The role of heterotrophic bacteria in the carbon and nitrogen flux of the pelagic food web was investigated during laboratory and field-based studies of the temporal development of the planktonic community after upwelling. Bacterial community structure, activity and production were closely coupled to the upwelling cycle and to the dynamics of the phytoplankton community. The initial bacterial population (<l x 10⁶ cells ml⁻¹, 20 to 40 μg C l⁻¹) was metabolically dormant. Increased availability of phytosynthetically produced dissolved organic carbon (PDOC) stimulated bacterial growth (0.016 h⁻¹) and abundance (8 to 10 x 10⁶ cells ml⁻¹, 140 to 200 μg C l⁻¹). Rapid successions in the dominant plateable strains were attributed to substrate preferences and substrate availability. Significant correlations of bacterial biomass with total standing stocks of phytoplankton and particulate carbon provided evidence of close coupling between bacteria and PDOC, and between bacteria and recalcitrant substrates available during phytoplankton decay. These relationships were best described by power functions, suggesting that bacterial biomass was relatively reduced at high levels by predation. A microcosm study indicated that zooflagellate predation could control bacterial biomass. Low net growth yields (34 to 36%) of flagellates suggested inefficient transfer of carbon to higher trophic levels, but considerable nitrogen regeneration (ca 6 to 7 μg N mg dry weight⁻¹ h⁻¹). Thymidine-measured bacterial production (TTI, <0.1 to 1.25 mg C m⁻³ h⁻¹) was linearly related to phytoplankton growth. Non-uniform response of bacteria to added tracer substrates may result in underestimates of bacterial production by 2 to 34 times by TTI, particularly in deep or oligotrophic waters, or during phytoplankton decay. Close coupling of copepod (Calanoides carinatus) production to the upwelling cycle suggested co-existence of the microbial food web and the classical diatom-copepod food chain. Recently upwelled water was dominated by phytoplankton. Assuming that all phytoplankton carbon was available for utilisation, copepods and bacteria were calculated to consume approximately 12 and 22% of primary production respectively. As the bloom declined the planktonic community was increasingly dominated by bacteria, detritus and mesozooplankton. On average, copepods consumed 60% of primary production, while bacteria consumed 49%. Carbon consumption requirements of both bacteria and copepods were satisfied by resource partitioning and carbon cycling. Under food-limiting conditions herbivorous copepods may switch to omnivory, ingesting microzooplankton of the microbial food web, and stimulating enhanced remineralisation to further sustain primary production. A generic size-based simulation model of the dynamics of the plankton community indicated that bacteria and the microbial food web increase the overall productivity of the planktonic food web, and that heterotroph predation in the smaller size classes (<200 μm) is an important mechanism in nutrient recycling.

Dans le cadre de l’implantation d’une centrale pilote à énergie thermique des mers (ETM) prévue au large des côtes caribéennes de la Martinique d’ici 2020, ces travaux de thèse visent à évaluer les impacts potentiels de la décharge d’eau profonde en surface sur le phytoplancton. La centrale pilote offshore NEMO conçue par DCNS et mise en oeuvre par Akuo Energy prévoit une production d’environ 10 MW. Les eaux froides et riches en nutriments pompées au fond et rejetées en surface par la centrale ETM avec un débit d’environ 100 000 m3.h-1 devraient enrichir les eaux de surface du site d’étude, particulièrement pauvres en nitrate et phosphate. Deux campagnes de mesures sur le terrain à deux saisons contrastées (saison humide en juin 2014 et saison sèche en novembre 2013) ont permis d’apporter une description des différents paramètres physiques et biogéochimiques susceptibles d’induire une modification de la communauté phytoplanctonique. Une variabilité saisonnière marquée de la stratification et des paramètres biogéochimiques a été mise en évidence avec en saison humide une forte influence océanique (advection d’eaux originaires de l’Amazone et de l’Orénoque) et atmosphérique (brumes des sables) enrichissant potentiellement la couche de surface en nutriments et en métaux traces. Des microcosmes in situ ont été développés afin de simuler le rejet d’eau de fond dans la couche de surface sous différents scénarios. De l’eau de surface prélevée dans le maximum de chlorophylle (45 m, où le phytoplancton est le plus abondant) et à la base de la couche euphotique (80 m, où le phytoplancton est présent en très faible abondance) a été enrichie avec un faible (2%) ou fort apport (10%) d’eau de fond (1100 m) et mise à incuber in situ pendant 6 jours. La production primaire a également été estimée dans le milieu naturel et dans les microcosmes. Ces expérimentations ont mis en évidence qu’un fort apport (10%) stimule le développement du micro-phytoplancton, des diatomées en particulier, au détriment des Prochlorococcus, tandis qu’un apport de 2% ne modifie que faiblement la communauté. La réponse des diatomées pourrait être liée à l’apport en nitrate et phosphate par les eaux profondes. La production primaire serait quant-à-elle dépendante de l’assemblage phytoplanctonique en présence, plutôt que de l’intensité de l’apport d’eau profonde. Enfin, les perturbations thermiques liées au rejet d’eau froide de fond ont été évaluées à partir du modèle numérique ROMS. Les seuils d’impact thermique de -3°C préconisés par la World Group Bank et de -0,3°C correspondant à 2% de dilution d’eau profonde ont été considérés. Même au seuil le plus bas (-0,3°C), la surface impactée sur les premiers 150 m de la colonne d’eau était trop faible pour être détectable par la simulation, quelle que soit la profondeur du rejet. L’impact thermique lié au rejet d’eau froide devrait donc être négligeable, et elle serait limitée à moins de 3 km2. Ces travaux constituent la première étape indispensable dans la compréhension de ce que pourrait être l’impact de ce rejet sur l’écosystème à plus long terme. / As part of the implementation of an Ocean thermal energy conversion (OTEC) pilot plant planned off the Caribbean coast of Martinique by 2020, this thesis aims to assess the potential impacts of deep seawater discharge at the surface on the phytoplankton. The offshore pilot plant NEMO, designed by DCNS and implemented by Akuo Energy anticipates production of approximately 10 MW. The cold and nutrient-rich waters that are pumped in the bottom and discharged at the surface by the heat engine with a flow of roughly 100 000 m3 h-1 should enrich surface waters of the study site, which are particularly poor in nitrate and phosphate. Two campaigns of field measurements in two contrasting seasons (the dry season in November 2013 and the wet season in June 2014) have allowed the description of different physical and biogeochemical parameters that may induce changes in the phytoplankton community. Marked seasonal variability in stratification and biogeochemical parameters occurred, with strong oceanic influences (advection of waters from the Amazon and Orinoco) and atmospheric influences (African dust) potentially enriching the surface layer in nutrients and trace metals during the wet season. In situ microcosms were designed to simulate the discharge of bottom waters into the surface layer under different scenarios. Surface water collected at the chlorophyll maximum(45 m, where the phytoplankton is the most abundant), and at the base of the euphotic layer (80 m, where the phytoplankton is present, but in very low abundance) was enriched with either a weak (2%) or strong (10%) input of bottom waters (1100 m), and incubated for 6 days. Primary production was estimated in both the natural environment, and in the microcosms. These experiments have shown that high input (10%) stimulates the development of micro-phytoplankton, especially diatoms, to the detriment of Prochlorococcus. The response of diatoms could be linked to the input of nitrate and phosphate by the deep seawater.Primary production would be dependent on the composition of the phytoplankton assemblage rather than on the intensity of deep water discharge. Finally, thermal disturbances linked to the discharge of cold water at the surface were assessed using a numerical model (ROMS), which considered the thermal impact threshold of -3°C as recommended by the World Bank Group, and -0.3 °C, corresponding to a 2% dilution with deep water. Even at the lowest threshold (-0.3 °C), the area impacted in the first 150 m of the water column was too low to be detected by the simulation, regardless of the discharge depth. The thermal impact of cold water should therefore be negligible and limited to an area of less than 3 km2. This work provides the first critical step in understanding how bottom water discharge may impact the ecosystem in the longer-term.

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references. Also available on the World Wide Web.

The aim of this thesis was to assess the influence of upwelling on alga-grazer interactions in rocky shore communities along the south coast of South Africa using grazer exclusion treatments with controls and procedural controls set out in a block design and monitored for algal cover roughly monthly for one year. In the first experiment grazers were excluded from treatment plots at two upwelling and two non-upwelling sites and the rates of algal biomass accumulation were then compared. The upwelling sites showed significantly faster algal colonisation rates, with Ulva rigida being the first species to colonise the rocks. Final algal cover and biomass did not differ significantly between upwelling and non-upwelling sites in control plots open to grazers, but were significantly higher in grazer exclusion plots at upwelling sites indicating stronger grazing effects. This was confirmed by estimating the intensity of grazing using the log-response ratio (LRR), which was calculated from treatment and control plots. Upwelling sites had significantly lower LLR values indicating stronger grazing effects, than at non-upwelling sites, despite no difference in grazer abundances. The second experiment examined the effects of nutrient addition on algal growth and community composition by comparing high nutrient enrichment plots with low enrichment plots at one upwelling and one non-upwelling site. ANOVA indicated faster growth rates and significantly higher final algal biomass in high enrichment plots compared to low enrichment and control plots at both upwelling and non-upwelling sites. A two-way ANOVA indicated significantly higher algal cover in high enrichment plots compared to the data from the grazer exclusion plots in experiment 1 at both sites, suggesting that nutrient addition plays a major role in algal growth and community composition. The findings of these studies have shown significant differences between treatments, sites and seasons, with significant differences not only occurring in algal cover but also accumulation of algal biomass and recruitment patterns between treatments. The small scale local processes acting within a few centimetres (plots) or tens of meters (among blocks) can also be reflected over larger scales such as sites (upwelling/non-upwelling shores). Further, these studies have demonstrated that various factors such as the effects from increased nutrients at upwelling cells and the change in grazing effects due to enhanced nutrients can determine the abundance and diversity of the community structure, including an increase in the abundance of the fast growing algae Ulva rigida, and a slow recovery of the brown and red algae.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 126-138). Also available on the World Wide Web.

Thesis (M.A.)--Stellenbosch University, 1988. / ENGLISH ABSTRACT: The Benguela upwelling system off southern and south western Africa is a zone of strong and extensive upwelling. Owing to the greater fIsh numbers found along the front between the upwelling and South East Atlantic Ocean the frontal zone is a key element in the ecology of the upwelling area. This discourse focuses on the perturbations of this front. The major data source used was the daily Meteosat satellite imagery for the years 1978, 1979 and 1982 to 1985 in the visible and infrared wavebands. These data enable the investigation of cross frontal activity for the entire Benguela Upwelling System at various spatial and temporal scales. NOAA satellite infrared imagery was also used. At the macroscale two upwelling zones are described. The fIrst is the upwelling core along the coast which exhibits well-developed and persistent upwelling. Offshore of this is an area in where the more transient fllament activity predominates. This outer zone is one of constant change and presents highly variable frontal boundary locations. As far as the persistent upwelling is concerned, the northern boundary closely approximates that suggested by Shannon (1985) of l7oS. Cape Agulhas was the effective southern boundary of any regular upwelling. The mean offshore extent of the outer upwelling is 270 kilometres off Liideritz and 45 kilometres off Cape Town. An analysis of the seasonal location of the front shows that the greatest upwelling extent at both Liideritz and Cape Town is observed in winter. Although the winter upwelling extent is the greater of the two seasons, the summer frontal location at Cape Town, in turn, exhibits remarkable stability. The upwelling off Liideritz, on the other hand, is prone to almost constant frontal location fluctuations. . Most of the variation occurs as a result of the growth and decay of fllaments. Filaments were seen along the entire upwelling zone from Cape Agulhas to Cape Frio. On average, the fllament sector was 270 kilometres wide off Liideritz. Between Cape Point and Cape' Agulhas the southwards extent of the upwelling rarely exceeded 40 kilometres, while the maximum fllament off Cape Point was about 200 kilometres. A fllament at Cape Point generally extends about 40 kilometres westwards and the upwelling zone off Walker Bay stretches about 20 kilometres southwards, onto the Agulhas Bank. Along the coast between Cape Agulhas and Cape Point the fllaments rapidly react to changes in the wind speed and direction. Mesoscale weather systems are therefore important factors in determining fllament activity there. This also true to some extent at Liideritz. The berg wind can induce rapid fllament growth off Liideritz. Despite an upwelling positive wind direction it is the wind speed that determines whether upwelling will develop at Cape Town at all. At Liideritz the wind speeds appear to determine the cross frontal temperature gradient. The greater the wind speed, the steeper the temperature gradient. Cross frontal temperature gradient of between 0.020C and .006oC per kilometre were calculated for Liideritz, which compares well with readings in the Californian upwelling zone (Koblinsky et al. 1984). In the way fllaments extend the length of the frontal zone greatly and the manner in which these cold water streams react to the changing winds, they are complex upwelling frontal features of great variability and importance in the Benguela upwelling system. / AFRIKAANSE OPSOMMING: geen opsomming

During an upwelling event the cold bottom-water is brought to the sea surface. This cools the atmosphere from below and the stratification becomes more stable. When the atmosphere is more stable the turbulence is reduced and, as a consequence, so are the turbulent fluxes. This study is investigating four periods of upwelling from the Östergarnsholm-site, in the Baltic Sea east of Gotland, during the summer of 2005. The air measurements are taken at a tower at the southernmost tip of Östergarnsholm while the measurements in the water are from a buoy moored 1 km south-southeast of the tower. During all the upwelling events the wind is south-westerly, along the coast of Gotland. This means that the buoy is not within the flux footprint area and is perhaps not always representative of what happens there. All the periods show a stabilization of the atmosphere as the SST (Sea Surface Temperature) decreases. The heat fluxes, especially the latent heat flux, decreases as the SST decreases. The amount of CO2 in the atmosphere, in the summer, is usually higher than the amount in the surface water of the seas because the oceans are a net sink of CO2. The air-sea flux of CO2 is to a large extent controlled by this difference. Therefore the flux of CO2 is usually directed to the sea. The deep-water contains more CO2 than the surface water because the phytoplankton near the surface removes CO2 through photosynthesis. The deep-water is also colder and can solve more CO2. During an upwelling event this CO2-rich water is brought to the surface. As an upwelling event progresses the difference in CO2-concentration between the air and the sea is reduced, sometimes reversed, and the flux decreases. This is what happens in three of the investigated periods in this study. During the fourth period a counter gradient flux is observed. / När en uppvällning inträffar förs kallt djupvatten upp till havsytan. Det kalla vattnet kyler atmosfären nedifrån, något som leder till mer stabil skiktning. När atmosfären blir mer stabilt skiktad dämpas turbulensen och det medför att de turbulenta flödena också avtar. I den här studien analyseras fyra perioder med uppvällning. Mätningarna kommer från Östergarnsholm, öster om Gotland, under sommaren 2005. Mätningarna i luften är tagna från en mast vid Östergarnsholms södra udde. Mätningarna i vattnet kommer från en boj som är förankrad 1 km sydsydöst om masten. Vid samtliga uppvällnings-perioder i den här studien är vinden sydvästlig (längs Gotlandskusten). Det betyder att bojen inte befinner sig inom flödenas footprint-area och dess mätningar är kanske inte hela tiden representativa för vad som händer i footprint-arean. Samtliga undersökta perioder visar på en stabilisering av atmosfären då havsytans temperatur avtar. Värmeflödena, i synnerhet det latenta värmeflödet, avtar i samband med att temperaturen i havsytan sjunker. Halten av CO2 i atmosfären är vanligtvis högre än halten i havens ytvatten (under sommaren) eftersom de är en nettosänka för CO2 globalt sett. CO2-flödet mellan havsytan och atmosfären styr till en stor del av denna skillnaden i CO2-halt. Det innebär att CO2-flödet är riktat neråt, mot havet. Havens djupvatten innehåller mer CO2 därför att växtplankton nära ytan reducerar CO2-halten genom fotosyntesen. Djupvattnet är också kallare och kan därför lösa mer CO2. Under en uppvällning förs detta CO2-rika vatten upp till ytan. När en uppvällning fortskrider minskar skillnaden i CO2-halt mellan hav och atmosfär (ibland kan CO2-halten i ytvattnet även komma att överstiga atmosfärens halt) och flödet avtar. Tre av perioderna i den här studien visar på ett avtagande flöde. Den fjärde perioden uppvisar ett flöde motriktat CO2-gradienten.

O trabalho tem o objetivo geral de estudar os efeitos transientes de alta frequência do regime de ventos na ressurgência de Cabo Frio, utilizando para este fim dados oceanográficos e saídas do modelo oceanográfico HYCOM. Para atingir este objetivo utilizou-se um conjunto de dados oceanográficos bem como de ventos obtidos junto ao Banco Nacional de Dados Oceanográficos (BNDO) do Centro de Hidrografia da Marinha (CHM). Estes dados são provenientes de duas comissões realizadas pelo ex-Navio Oceanográfico Almirante Saldanha, uma no período de 16 a 23 de janeiro de 1986 e outra no período de 09 a 22 de setembro de 1972. Os dados mostram uma flutuação na estrutura termohalina da região de Cabo Frio, presumivelmente, associada aos eventos de ressurgência ocorridos devido à variação no campo de ventos predominantes na região, mais especificamente, perturbações de alta frequência como a brisa do mar (BM) e a passagem de sistemas frontais na região. Com os resultados preliminares do presente trabalho podemos inferir a existência de uma correlação entre a atuação da BM no regime de ventos com uma intensificação da ressurgência em Cabo Frio já que a circulação local tem o efeito de alterar tanto a intensidade quanto a direção dos ventos predominantes naquela região fazendo com que o vento resultante se torne mais intenso e com uma tendência de ficar paralelo à costa o que favorece à ocorrência do fenômeno da ressurgência. Com os dados de setembro de 1972 observamos também um comportamento interessante da profundidade da isoterma de 16ºC, que é um bom indicador da intensidade da ressurgência, quando a mesma altera sua profundidade em torno de 50m, passando de 70m para 20m, fato este visivelmente associado à alteração no campo de ventos devido à passagem de um sistema frontal na região. / The overall objective of this work is to study the transient hight-frequency effects of the wind regime on the Cabo Frio upwelling. For this, oceanography data and outputs of the oceanographic model HYCOM were used. In order to obtain this objective, a set of oceanographic and wind data, obtained by means of the National Bank of Oceanographic Data (BNDO) of the Hydrographic Center of the Navy (CHM), was used. This data is a result of two commissions carried out by the ex-oceanographic vessel Almirante Saldanha, one between January 16th and 23rd, 1986, and the other from September 9th to 22rd, 1972. The data showed a fluctuation in the thermohaline structure in the Cabo Frio region, presumably associated to the upwelling events which occur due to variations in the predominant wind fields in the region, specifically high frequency disturbances such as the sea breeze (SB) and the passing of frontal systems in the region. Based on preliminary results of this work, we may infer the existence of a correlation between the role of the SB on the wind regime and an intensification of the Cabo Frio upwelling since the local circulation has the effect of altering the intensity as well as the direction of the predominant winds in the region. Consequently, the resulting wind is intensified and has a tendency of becoming parallel to the coast which, in turn, favors the occurance of the upwelling phenomenon. Based on the September 1972 data, we observed an interesting behavior of the depth of the 16ºC isotherm, which is a good indicator of the intensity of the upwelling process. The depth of this isotherm is altered in approximately 50 m going from 70 m to 20 m, which in noticeably associated to the alteration in the wind field due to the passing of a frontal system in the region.

O trabalho tem o objetivo geral de estudar os efeitos transientes de alta frequência do regime de ventos na ressurgência de Cabo Frio, utilizando para este fim dados oceanográficos e saídas do modelo oceanográfico HYCOM. Para atingir este objetivo utilizou-se um conjunto de dados oceanográficos bem como de ventos obtidos junto ao Banco Nacional de Dados Oceanográficos (BNDO) do Centro de Hidrografia da Marinha (CHM). Estes dados são provenientes de duas comissões realizadas pelo ex-Navio Oceanográfico Almirante Saldanha, uma no período de 16 a 23 de janeiro de 1986 e outra no período de 09 a 22 de setembro de 1972. Os dados mostram uma flutuação na estrutura termohalina da região de Cabo Frio, presumivelmente, associada aos eventos de ressurgência ocorridos devido à variação no campo de ventos predominantes na região, mais especificamente, perturbações de alta frequência como a brisa do mar (BM) e a passagem de sistemas frontais na região. Com os resultados preliminares do presente trabalho podemos inferir a existência de uma correlação entre a atuação da BM no regime de ventos com uma intensificação da ressurgência em Cabo Frio já que a circulação local tem o efeito de alterar tanto a intensidade quanto a direção dos ventos predominantes naquela região fazendo com que o vento resultante se torne mais intenso e com uma tendência de ficar paralelo à costa o que favorece à ocorrência do fenômeno da ressurgência. Com os dados de setembro de 1972 observamos também um comportamento interessante da profundidade da isoterma de 16ºC, que é um bom indicador da intensidade da ressurgência, quando a mesma altera sua profundidade em torno de 50m, passando de 70m para 20m, fato este visivelmente associado à alteração no campo de ventos devido à passagem de um sistema frontal na região. / The overall objective of this work is to study the transient hight-frequency effects of the wind regime on the Cabo Frio upwelling. For this, oceanography data and outputs of the oceanographic model HYCOM were used. In order to obtain this objective, a set of oceanographic and wind data, obtained by means of the National Bank of Oceanographic Data (BNDO) of the Hydrographic Center of the Navy (CHM), was used. This data is a result of two commissions carried out by the ex-oceanographic vessel Almirante Saldanha, one between January 16th and 23rd, 1986, and the other from September 9th to 22rd, 1972. The data showed a fluctuation in the thermohaline structure in the Cabo Frio region, presumably associated to the upwelling events which occur due to variations in the predominant wind fields in the region, specifically high frequency disturbances such as the sea breeze (SB) and the passing of frontal systems in the region. Based on preliminary results of this work, we may infer the existence of a correlation between the role of the SB on the wind regime and an intensification of the Cabo Frio upwelling since the local circulation has the effect of altering the intensity as well as the direction of the predominant winds in the region. Consequently, the resulting wind is intensified and has a tendency of becoming parallel to the coast which, in turn, favors the occurance of the upwelling phenomenon. Based on the September 1972 data, we observed an interesting behavior of the depth of the 16ºC isotherm, which is a good indicator of the intensity of the upwelling process. The depth of this isotherm is altered in approximately 50 m going from 70 m to 20 m, which in noticeably associated to the alteration in the wind field due to the passing of a frontal system in the region.

In this thesis, the phenomenon of flow-topography interaction is considered in the context of two dynamically distinct case studies. In the first study, tidally-driven upwelling is investigated usingfield data collected in Hydrographers Passage (20????S), a narrow, navigable channel in the dense outer reef matrix of the southern Great Barrier Reef, Australia. In the second study, island wake formations at Cato Island (155????32????E, 23????15????S) in the deep, Western Coral Sea are examined using a combination of field data and numerical experiments. The result of the Hydrographers Passage study are of considerable scientific interest since they apply to numerous smaller non-navigable reef-edge passages dotted throughout the southern Great Barrier Reef. Strong, semi-diurnal flood tides flowing through a gap in a distal patch reef system at the shelf break generate strong upwelling, providing a pulsed, semi-diurnal input of nutrients to the reefs offshore of the passage. If stable in the long term, this mechanism could have profound evolutionary implications for large reefal areas in the southern Great Barrier Reef. In the second study, two sets of field observations at Cato Island coincided with conditions of strong (~0.7m s-1), vertically sheared incident currents and weaker (~0.3m s-1), more variable incident flows. The combination of dynamically distinct flow regimes and a tall, steep-sided island penetrating oligotrophic surface waters provides a unique opportunity to investigate the impact of island wakes on hydrographic structure and biological enhancement. Field data indicate that flow disturbances downstream of Cato Island are likely to generate biological enhancement during conditions of eddy shedding and non-shedding wakes. A primitive equation numerical model configured on the basis of field observations faithfully reproduces the key features of both data sets; mechanisms responsible for producing these key features are proposed. Previous numerical studies of island wakes have concentrated primarily on eddy shedding flows. In this thesis, the sub-critical (non-shedding) flow scenario is also considered. It is demonstrated that particle retention in island wakes has a ????hair trigger???? characteristic controlled by incident flow speed. This observation leads to a new proposal to explain the long-standing recruitment problem of biological oceanography.