The west coast of Vancouver Island is located at the northern end of the California Current System, one of the world’s Eastern Boundary Current Systems. The region is characterized by wind driven coastal upwelling and high productivity, which supports fisheries and related industries. Climate change poses a challenge to these industries by increasing seawater acidity and decreasing dissolved oxygen levels, which are two of the multi-stressors of marine organisms. This thesis explores the relative importance of different physical and biological mechanisms that affect oxygen and carbon extremes in the region. The relatively weak local wind in the region is not well-correlated with local currents and temperature. Results of coherence analyses between multi-depth current and temperature measured at a single mooring site (48.5 ◦ N, 126 ◦ W) in the west coast of southern Vancouver Island and coincident time series of North America Regional Reanalysis (NARR) 10 m wind stress in the geographic domain 36 – 54 ◦ N, 120 – 132 ◦ W are presented. The two-decade long (1989 – 2008) current records from the three shallowest depths (35, 100 and 175 m) show a remote response to winds from as far south as 36 ◦ N. In contrast, temperature only at the deepest depth (400 m) show strong coherences with remote winds. The frequency window of maximum coherence and the estimated average time-lags are consistent with the frequencies and pole-ward propagating phase speeds of coastal trapped waves. Lack of coherence between remote winds and the 400 m currents suggests that the temperature variations at that depth are driven by vertical motion resulting from poleward travelling coastal trapped waves (CTWs). In order to study the relative roles of physical and biological processes on controlling oxygen and carbon tendencies, oxygen cycle has been successfully added to an existing biogeochemical model of the west coast of Vancouver Island. This idealized model then was forced with a long synthetic record of present-day conditions, specifically 1017 years of stochastically generated daily resolved forcing including local and remote winds. The seasonal cycles of the modelled DIC and O2 compare well with depth averaged observational data. They are also found to be strongly coupled in the lower layers, where biological processes are more important. In the upper layer, physical processes such as the differing gas exchange rates partially decouple DIC and O2 . Robust statistics on DIC and oxygen extreme events were calculated by using the long realizations of the model baseline experiment. In the upper mixed layer, O2 extreme events occur 2–3 times more frequently than DIC extreme events. Both extreme events show a much larger interannual variability in the lower layer. In this layer, oxygen extreme events events occur late in the summer, following intense upwelling events early in the upwelling season. Counter-intuitively, within the summer upwelling season, when sporadic upwelling events are expected to cause extreme conditions, the fraction of days with joint DIC–O2 extreme events is negligible. Sensitivity analysis shows that increased primary production, via increased phytoplankton growth rate, decreases the small fraction of days with joint DIC-O2 extreme events in the upper layers during the summer upwelling season but increases it in the winter downwelling season. Lowering upwelling intensities lowers the fraction of days with joint DIC–O2 extreme events. Increasing the upwelling intensities had the opposite effect on this fraction. Changes in up/downwelling intensity did not change this fraction within the summer upwelling season. A non-monotonic response by oxygen extreme events in the lower layer is observed when phytoplankton growth rate was increased. Generally, a moderate decrease in growth rate increases the chances of model lower layer O2 extreme events, while near-zero growth rate does not. In some cases, the same parameter perturbation results in different responses by the mean and the extreme events of DIC and O2 , suggesting that results of studies focusing on physical and biological forcing of the mean state may not directly translate result to extremes. This thesis has identified relative locations within the study domain of priority for effective monitoring of dissolved oxygen and carbon extremes in the study region. Finally, joint DIC- O2 extreme events are found to be common at the end of the summer. This information can be used to inform adaptation and mitigation plans aimed at protecting the economic and bequest value of the coast from potential hazards associated with oxygen and carbon extremes. / Graduate

La marge Sud-Est Atlantique a été le siège d'une accumulation très importante de carbone organique durant les<br />derniers cycles climatiques : les teneurs y sont parmi les plus élevées du monde pour des sédiments océaniques<br />(de 5 à 18-20% à 1000 m de profondeur, de 0,5% à 8% à 3500 m). Ces accumulations sont liées à l'intense<br />activité des cellules d'upwelling associées au système du Courant du Benguela, elles-mêmes fonctions de<br />l'intensité des alizés circulant le long de la côte.<br />Une étude a été réalisée sur des carottes réparties le long de la marge, entre le Dernier Maximum Glaciaire<br />(DMG) et l'Optimum Climatique Holocène (OCH), dans le but de comprendre et contraindre les différents<br />facteurs à l'origine de cette importante sédimentation organique profonde. Les résultats acquis par différentes<br />méthodes (pyrolyse Rock-Eval, spectrométrie Infra Rouge à Transformée de Fourier, observation de lames de<br />palynofaciès...) montrent un enrichissement général du contenu organique des sédiments au DMG par rapport à<br />l'OCH. Cet enrichissement n'est pas homogène, et présente des valeurs maximales à l'aplomb des cellules<br />d'upwelling les plus actives (Lüderitz et Walvis Bay). Il existe une corrélation négative entre le pourcentage de<br />carbone organique total et celui des carbonates, due d'une part à la dilution de la matière organique par la<br />fraction minérale, et d'autre part à la dissolution des carbonates lors de la biodégradation de la matière<br />organique. La distribution de la silice biogène répond plus aux variations de facteurs externes plutôt qu'à la<br />productivité différentielle des cellules d'upwelling.<br />Les études optiques des constituants organiques ont permis l'identification de deux types de matière organique<br />amorphe : un type granulaire, floconneux, et un type gélifié. Le type gélifié est associé aux cellules les plus<br />actives (Lüderitz et Walvis Bay) et caractérisé par un processus de préservation par sulfuration naturelle, le type<br />granulaire, associé à un processus d'adsorption sur des particules argileuses, se rencontre au niveau des cellules<br />relativement moins actives.<br />Ces différents résultats mettent en évidence des modulations de l'enregistrement organique durant la transition<br />DMG/OCH, contrôlées par des processus internes et externes au système d'upwelling. Les deux paramètres<br />majeurs étant la variabilité de l'intensité de la productivité se développant dans la zone photique, et la migration<br />des dépôts lors de la transgression marine associée au réchauffement global. Les processus externes sont<br />principalement liés aux différents apports de masses d'eaux via le Nord (Courant d'Angola) et le Sud (Courant<br />des Aiguilles, Courant Antarctique Intermédiaire).<br />La détermination du potentiel pétrolier de ces sédiments montre que la zone de haute productivité de Lüderitz<br />peut potentiellement être à l'origine du dépôt de roches mères d'hydrocarbures parmi les plus productives au<br />monde.<br />Une comparaison avec un cycle de même nature mais plus ancien (Pléistocène) a été faite après l'étude d'une<br />carotte du leg ODP 175-1084. Les résultats acquis, complétés par des données sur les biomarqueurs, nous ont<br />permis de supposer un type de fonctionnement très différent de celui mis en évidence au Quaternaire terminal.<br />Celui-ci est associé au rôle prépondérant des apports détritiques dans la sédimentation organique et inorganique sur le site de Lüderitz au Pléistocène basal, ainsi qu'à l'existence d'un changement climatique majeur, caractérisé par un pic de productivité associé à des organismes siliceux (diatomées) puis carbonaté (coccolithes).

L'objet de cette thèse est la compréhension de la variabilité des propriétés biogéochimiques dans les régions d'upwelling de bord Est. A l'aide d'estimations par satellite, les variations de la concentration en chlorophylle de surface sont analysées le long de la côte nord-ouest africaine. La variabilité le long de la côte est essentiellement due à la richesse en nutriment des eaux sources. L'extension vers le large de la bande côtière riche en phytoplancton est déclenchée par la présence en excès de nutriments. Cette extension vers le large est accompagnée par une augmentation de la concentration des nutriments en surface et par une absence de lien entre les variabilités intra-saisonnières de chlorophylle et de vent. D'autres mécanismes ont un impact sur la largeur de la bande côtière : la dynamique de la mésoéchelle induit des échanges entre la côte et le large qui exportent vers le large les eaux côtières riches. Un modèle idéalisé d'upwelling côtier a été conçu pour étudier cet impact. A l'aide d'une paramétrisation du courant d'alimentation de l'upwelling, la circulation est reproduite de façon réaliste avec notamment la présence d'un jet côtier de surface et d'un sous-courant le long du talus. La comparaison d'une simulation résolvant la dynamique de mésoéchelle et d'une simulation ayant la même circulation moyenne sans circulation de mésoéchelle montre que la largeur de la bande côtière riche est fortement augmentée par la circulation de mésoéchelle et que le contenu global en phytoplancton est globalement réduit par celle-ci. Cette baisse est au moins en grande partie due à l'export de phytoplancton par des filaments de vitesse négative associés à la dynamique de mésoéchellle.

Cyclonic oceanic vortices (eddies) ranging from ~10 to 150km in diameter that travel along the Florida Keys are investigated. This study employs hydrodynamic parameters from simulations in a high-resolution (~900m horizontally), three-dimensional (26 vertical levels) HYbrid Coordinates Ocean Model regional application to study coastal to offshore interactions along the Florida Keys. These parameters are compared qualitatively to observations from Chlorophyll-a Satellite (SEAWiFs) and HF Radar (WERA). Further, eddy characteristics along the Florida Keys are determined using the Okubo-Weiss parameter combined with Sea-Surface Height fields for the period 2004- 2008. Additionally, their temporal scales are assessed using spectral time-series analysis via Welch?s Fast Fourier Transform and Wavelet Transforms. Some processes that influence eddy evolution along the Florida Keys are presented in the form of case studies. And finally, the relative contribution of mesoscale and submesoscale eddies to the upwelling along the Florida Keys is assessed, supporting the argument that these features contribute to produce water exchanges between the offshore flow and the coastal areas.

The climate response of the equatorial Pacific to increased greenhouse gases is investigated using numerical experiments from five climate models participating in the Intergovernmental Panel on Climate Change Fourth Assessment Report. Changes in the heat budget of the surface layer in response to CO2 doubling (2xCO2) are analyzed in experiments with full-coupled ocean dynamics; and compared to experiments with uncoupled ocean dynamics. In full-coupled experiments, weaker ocean zonal currents driven by a slowing down of the Walker circulation reduce the ocean heat flux divergence throughout the equatorial Pacific. The resulting ocean dynamical heating enhances the surface warming due to increased clear-sky surface radiation in response to 2xCO2. The total radiative plus ocean dynamical heating are stabilized by evaporation and cloud feedbacks over the warm pool and by increased ocean vertical heat transport over the cold tongue. Increased near-surface thermal stratification enhances vertical heat transport in the cold tongue despite a reduction in vertical velocity. This ocean dynamical cooling is the dominant negative term in the heat budget changes over the eastern Pacific; and represents a strengthening of the processes leading to the annual cycle of the cold tongue, which increases by 0.4 K as a result. The stratification response is found to be a permanent feature of the equilibrium climate potentially linked to both thermodynamical and dynamical changes within the equatorial Pacific. To conclude, the relationship between the heat budget changes and the SST response is discussed along with implications for detecting these signals in the modern observational record.

The features of upwelled water are cold, salty and nutrient-rich. However, factors such as the air-sea exchanges of heat affect temperature, and freshwater input from rivers, precipitation and evaporation affect salinity. As biologically important elements are mostly in the dissolved inorganic forms in young upwelled waters, and are mostly in the particulate organic forms in old upwelled waters, the aging status of upwelled waters can be expressed as the relative percentages of biologically important elements in the inorganic and organic forms. Further, nutrients may be consumed by biological productivity. For these reasons, we hereby judge upwelling in the Taiwan Strait (TS) between 2000 and 2002 by the Degree of Nutrient Consumption (DNC, DNCC = and DNCX = ¡AX is nitrogen or phosphorus). The value of DNC is low in young upwelled waters but high in old upwelled waters. In summer, autumn and winter, waters at, or east of, a front in the northeastern Taiwan Strait were affected by the Kuroshio off eastern Taiwan. This front divides the Kuroshio water, the South China Sea (SCS) water that flows through the TS and the Coastal China Current water (in winter). The implications are that not all currents in the Taiwan Strait flow in a northerly direction, even in summer. Because the axis of Kuroshio moved away from eastern Taiwan and upwelling weakened in SCS in 2002, salinity east of the front was fresher, and nutrient and DON were lower in 2002 than 2001. On the other hand, upwelling induced higher DON west of the front. In August, 2002, the water in the southern TS was higher in temperature, more salty, but nutrient and DON were lower than in 2001 because of weakened upwelling in the SCS, and water that intruded into the TS had a higher percentage of Kuorshio. The trend of upwelling, DNCC,P,N was along the west Penghu Channel from bottom to surface. Rates of temperature, salinity and DNCC,P,N variation were greater during 2001 than in 2002, reflecting slower rate of upwelling in 2002.

The objective of this study is to investigate and characterize the mechanism of the island wake behind an island called Liu Chiu Yu off the southwestern Taiwan coast based on the in-situ data of Sb-ADCP, CTD and satellite images. The findings suggest that a counter-clockwise eddy and a clockwise eddy both are with 0.01 S vortice appears in the wake of Liu Chiu Yu when the background flows are toward the northwest. The system of two eddies with opposite rotation and a central return flow develops an unsteady eddy shedding. On the other hand, when the background flows are toward the southeast, island wake generated in the lee of Liu Chiu Yu is attached system of two eddies with opposite rotation and a central return flow. The Sb-ADCP data shows that the flow pattern in the northeastern coast of Liu Chiu Yu is mainly semidiurnal. The major axis of the ellipse of the semidiurnal current is parallel to the orientation of the coast line (northeast to southwest) and the shape of the ellipse is quite long and narrow. The amplitude of the semidiurnal current is approximately two times that of the diurnal current. Generally, the currents are stronger and the occurring probability of the island wake is higher during spring tide. The CTD data shows that the eddy center appears to be divergent and upwelling occurs in the areas under the influence of island wakes. The upwelling pumps deep seawater to the surface and results in low temperature, high salinity, high oxygen concentration and low chlorophyll concentration. On the other hand, in the eddy edges, downwelling occur causing high temperature, low salinity, low oxygen concentration and high chlorophyll concentration. Strong shear was formed at the depth of 60m inside the island wake which generates thermocline so that the mixing phenomenon is quite obvious there. Moreover, in the regions without the influence of island wakes, the stratifying effect is clear and the horizontal variation of temperature, salinity and oxygen concentration is small. Therefore, neither upwelling nor downwelling occurs there. Furthermore, along the edge between blocking and free-stream areas, the shear stress increases and the mixing phenomenon arises to a certain degree. The satellite images show that an island wake appears in the southeastern Liu Chiu Yu during spring tide. The island wake develops a phenomenon called von Karman vortex street. At the same time, a counter-clockwise eddy with heavy suspensions appears in the northern Liu Chiu Yu. The radius of the eddy is around 4 Km. The area of the lowest chlorophyll concentration is located at the center of the eddy. By analyzing all these data, it is concluded that the island wake in Liu Chiu Yu usually appears during spring tide.

This study explored the effects of seasonal variability on the geochemistry of sinking pthesiss and on the nitrogen cycle of the Cariaco Basin. Pthesis fluxes were measured at the base of the euphotic zone (the depth of 1% of photosynthetically active radiation - PAR) with drifting sediment traps during months of upwelling and non-upwelling regimes from March 2007 to November 2009. Flux estimates were analyzed in the context of seasonal variations in sea surface temperature, primary productivity, and chlorophyll a concentrations using data generated by the CARIACO Time-series Program as well as satellite data. Additionally, nine years (1996-2000 and 2004-2007) of nutrients, phytoplankton taxonomy and δ15N of sinking pthesis data within the twilight zone (225 m) from the CARIACO Time-series Program were examined. Results showed that the flux of organic matter responded to changes in surface chlorophyll a but not to primary production. Sinking organic matter decreased by an order of magnitude from the base of the euphotic zone to the oxic-anoxic interface; most of the organic matter produced in surface waters was remineralized before leaving the upper 50-100 m. Lithogenic material often represented a large fraction of the flux. Isotopic analyses showed that 13C/12C ratios of sinking organic carbon were enriched (~-19‰) during the upwelling period and depleted during relaxation (~-23‰). This reflects seasonal changes in inorganic carbon utilization by phytoplankton and suggests that the δ13C of organic carbon in Cariaco sediments can be used as a proxy for carbon fixation by primary producers. The δ15N of the settling flux was influenced by the strength of the upwelling and the presence of the nitrogen fixer Trichodesmium thiebautii in the basin in different seasons; the 15N/14N ratio of sinking nitrogen reflects both imported and local nitrogen fixation signals. This result argues against previous interpretations of the δ15N from the basin's sedimentary record, which suggested that the nitrogen isotopic composition of flux is influenced by denitrification at the oxic-anoxic interface. Dissolved gas samples from the Cariaco eastern and western sub-basins from September 2008 (non-upwelling) and March 2009 (upwelling) were studied to assess the production of biogenic nitrogen gas through mass spectrometric N2/Ar ratiometry. Excess nitrogen gas indicated that upwelling affects the intensity of denitrification at the oxic-anoxic interface. In four of the six stations the concentration of biogenic nitrogen gas at the oxic-anoxic interface was 2.7-6.1 µM N higher during the upwelling period than during the relaxation season (p< 0.001), implying that denitrification in the basin was stimulated by the vertical flux of organic matter and/or the ventilation of the oxic-anoxic interface by oxygenated and nutrient-rich intermediate Caribbean waters.

A coupled, three-dimensional, time-dependent numerical model of water circulation, spectral light, plankton dynamics, nutrient/CDOM loadings, and zooplankton grazing provided an assessment of the factors affecting the growth and maintenance of red tides on the west Florida shelf (WFS). The coupled biophysical model consisted of state variable quantities for temperature, salinity, horizontal/vertical velocity components, turbulent diffusion, spectral light, colored dissolved organic matter (CDOM), dissolved organic and inorganic carbon, particulate silica, four dissolved inorganic nutrient pools (nitrate, ammonium, phosphate, and silicate), and four phytoplankton groups (diatoms, microflagellates, non-toxic dinoflagellates, and the red tide organism Karenia brevis). The model also included a complex grazing scheme that utilized thirteen different zooplankton groups to explore the effects of selective herbivory, feeding periodicity, diel vertical migration, fecal pellet egestion, and ammonium/phosphate excretion within a diverse zooplankton community. Over the shelf and slope of the eastern Gulf of Mexico, from the Mississippi River delta to the Florida Keys, four cases of the model were run during August -- November to explore the dynamics of red tide maintenance with respect to: (1) no refuge from grazing for K. brevis; (2) grazer avoidance of K. brevis during CDOM shading; (3) grazer avoidance of K. brevis in Case II waters; and (4) increased grazing stress on K. brevis competitors. NEGOM and ECOHAB data sets during July -- November 1999 were used to establish the initial/boundary conditions and provided validation data for the coupled model as well. Model results indicate that the red tide of 5.9 x 10 6 cells L-1 witnessed offshore Sarasota, Florida on 07 October 1999 was initiated by an inoculum of K. brevis observed in near-bottom waters above the 30 m isobath offshore Sarasota on 31 August 1999. Flowfields measured at moored ADCPs, observations from AVHRR satellite imagery, and west Florida shelf circulation models indicate that conditions of coastal upwelling existed during the period of bloom development, such that the K. brevis inoculum was delivered to the coast in the bottom Ekman layer. As a shade-adapted species capable of vertical migration, K. brevis cells aggregated near the bottom in order to escape photo-inhibitive light intensities in the overlying water column during the day and harvested the recycled nitrogen excreted by zooplankton grazers. This concomitant relaxation of light inhibition and nitrogen-limitation ultimately led to the growth and maintenance of the red tide, constrained in near-bottom waters during much of the day and preferentially advected inshore as a result of coastal upwelling. As K. brevis was advected inshore, self-shading, CDOM, and suspended inorganic particulates all contributed to the prevention of photo-inhibitive light intensities that, in combination with the excretion of recycled ammonium, ultimately led to the maintenance of a significant red tide at the coast.

Late Pleistocene sediments recovered from ODP Leg 175, Site 1085 are used to generate a high-resolution (500 yr) record of continental climate change in Southern Africa. The location of Site 1085, the SW African continental slope, provides a continuous hemipelagic section with a significant terrigenous component. Terrigenous sediments are transported via fluvial and/or eolian transport mechanisms with MIS 1 being dominated by eolian transport. Analyses, including grain-size, color reflectance, biogenic sediment geochemistry (%CaCO3, %TOC, and C/N), bulk sediment geochemistry, and clay mineralogy, are used to identify continental climate conditions in southern Africa. Analyses indicate glacial/interglacial variation. Median grain-size peaks are associated with changes in transport. Clay mineralogy indicates the presence of kaolinite, smectite, and illite in varying percentages. Smectite and illite dominate the clay mineral assemblages except during MIS 2. Maximum kaolinite was found during MIS 2 and is associated with poleward transport by the Angola Counter Current.