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Fawkes, Keva. "Upwelling." Thesis, University of Iowa, 2017. https://ir.uiowa.edu/etd/5467.
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Presently, my practice is multi-disciplinary and includes ceramics, sculpture, metals, design, and social practice — the work explores cultural identity, immigration, and cultural imagery using found objects and vernacular architectural references. Many of which are rooted in a post-colonial Anglo Caribbean history, but have grown to include new environments, narratives, and histories that parallel the latter.
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Pickett, Mark H. "Improving wind-based upwelling estimates off the west coasts of North and South America." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FPickett.%5FPhD.pdf.
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Malauene, Bernardino Sergio. "Shelf edge upwelling off Northern Mozambique." Master's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/6127.
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A combination of satellite and in situ data were used to infer the occurrence and temporalspatial variability of upwelling near Angoche. The data were derived from MODIS SST and Chl-a between 2003 and 2007, in situ moored underwater temperature recorder at a depth of 18 m for the period 2003ô2007 and two shipboard surveys providing CTD and XBT data in December 2008 and in August 2009 in the northern Mozambique region. The results con rm that shelf edge upwelling occurs along the northern coast of Mozambique near Angoche between 15 and 18oS, covering an area of approximately 68 000 km2. The upwelling signature was not strong at the surface. Two upwelling core regions were identi ed: (1) the shelf core region and (2) the slope core region. At the shelf core region upwelling was more persistent than at the slope core upwelling. The upwelling displayed seasonal variation between persistent downwelling (warm water) between AprilôJuly and intermittent upwelling (cool water) events between AugustôMarch. Generally the upwelling lasted for a period of about two months but, shorter periods between 8 and 30 days were also observed. The driving mechanism for the shelf edge upwelling o northern Mozambique was determined from satellite observations (NOAA/NCDC) of blended sea surface wind data, and by multi-satellite (AVISO) altimeter sea surface anomaly data between 2003 and 2007 and also during the two cruise surveys in December 2008 and August 2009. These data showed upwelling is in part wind-driven in response to the northôeasterly (NE) monsoon weak-wind velocities between AugustôMarch in the austral spring-summer. The intermittent nature of the upwelling season is also partly due to uctuations in wind direction during the NE monsoon winds. Eddies appear to play a limited role in driving the upwelling.
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Amieroh, Abrahams. "Detecting patterns of upwelling variability in Eastern Boundary Upwelling Systems with special emphasis on the Benguela region." University of Western Cape, 2020. http://hdl.handle.net/11394/7827.
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Magister Scientiae (Biodiversity and Conservation Biology)Coastal upwelling is one of the most important oceanographic processes relating to ecosystem function at local and global spatial scales. To better understand how changes in upwelling trends may occur in the face of ongoing anthropogenically induced climate change it is important to quantify historical trends in climatic factors responsible for enabling coastal upwelling. However, a paucity of conclusive knowledge relating to patterns concerning changes in upwelling across the world’s oceans over time makes such analyses difficult. In this study I aimed to quantify these patterns by first identifying when upwelling events occur using a novel method for predicting the behaviours of coastal upwelling systems over time. By using remotely sensed SST data of differing resolutions as well as several wind variables I was able to identify and quantify upwelling signals at several distances away from the coastline of various upwelling systems. Using this novel method of determining upwelling, I then compared upwelling patterns within all Eastern Boundary Upwelling Systems (EBUS) over a period of 37 years, with the assumption that climate change was likely to have driven variable wind patterns leading to a more intense upwelling over time. Overall, upwelling patterns and wind variables did not intensify overtime. This method of identifying upwelling may allow for the development of predictive capabilities to investigate upwelling trends in the future.
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Abrahams, Amieroh. "Detecting patterns of upwelling variability in Eastern Boundary Upwelling Systems with special emphasis on the Benguela region." University of the Western Cape, 2020. http://hdl.handle.net/11394/7919.
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Magister Scientiae (Biodiversity and Conservation Biology)Coastal upwelling is one of the most important oceanographic processes relating to ecosystem function at local and global spatial scales. To better understand how changes in upwelling trends may occur in the face of ongoing anthropogenically induced climate change it is important to quantify historical trends in climatic factors responsible for enabling coastal upwelling. However, a paucity of conclusive knowledge relating to patterns concerning changes in upwelling across the world’s oceans over time makes such analyses difficult. In this study I aimed to quantify these patterns by first identifying when upwelling events occur using a novel method for predictingthe behaviours of coastal upwelling systems over time. By using remotely sensed SST data of differing resolutions as well as several wind variables I was able to identify and quantify upwelling signals at several distances away from the coastline of various upwelling systems. Using this novel method of determining upwelling, I then compared upwelling patterns within all Eastern Boundary Upwelling Systems (EBUS) over a period of 37 years, with the assumption that climate change was likely to have driven variable wind patterns leading to a more intense upwelling over time. Overall, upwelling patterns and wind variables did not intensify overtime. This method of identifying upwelling may allow for the development of predictive capabilities to investigate investigate investigate upwelling trends in the future.
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Koehler, Kim A. "Observations and modeling of currents within the Monterey Bay during May 1988." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA238699.
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Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, June 1990.Thesis Advisor(s): Ramp, Steven R. Second Reader: Smith, David C. "June 1990." Description based on title screen as viewed on 20 October 2009. DTIC Identifier(s): Ocean currents, ocean circulation, Pacific Ocean, Monterey Bay (California), Monterey submarine canyon, oceanographic data, ADCP (Acoustic Doppler Current Profiler), meteorological data, air water interactions, mean flow, theses. Author(s) subject terms: Monterey Bay, currents, observations, modeling, upwelling. Includes bibliographical references (p. 103-107). Also available in print.
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Hagelin, Susanna. "Effects of Upwelling Events on the Atmosphere." Thesis, Uppsala universitet, Luft-, vatten och landskapslära, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-303882.
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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.
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Ramanantsoa, Heriniaina Juliano Dani. "Variability of coastal upwelling south of Madagascar." Doctoral thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29859.
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Madagascar’s southern coastal marine zone is a region of high biological productivity which supports a wide range of marine ecosystems, including fisheries. This high biological productivity is attributed to coastal upwelling. The thesis seeks to characterise the variability of the coastal upwelling south of Madagascar. The first part of the thesis provides new insights on the structure, variability and drivers of the coastal upwelling south of Madagascar. Satellite remote sensing is used to characterize the spatial extent and strength of the coastal upwelling. A front detection algorithm is applied to thirteen years of Multi-scale Ultra-high Resolution (MUR) Sea Surface Temperatures (SST) and an upwelling index is calculated. The influence of winds and ocean currents as drivers of the upwelling are investigated using satellite, in-situ observations, and a numerical model. Results reveal the presence of two well-defined upwelling cells. The first cell (Core 1) is located in the southeastern corner of Madagascar, and the second cell (Core 2) is west of the southern tip of Madagascar. These two cores are characterized by different seasonal variability, different intensities, different upwelled water mass origins, and distinct forcing mechanisms. Core 1 is associated with a dynamical upwelling forced by the detachment of the East Madagascar Current (EMC), which is reinforced by upwelling favourable winds. Core 2 which appears to be primarily forced by upwelling favourable winds, is also influenced by a poleward eastern boundary flow coming from the Mozambique Channel. This intrusion of Mozambique Channel warm waters could result in an asynchronicity in seasonality between upwelling surface signature and upwelling favourables winds. The second part of the thesis focuses on the interaction between the intrusion of warm water from Mozambique channel and the upwelling cell in Core 2. Cruise datasets, satellite remote sensing observations and model data analyses are combined to highlight the existence of a coastal surface poleward flow in the south-west of Madagascar: the South-west MAdagascar iv Coastal Current (SMACC). The SMACC is a relatively shallow (Coastal Current (SMACC). The SMACC is a relatively shallow (<300 m) and narrow (<100km wide) warm and salty coastal surface current, which flows along the south western coast of Madagascar toward the south, opposite to the dominant winds. The warm water surface signature of the SMACC extends from 22◦S (upstream) to 26.4◦S (downstream). The SMACC exhibits a seasonal variability: more intense in summer and reduced in winter. The average volume transport of its core is about 1.3 Sv with a mean summer maximum of 2.1 Sv. It is forced by a strong cyclonic wind stress curl associated with the bending of the trade winds along the southern tip of Madagascar. The SMACC directly influences the coastal upwelling regions south of Madagascar. Its existence is likely to influence local fisheries and larval transportpatterns, as well as the connectivity with the Agulhas Current, affecting the returning branch of the global overturning circulation. The last part of the thesis provides a holistic understanding of the inter-annual variability of the upwelling cells associated with the multiple forcing mechanisms defined in the first two parts of this work. Results reveal that the upwelling cells, Core 1 and Core 2, have different inter-annual variabilities. Inter-annual variability of Core 1 is associated with the East Madagascar Current (EMC) while Core 2 is linked with the South-west MAdagascar Coastal Current (SMACC). Inter-annual changes in the EMC occur as a result of oscillations in the South Equatorial Current (SEC) bifurcation off Madagascar, while the inter-annual variability in the SMACC is influenced by the cyclonic wind stress curl inter-annual variability. The upwelling is also linked with global/regional climate modes. Both Cores are highly correlated with the Subtropical Indian Ocean Dipole (SIOD). Core 2 is also correlated to the Indian Ocean Dipole (IOD). Both cores are significantly correlated with the El Ni˜no-Southern Oscillation (ENSO) after 12 months lag.
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Arthur, William Craig School of Mathematics UNSW. "The Flinders current and upwelling in submarine canyons." Awarded by:University of New South Wales. School of Mathematics, 2006. http://handle.unsw.edu.au/1959.4/28871.
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The continental shelf off South Australia is incised by some of the largest known submarine canyons. Extensive observations of submarine canyons in other parts of the world have shown submarine canyons can result in locally persistent upwelling regions. Along the southern coastline, westward slope currents including anticyclonic eddies and the Flinders Current (FC) can result in favourable conditions for upwelling in the vicinity of these canyons. Little data is available to describe the FC and so we review three global ocean circulation models and their representation of the FC. Though there are considerable differences between the outputs of these three models, this analysis provides a range of potential scales for the structure and transport of the FC. The reasons for the differences between the output of the three models are extensive, but to a first approximation, climatological surface wind stress products are compared. Dynamical descriptions of the flow past submarine canyons are reviewed and in part extended, in particular the vertical scale of the induced motion is estimated as the Rossby height RH. A description of upwelling and downwelling flow incorporating vorticity stretching is also presented. An idealised model of the southern Australian continental shelf and the submarine canyons reveals the circulation is heavily modified by the presence of the canyons, inducing persistent upwelling of dense water onto the downstream shelf. In addition, one prominent feature of the induced circulation ??? a coastal jet ??? is found to be peculiar to flat inner shelf topographies. More realistic topography including a sloped inner shelf results in reduced shoreward transport within the canyon and hence reduced upwelling.
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Li, Z. "A numerical study of basic coastal upwelling processes." Thesis, University of Reading, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234709.
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Barth, John A. "Stability of a coastal upwelling front over topography." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/51462.
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Sankey, David. "Dynamics of upwelling in the equatorial lower stratosphere." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.625019.
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Little, Mark G. "Late Quaternary palaeoceanography of the Benguela upwelling system." Thesis, University of Edinburgh, 1997. http://hdl.handle.net/1842/12437.
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Planktonic foraminifera recovered from nine cores in the Benguela Current system are used to ascertain the variability of upwelling intensity for the Late Quaternary and its impact on atmosphere-ocean-cryosphere linkages. The analyses from high-resolution planktonic foraminiferal records for cores GeoB 1706, GeoB 1711 and PG/PC 12, reveal striking variations in upwelling intensity during the last 160,000 years. Four species make up over 95% of the variation within the cores, and enable the record to be divided into episodes characterised by particular planktonic foraminiferal assemblages which have meaningful ecological significance when compared to those of the present-day and the relationship to their environment. The cold-water planktonic foraminifer, Neogloboquadrina pachyderma sinistral [N. pachyderma (s))], dominates the modern-day, coastal upwelling centres, and Neogloboquadrina pachyderma dextral and Globigerina bulloides characterise the fringes of the upwelling cells. Globorotalia inflata is representative of the offshore boundary between newly upwelled waters and the transitional, reduced nutrient levels of the sub-tropical waters. In the fossil record, episodes of high N. pachyderma (s) abundances are interpreted as evidence of increased upwelling intensity and the associated increase in nutrients. The N. pachyderma (s) record suggests rapid shifts in the intensity of upwelling, and corresponding trophic domains, that do not follow the typical glacial - interglacial pattern, but instead reflect the shifts of the Angola-Benguela front situated to the north of the Walvis Ridge. Absence of high abundances of N. pachyderma (s) from the continental slope of the southern Cape Basin indicate that Southern Ocean surface water advection has not exerted a major influence on the Benguela Current system. The periods of high abundance in N. pachyderma (s) are referred to as 'PS events' and indicate increased intensity and zonality of the South Atlantic trade winds controlling the Benguela upwelling system. During these intense upwelling phases, total organic carbon, abundance of N. pachyderma (s) and the benthic/planktonic foraminiferal ratio, provide the best indicators for palaeoproductivity away from coastal re-suspension. The offshore record of GeoB 1711 is used as the indicator for maximum offshore divergence and shelf-edge upwelling and is regarded as the best indicator for palaeoceanographic and palaeoproductivity variability.
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Painting, Suzanne Jane. "Bacterioplankton dynamics in the Southern Benguela upwelling region." Doctoral thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/23358.
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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.
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Risien, Craig Miller. "Wind-stress variability over the Benguela upwelling system." Master's thesis, University of Cape Town, 2002. http://hdl.handle.net/11427/6500.
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Bibliography: leaves 119-133.Regional wind-stress variability over the Benguela Upwelling System is described using 16 months (01 August 1999 29 November 2000) of satellite derived QuikSCA T wind data. The QuikSCA T data are compared to the climatologies presented by Kamstra (1985) and Bakun and Nelson (1991), as well as the long-term climatology (1968-1996) of the surface vector wind speed field off the coast of southern Africa, as derived from the 2.5° resolution NCEPINCAR reanalysis dataset. Broad scale similaritie"s are found between the QuikSCA T and the long-term NCEPINCAR climatology (1968-1996) data sets. This allows one to have confidence in using this scatterometer data to investigate details of spatial and temporal variability over the Benguela System. During summer, wind-stress maxima are found at approximately 17, 29 and 34°S. These maxima strengthen in late summer. The seasonal northward migration of the South Atlantic Anticyclone becomes apparent in late autumn, when the strongest wind-stress occurs north of 28°S. A significant wind-stress minimum is observed to develop slightly north of Cape Columbine (33°S) during autumn. To the north (10-23.5°S) the Benguela is characterised by relatively strong south-easterly wind-stress during winter. To the south (24-35°S) the Benguela is characterised by relatively weak westerly to south-westerly wind-stress during winter. A southward migration of southeasterly wind-stress is observed during early spring. By November the entire Benguela Upwelling System is once again characterised by southerly to south-easterly wind stress. Wind-stress variability is investigated using both a type of artificial neural network, known as the Kohonen Self Organising Map (SOM), as well as a wavelet analysis. Two independent SOM studies are conducted. The first study produced a 6x4 SOM output array, which is used to examine seasonal variability as well as the temporal evolution of two synoptic-scale wind events. For the second study both a SOM and a wavelet analysis are applied to an extracted data set to find that the system can be divided into six discrete wind regimes, 10-15°S; 15.5-18.5°S; 19-23.5°S; 24-28.5°S; 29-32.5°S; and 33-35°S. The wavelet power spectra for these wind cells span a range of frequencies from 4 to 64 days, with each region appearing to contain distinct periodicities. To the north, 10-23.5°S, the majority of the power occurs during winter, with a 6-16 day periodicity. Further south, 24-35°S, the majority of the power occurs in the summer. Here a bi-modal distribution occurs, with peaks of 6-16 and 35-40 days. Lastly a case study sequence of the spatial distribution of wind-stress, windstress curl and SST, at a location off the west coast of southern Africa (25-300S and 12-17°E), is discussed in relation to an intense, upwelling favourable, wind event that occurred from 11-20 February 2000.
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MacFadyen, Amoreena. "Observational and modeling studies of the Juan de Fuca Eddy : a mesoscale, topographically-linked upwelling eddy in the northern California Current system /." Thesis, Connect to this title online; UW restricted, 2008. http://hdl.handle.net/1773/11036.
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Cheung, Yee Ying. "Modeling upwelling circulation over continental shelf in the northern South China sea /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?AMCE%202006%20CHEUNG.
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Youssara, Faïçal. "Variations pondérales, structurales et physiologiques du zooplancton en relation avec différents types de structures : upwelling marocain (région d'Agadir), front Alméria-Oran (ouest de la mer d'Alboran), Courant Nord Méditerranéen et zone de dilution rhodanienne (Golfe du Lion)." Aix-Marseille 2, 2002. http://www.theses.fr/2002AIX22034.
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Etourneau, Johan [Verfasser]. "Pliocene-Pleistocene variability of upwelling activity, productivity and nutrient cycle in the Benguela Upwelling System and the Eastern Equatorial Pacific / Johan Etourneau." Kiel : Universitätsbibliothek Kiel, 2009. http://d-nb.info/1019866934/34.
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Steele, Nikita. "Geographical variation in effects of nutrient levels and grazing intensity on community structure between upwelling and non-upwelling regions of South Africa." Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1013013.
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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.
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Johnson, David L. "Airborne synthetic aperture radar images of an upwelling filament." Thesis, University of Hawaii at Manoa, 2003. http://hdl.handle.net/10125/7036.
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The Cape Mendicino upwelling filament was imaged in 1989 using the NASA/JPL AIRSAR multiband Synthetic Aperture Radar (SAR) and NOAA AVHRR thermal and optical radiometry. To first order, SAR images of the ocean are solely dependent on the surface wave field, but they ultimately reflect the synergy of a vast number of geophysical processes. The complexity of surface wave processes leaves a large gap between the information contained in SAR images, and our ability to describe them without conjectures. Investigated here are features associated with thermal fronts, vortices, geostrophic jets, and internal waves. SAR spectra suggest infragravity waves aligned with the wind swell. Cross jet SAR profiles were investigated in detail; comparison with results from a simple model suggest that some processes not included in the simulation are dominating in physical environment. Band dependent asymmetry of the profiles is consistent with convergence and accumulation of surfactants; band independent location of the peaks suggests that such convergence may be a jet driven process. The band independent position of humps in the profiles suggests critical reflection of strongly imaged intermediate (A>ABragg) waves or alternately a persistent and complex jet velocity profile. Apparently anomalously high damping of longer Bragg waves at some jet orientations is inconsistent with historical measurements of the modulus of elasticity of ocean surfactants and might indicate the hyperconcentration of surfactants within a zone of strong convergence. Net changes in radar cross-section across some sections of the jet could indicate a number a wave or current processes, which are discussed.iv, 124 leaves
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Jardine, Ian David. "Coastal upwelling along the west coast of Vancouver Island." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/28946.
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Wind-driven up welling events near Brooks Peninsula off the west coast of Vancouver Island have been identified during the summers of 1988 and 1989 from sea surface NOAA AVHRR thermal imagery obtained at the UBC Satellite Oceanography and Meteorology Laboratory. Software has been developed to characterize the strength and extent of the surface cooling associated with the upwelling. A two-dimensional, 2-layer finite difference model with 1 km resolution has been formulated to examine the small-scale dynamics of the upwelling events. The model uses local wind and includes realistic coastline and bathymetry. The wind-stress and coastline configuration appear to be the main factors contributing to favourable upwelling regions. The results of the model compare favourably to the observed starting location of the upwelling.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
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Fasciano, William Culp. "Meandering of the coastal upwelling jet near Cape Mendocino." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27126.
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Brodie, Ian Raymond Alexander. "Micro facies analysis of late Quaternary Peruvian upwelling sediments." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241249.
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Seeyave, Sophie. "Nitrogen nutrition of harmful algal blooms in upwelling systems." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/145737/.
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Blooms of toxic, or otherwise harmful phytoplankton species are known to occur in eastern boundary upwelling systems, coincident with the relaxation of upwelling in late summer/autumn. Field studies were carried out in 3 consecutive summers (March/April 06-08) in the Benguela and in the autumn (Sept 06) and summer (June 07) in the Iberian upwelling system (Ría de Vigo), with the aim of identifying common nitrogen nutrition strategies of HAB species that may allow them to succeed in upwelling systems. Two summer field studies were also carried out in the Fal Estuary (UK) to identify possible differences between a UK estuary and these upwelling systems. In the Benguela, three toxic phytoplankton species were dominant under different nutrient conditions. Pseudo-nitzschia spp. were abundant during a period of strong upwelling and high NO3-, peaking during short periods of wind relaxation. During these periods, a switch from high nitrate uptake [(NO3 -)] to regenerated nitrogen uptake [(NH4 +) and (urea)] occurred, with ƒratios dropping from 0.79 to 0.12. Alexandrium catenella bloomed during a period of upwelling, displaying high (NO3-) and ƒ-ratios up to 0.87. Dinophysis acuminata dominated when NO3 - concentrations were <0.5 μmol l-1 and ƒ-ratios <0.1 in 2007, although in 2008 it formed a subsurface maximum, often associated with high NO3- concentrations. Nutrient uptake kinetics showed that Pseudo-nitzschia spp. displayed the highest maximum specific uptake rates (max). D. acuminata displayed the highest affinity for NH4+, as shown by its values (slope of the nutrient uptake vs. concentration curve). Thus, A. catenella was adapted to utilising high NO3- concentrations during upwelling pulses, whereas both Pseudo-nitzschia and D. acuminata were able to acclimate to both high and low NO3- concentrations during the upwelling/relaxation cycles. In the Ría de Vigo, warm water from the stratified shelf entered the ría and downwelled in September, resulting in a well-mixed water column. The phytoplankton assemblage, dominated by Ceratium spp., Dinophysis acuminata and Gymnodinium catenatum, appeared to be advected in to the ría. Nitrate concentrations were consistently low, whereas NH4+ concentrations increased towards the head of the ría and with depth. The phytoplankton community was dependent on regenerated nitrogen, with ƒ-ratios <0.2. In contrast, positive circulation in June resulted in strong vertical gradients in temperature, salinity and nutrients and a community dominated by diatoms. Nitrate and NH4+ were depleted in surface waters although uptake rates were higher than in September, as were the ƒ-ratios (0.1-0.3). In both systems, upwelling winds favoured diatoms, although they were able to utilise regenerated nitrogen when NO3- was depleted, whereas upwelling relaxation created favourable conditions for HAB development. Dinophysis spp. occurred in both systems and were able to grow on recycled nitrogen in the absence of NO3-. The Benguela showed high variability in the selection of particular HAB species, perhaps due to greater variability in upwelling-downwelling cycles. In the Ría de Vigo, the occurrence of downwelling and associated nutrient conditions leading to blooms of Dinophysis spp. and Gymnodinium catenatum seems more predictable. In the Fal Estuary, Alexandrium spp. was favoured by low irradiance and the combination of strong stratification and high nutrient concentrations, and its growth was sustained predominantly by NH4+. A. minutum strains isolated from both upwelling systems and from a UK Lagoon all displayed higher max for NH4+ relative to NO3- but higher growth rates on the latter. This was consistent with field results from all 3 regions, suggesting that the upwelling systems did not display a different order of nitrogen preference, although they did display a higher affinity for NO3-.
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El, Aouni Anass. "Lagrangian coherent structures and physical processes of coastal upwelling." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0146.
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L’étude des processus physiques d’un système d’upwelling est essentielle pour comprendre sa variabilité actuelle et ses changements passés et futurs. Cette thèse présente une étude interdisciplinaire du système d’upwelling côtier à partir de différentes données acquises par satellite, l’accent étant mis principalement sur le système d’upwelling d’Afrique du Nord-Ouest (NWA). Cette étude interdisciplinaire aborde (1) le problème de l’identification et de l’extraction automatiques du phénomène d’upwelling à partir d’observations satellitaires biologiques et physiques. (2) Une étude statistique de la variation spatio-temporelle de l’upwelling de la NWA tout au long de son extension et de ses différents indices d’upwelling. (3) Une étude des relations non linéaires entre le mélange de surface et l’activité biologique dans les régions d’upwelling. (4) études lagrangiennes de tourbillons cohérents; leurs propriétés physiques et identification automatique. (5) L’étude des transports effectués par les tourbillons lagrangiens de la NWA Upwelling et leur impact sur l’océanStudying physical processes of an upwelling system is essential to understand its present variability and its past and future changes. This thesis presents an interdisciplinary study of the coastal upwelling system from different satellite acquired data, with the main focus placed on the North West African (NWA) upwelling system. This interdisciplinary study covers (1) the problem of the automatic identification and extraction of the upwelling phenomenon from biological and physical satellite observations. (2) A statistical study of the spatio-temporal variation of the NWA upwelling throughout its extension and different upwelling indices. (3) A Study of the nonlinear relationships between the surface mixing and biological activity in the upwelling regions. (4) Lagrangian studies of coherent eddies; their physical properties and automatic identification. (5) The study of transport made by Lagrangian eddies off the NWA Upwelling and their impact on the open ocean. [...]
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Bain, Cairns Alexander Robertson. "Empirical dynamics of a small scale coastal upwelling region." Doctoral thesis, University of Cape Town, 1991. http://hdl.handle.net/11427/21855.
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The study investigates the dynamics of a small space scale (less than 10 km) coastal upwelling region at the temporal scales spanning hours to years. Three to four year time series data sets of, sea temperatures at different depths (2m, 5 m and 8,5 m) one kilometer offshore, of wind and of waves, obtained from Eskom for the Koeberg nuclear power station site study near Melkbosstrand (33° 41'S, 18° 26'E) were digitized on an hourly basis. An emphasis is placed on the study of the wind and sea temperature data, the latter being an unique data set in the South African context. The data were filtered into different frequency bands (<12,0 <0,5 <0,025 cpd). Simple statistics, linear correlation and spectral analysis were used to characterize these bands. Dominant temporal scales were identified as the seasonal, event (synoptic) and diurnal time scales. The characterization of the latter two time scales were supplemented with field work which inter alia measured: sea temperature profiles and transects; sea surface temperature distribution with the airborne radiation thermometry technique and Lagrangian currents.
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Swart, Neil C. "Lateral carbon export from the southern Benguela upwelling system." Master's thesis, University of Cape Town, 2008. http://hdl.handle.net/11427/6453.
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Includes bibliographical references (leaves 153-[169]).The objective of this study was to quantify the lateral export of organic carbon from the continental shelf of the southern Benguela upwelling system to the open ocean. The flux is potentially important because the Benguela is one of the most productive and biogeochemically active ecosystems in the global ocean. Furthermore, a significant fraction of oceanic carbon storage is modulated through the biological pump mechanism, and on millennia 1 timescales the global ocean regulates atmospheric concentrations of carbon dioxide. The current study builds on previous work, and examines both the physical and biogeochemical aspects of the lateral carbon flux from the southern Benguela. Multiple physical mechanisms capable of inducing cross-shelf advection were examined, including dynamic interaction with Agulhas Rings and upwelling front instability, however the bottom boundary layer (BBL) was the focus.
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Gebe, Zimkhita. "The ecology of picophytoplankton in a coastal upwelling ecosystem." Doctoral thesis, Faculty of Science, 2021. http://hdl.handle.net/11427/33737.
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The dynamic Benguela Upwelling System is one of four major upwelling regions in the world and is subdivided into two sub-systems, the northern and southern Benguela. This current study was conducted within the southern Benguela, which lies between 27°S and 35°S (Orange River Mouth to East London) and is characterized on the west coast by seasonal, wind-driven, coastal upwelling. The study targeted three picophytoplankton groups, Synechococcus, Prochlorococcus and picoeukaryotes, which are the three most abundant < 2 µm size class phytoplankton. Flow cytometry was employed to enumerate picophytoplankton abundances, using their pigments and cell sizes to identify the different groups. The aim of the study was to investigate the role of picophytoplankton in the southern Benguela coastal upwelling ecosystem. These aims were met by: i) determining the spatiotemporal variability of each of the three picophytoplankton groups over a period of 8 sampling cruises at 44 stations across four latitudinal lines in the study region, ii) determining short-term changes in carbon and nitrogen biomass of picophytoplankton and their growth rates over a 10-day period, using abundance estimates from a station off St. Helena Bay, and iii) estimating mortality of microbial communities in a laboratory study using samples collected from a coastal upwelling environment. Results showed no strong seasonality in picophytoplankton abundances but evidence of latitudinal and zonal effects. Investigations over the short term showed that populations of picophytoplankton in the southern Benguela change on the same timescale of ~3 days as the larger phytoplankton during an upwelling event. Determining mortality rates using a dilution experiment presented some challenges. Instead of increased growth rates, the study showed decreased growth rates as predator numbers decreased. These shortcomings were investigated in a second experiment, which both excluded large predators (<200µm) and also ran a parallel experiment excluding smaller predators (10-200 µm). The last of these experiments resulted in increased growth rates as predator numbers decreased. The complexity of the southern Benguela system, with its pulsed, high productivity and large concentrations of nutrients, traditionally is known to show variability through effects on the biology of large phytoplankton. However, picophytoplankton also were variable in the study area, resulting from bottom up effects of the environment, confounded by biotic factors such as predation, parasitism and competition
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Civiero, Chiara. "Understanding the nature of mantle upwelling beneath East Africa." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/33345.
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Over the last decade several theories have been used to explain hotspot phenomena occurring at Earth's surface. The most prominent is that of hot upwelling material, so called mantle plumes. To date, our understanding of these structures is limited due to seismic images of the deep upper mantle/lower mantle lacking the resolution to image these features. One of the best locations to address this is the northern East African Rift (EAR), the location of the Afar hotspot, where, due to its presence on land, many broadband seismometers have been deployed over the last 20 years. Despite this, numerous models exist about the nature of mantle upwelling beneath this region. This study uses these data to provide P- and S/SKS-wave velocity models of the structure below EAR extending from the surface to the top of the lower mantle of a higher resolution than have been available to date. Both our P- and S-wave images provide evidence of two clusters of low-velocity structures with diameter of 100-200 km that extend through the transition zone, the first beneath Afar and a second just west of the Main Ethiopian Rift. Considering seismic sensitivity to temperature, we interpret these features as predominantly thermal upwellings with excess temperatures of 100±50K. Dynamic models for realistic Earth parameters can match the geometry and spacing of these features and synthetic tests of these numerical models, accounting for resolution of the tomographic models show that the likely source of these upwellings is from a thermal boundary layer at the top of the lower mantle. Finally, our tests show that due to resolution issues tomographically imaged structures from small-scale upper-mantle plumes may look substantially more complex than the simple vertical cylinders that are often anticipated and that tomographic studies of other hotspot regions should be reanalysed with this in mind.
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Montague-Judd, Danielle Dawn. "Paleo-upwelling and the distribution of Mesozoic marine reptiles." Diss., The University of Arizona, 1999. http://hdl.handle.net/10150/283980.
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Marine upwelling occurs when surface currents diverge or are deflected. Deeper water, often nutrient-rich, rises and generates a cascade of biological effects including elevated productivity and a unique assemblage of organisms. Macrofaunal characteristics of upwelling provide key evidence for oxygen-minimum zones, upwelling of cool water, and high productivity and are potentially useful indicators of ancient upwelling. The Upper Triassic Luning Formation in Nevada contains abundant, large ichthyosaurs and was deposited in a back-arc basin that could have experienced upwelling conditions. Luning Formation rocks at West Union Canyon were analyzed for sedimentological, geochemical, and paleontological upwelling indicators. Abundant suspension feeders, lack of corals and calcareous algae, modest total organic carbon and minor element concentrations in deeper marine facies, abundant cosmopolitan molluscs but no taxa restricted to low latitudes, and abundant fecal pellets and clotted fabrics in most facies suggest that upwelling could have influenced Luning deposition. Moderate-scale upwelling likely contributed to eutrophic conditions and ichthyosaur abundance at West Union Canyon. Marine reptiles might have had ties to upwelling areas to provide food, as do modern whales. A relational database containing 817 locality records and 1365 taxon-localities was assembled for ichthyosaurs, plesiosaurs, and mosasaurs. Marine reptile localities were compared with model-predicted upwelling and with upwelling-related lithologies (organic-rich rock, biogenic silica, phosphorite, and glauconite). Marine reptile occurrences intersected predicted upwelling more often than expected by chance for the Upper Cretaceous, Callovian, and Norian stages, and for all of the data together (P = 0.05). For age-restricted data, occurrences of Mosasauridae, Pliosauridae, and Plesiosauria intersected upwelling more often than expected by chance (P = 0.05). Average shortest distances between reptile fossil and upwelling lithology occurrences were smallest (one grid cell adjacent or smaller) for the Pliensbachian and four of five Cretaceous stages. Analytical biases and other aspects of reptile ecology may have affected the results, but overall, upwelling could have influenced marine reptile distribution, particularly for the Upper Cretaceous. Multiple radiations into the high-productivity, top-predator niche over the Mesozoic are suggested by the dominance of different taxa in grid cells containing upwelling lithologies: ichthyosaurs (early Mesozoic), plesiosaurs (middle Mesozoic), and finally mosasaurs (late Mesozoic).
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Braconnot, Pascale. "Validation objective de modeles d'ocean tropical a l'aide des donnees focal sequal." Paris 6, 1992. http://www.theses.fr/1992PA066068.
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La methode statistique multivariee de validation des modeles oceaniques de frankignoul et al. (1989) est etendue au cas general de la validation d'un modele sur une periode fixee. La procedure de test permet d'evaluer un ecart modele-realite en tenant compte des incertitudes des donnees oceanique servant de reference, des incertitudes du forcage atmospherique applique au modele et de l'incertitude des conditions initiales. Les performances du modele sont estimees dans un espace de dimensions reduites determine par une double analyse en composantes principales communes. La methode est utilisee pour evaluer l'aptitude du modele lineaire multimode de cane (1984) et du modele de circulation generale du lodyc a reproduire les variations de la profondeur de l'isotherme 20c dans l'ocean atlantique equatorial de 1982 a 1984. Meme pendant cette periode bien echantillonnee, les incertitudes de la tension de vent, simulees suivant les techniques de monte-carlo, sont loin d'etre negligeables. Les incertitudes correspondantes sur la reponse d'un modele sont du meme ordre de grandeur que la variabilite interannuelle ou peuvent etre equivalentes aux ecarts entre les deux versions du gcm. Il faut donc en tenir compte dans les comparaisons modele-realite. Les incertitudes du forcage n'expliquent cependant pas toutes les differences entre les simulations et les observations, mais le gcm est beaucoup plus realiste que le modele lineaire. Les tests montrent aussi que la parametrisation tke du melange vertical a ameliore la representation de l'upwelling equatorial et le signal moyen a l'est du bassin. Les performances du gcm sont egalement discutees pour differentes regions de l'ocean atlantique tropical
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Castellanos, Ossa Paola. "Wind-driven currents in the coastal and equatorial upwelling regions." Doctoral thesis, Universitat Politècnica de Catalunya, 2012. http://hdl.handle.net/10803/119266.
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During the last two decades the scientific community has recognised the importance of the tropical Atlantic Ocean and the upwelling regions on the Earth's climate. This recognition has opened new questions such as: ¿What are the mechanisms for the ocean to adjust to variations in atmospheric forcing?, ¿Is there any indirect relation between the atmospheric seasonal cycle and the response of the surface ocean?, ¿How are the meridional boundary flows connected with the zonal jets in the interior ocean?, ¿What is the relevance of these processes in the redistribution of properties such as water mass, heat and fresh water?
In this dissertation we explore several elements that determine the effect of the surface wind stress onto the processes within the near-surface ocean. The work focuses on recognizing the (subinertial) response mechanisms of the ocean surface to the spatial and temporal wind variations in two upwelling regions: a coastal region off Northwest Africa, in the area near Cape Blanc, and an oceanic region, in the equatorial Atlantic. With this purpose we use in situ and satellite data as well as numerical data from a high-resolution circulation model. The analysis of these data has been done with several methodologies, in some cases requiring substantial developments and tuning for local applications.
The implementation of the Maximum Cross-Correlation Method has allowed determining some of the characteristics of the instantaneous and mean surface fields, during winter and spring, in the upwelling region north and south of Cape Blanc. We have identified three regions which are characterized by different responses to short-time changes of the along-shore wind stress. North of Cape Blanc stands out the intensity of the coastal baroclinic jet, in the Cape Verde basin the mesoscalar structures are relatively weak and large, and off Cape Blanc there is along-shore convergence which traduces in the formation of a normal-to-shore giant surface filament.
The analyses of time series corresponding to several upwelling indexes show that the atmospheric forcing and the oceanic response are different north and south of Cape Blanc and during the first and second trimester of the year. The total subinertial flux may be represented as the combination of a surface Ekman flux (calculated as the Ekman transport divided by the thickness of the surface mixed layer) and the surface geostrophic current (deduced from altimetry satellite images). One of the most relevant results is that the temporal and spatial changes in the normal-to-shore Ekman transport influence the intensity of the geostrophic (baroclinic) coastal jet, therefore affecting the corresponding along-shore convergence (e.g. becoming intensified off Cape Blanc) and the offshore transport of upwelled waters.
The dissertation has also aimed at understanding the patterns of seasonal variability in the equatorial Atlantic Ocean through the statistical analysis of time series of sea level pressure, sea surface wind stress, sea surface height, and the circulation of the near-surface ocean. The data reveals a predominant annual component in all these variables, closely related to the latitudinal oscillation of the Inter-Tropical Convergence Zone. The equatorial divergence of the Ekman transport is well correlated with the intensity of the zonal system of equatorial currents, which includes the Equatorial Undercurrent and its northern and southern branches. Additionally, the seasonal appearance of the North Equatorial Counter Current during (boreal) summer and fall is related to the meridional convergence of the Ekman transport during those same seasons, which leads to a temporal rise of sea level and the generation of an eastward current in geostrophic balance. In general, the divergence/convergence of meridional Ekman transport is dominant in the northern hemisphere and of lesser relevance in the southern hemisphere.Durante las últimas dos décadas la comunidad científica internacional ha pasado a reconocer la importancia del Océano Atlántico tropical y las regiones de afloramiento en el clima terrestre. Este reconocimiento ha abierto nuevos interrogantes, tales como: ¿Cuáles son los mecanismos de ajuste del océano a las variaciones en el forzamiento atmosférico?, ¿Existe algún tipo de relación indirecta entre el ciclo estacional atmosférico y la respuesta del océano superficial?, ¿Cómo se conectan los flujos oceánicos meridionales en los contornos con los flujos zonales en el océano interior?, ¿Cuál es la importancia de estos procesos en la redistribución de propiedades tales como masa, calor y agua dulce? En esta tesis se exploran diversos elementos que determinan el efecto del esfuerzo del viento superficial sobre los procesos que ocurren en el océano superficial. El trabajo se centra en reconocer cuales son los mecanismos (subinerciales) de respuesta de la superficie del océano a las variaciones espaciales y temporales del viento en dos regiones de afloramiento: una costera al Noroeste de África, en el área cercana a Cabo Blanco, y otra oceánica, en el Atlántico ecuatorial. Para ello se emplean observaciones in situ, datos satelitales y datos numéricos provenientes de un modelo de circulación de alta resolución. El análisis de estos datos se ha realizado con diversas metodologías, cuya aplicación en algunos casos ha requerido un esfuerzo substancial de desarrollo y puesta a punto. La implementación del método de Máximas Correlaciones Cruzadas ha permitido determinar algunas de las características de los campos instantáneos y medios de velocidades superficiales, durante invierno y primavera, en la región del afloramiento de Cabo Blanco. Se han identificando tres regiones caracterizadas por tener respuestas distintas a los cambios que el viento paralelo a la costa experimenta en escalas temporales cortas. Al norte de Cabo Blanco destaca la intensidad del chorro baroclino costero, en la cuenca de Cabo Verde se aprecian estructuras mesoscalares relativamente débiles y grandes, y frente a Cabo Blanco existe convergencia paralela a costa que se traduce en flujo normal a costa en forma de un gran filamento superficial. El análisis de las series temporales de diversos índices de afloramiento muestra que los forzamientos atmosféricos y las respuestas oceánicas son distintas al norte y sur de Cabo Blanco y durante el primer y segundo trimestre del año. El flujo subinercial resultante se puede representar como la combinación de un flujo superficial de Ekman (calculado como el transporte de Ekman dividido por la profundidad de la capa de mezcla) y la corriente geostrófica superficial (deducida a partir de imágenes satelitales de altimetría). Uno de los resultados más relevantes es que los cambios espaciales y temporales en el transporte de Ekman perpendicular a costa influyen sobre la intensidad del chorro geostrófico (baroclíno) costero, y por tanto afectan su convergencia a lo largo de la costa intensificándose, por ejemplo, frente a Cabo Blanco) y la transferencia neta de aguas afloradas hacia el océano interior. La tesis también se ha encaminado a investigar los patrones de variabilidad estacional del Océano Atlántico ecuatorial, a través del análisis estadístico de series temporales de presión a nivel de mar, esfuerzo cortante del viento sobre la superficie oceánica, elevación del océano superficial, y la circulación oceánica superficial. Los datos revelan una fuerte componente anual en estas variables, estrechamente vinculada con la oscilación meridional de la Zona de Convergencia Intertropical. La divergencia ecuatorial del transporte de Ekman se correlaciona adecuadamente con la intensidad del sistema de corrientes zonales ecuatoriales, que incluyen la Corriente Ecuatorial Subsuperficial y sus ramales norte y sur. Asimismo, la aparición estacional de la Contra-Corriente Ecuatorial durante verano y otoño (boreal) se relaciona con la convergencia meridional en el transporte de Ekman que tiene lugar durante estas épocas, lo cual conduce a una subida del nivel del mar y la generación de una corriente hacia el este en balance geostrófico. En general se aprecia que los procesos de divergencia/convergencia del transporte meridional de Ekman son dominantes en el hemisferio norte y de menor relevancia en el hemisferio sur. Finalmente, con el fin de comprender mejor la dinámica ecuatorial, se ha desarrollado un modelo sencillo que permite cuantificar el aporte de la divergencia de Ekman al flujo zonal en varias bandas zonales características. Se han identificado dos condiciones típicas extremas, en primavera y otoño, y se han calculado la divergencia/convergencia meridional a través de líneas definidas por un máximo en la elevación de la superficie del mar. Bajo la suposición de que el transporte zonal cerca del contorno oriental (aquí tomada a una longitud de 0º) es nulo, se estima que la franja ecuatorial presenta, en su margen occidental, valores máximos de transporte correspondientes a 58 Sv en primavera y 27 Sv durante otoño, cuyo origen es el sistema de corrientes de frontera oeste.
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Mejia-Trejo, Adan. "Upwelling off the coast of Oman during the S.W. monsoon." Thesis, Bangor University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.304305.
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Handoh, Itsuki C. "Oceanic upwelling through the evolution of the tropical Atlantic basin." Thesis, University of East Anglia, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.251498.
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Brown, Christopher. "Seaglider observations of biogeochemical variability in the Iberian upwelling system." Thesis, University of East Anglia, 2013. https://ueaeprints.uea.ac.uk/48788/.
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Seasonal upwelling events along the Galician coastline of the North Atlantic furnish the upper watercolumn with nutrients, resulting in strong summer phytoplankton blooms and the sustenance of one of Europe’s largest fisheries. The episodic nature of these upwelling events result in considerable challenges studying the region using traditional shipboard observations. This thesis demonstrates an alternative sampling technique, providing high spatial and temporal resolution biogeochemical data through the use of an autonomous underwater gliderthe Seaglider. SG510 “Orca” was outfitted with sensors to measure dissolved oxygen, temperature, salinity, chlorophyll a (chl a), coloured dissolved organic material (CDOM) and optical backscatter. Deployed for 113 days over summer 2010, Orca completed 17 zonal transects across the shelf, continental slope and open ocean at 42.1° N. Data collected during the campaign was used to assess both the physics of the watercolumn, and the effect these physical processes have on the region’s biogeochemistry. As part of this biogeochemical study, a novel attempt at calculating net community production (NCP) was completed using an oxygen inventory technique. Two major phytoplankton bloom events occurred during the deployment period, with respective peak Chl a concentrations of 9.65 and 11.23 mg m3. During these bloom events, NCP varied between (net autotrophic) values of 25 and 123 (±17 ) mmol m2. d1. Negative values of NCP were only observed twice for 24 and 60 hours respectively, with a maximum heterotrophy of 44 (±17) mmol m2 d1. Overall, the summer season featured a net autotrophic metabolic balance of +27 mmol m2 d1 .thus highlighting the importance of the region for net carbon sequestration. Finally, this thesis also demonstrates the success of using autonomous glider platforms for sustained biogeochemical and physical observations within a highly dynamic and challenging operational environment with strong currents and considerable shipping traffic.
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Stockton, P. L. (Philip Leslie). "Aspects of the filament activity within the Benguela upwelling system." Thesis, Stellenbosch : Stellenbosch University, 1988. http://hdl.handle.net/10019.1/66061.
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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
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Muir, David Gordon. "Bacterial populations and their activity in the Benguela upwelling system." Doctoral thesis, University of Cape Town, 1986. http://hdl.handle.net/11427/21826.
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Bibliography : pages 267-315.An investigation of variability in hydrological and bacterial parameters at a fixed coastal station (Oudekraal. Cape Peninsula 33°59'S 17°21'E) showed that bacterial populations varied in numbers and biomass on both a short term (daily) and seasonal basis in response to changes in hydrological conditions which were largely wind induced.
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Guastella, L. A.-M. "The sea surface heat balance in the Benguela upwelling region." Master's thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/22447.
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Bibliography: pages 191-202.The surface heat balance of the Benguela upwelling area on the west coast of southern Africa is analysed. Measurements of the components of the heat balance were made in the St Helena Bay area from 14-21 October 1986. Additional long-term data was obtained from Alexander Bay and Cape Town. An average net heat gain of 227 W.m⁻² was received over the eight days of the field study. The presence of cold water determined that latent heat loss by the sea surface was small, while the sensible heat flux represented a small gain by the sea. These two turbulent heat fluxes are roughly equal and opposite and therefore approximately cancel each other. Use of a model, assuming idealised conditions, indicated that most turbulent heat exchange between the air and takes place in the nearshore region where air-sea contrasts are greatest. The net radiation was found to provide a good estimate of the total heat balance, thus the major contributing term to a high heat balance over the Benguela area is the input solar radiation. Minimal synoptic variation in the heat balance during the eight-day field programme was observed, but additional global radiation data analysed revealed that synoptic variations over the 3-6 day period are in fact more significant than the longer term seasonal variations. Both synoptic and seasonal variations in the heat balance are greater in the south than in the north. The high heat flux into the sea surface is capable of increasing the temperature of the upwelled water at a fairly rapid rate. During summer the heat exchange is capable of increasing the temperature of the upper 10 m mixed layer by as much as 0.65°C over one day. This input heat is used to realise the high biological potential of the upwelled waters.
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Villela, de Oliveira Lessa Douglas. "Paléocéanographie du système d'upwelling de Cabo Frio (Rio de Janeiro) durant les 12000 dernières années déduite de la géochimie et des assemblages de foraminifères planctoniques." Paris 6, 2013. http://www.theses.fr/2013PA066806.
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Ndoye, Siny. "Fonctionnement dynamique du centre d'upwelling Sud-Sénégalais : approche par la modélisation réaliste et l'analyse d'observations satellite de température de surface de la mer." Electronic Thesis or Diss., Paris 6, 2016. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2016PA066372.pdf.
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L’extrémité sud du système du courant des Canaries comprend un centre d’upwelling (résurgence localisée d’eaux froides sous l’action de vents favorables) qui a jusqu’ici reçu peu d’attention. Ma thèse porte sur la dynamique de ce centre d’upwelling sud Sénégal ou SSUC (Southern Senegal Upwelling Center en anglais). Elle s’intéresse donc à la circulation et à la structure thermohaline sur le large plateau sud-sénégalais, entre la côte et _100-200 km au large en se focalisant sur la période d’upwelling (Novembre-Mai). Une des particularités de la zone est la séparation entre la zone d’upwelling au centre du plateau et des eaux plus chaudes au large et à la côte. Mes travaux combinent analyse d’images satellite et d’observations in-situ, avec la réalisation et l’analyse de simulations numériques dans l’état de l’art. Par une analyse fine des conditions physiques de la zone, ils posent la base à une approche intégrée du fonctionnement de l’environnement marin sénégalais. Une première partie des résultats se base sur l’examen et l’analyse de plus de 1500 images satellite de température de surface de la mer SST MODIS, contextualisées par rapport aux conditions synoptiques de vent. Cette analyse met en lumière l’existence d’états récurrents du SSUC, en termes de SST. Elles confirment plus généralement la régularité et la stabilité du fonctionnement dynamique du système, mais aussi révèlent des aspects subtils de la structure de l’upwelling : refroidissement des eaux de surface probablement dû au déferlement et au mélange associé à la marée interne ; interaction complexe entre la remontée locale, le courant de Mauritanie et le jet côtier ; complexité probable des échanges entre les différentes parties du plateau (plateau intérieur accueillant des eaux réchauffées, plateau central où est fréquemment situé la langue d’eau froide). L’amplitude du cycle diurne suggère que de grandes incertitudes restent à lever dans le budget de chaleur de l’upwelling . Les limites des études soulignent la nécessité de continuer la mesure in situ dans le SSUC, en particulier des vents. Le fonctionnement dynamique du SSUC est aussi étudié par la modélisation hydrodynamique (ROMS) à haute résolution (_2km). Différentes simulations ont été réalisées en variant les forçages (climatologiques ou synoptiques pour le vent ; modification fine échelle des flux de chaleur en domaine côtier ; présence ou absence de marée). Les solutions numériques montrent en général un bon accord avec les observations satellite et in situ disponibles. Ces solutions éclairent le fonctionnement dynamique du système notamment en termes de circulation, de position de remontée d’upwelling, mais également du devenir des eaux upwellées grâce à une analyse lagrangienne. Nous avons notamment pu montrer que la zone nord du SSUC est la zone principale de remontée et les eaux qui y remontent, proviennent en grande majorité de la zone sud du SSUC d’où elles sont amenées par le courant de Mauritanie. Les analyses lagrangiennes ont aussi permis de - 3 - révéler la dynamique associée à la zone côtière de nourricerie et de nuancer le schéma conceptuel de rétention précédemment admis. La sensibilité de la dynamique du SSUC aux forçages atmosphériques est modeste avec néanmoins des modulations des échanges cross-shore qui peuvent être importantes pour l’écosystèmeThe southern end of the Canary current system comprises of an original upwelling center that has so far received little attention. This Ph.D. Thesis focuses on the dynamical functioning of the Southern Senegal-Gambia Upwelling Center (SSUC). We are interested in the upwelling circulation and thermohaline structure on the shelf between the coastline and 100-200 km offshore. Our focus is on the upwelling period (November to May). The main originality of the SSUC compared to other upwelling centers stems from its continental shelf that is broad and shallow (20–30 m over tens of kilometers). The normal state of the system comprises the classical upwelling front but also a well-defined inner-shelf front that separates cold upwelled waters from nearshore warmer waters. We investigate its dynamical functioning using analysed satellite images, in situ data and state-of-theart 3D numerical simulations. Through a fine-scale analysis of the physical conditions of the SSUC, this work poses the basis of an integrated approach to the Senegalese marine environment functioning. A first part of results is based on the careful examinations and analysis of over 1500 satellite images of sea surface temperature scenes contextualized with respect to wind conditions. Analysis confirm the regularity and stability of the SSUC dynamical functioning (as manifested by the recurrence and persistence of particular SST patterns). The analysis also reveal subtle aspects of its upwelling structure : shelf break cooling of surface waters consistent with internal tide breaking/mixing ; complex interplay between local upwelling and the Mauritanian current off the Cape Verde headland ; complexity of the inner-shelf/mid shelf frontal transition. The amplitude of the diurnal cycle suggests that large uncertainties exist in the SSUC heat budget. The studies limitations underscore the need for continuous in situ measurement in the SSUC, particularly of winds. The dynamical functioning of SSUC is also investigated by means of numerical simulations, using the hydrodynamical Regional Ocean Modeling System ROMS (_x _ 2 km). Different simulations have been carried with varying forcings (climatological or synoptic wind ; fine-scale adjustments of heat flux in coastal area ; presence or absence of tides). Numerical solutions show a good agreement with available satellite and in situ observations . These solutions clarify the dynamical functioning of the system especially in terms of circulation, location of cold water upwelling but also fate of upwelled water through a Lagrangian analysis. We show in particular that the northern part of the SSUC is the main upwelling area. Waters that upwelled in this area predominantly come from the southern of the SSUC, through advection by the Mauritanian current. Lagrangian analysis also revealed the dynamics associated with the coastal area of nursery and nuance the conceptual retention scheme previously admitted. The sensitivity of the dynamics of SSUC to atmospheric forcings is modest with nevertheless some modulations of the cross-shore exchanges that may be important to the ecosystem
42
Ndoye, Siny. "Fonctionnement dynamique du centre d'upwelling Sud-Sénégalais : approche par la modélisation réaliste et l'analyse d'observations satellite de température de surface de la mer." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066372/document.
Full textAbstract:
L’extrémité sud du système du courant des Canaries comprend un centre d’upwelling (résurgence localisée d’eaux froides sous l’action de vents favorables) qui a jusqu’ici reçu peu d’attention. Ma thèse porte sur la dynamique de ce centre d’upwelling sud Sénégal ou SSUC (Southern Senegal Upwelling Center en anglais). Elle s’intéresse donc à la circulation et à la structure thermohaline sur le large plateau sud-sénégalais, entre la côte et _100-200 km au large en se focalisant sur la période d’upwelling (Novembre-Mai). Une des particularités de la zone est la séparation entre la zone d’upwelling au centre du plateau et des eaux plus chaudes au large et à la côte. Mes travaux combinent analyse d’images satellite et d’observations in-situ, avec la réalisation et l’analyse de simulations numériques dans l’état de l’art. Par une analyse fine des conditions physiques de la zone, ils posent la base à une approche intégrée du fonctionnement de l’environnement marin sénégalais. Une première partie des résultats se base sur l’examen et l’analyse de plus de 1500 images satellite de température de surface de la mer SST MODIS, contextualisées par rapport aux conditions synoptiques de vent. Cette analyse met en lumière l’existence d’états récurrents du SSUC, en termes de SST. Elles confirment plus généralement la régularité et la stabilité du fonctionnement dynamique du système, mais aussi révèlent des aspects subtils de la structure de l’upwelling : refroidissement des eaux de surface probablement dû au déferlement et au mélange associé à la marée interne ; interaction complexe entre la remontée locale, le courant de Mauritanie et le jet côtier ; complexité probable des échanges entre les différentes parties du plateau (plateau intérieur accueillant des eaux réchauffées, plateau central où est fréquemment situé la langue d’eau froide). L’amplitude du cycle diurne suggère que de grandes incertitudes restent à lever dans le budget de chaleur de l’upwelling . Les limites des études soulignent la nécessité de continuer la mesure in situ dans le SSUC, en particulier des vents. Le fonctionnement dynamique du SSUC est aussi étudié par la modélisation hydrodynamique (ROMS) à haute résolution (_2km). Différentes simulations ont été réalisées en variant les forçages (climatologiques ou synoptiques pour le vent ; modification fine échelle des flux de chaleur en domaine côtier ; présence ou absence de marée). Les solutions numériques montrent en général un bon accord avec les observations satellite et in situ disponibles. Ces solutions éclairent le fonctionnement dynamique du système notamment en termes de circulation, de position de remontée d’upwelling, mais également du devenir des eaux upwellées grâce à une analyse lagrangienne. Nous avons notamment pu montrer que la zone nord du SSUC est la zone principale de remontée et les eaux qui y remontent, proviennent en grande majorité de la zone sud du SSUC d’où elles sont amenées par le courant de Mauritanie. Les analyses lagrangiennes ont aussi permis de - 3 - révéler la dynamique associée à la zone côtière de nourricerie et de nuancer le schéma conceptuel de rétention précédemment admis. La sensibilité de la dynamique du SSUC aux forçages atmosphériques est modeste avec néanmoins des modulations des échanges cross-shore qui peuvent être importantes pour l’écosystèmeThe southern end of the Canary current system comprises of an original upwelling center that has so far received little attention. This Ph.D. Thesis focuses on the dynamical functioning of the Southern Senegal-Gambia Upwelling Center (SSUC). We are interested in the upwelling circulation and thermohaline structure on the shelf between the coastline and 100-200 km offshore. Our focus is on the upwelling period (November to May). The main originality of the SSUC compared to other upwelling centers stems from its continental shelf that is broad and shallow (20–30 m over tens of kilometers). The normal state of the system comprises the classical upwelling front but also a well-defined inner-shelf front that separates cold upwelled waters from nearshore warmer waters. We investigate its dynamical functioning using analysed satellite images, in situ data and state-of-theart 3D numerical simulations. Through a fine-scale analysis of the physical conditions of the SSUC, this work poses the basis of an integrated approach to the Senegalese marine environment functioning. A first part of results is based on the careful examinations and analysis of over 1500 satellite images of sea surface temperature scenes contextualized with respect to wind conditions. Analysis confirm the regularity and stability of the SSUC dynamical functioning (as manifested by the recurrence and persistence of particular SST patterns). The analysis also reveal subtle aspects of its upwelling structure : shelf break cooling of surface waters consistent with internal tide breaking/mixing ; complex interplay between local upwelling and the Mauritanian current off the Cape Verde headland ; complexity of the inner-shelf/mid shelf frontal transition. The amplitude of the diurnal cycle suggests that large uncertainties exist in the SSUC heat budget. The studies limitations underscore the need for continuous in situ measurement in the SSUC, particularly of winds. The dynamical functioning of SSUC is also investigated by means of numerical simulations, using the hydrodynamical Regional Ocean Modeling System ROMS (_x _ 2 km). Different simulations have been carried with varying forcings (climatological or synoptic wind ; fine-scale adjustments of heat flux in coastal area ; presence or absence of tides). Numerical solutions show a good agreement with available satellite and in situ observations . These solutions clarify the dynamical functioning of the system especially in terms of circulation, location of cold water upwelling but also fate of upwelled water through a Lagrangian analysis. We show in particular that the northern part of the SSUC is the main upwelling area. Waters that upwelled in this area predominantly come from the southern of the SSUC, through advection by the Mauritanian current. Lagrangian analysis also revealed the dynamics associated with the coastal area of nursery and nuance the conceptual retention scheme previously admitted. The sensitivity of the dynamics of SSUC to atmospheric forcings is modest with nevertheless some modulations of the cross-shore exchanges that may be important to the ecosystem
43
Verstraete, Jean-Marc. "Les upwellings saisonniers dans le golfe de guinee." Paris 6, 1990. http://www.theses.fr/1990PA066776.
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Le probleme des upwellings equatorial et cotier dans le golfe de guinee est reexamine afin de determiner la source froide et le mecanisme qui controle ces phenomenes. Les variations saisonnieres du niveau de la mer, de la thermocline et du contenu thermique dependent des echanges de chaleur entre l'eau tropicale de surface et les eaux centrales de l'atlantique sud, identifiees comme etant la source froide. Deux cycles saisonniers de la structure thermique ont ete analyses pendant le programme focal (1982-1984). La penetration de la force de friction du vent est estimee a 130 m a l'ouest de 10w et a 25 m a 4w. Alors que les vents etaient nuls a l'equateur en fevrier 84, la thermocline s'enfonca de 50 m, le niveau moyen s'eleva de 13 cm et le gradient zonal de pression etait positif de o a 400 m a 6e. La theorie du guide d'onde equatorial montre que l'evenement chaud observe dans le golfe de guinee au debut de 1984 est du a des ondes internes de kelvin du second mode barocline, forcees a distance dans l'atlantique centre-ouest (10-30w) suite a l'effondrement (au retablissement) des alizes en dec. 83-jan 84 (avril-mai 84). Ces resultats soutiennent l'existence du second mode barocline dans l'ocean atlantique equatorial
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Combes, Vincent. "Upwelling and cross-shelf transport dynamics along the Pacific Eastern Boundary." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34814.
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The upwelling and cross-shelf transport dynamics along the Pacific Eastern Boundary is explored using a high resolution ocean model for the last 60 years. Three ocean circulations have been modeled. From North to South, we investigate the dynamics of the Gulf of Alaska (GOA), the California Current System (CCS) and the Humboldt Current System (HCS, also known as the Peru-Chile Current System). The statistics of coastal waters transport are computed using a model passive tracer, which is continuously released at the coast. By looking at the passive tracer concentration distribution, we find that the Pacific Decadal Oscillation modulates the coastal variability of the GOA, the North Pacific Gyre Oscillation controls the upwelling of the CCS, while the El-Niño Southern Oscillation affects the upwelling of Peru and Chile mainly through coastally trapped Kelvin waves. Results also emphasize the key role of the mesoscale eddies in the offshore transport of coastal waters masses. The passive tracer experiments, performed in this study in the GOA, CCS, and HCS, therefore could provide a dynamical framework to understand the dynamics of the upwelling/downwelling and offshore transport of nutrient rich coastal water and to interpret how it responds to atmospheric forcing. This also could reinforce our interpretation (and therefore predictions) in the changes in vertical and offshore advection of other important biogeochemical quantities, essential in understanding ecosystem variability.
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Ianson, Debby C. "A carbon and nitrogen flux model in a coastal upwelling region." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq61115.pdf.
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Magde, Laura Suzan. "Mantle upwelling, melt generation, and magma transport beneath mid-ocean ridges." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/55052.
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Samuel, Sarah Louise 1974. "An estimate of the upwelling rate in the tropical Pacific Ocean." Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/57860.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, February 2000.Includes bibliographical references (p. 84-87).
An inverse box model of the tropical Pacific Ocean from 321S - 10N is constructed from two zonal and six meridional hydrographic sections. This data is supplemented with LADCP data close to the equator where geostrophy fails. A consistent solution is found despite the presence of a number of mid-ocean crossing points and the data being spread over many years and seasons. The total upwelling across the ... = 23.5 isopycnal surface in a 60 latitude band centered on the equator is estimated to be 55 ± 27Sv. The zonal mean cross-isopycnal velocity for the same surface in the same latitude band is estimated to be 6.88 t 3.23 x 10 4 cms- 1. The addition of radiocarbon data places a strong constraint on the vertical transfers in the model and significantly reduces the error on the estimated vertical transport and velocity. When radiocarbon constraints are included, the upwelling across the ... = 23.5 isopycnal surface in the equatorial zone is estimated to be 52 ± 16Sv and the zonal mean cross-isopycnal velocity across the same surface is estimated as 7.15 t 1.90 x 10- 4 cms-1 . That a consistent solution can be found is encouraging but it remains unclear whether one-time data is representative of mean conditions in a region which is known to be highly variable.
by Sarah Louise Samuel.
S.M.
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Mashifane, Thulwaneng. "Shelf biogeochemical interactions and feedback processes in the Benguela upwelling system." Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27309.
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Two coupled physical-biogeochemical models namely, (Regional Ocean Modelling System and Biogeochemical of Eastern Boundary Upwelling Systems) ROMS-BioEBUS (3D) and (Nucleus for European Modelling of the Ocean and Biogeochemical Flux Model) NEMO-BFM (1D) are applied in the Benguela upwelling system to understand biogeochemical interactions and their related feedback processes. The models are formulated differently but achieve similar objectives with respect to the physics and biogeochemistry. The BioEBUS model is used to simulate nitrogen processes under oxic and suboxic conditions in upwelling systems with no option for other cycles. Intermediary nitrogen processes, nitrous oxide production and nitrogen loss mechanisms are studied using this model. Physical and advection processes that drive the oceanic nitrogen cycle in the region are also studied with BioEBUS. The BFM is used to understand the implications of the nitrogen loss and suboxic-anoxic conditions on related biogeochemical cycles. The 1D model was selected for its low computational costs and flexibility for addition of new code. BFM includes the carbon, nitrogen, phosphorus, silicate, iron cycles and hydrogen sulphide production, which is a known occurrence in the Namibian shelf waters. New variables, nitrite and nitrous oxide production, are added in BFM to complete the nitrogen cycle. The nitrification process in BFM is also formulated in two stages as in BioEBUS to obtain comparative results in both models. Both models are compared and validated with data from the Maria S. Merian (MSM) 19/1b cruise and available products respectively. Simulated results from BioEBUS show primary and secondary nitrite maxima in the Benguela shelf waters. The primary nitrite maxima are attributed to nitrification and nitrate assimilation. Secondary nitrite maxima accumulate in the Angola-Benguela Front (ABF) oxygen minimum zone (OMZ) and are attributed to denitrification. Off Walvis Bay, these secondary nitrite maxima and ammonium are thought to be consumed by high rates of anaerobic ammonium oxidation (anammox). The nitrite maxima are restricted to the shelf off Walvis Bay and advected offshore in the ABF region. Interchanges between the poleward South Atlantic Central Water (SACW) and the equatorward, well-oxygenated Eastern South Atlantic Central Water (ESACW) drive the seasonality of nitrogen processes in the Benguela. Nitrous oxide concentrations are high in the ABF as a result of nitrification and accelerated production under suboxic conditions. Off Walvis Bay, nitrous oxide production is low when compared to the ABF. Nitrous oxide production in the ABF occurs in thermocline, intermediate and deeper water masses. Off Walvis Bay, nitrous oxide production in deeper water masses is missing because of the shallow coast. High fixed nitrogen fluxes in the Benguela are attributed to nitrification rather than anammox and denitrification. Simulated results show denitrification to be the dominant nitrogen loss mechanism in the Benguela shelf waters. Simulated results from BFM show higher nitrogen uptake rates than phosphate in shelf and offshore stations. The uptake rates are high on the shallow shelf due to luxury nutrient uptake. High N:P ratios occur at the stations at 21ᵒS than off Walvis Bay and are attributed to the presence of nutrient-rich, oxygen depleted SACW and denitrification respectively. Increased fixed nitrogen deficits (N*) occur in surface and subsurface waters at shallow stations as opposed to offshore. The positive N* anomalies off Walvis Bay are attributed to organic matter remineralization in deep, offshore stations. In contrast, increased phosphate (P*) concentrations occur in surface and subsurface waters. Phosphate is regenerated in subsurface waters and released under suboxic-anoxic conditions increasing P* concentrations. Nitrogen loss coupled with hydrogen sulphide production accelerate phosphate release in suboxic-anoxic bottom waters. The N:P stoichiometry, uptake rates, N* and P* concentrations appear to have considerable implications on potential estimated nitrogen fixation in the Benguela. BFM results suggest that the Benguela is a system characterized by excess nitrate in relation to silicate. This has been drawn from the low Si:N ratios observed at the simulated stations. A secondary Si:N peak is shown on the shallow coast due to high denitrification rates in suboxic waters. Note that high silicate concentrations occur in suboxic conditions and can be attributed to organic matter remineralization. The high silicate concentrations in the well-oxygenated offshore station are linked to sinking particles in deep waters. Increased silicate dissolution occurs in warm, surface waters and the particles that pass through the water column undissolved settle at the bottom where dissolution continues. From these results, it can be assumed that increased warming in the Benguela coastal waters should result in silicate being a limiting nutrient. This could affect carbon export as it has been shown that increased POC export is high in coastal waters due to ballasting of diatom biomass. The models used in this study simulated biogeochemical interactions in the Benguela fairly-well and can be applied in other regions.
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Chang, Nicolette. "Descriptive analysis of a virtual transect through the Benguela Upwelling System." Master's thesis, University of Cape Town, 2003. http://hdl.handle.net/11427/6465.
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Bibliography: leaves 72-76.With the limitations of in situ observations of the ocean, numerical modeling of the ocean can easily provide clues to the structures and processes that lie therein. This project is an example of the examination of numerical model output. In this case, the area of interest is an area of ocean off Namaqualand which displays a reaction to local wind forcing. A transect was performed off the coast using output from ROMS (Regional Ocean Modeling System), forced under realistic winds obtained from weekly averaged ERS data. Temporal and spatial analysis yield information on the climatological characteristics of this region.
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Johnson, Ashley Stratton. "Analysis of variable scatterometer wind fields in the Benguela upwelling region." Master's thesis, University of Cape Town, 2001. http://hdl.handle.net/11427/6484.
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Bibliography: p. 142-149.The dissertation seeked to understand the effectiveness of satellite based data collection of wind fields along the west coast of southern Africa, pertaining to particular synoptic atmospheric systems. A comparison between data from two automatic coastal weather stations and measurements obtained by the NASA scatterometer (NSCAT) for the period 1 December 1996 to 31 May 1997 yielded a correlation coefficient of 70%.