothesis that spatial and temporal variations in meteorology and oceanography in the EGAB will drive spatial and temporal variations in phytoplankton size structure, and primary and secondary productivity. It examines variations in primary and secondary productivity in the EGAB during the upwelling and downwelling seasons of 2004, and the upwelling seasons of 2005 and 2006. Daily integral productivity calculated using the vertically generalised production model (VGPM) showed a high degree of spatial variation. Productivity was low (<800 mg C m⁻² day⁻¹) in offshore central and western regions of the EGAB. High productivities (1600-3900 mg C m⁻² day⁻¹) were restricted to hotspots in the east that were influenced by the upwelled water mass. There was a strong correlation between the depth of the euphotic zone and the depth of the mixed layer that suggested that ~50% of the euphotic zone lay below the mixed layer depth. As a result, high rates of primary productivity did not require upwelled water to reach the surface. A significant proportion of total productivity in the euphotic zone (57% in 2005 and 65% in 2006) occurred in the upwelled water mass below the surface mixed layer. This result has implications for daily integral productivities modelled with the VGPM, which uses surface measures of phytoplankton biomass to calculate productivity. Macro nutrient concentrations could not be used to explain the difference in the low and high productivities (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). Mixing patterns or micro-nutrient concentrations are possible explanations for spatial variations in primary productivity in the EGAB. On a global scale, daily rates of primary productivity of the EGAB lie between the highly productive eastern boundary current upwelling systems, and less productive coastal regions of western and south eastern Australia, and the oligotrophic ocean. However, daily productivity rates in the upwelling hotspots of the EGAB rival productivities in Benguela and Humbolt currents. Temporal variation in mixing and primary productivity was examined in upwelling influenced nearshore waters off south western Eyre Peninsula (SWEP) in the EGAB. Mixing/stratification in the region was highly temporally variable due to the unique upwelling circulation in summer/autumn, and downwelling through winter/spring. Highest productivity was associated with pwelled/stratified water (up to 2958 mg C m⁻² d⁻¹), with low productivity during periods of downwelling and mixing (~300-550 mg C m⁻² d⁻¹), yet no major variations in macro-nutrient concentrations were detected between upwelling and downwelling events (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). We hypothesise that upwelling enriches the region with micro-nutrients. High productivity off SWEP appears to be driven by a shallowing of mixed layer depth due to the injection of upwelled waters above Z[subscript]cr. Low productivity follows the suppression of enrichment during downwelling/mixing events, and is exacerbated in winter/spring by low irradiances and short daylengths. Phytoplankton abundance and community composition was also examined in the shelf waters of the EGAB. Phytoplankton abundances were generally higher in near shore waters compared with offshore waters, and during the summer/autumn upwelling season compared with the winter/spring downwelling season. Three distinctly different phytoplankton communities were present in the region during the upwelling and downwelling seasons of 2004, and the upwelling season of 2005, with distinctions manifest in variations in the abundance of dominant types of phytoplankton, and differences in average cell sizes. In summer/autumn, waters influenced by upwelling were characterised by high phytoplankton abundances (particularly diatoms) and larger average cell sizes, while the warmer high-nutrientlow- chlorophyll (HNLC) waters in the region had lower phytoplankton abundances and smaller average cell sizes. The winter/spring community was made up of low abundances of relatively large cells. Diatoms always dominated, but evidence of Si limitation of further diatom growth suggests there may be an upper limit to diatom productivity in the region. The maximum observed diatom concentration of ~164,000 cells L⁻¹ occurred in February/March 2004, in an area influenced by the upwelled water mass. Variations in phytoplankton biodiversity in the shelf waters of southern Australia appear to be related to variations in the influence of upwelling in the region. Meso-zooplankton abundance and community composition was examined in the coastal upwelling system of the EGAB. Spatial and temporal variations were influenced by variations in primary productivity and phytoplankton abundance and community composition, which were driven by variations in the influence of upwelling in the region. Peak meso-zooplankton abundances and biomass occurred in the highly productive upwelling influenced nearshore waters of the EGAB. However, abundances were highly variable between regions and years, reflecting the high spatial and temporal variations in primary productivity and phytoplankton abundance that characterise the shelf waters of the region. Spatial and temporal variations in community composition were driven by changes in the abundance of classes of meso zooplankton common to all regions in both years of this study. Meroplanktonic larvae and opportunistic colonizers dominated the community through the upwelling season, in response to increased primary productivity and phytoplankton blooms. Differences in community composition between upwelling influenced waters and the more HNLC regions appear to be reflected in the relative abundances of cladocera and appendicularia, with cladocera more abundant in productive upwelling influenced areas, and appendicularia thriving in the more HNLC regions of the EGAB. Highest potential grazing rates in the EGAB occurred in nearshore regions with highest mesozooplankton biomass, most likely in response to the high phytoplankton biomass that occurs in the same regions. Peak meso-zooplankton grazing rates in the EGAB were ~80% less than those measured in south west Spencer Gulf in March 2007, and ~35% greater than grazing rates in the Huon Estuary in February 2005. Productivity in the EGAB shows significant spatial and temporal variation, with changes reflecting regional and seasonal variation in meteorology and oceanography, and the water masses present in the region. The overall productivity of a summer/autumn upwelling season was highly dependent on within-season variations in wind strength and direction, which dictate the number, intensity, and duration of upwelling events. Rates of primary productivity measured in the EGAB at a given time depended on the meteorological and oceanographic conditions in the region in the lead up to, and during, the sampling event. We hypothesise that during upwelling events, high productivity in the EGAB is driven by the enrichment of waters above Z[subscript]cr, but below the surface mixed layer, with micro-nutrients. Low productivity within summer/autumn upwelling seasons follows the suppression of this enrichment during downwelling/mixing events, and the overall productivity of the upwelling season will depend on the number, duration and intensity of these downwelling/mixing events. Low productivity during winter/spring is driven by the absence of upwelling, low irradiances and short daylengths. / Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2009

The Great Australian Bight (GAB) was for many years thought to be an area of limited biological productivity due to a perceived lack of nutrient enrichment processes. These conclusions, however, were based on data from few studies in the western GAB which were assumed to reflect conditions throughout the entire GAB. More recent studies have reported the occurrence of coastal upwelling in the eastern GAB (EGAB) during summer/autumn (November-April), characterized by low sea surface temperatures and elevated concentrations of chlorophyll α, which suggests that certain areas of the GAB may be highly productive during certain times of the year. The eastern Great Australian Bight (EGAB) forms part of the Southern and Indian Oceans and is an area of high ecological and economic importance. Although it supports the largest fishery in Australia (the South Australian Sardine fishery, annual catches since 2004 ~ 25,000 to 42,500 t), quantitative estimates of the primary productivity underlying this industry are open to debate. Estimates range from < 100 mg C m⁻² day⁻¹ to > 500 mg C m⁻² day⁻¹. Part of this variation may be due to the unique upwelling circulation of shelf waters in summer/autumn (November-April), which shares some similarities with highly productive eastern boundary current upwelling systems, but differs due to the influence of a northern boundary current, the Flinders current, and a wide continental shelf. Shelf waters encompass an area of ~115,000 km², and the diverse coastal topography forms part of one of the longest stretches of southward facing coastline in the world. In summer-autumn, winds are upwelling favourable, and the Flinders current running along the continental slope causes the upwelling of the deep permanent thermocline from around 600 m depth (dynamic uplift), allowing nutrient rich cold water to entrain onto the shelf. In winterspring, the EGAB is dominated by westerly downwelling-favourable winds, and upwelling via the Flinders current is suppressed. Thus, the area is highly dynamic, with significant spatial and temporal variations in meteorology and oceanography which may drive variations in nutrient enrichment and productivity. This study represents the first intensive investigation of the primary and secondary productivity of the EGAB, and was designed to evaluate the general hypothesis that spatial and temporal variations in meteorology and oceanography in the EGAB will drive spatial and temporal variations in phytoplankton size structure, and primary and secondary productivity. It examines variations in primary and secondary productivity in the EGAB during the upwelling and downwelling seasons of 2004, and the upwelling seasons of 2005 and 2006. Daily integral productivity calculated using the vertically generalised production model (VGPM) showed a high degree of spatial variation. Productivity was low (<800 mg C m⁻² day⁻¹) in offshore central and western regions of the EGAB. High productivities (1600-3900 mg C m⁻² day⁻¹) were restricted to hotspots in the east that were influenced by the upwelled water mass. There was a strong correlation between the depth of the euphotic zone and the depth of the mixed layer that suggested that ~50% of the euphotic zone lay below the mixed layer depth. As a result, high rates of primary productivity did not require upwelled water to reach the surface. A significant proportion of total productivity in the euphotic zone (57% in 2005 and 65% in 2006) occurred in the upwelled water mass below the surface mixed layer. This result has implications for daily integral productivities modelled with the VGPM, which uses surface measures of phytoplankton biomass to calculate productivity. Macro nutrient concentrations could not be used to explain the difference in the low and high productivities (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). Mixing patterns or micro-nutrient concentrations are possible explanations for spatial variations in primary productivity in the EGAB. On a global scale, daily rates of primary productivity of the EGAB lie between the highly productive eastern boundary current upwelling systems, and less productive coastal regions of western and south eastern Australia, and the oligotrophic ocean. However, daily productivity rates in the upwelling hotspots of the EGAB rival productivities in Benguela and Humbolt currents. Temporal variation in mixing and primary productivity was examined in upwelling influenced nearshore waters off south western Eyre Peninsula (SWEP) in the EGAB. Mixing/stratification in the region was highly temporally variable due to the unique upwelling circulation in summer/autumn, and downwelling through winter/spring. Highest productivity was associated with pwelled/stratified water (up to 2958 mg C m⁻² d⁻¹), with low productivity during periods of downwelling and mixing (~300-550 mg C m⁻² d⁻¹), yet no major variations in macro-nutrient concentrations were detected between upwelling and downwelling events (silica >1 μmol L⁻¹, nitrate/nitrite >0.4 μmol L⁻¹, phosphate >0.1 μmol L⁻¹). We hypothesise that upwelling enriches the region with micro-nutrients. High productivity off SWEP appears to be driven by a shallowing of mixed layer depth due to the injection of upwelled waters above Z[subscript]cr. Low productivity follows the suppression of enrichment during downwelling/mixing events, and is exacerbated in winter/spring by low irradiances and short daylengths. Phytoplankton abundance and community composition was also examined in the shelf waters of the EGAB. Phytoplankton abundances were generally higher in near shore waters compared with offshore waters, and during the summer/autumn upwelling season compared with the winter/spring downwelling season. Three distinctly different phytoplankton communities were present in the region during the upwelling and downwelling seasons of 2004, and the upwelling season of 2005, with distinctions manifest in variations in the abundance of dominant types of phytoplankton, and differences in average cell sizes. In summer/autumn, waters influenced by upwelling were characterised by high phytoplankton abundances (particularly diatoms) and larger average cell sizes, while the warmer high-nutrientlow- chlorophyll (HNLC) waters in the region had lower phytoplankton abundances and smaller average cell sizes. The winter/spring community was made up of low abundances of relatively large cells. Diatoms always dominated, but evidence of Si limitation of further diatom growth suggests there may be an upper limit to diatom productivity in the region. The maximum observed diatom concentration of ~164,000 cells L⁻¹ occurred in February/March 2004, in an area influenced by the upwelled water mass. Variations in phytoplankton biodiversity in the shelf waters of southern Australia appear to be related to variations in the influence of upwelling in the region. Meso-zooplankton abundance and community composition was examined in the coastal upwelling system of the EGAB. Spatial and temporal variations were influenced by variations in primary productivity and phytoplankton abundance and community composition, which were driven by variations in the influence of upwelling in the region. Peak meso-zooplankton abundances and biomass occurred in the highly productive upwelling influenced nearshore waters of the EGAB. However, abundances were highly variable between regions and years, reflecting the high spatial and temporal variations in primary productivity and phytoplankton abundance that characterise the shelf waters of the region. Spatial and temporal variations in community composition were driven by changes in the abundance of classes of meso zooplankton common to all regions in both years of this study. Meroplanktonic larvae and opportunistic colonizers dominated the community through the upwelling season, in response to increased primary productivity and phytoplankton blooms. Differences in community composition between upwelling influenced waters and the more HNLC regions appear to be reflected in the relative abundances of cladocera and appendicularia, with cladocera more abundant in productive upwelling influenced areas, and appendicularia thriving in the more HNLC regions of the EGAB. Highest potential grazing rates in the EGAB occurred in nearshore regions with highest mesozooplankton biomass, most likely in response to the high phytoplankton biomass that occurs in the same regions. Peak meso-zooplankton grazing rates in the EGAB were ~80% less than those measured in south west Spencer Gulf in March 2007, and ~35% greater than grazing rates in the Huon Estuary in February 2005. Productivity in the EGAB shows significant spatial and temporal variation, with changes reflecting regional and seasonal variation in meteorology and oceanography, and the water masses present in the region. The overall productivity of a summer/autumn upwelling season was highly dependent on within-season variations in wind strength and direction, which dictate the number, intensity, and duration of upwelling events. Rates of primary productivity measured in the EGAB at a given time depended on the meteorological and oceanographic conditions in the region in the lead up to, and during, the sampling event. We hypothesise that during upwelling events, high productivity in the EGAB is driven by the enrichment of waters above Z[subscript]cr, but below the surface mixed layer, with micro-nutrients. Low productivity within summer/autumn upwelling seasons follows the suppression of this enrichment during downwelling/mixing events, and the overall productivity of the upwelling season will depend on the number, duration and intensity of these downwelling/mixing events. Low productivity during winter/spring is driven by the absence of upwelling, low irradiances and short daylengths. / Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2009

[Truncated abstract] This work was the first large-scale biological oceanographic study to be undertaken in the coastal eastern Indian Ocean adjacent to Western Australia, and covered both northwest (Exmouth Peninsula to the Abrolhos Islands) and southwest (Cape Naturaliste to Cape Leeuwin) regions. The study area was dominated by the Leeuwin Current (LC), an anomalous eastern boundary current that transports tropical water poleward and prevents deep nutrients from reaching the surface by creating large-scale downwelling. Indeed, LC and offshore waters were consistently associated with low nitrate concentrations and low phytoplankton biomass and production (< 200 mg C m-2 d-1). However, the physical forcing of the LC was offset, during the summer months, by upwelling associated with wind-driven inshore countercurrents (Ningaloo and Capes Currents), which provided a mechanism to access high nutrient concentrations normally confined to the base of the LC. ... Limited seasonal investigations off the Capes region of southwestern Australia showed that the winter production scenario can be very different than summer conditions, with strong Leeuwin Current flow that meanders onto the continental shelf and entrains seasonally nutrient-enriched shelf waters. However, production in the LC was still low (≤450 mg C m-2 d-1) due to light limitation resulting from both increased light attenuation and reduced surface irradiance characteristic of the winter months. This investigation provides fundamental knowledge on physical-biological coupling off Western Australia, with implications for fisheries management in view of seasonal and inter-annual variability in the strength of both the Leeuwin Current and inshore countercurrents.

Current meter records from a long term mooring site on the continental slope off the west coast of Vancouver Island, British Columbia, Canada are used to investigate the scales of variability of the subsurface California Undercurrent and its relation to possible driving mechanisms. Observed along the west coast of North America from Baja California to Vancouver Island, the California Undercurrent is part of the California Current System, a typical basin-scale eastern boundary circulation system. Of the four instruments at nominal depths of 35, 100, 175, and 400 m, the upper two show seasonally reversing flow, while the 175 m instrument registers a year-round poleward flow. The deepest current meter, located approximately 100 m above the bottom, reflects the influence of a nearby submarine canyon. The flow at 100 and 175 m depths, as well as the water properties sampled in the region with CTD casts, are characteristic of the temporal and spatial variability of the California Undercurrent over the continental slope off central and southern Vancouver Island. The correlation of the 175 m flow with local atmospheric forcing (wind stress) in the low-frequency band (periods of months) is higher than with ocean-wide climatic indices, suggesting that regional processes play a key role in the forcing of the subsurface flow.

A partir d'un ensemble de données d'observation ainsi qu'un modèle couplé physiquebiogéochimique à haute résolution (CROCO-PISCES), cette thèse explore les processus biophysiques associés à l’une des plus grandes floraisons phytoplanctoniques de l’océan global, au Sud-Est de Madagascar, et le possible rôle des tourbillons sur ces blooms. L’étude montre que ce phénomène se produit dans une région caractérisée par une couche de mélange peu profonde, avec des eaux de surface moins salées probablement associées au courant Sud-Est de Madagascar (SEMC), et avec une structure dipolaire dans la circulation moyenne. Les observations ont révélé une diminution des remontées d’eaux froides (upwelling) le long des côtes sud-est de Madagascar pendant les mois de bloom. Dans le modèle, les nitrates provenant des niveaux de subsurface (advection verticale ; upwelling) ainsi que de la côte malgache (advection horizontale) favorisent la production phytoplanctonique simulée. Une expérience lagrangienne de particules montre une plus forte advection de ces dernières dans la zone de floraison pendant les périodes de bloom alors qu’elles sont déviées vers le sud de Madagascar vers le continent Africain pendant les années sans floraison. Une étude est réalisée à partir d’un jeu de données de suivi des tourbillons co-localisés avec des flotteurs de profilage Argo, pour mieux comprendre des tourbillons intensifiés en surface et subsurface. Une méthode d’identification des structures tourbillonnaires de subsurface a été mise en place en se basant sur l’anomalie de la hauteur dynamique stérique. Ces tourbillons, appelés ‘SIDDIES’ (South Indian ocean eDDIES), se produisent en tant que tourbillon intensifié en surface (surfSIDDIES) et en subsurface (subSIDDIES). Ils se déplacent le long d’une bande de latitude située entre 15°S et 35°S appelée « couloir SIDDIES ». Au cours de leurs déplacements, les subSIDDIES cycloniques (anticycloniques) transportent via les processus d’advection, des masses d’eaux chaudes et peu salées de l’Est vers l’Ouest de l’Océan Indien, contribuant ainsi à environ 58% (32%) du flux total de chaleur par tourbillons dans le sud de l'océan Indien. / Using observational datasets and a high resolution coupled biophysical model (CROCOPISCES), the main aims of this thesis is to study the biophysical processes associated with one of the largest phytoplankton blooms in global ocean, southeast of Madagascar, and the possible role of mesoscale eddies.The study has shown that the bloom occurs in a region of shallow-stratified mixed layer water, with low-salinity waters at the surface possibly associated with the South-East Madagasacar Current (SEMC), and dipole structure in the mean circulation. Observations show that curren-driven upwelling south of Madagascar is reduced during bloom months. It is shown in the model that nitrate from subsurface levels (upwelling) as well as from the Madagascan coast (advection) fertilize the simulated bloom. A Lagrangian analysis shows dispersion of higher percentages of particles in the bloom region during bloom years and south of Madagascar during non-bloom years.Using co-located Argo profiles and an eddy detected algorithm dataset, surface and subsurface-intensified eddies are studied. Subsurface eddies are identified using a detection method based on their steric dynamic height anomaly. Referred to as `SIDDIES’ (South Indian ocean eDDIES), they occur as surface (surfSIDDIES) or subsurface (subSIDDIES) and propagate along a latitudinal band (15°S-35°S) termed as `SIDDIES Corridor’. Advecting warm and fresh water during their propagation, cyclonic (anticyclonic) subSIDDIES contribute about 58% (32%) of the total eddy-heat flux in the South Indian Ocean.

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2016-09-19T17:07:03Z No. of bitstreams: 1 Tese UFF-UPMC Douglas Lessa.pdf: 6010651 bytes, checksum: 86b3d1d49b00abc23751b8883b42dfe0 (MD5) / Made available in DSpace on 2016-09-19T17:07:03Z (GMT). No. of bitstreams: 1 Tese UFF-UPMC Douglas Lessa.pdf: 6010651 bytes, checksum: 86b3d1d49b00abc23751b8883b42dfe0 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geociências - Geoquímica. Niterói, RJ / A presente tese teve o objetivo de reconstruir a paleoceanografia do Sistema de Ressurgência de Cabo Frio (SRCF) nos últimos 12.000 anos através da utilização de proxies ecológicos (comparação entre as assembleias do SRCF com as assembleias das áreas adjacentes com diferentes feições oceanográficas) e geoquímicos de foraminíferos planctônicos, além de obter maior conhecimento sobre a distribuição das espécies sob diferentes configurações oceanográficas, e avaliar e aplicar a recente metodologia de ablação a laser + ICP-MS para análises elementares em carbonatos de foraminíferos. Para isso, 34 topos de box-cores englobando o SRCF e as áreas adjacentes nas bacias de Santos e Campos e dois testemunhos a gravidade foram usados. O agrupamento das assembleias na Margem Continental do Rio de Janeiro (MCRJ) indicou a ocorrência de quatro principais biofáciess espacialmente bem-separadas: biofácies A - talude da bacia de Campos (contribuição de espécies tropicais e subtropicais caracterizando a frente da Corrente do Brasil, CB), biofácies B - bacia de Santos (maiores contribuições de espécies relacionadas à produtividade, caracterizando sinal de mistura de massas de água costeiras produtivas e oceânicas oligotróficas), biofácies C – setor norte do SRCF (contribuições de G. ruber e Globigerina bulloides, caracterizando ambiente de ressurgência com frequentes atenuações por águas quentes) e a biofácies D – setor sul do SRCF (contribuição de espécies indicadoras de águas frias e produtivas, caracterizando uma configuração influenciada pela ressurgência Ekman). Além disso, a distribuição espacial de Globoturborotalita rubescens revelou preferencia desta espécie por águas de plataforma continental e Globigerinella calida sendo associada a pós-ressurgência. Os testemunhos CF10-01B (mais distante da costa) e CF10-09A (mais próximo da costa) cobrem os últimos 11,5 e 7,1 ka cal, respectivamente sendo o primeiro mais influenciado pela Corrente do Brasil, expressando um sinal mais fraco da ressurgência que o segundo. No testemunho CF10-01B, o 18O de G. ruber foi mais variável que o 18O de G. bulloides apresentando dois períodos de diminuição após 9,0 ka cal AP e após 4,0 ka cal AP, enquanto o 18O de G. bulloides diminui após 9,0 ka cal AP e permanece constante até o topo. No testemunho CF10-09A, o 18O das duas espécies variaram de forma antagônica com uma mudança entre 5,0 e 4,5 ka cal AP onde o 18O de G. ruber diminui de -0,4 para -1,0 ‰ e o 18O de G. bulloides aumenta de -0,8 para 0,0 ‰. Os resultados da razão Mg/Ca obtidos pelo método de ablação a laser indicaram uma heterogeneidade intra-câmara que resultou em uma incerteza de 1,49°C para reconstruções com G. ruber e 0,6°C para G. bulloides, assim como amplitudes individuais de 3,0 a 4,0 mmol/mol para G. ruber e de 3,0 a 5,0 mmol/mol para G. bulloides e diferenças significativas entre a última câmara (f) e as anteriores (f-1 e f-2) para as duas espécies. Tais efeitos foram associados ao efeito vital de simbiontes, a grande amplitude de temperatura existente sazonalmente no SRCF e a migração das espécies para águas mais profundas durante a reprodução. As razões Mg/Ca obtidas pelo método clássico foram geralmente mais altas que as razões obtidas pelo método de ablação a laser (LA-ICP-MS) mas se aproximaram e apresentaram variação temporal semelhante aos valores médios obtidos nas câmaras f-1 e f-2. Dessa forma podemos usar a razão Mg/Ca média das câmaras f-1 e f-2 para reconstruções de paleotemperatura de superfície, habilitando também a utilização da diferença entre as razões Mg/Ca das câmaras anteriores e final de G. ruber para reconstruir a estratificação da água. Entretanto, a diferente variabilidade entre a razão Mg/Ca da câmara f de G. ruber e a razão média de G. bulloides indicou possíveis sucessões sazonais, o que nos fez associar as temperaturas reconstruída por G. bulloides como temperaturas da camada de máximo de clorofila, podendo ser associada a intensidade da ressurgência. O período de variação do nível do mar (11,5 – 6,0 ka cal AP) foi marcado pela presença de águas frias, produtivas e homogêneas associadas possivelmente à ressurgência costeira cuja contribuição diminuiu à medida que a transgressão seguia e a frente da CB se aproximava, alcançando um primeiro máximo entre 7,0 e 6,0 ka cal AP no ponto 1 e entre 6,0 e 5,5 ka cal AP no ponto 9, marcado por águas quentes na superfície e frias na subsuperfície. Entre 5,5 e 3,5 ka cal AP, a ressurgência gradualmente se intensifica com maiores efeitos próximo a costa e mais restrita a subsuperfície na porção distal. A influência costeira apresenta um aumento em 5,0 ka cal AP na porção proximal e 4,0 ka cal AP na região distal. Entre 3,5 e 2,5 ka cal AP um forte sinal de águas quentes pouco estratificadas foi observado com maior influência de águas oligotróficas no ponto 9 e mistura de águas costeiras e oceânicas no ponto 1. Após 2,5 ka cal AP, o SRCF adquire suas configurações atuais marcadas por eventos intensos de ressurgência na porção proximal da plataforma e mais restritos a subsuperfície na porção distal. Isso pode ser associado ao fortalecimento da ZCAS ligado a intensificação da monsão Sulamericana no Holoceno Superior devido ao aumento da insolação de verão. / This thesis aimed to rebuild the palaeoceanography of Cabo Frio Upwelling System (CFUS) in the last 12,000 years through the use of ecological (comparison between the CFUS assemblages and adjacent areas assemblages with different oceanographic features) and geochemical proxies of planktonic foraminifera, and obtain more knowledge about the distribution of species under different oceanographic settings, and evaluating and implementing the recent LA-ICP-MS methodology for elemental analysis in foraminifera carbonates. For this, 34 box-cores tops encompassing the CFUS and adjacent areas in the Santos and Campos basins and two gravity cores were used. The group analysis of the assemblages in the Rio de Janeiro Continental Margin (RJCM) indicated the presence of four major biofacies spatially well separated: biofacies A - Campos Basin continental slope (contribution of tropical and subtropical species characterizing the Brazil Current front, BC), biofacies B - Santos basin (largest contributions of productivity related species, characterizing a signal of mixing of coastal productive and oceanic oligotrophic waters), biofacies C - northern sector of CFUS (G. ruber and contributions of Globigerina bulloides, featuring environment with frequent attenuated upwelling by warm water intrusions) and biofacies D - southern sector of CFUS (contribution of cold and productive waters species, featuring the Ekman upwelling setting). In addition, the spatial distribution of Globoturborotalita rubescens revealed preference of this species for continental shelf waters and Globigerinella calida being associated with post-upwelling conditions. The cores CF10-01B (offshore) and CF10-09A (inshore) covered the last 11.5 and 7.1 ka cal, respectively being the first most influenced by the Brazil Current and expressing a weaker upwelling signal than the second. In the core CF10-01B, the G. ruber 18O was more variable than the G. bulloides 18O with two decreases after 9.0 ka cal AP and after 4.0 ka cal BP, while the 18O of G. bulloides decreased only after 9.0 ka cal AP and remains constant up to the top. In the core CF10-09A, the 18O of the two species varied opposite with a change between 5.0 and 4.5 cal ka AP where the 18O G. ruber decreases from -0.4 to -1.0 ‰ and 18O of G. bulloides increases from -0.8 to 0.0 ‰. Mg/Ca ratio results by laser ablation method indicated heterogeneity intra-chamber which resulted in uncertainties for reconstructions up to 1.49°C for G. ruber and up to 0.6°C for G. bulloides as well as individual amplitudes from 3.0 to 4.0 mmol/mol to G. ruber and 3.0 to 5.0 mmol/mol to G. bulloides and significant differences between the last chamber (f) and previous (f-1 and f-2) for both species. These effects were associated with the symbiont vital effect, the wide seasonal temperature range in the SRCF and species migration to deeper waters during reproduction. The Mg/Ca ratio generated by the traditional method were generally higher than the ratios Mg/Ca reconstructed through LA-ICP-MS, although, when compared to the average of f-1 and f-2 chambers only, the values show similar mean and variability indicating both methods agree in reconstruction for surface paleotemperatures. It also allows the use of difference between the ratios of final and previous chamber of G. ruber for paleostratification reconstructions. However, the distinct variability between G. ruber f chamber Mg/Ca ratios and average G. bulloides Mg/Ca ratio indicated possible seasonal succession, which made us associate the temperatures reconstructed by G. bulloides to chlorophyll layer temperatures which may be associated with upwelling intensity. The sea level rise (from 11.5 to 6.0 ka cal BP) was marked by the presence of cold productive and homogeneous waters, possibly associated with coastal upwelling whose contribution gradually decreased during the course of the transgression, followed by the penetration of BC front on the shelf, reaching a first maximum between 7.0 and 6.0 ka cal BP offshore and between 6.0 and 5.5 ka cal BP inshore, marked by warm surface waters and cold subsurface waters. Between 5.5 and 3.5 ka cal BP, the upwelling gradually intensifies mainly inshore and restricted to subsurface offshore. An increased coastal influence is also detected with peaks at 5.0 ka cal BP inshore and 4.0 cal ka BP offshore. Between 3.5 and 2.5 ka cal BP a strong signal of warm water was observed with greater influence of oligotrophic waters inshore and mixture of coastal and oceanic waters offshore. After 2.5 ka cal BP, the SRCF acquires its current settings marked by intense upwelling events, better expressed inshore and restricted to subsurface offshore. This change may correspond to an intensification of the SACZ linked to the strengthening of the South American Monsoon during the late Holocene due to the increase in summer insolation.