Dissertations / Theses on the topic 'Downwelling'

Flow dynamics around a downwelling submarine canyon were analyzed with the Massachusetts Institute of Technology general circulation model. Blanes Canyon (Northwest Mediterranean) was used for topographic and initial forcing conditions. Fourteen scenarios were modelled with varying forcing conditions. Rossby number and Burger number were used to determine the significance of Coriolis acceleration and stratification (respectively) and their impacts on flow dynamics. A new non-dimensional parameter (χ) was introduced to determine the significance of vertical variations in stratification. Downwelling (downwards advection of density) occurs under all forcing conditions and is enhanced within the canyon. High Burger numbers lead to negative vorticity and a trapped anticyclonic eddy within the canyon, as well as an increased density anomaly. Low Burger numbers lead to positive vorticity, cyclonic circulation and weaker density anomalies. Vertical variations in stratification affect zonal jet placement. Under the same forcing conditions, the zonal jet is pushed offshore in more uniformly stratified domains. Offshore jet location generates upwards density advection away from the canyon, while onshore jets generate downwards density advection everywhere within the model domain. Increasing Rossby values across the canyon axis, as well as decreasing Burger values, increase negative vertical flux at shelf break depth (150 m). Increasing Rossby numbers lead to stronger downwards advection of a passive tracer (nitrate). Comparisons were made to previous studies to explain how variations in initial forcing conditions impact regional flow dynamics.

The spectral polarized radiance distribution provides the most complete description of the light field that can be measured. However, this is a very difficult parameter to measure near the surface because of its large dynamic range, dependence on incoming sky conditions, and waves at the air-sea interface. The measurement of the Stokes vector of the downwelling polarized light field requires the combination of at least four images, all of which must be obtained simultaneously. To achieve this, a new polarimeter (which we call DPOL) has been designed, characterized, calibrated and deployed. The description of the DPOL, its calibrations and characterizations are discussed. The uncertainties in the retrieval of Stokes vector and other derived parameters are also discussed. This instrument is equipped with four fish-eye lenses (180° field of view) with polarizers behind each lens in a different orientation, a coherent optical fiber bundle with 4 arms, a spectral filter changer assembly and a charged coupled-device (CCD) imaging camera. With this system, a single image contains 4 separate fisheye images, each a whole hemisphere of the same scene, each with different polarization information. Using these 4 images and applying appropriate calibration parameters allows us to calculate the four-element Stokes vector and then the total degree of polarization and the angle of plane of polarization of the incoming light field in a hemisphere of desired directions. Under the Office of Naval Research RaDyO (Radiance under a Dynamic Ocean) program, DPOL has been used in the Santa Barbara Channel and Hawaii field experiments. In most cases, data on sky polarization were collected with a separate camera (Sky-Cam) simultaneously with the DPOL. The data and results with these two camera systems in these experiments are presented and are compared. Data on the inherent optical properties of water from the same field experiments collected by collaborators will be shown. Our measurements show that very near the surface, for clear sky conditions, the dominant source of polarization is the refracted sky light. As one progresses in the water column, the polarization due to light scattering by the water increases and polarization due to the water becomes dominant. The dependence of the in-water light field polarization on the sky and surface wave conditions, solar zenith and azimuth angles, the depth of the instrument, the viewing angle, the wavelength of light, the inherent optical properties (IOP’s) of water are discussed.

Submarine canyons can impact regional oceanography and provide a conduit for shelf-slope exchanges via topographically induced processes such as canyon upwelling and downwelling. Between Virginia and New York in the Mid-Atlantic Bight (MAB), there are five major shelf-incising canyons (Norfolk, Washington, Baltimore, Wilmington, and Hudson canyons) and four sizable slope-confined canyons (Accomac, Spencer, Lindenkhol, and Toms canyons). Canyon upwelling and downwelling at these canyons have not been well studied. Consequently, the associated hydrographic variability and dynamics inside the canyons and on the adjacent shelf are largely unknown, and the integrated impact of submarine canyons on MAB shelf hydrography and shelf-slope exchanges is poorly understood. This dissertation was inspired by a glider-based survey at Wilmington Canyon, and mainly used numerical modeling simulations for the MAB with an unstructured-grid three-dimensional ocean model to answer these questions. Using glider observations and realistic numerical modeling for February 25–March 7, 2016, Chapter 2 investigated the hydrographic variability associated with the Wilmington Canyon and adjacent outer shelf and shelf-break amid two consecutive events of upwelling and downwelling. Then focusing on the same Wilmington Canyon upwelling and downwelling events and using a realistically forced numerical modeling simulation as well as one without tidal forcing, Chapter 3 tested the dynamical drivers of winds and tides in canyon upwelling and downwelling events, also compared the differences in dynamics between the canyon and adjacent shelf-break. Chapter 4 presented the occurrences and integrated impact of 12 cycles of spatially coherent upwelling and downwelling through nine canyons between Virginia and New York, based on a realistic numerical modeling experiment and a No-Canyon experiment for January 1–April 14, 2016. Chapter 4 also analyzed the frequency of canyon upwelling and downwelling based on a 22-year record (1994–2015) of sea surface elevation. This dissertation found that the submarine canyons in the MAB induced significant spatial and temporal hydrographic variabilities on the shelf and enhanced shelf-slope water exchange. Due to favorable winds, sea surface tilts, and shelf-scale background ocean currents, as well as canyon topography, cycles of spatially coherent multi-canyon upwelling and downwelling frequently occurred in the MAB. Plumes of upwelled slope water from the canyons intruded the outer and mid shelf during the upwelling episodes, and dense water from the shelf retreated into the canyons during the downwelling episodes. For each cycle of upwelling and downwelling, upwelled water from the canyons caused shelf-scale anomalies of low temperature, high density, and northeastward velocity on the MAB outer shelf that were significant when averaged over the course of the season. This thesis suggests that submarine canyons are an integral part of MAB oceanography and deserve further investigations.

Mestrado em Ciências do Mar e da Atmosfera
Circulation patterns inside some of the Rías Baixas have been widely studied, but this is not the case of the Ría de Pontevedra. Through this thesis, we try to enhance the knowledge about the circulation pattern of this Ría. A ROMS-AGRIF system con guration was used in this study. This con guration was validated through the comparison with weekly temperature and salinity data measured by INTECMAR. The analysis done in this work is based on the study of three representative events of the circulation patterns: one upwelling event and two downwelling events, one of them with Lérez river ow increase. Also, was analyzed temporal series of uxes and ushing times through the external mouths and the correlations between these series and the forcing parameters (winds and average of the rivers ow). An EOF's study was applied to the subinertial normal velocities at the sections. Upwelling events are characterized by a reinforcement of the positive estuarine circulation, consistent with surface layer out ows and deep layer in ows at the main channel of the Ría, and in ows/out ows at the north/south mouths. Downwelling events have an opposite behaviour to the event described before. There are evidences of the vertical mixing through clockwise circulations at the outer part of the Ría, associated with the ocean waters subduction that enter into the Ría through the surface layer. As a consequence, a blocking can be generated at the middle part of the Ría, which has been associated by other authors with the "red tides". Fluxes for downwelling events are higher than for upwelling events. Flushing times are around 2 days for downwelling and around 4 days for upwelling events. The EOF's study con rms the circulation described for upwelling and downwelling events, in this work. The forecast of the physical conditions at Ría de Pontevedra are important for the understanding of the processes behind the production of HABs.
Diversos estudos tem sido realizados sobre os padrões de circulação em algumas das Rías Baixas, mas este não é o caso da Ría de Pontevedra. Ao longo desta tese tentaremos completar os conhecimentos sobre esta Ría. Uma con guração do sistema ROMS-AGRIF foi utilizada neste estudo, sendo esta validada com base na comparação com dados de temperatura e salinidade medidos semanalmente pelo INTECMAR. A analise realizada baseia-se no estudo de três episódios representativos da circulação: um de a oramento e dois de afundamento, um destes com caudal do río Lérez signi cativo. Foram ainda analisadas séries temporais de uxos e de tempos de renovação através de diversas secções. Foi analisada a correlação entre estas séries e os parâmetros forçadores (ventos e caudais dos rios). Foi realizado um estudo utilizando técnicas de funções empíricas ortogonais aplicado ao campo de velocidades normal às secções. Os eventos de a oramento são caracterizados por um reforço da circulação positiva na Ría, consistente com os uxos de saída pela camada superior e uxos de entrada pela camada inferior do canal principal da Ría, e com uxos de entrada pela boca norte e os uxos de saída pela boca sul. Nos eventos de afundamento o comportamento é oposto ao anterior. São discutidas evidências de recirculação vertical em forma de células no sentido dos ponteiros do relógio na zona externa da Ría, associado à subdução de águas oceânicas que entram na Ría pela camada superior. Este fenómeno parece criar uma zona de bloqueio no meio do eixo da Ría, que pode ser um mecanismo responsável pelo desenvolvimento das denominadas marés vermelhas. Os uxos para o evento de afundamento são superiores aos dos eventos de a oramento. O tempo de renovação é próximo dos 2 dias para o afundamento e dos 4 dias para o a oramento. O estudo por funções empíricas ortogonais con rma a circulação descrita durante os episódios de a oramento e afundamento discutidos neste trabalho. A previsão das condições físicas na Ría de Pontevedra é importante para a compreensão dos processos associados ao desenvolvimento de marés vermelhas.

Hyperspectral images are made up of energy measurements at different wavelengths of light. The case is considered where these measurements are dependent on temperature, the self-emitted energy (emissivity), and reflected energy (downwelling radiance) from the surroundings. The process where the downwelling radiance is fixed and the temperature and emissivity are estimated is referred to as temperature/emissivity separation. Due to the way these terms mix, for a given set of measurements, there exist many pairs of temperatures and emissivities that satisfy the model. This creates ambiguity in the solution that must be resolved for the result to have any significance. A new model is developed which reduces this ambiguity. This model is used to form an objective function. The temperature and emissivity which maximize the value of the objective function are solved for given a set of measurements. As part of the solution, a new algorithm is developed which exploits the shape of the objective function to estimate the temperature and emissivity quickly and accurately. Extensive testing of this algorithm is performed to gain an understanding of its average speed and accuracy.

Atmospheric downwelling longwave radiation is an important component of the terrestrial energy budget; since it is strongly related with the greenhouse effect, it remarkably affects the climate. In this study, I evaluate the estimation of the downwelling longwave irradiance at the terrestrial surface for cloudless and overcast conditions using a one-dimensional radiative transfer model (RTM), specifically the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART). The calculations performed by using this model were compared with pyrgeometer measurements at three different European places: Girona (NE of the Iberian Peninsula), Payerne (in the East of Switzerland), and Heselbach (in the Black Forest, Germany). Several studies of sensitivity based on the radiative transfer model have shown that special attention on the input of temperature and water content profiles must be held for cloudless sky conditions; for overcast conditions, similar sensitivity studies have shown that, besides the atmospheric profiles, the cloud base height is very relevant, at least for optically thick clouds. Also, the estimation of DLR in places where radiosoundings are not available is explored, either by using the atmospheric profiles spatially interpolated from the gridded analysis data provided by European Centre of Medium-Range Weather Forecast (ECMWF), or by applying a real radiosounding of a nearby site. Calculations have been compared with measurements at all sites. During cloudless sky conditions, when radiosoundings were available, calculations show differences with measurements of -2.7 ± 3.4 Wm-2 (Payerne). While no in situ radiosoundings are available, differences between modeling and measurements were about 0.3 ± 9.4 Wm-2 (Girona). During overcast sky conditions, when in situ radiosoundings and cloud properties (derived from an algorithm that uses spectral infrared and microwave ground based measurements) were available (Black Forest), calculations show differences with measurements of -0.28 ± 2.52 Wm2. When using atmospheric profiles from the ECMWF and fixed values of liquid water path and droplet effective radius (Girona) calculations show differences with measurements of 4.0 ± 2.5 Wm2. For all analyzed sky conditions, it has been confirmed that estimations from radiative transfer modeling are remarkably better than those obtained by simple parameterizations of atmospheric emissivity.
La radiació infrarroja a l’atmosfera és una component important del balanç energètic del planeta; en estar fortament relacionada amb l’efecte hivernacle influeix de manera remarcable en el clima. En aquest estudi s’avalua la bondat de les estimacions de la irradiància infrarroja incident en superfície (DLR) fetes amb un model unidimensional de transferència radiativa, el Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART), per a condicions de cel serè o bé completament ennuvolat. Els càlculs realitzats amb aquest model han estat comparats amb mesures de pirgeòmetre realitzades en tres emplaçaments a Europa: Girona (NE de la Península Ibèrica), Payerne (a l’est de Suïssa), i Heselbach (a la Selva Negra, Alemanya). Els estudis de sensibilitat fets amb el model de transferència radiativa han mostrat l’especial importància que tenen els perfils atmosfèrics de temperatura i contingut d’aigua en absència de núvols; per cels completament ennuvolats l’estudi de sensibilitat mostra que, a banda dels perfils atmosfèrics esmentats, l’altura de la base dels núvols és molt rellevant. S’ha estimat la DLR per indrets on no es disposava de radiosondatges, substituint-los bé per un radiosondatge proper, o bé per perfils interpolats espacialment en l’anàlisi del model de predicció meteorològica de l’European Centre of Medium-Range Weather Forecast (ECMWF). Els càlculs han estat comparats amb mesures per tots els llocs. Per condicions de cel serè, i quan es disposa de radiosondatge, els càlculs mostren una diferència amb les mesures de -2.7 ± 3.4 Wm-2 (Payerne). Quan no es disposa d’aquests perfils, la diferència entre les modelitzacions i les mesures és de 0.3 ± 9.4 Wm-2 (Girona). Per condicions de cel cobert, quan es disposa del radiosondatge i les propietats dels núvols (derivades a partir d’un algoritme que empra mesures espectrals en infraroig i en la banda de microones en superfície, Selva Negra), els càlculs mostren una diferència amb les mesures de -0.28 ± 2.52 Wm-2. Quan es fan servir els perfils del ECMWF i es fixa el valor de la columna d’aigua líquida i el radi efectiu de les gotes d’aigua (Girona) els càlculs mostren una diferència amb les mesures de 4.0 ± 2.5 Wm-2. També s’ha confirmat per totes les condicions estudiades que les estimacions amb el model de transferència radiativa són notablement millors que les obtingudes amb parametritzacions senzilles de l’emissivitat atmosfèrica.

Des épisodes à Dinophysis affectent périodiquement l'exploitation des fruits de mer dans le Bassin d'Arcachon. Le réseau de surveillance interne au Bassin d'Arcachon montre que Dinophysis est advecté de l'océan ouvert. Le but de cette étude est de déterminer l'origine de Dinophysis. Des campagnes en mer sur le plateau continental Aquitain ont permis d'identifier une zone propice au développement de Dinophysis au large de Capbreton. Les épisodes à Dinophysis dans le bassin d'Arcachon se produisent suite à des vents d'Ouest qui induisent des courants vers le Sud d'après la littérature. L'étude des données hydrodynamiques acquises pendant les campagnes met en évidence un processus complexe et nouveau suite aux vents d'Ouest: de forts courants le long de la côte vers le Nord capables de transporter Dinophysis de Capbreton jusqu'au Bassin d'Arcachon. Un travail de modélisation a permis de reproduire ce courant et d'étudier son mécanisme particulier lié coin Sud-Est du Golfe de Gascogne
Abstract

A numerical study is made of the wintertime circulation within the Southeast Indian Ocean (SEIO). The downwelling favourable winds result in a continuous eastward Coastal Current (CC) extending from Cape Leeuwin to the eastern coast of Tasmania, where it forms a confluence with the south branch of the East Australian Current. An additional forcing mechanism for the CC is the Leeuwin Current in the western part of the domain. The study here is divided in two parts: (1) available data and the wintertime averaged results from the Ocean Circulation and Climate Advanced Model (OCCAM) are analysed to provide a first order description of the large-scale circulation; (2) a high resolution model (Princeton Ocean Model) is nested within OCCAM to examine the shelf-slope circulation within the eastern SEIO. The nested model is forced with climatological monthly average winds and several experiments were run to simulate the effects of surface fluxes of density, enhanced bottom friction and stronger winds. In summary, the shelf-slope circulation is governed by a surface south-eastward CC that carries around 2 Sv and reaches velocities of up to 50 cm/s, where the shelf is narrowest. The core of the current is generally constrained to the shelf-break region. Zonal winds and geostrophic control of the CC lead to a transport of 1 Sv through Bass Strait and a north-eastward jet that is directed into the strait between King Is. and Tasmania. Further south, the CC is poleward and known as the Zeehan Current (ZC). Between Cape Leeuwin and Tasmania and over the slope region, a westward current (the Flinders Current) is found at depths of 500-1000 m and has an associated transport of 5-7 Sv. The current is shown to result from a northward Sverdrup transport in the deep ocean. Meso-scale eddies are shown to result from baroclinic instability and have wavelengths of around 250 km and transports of 3-4 Sv, and can dominate the slope circulation. A comparison of the numerical results is also made with two current meter data sets and results show an interannual variability in the ZC strength, that is probably related to ENSO.

O presente trabalho teve como objetivo principal descrever a distribuição espaço-temporal do ictioplâncton da região do cabo Frio (RJ) em relação aos processos físicos de mesoescala, com ênfase na distribuição vertical. A amostragem foi realizada em verão e inverno de 2001, com o N/Oc. Prof. W. Besnard, durante dois cruzeiros do projeto DEPROAS. O ictioplâncton foi coletado com rede Multinet, com 5 redes de 333 m, sendo que cada estrato amostrado teve 20 m, até os 100 m de profundidade. Em laboratório, foram realizadas a triagem do ictioplâncton e identificação das larvas. A análise dos dados foi realizada através de testes estatísticos paramétricos e não paramétricos e análises multivariadas. Não houve um padrão claro de distribuição vertical das larvas em função das classes de comprimento, salvo em alguns casos particulares, como Bregmaceros cantori que teve maior frequência de larvas em pré-flexão associadas à termoclina e também baixa frequência de larvas em pós-flexão próximas à superfície. O padrão de distribuição do ictioplâncton foi determinado, em parte, pelas porcentagens de ACAS, de AC e a concentração de clorofila-a, tanto nos dois períodos. Com base nos resultados obtidos, foi possível demonstrar a influência direta dos processos físicos de mesoescala (i.e. ressurgência e subsidência) e dos padrões de distribuição de clorofila-a sobre a distribuição vertical do ictioplâncton na região do cabo Frio.
The aim of the present work was to describe the spatial and temporal distributions of the ichthyoplankton in the cabo Frio (RJ) region in relation to mesoscale physical processes, with emphasis on its vertical distribution. Samples were taken in the summer and winter 2001 onboard the R/V Prof. W. Besnard, during the two sampling surveys of the DEPROAS project. The ichthyoplankton was collected using a Multinet device with 5 nets of 333 mm meshed; being that each layer had 20 m up to 100m depth. Ichthyoplankton sorting and larvae identification were done in the laboratory. Data analyses were performed using parametric and non-parametric statistical tests, and also multivariate analyses. A clear vertical distributional pattern of larvae in relation to their length classes was not observed, except in some particular cases such as Bregmaceros cantori, which had a higher frequency of pre-flexion larvae associated to the thermocline and also a low frequency of pos-flexion larvae near the surface. The distributional pattern of ichthyoplankton was determined in part, by the percentages of SACW, CW and chlorophyll-a concentration in both periods. Based on these results, it was possible to demonstrate the direct influence of mesoscale physical processes (i.e. upwelling and downwelling) and chlorophyll-a distribution patterns on the vertical distribution of the ichthyoplankton in the cabo Frio region.

Shortwave radiation is a key quantity to estimate the surface radiation budget which has a close relationship with the climate of a given region. Shortwave radiation is affected by aerosols and clouds. Aerosols modify the Earth’s radiation budget and boundary layer meteorology by reflecting sunlight to space and absorbing radiation in the atmosphere. Clouds modulate the vertical and horizontal distributions of solar radiative heating, latent heat, and cooling by thermal radiation that drive the atmospheric circulation. The main objective of this thesis is to analyze in detail the methodology presently used to derive the Downwelling Surface Shortwave Flux (DSSF) based on information from geostationary satellites. The study is closely related to operational activities developed within the framework of the Satellite Application Facility on Land Surface Analysis (LSA SAF). An already existing operational DSSF algorithm, developed within the framework of the Ocean and Sea Ice (O&SI) SAF, is tested and improved for clear and cloudy sky conditions. In the case of clear sky, the parameterisation for atmospheric absorption accounts for the variation of the concentration of the atmospheric components. In the case of cloudy sky, radiation interactions are more complex and, besides the interaction with the atmosphere, the parameterisation scheme accounts for cloud albedo and relies on a predefined value characterizing the absorption by clouds. Both methodologies are analyzed and two parameterizations are proposed; for cloudy sky pixels the new parameterisation takes cloud types into account whereas, in the clear sky case, diffuse radiation is explicitly included in the DSSF model, based on information about aerosol optical thickness. Model performance is significantly improved and for both methodologies an approach to their integration in an operational environment is proposed.
A elaboração de cenários do clima futuro pressupõe um conhecimento sólido do estado do clima, quer do passado, quer do presente. O Sol é a fonte primária de energia do sistem climático, estando na origem das circulações oceânica e atmosférica que modulam as interacções entre a atmosfera e a hidrosfera, bem como entre estas e as restantes componentes do Sistema Climático, nomeadamente a criosfera, a litosfera e a biosfera. Os ciclos hidrológico e do carbono constituem exemplos de tais interacções e o seu conhecimento afigura-se crucial para que se possam antecipar possíveis comportamentos do clima no futuro. No contexto acima descrito, o conhecimento do balanço radiativo à superfície do solo é fundamental em inúmeras aplicações, tais como na previsão numérica do estado do tempo e na gestão de recursos naturais. Em particular, revela-se essencial possuir um conhecimento aprofundado das interacções da energia solar com a atmosfera e com a superficíe do solo a fim de que se possa dar resposta a um leque vasto de questões relacionadas com a evolução do clima actual. Assim é, por exemplo, que o facto de a absorção de pequeno comprimento de onda ter vindo a ser subestimada, seja em condições de céu limpo, seja de céu nublado, tem implicações profundas para o balanço energético nos modelos de circulação global. Nesta conformidade, uma maior precisão na estimativa da radiação de pequeno comprimento de onda deverá ter repercussões positivas na caracterização do clima e na elaboração de cenários do clima futuro.
Fundação para a Ciência e a Tecnologia

The Michigan basin has long been established as the type example of an intracratonic basin due to its near circular geometry and gently inward-dipping Paleozoic formations. The backstripping of major formations within the basin reveals that its geometry varied over the duration of the Paleozoic, displaying two distinct subsidence signals consisting of quasi-circular basin-centered subsidence interspaced with periods of irregular basin geometry. The quasi-circular basin-centred subsidence is thought to represent the surface expression of a driving mechanism located beneath the Michigan basin, which persisted for the duration of the Paleozoic. An irregular subsidence geometry periodically interrupts the quasi - circular basin-centred pattern and is contemporaneous with the Ordovician Taconic and Devonian Acadian orogenies. Through the use of scaled analogue experiments, the effects of convective mantle downwelling and long wavelength folding are explored as potential driving mechanisms to explain the subsidence patterns of the Michigan basin. Convective mantle downwelling is hypothesized as the process responsible for the quasi-circular basin-centered subsidence patterns and the relationship between mantle flow velocities and a variety of continental strength profiles is explored. A series of scaled analogue vice experiments explore the effects of regional orogeny on a continental hinterland, with some experiments containing a strong lower crustal strength heterogeneity, designed to test the possible influence of the Mid Continental rift beneath the Michigan basin. The results of both types of experiment demonstrate that quasi-circular subsidence patterns within the Michigan basin may have been formed due to convective mantle downwelling, while the effects of regional orogeny and long wavelength folding dramatically influenced subsidence patterns during the Taconic and Acadian orogenies.

碩士
國立臺灣海洋大學
海洋環境資訊系
107
The South China Sea (SCS) is a semi-enclosed marginal sea, where is an eddy-active zone. Eddies play an important role in transporting heat and matters in the ocean. When a cyclonic eddy is generated, upwelling will occur at its center, but the situation is reversed for an anticyclonic eddy. Previously, satellite altimeters were often used to track eddies, and the upwelling and downwelling at eddy centers could be observed through satellite-measured sea surface temperature. However, we found that no significant upwelling or downwelling at some eddy centers in Northern South China Sea (NSCS), based on the Expendable-bathythermograph (XBT) routine surveys. Thus, the main purpose of this study is to find out the marine environments that are favorable for the upwelling or downwelling to occur at the eddy centers in the NSCS, by using in-situ and satellite observations. Our finding showed that when cold waters transported into the NSCS, the local ocean stratification became weaker, making significant upwelling and downwelling at the eddy centers.

碩士
國立成功大學
水利及海洋工程學系
105
In recent years, the hyporheic zone is getting more and more attention on extended knowledge, academic research, and water resources usage issues. It is of great importance to economic, environmental, biological phase. Besides field investigate, using known data for coordinate with numerical simulation to model deeper or wider unknown area is more often seen in the hyporheic zone. This study used field investigation to obtain hydrological and geographical information, then with the used of numerical simulation to model the correlations between surface water and hyporheic water. In modeling process, we used a three-dimensional MODFLOW model to simulate both hyporheic head and flux rate situation, and paired with MT3D to simulate the distribution of upwelling and downwelling area along a narrow stream. Modeling results in MODFLOW indicated that the net stream flux rate is 0.0765 m3/day, and surface water is gaining water at Wu Gou Shui Chihshan stream. If model boundary from Chihshan stream extended to Donggang River, the net stream flux rate is -0.0517 m3/day, and from junction to Donggang River surface water is losing water. Results from MT3D showed that the distribution of upwelling and downwelling area is the similar to our field investigated results. The difference is that model can help us to understand the distribution of ‘‘area’’; however, field investigation can only survey the distribution of ‘‘point’’ locations. The distribution of upwelling and downwelling areas can be easily combined with physical factors (e.g. pool-riffle sequence) and chemical factors (e.g. dissolved oxygen, DO). In this study, it showed that upwelling generally occurred at the beginning of pool, and downwelling occurred frequently at the beginning of riffle.

Despite recent interest in understanding long-term trends in ocean acidity, natural variations of carbon chemistry on short timescales are still poorly understood. Unfortunately, historical observations of the oceanic CO2 system are relatively few in number. Such data are particularly scarce along the highly productive Canadian Pacific coast. However, hydrographic data such as temperature, salinity, oxygen and nutrients have been collected regularly in this region. I developed a fully cross-validated statistical model to predict the aragonite saturation state (Ωarag), a biologically relevant measure of the carbonate system. Different sensitivity tests were performed to assess the robustness of the statistical modelling skill to different model structures. In particular, this study found that in situ temperature and O2 used together were strong predictors of Ωarag. The carbon data used to build this statistical model came from five hydrographic surveys along the Pacific coast of Canada (in July 1998, August 2004, late May 2007, February 2010 and early August 2010) that contain direct measurements of CO2 system parameters. Only data from a depth range of 0-750 m were used, as data from below 750 m showed biases due to calcium carbonate dissolution. Although processes such as solar warming and gas exchange occur in the surface and could possibly introduce biases in the model, I show that these surface data can be included. The ability of the statistical models to compute robust estimates of Ωarag was assessed by exploring the generalizability of the model through cross-validation procedures using different partitions of the data. By predicting lnΩarag rather than Ωarag directly, I obtained a strong and robust predictive relationship. This MLR model form yielded a high value in the squared correlation coefficient between predicted and observed values (0.96) and a low percentage in erroneous prediction of undersaturated conditions (3.1%). This relationship was found to be insensitive to changes in spatial domain or interannual variability in the data. These results suggest that the model can be used to estimate the distribution of Ωarag along the outer west coast of Canada when basic hydrographic data on temperature and O2 are available. Predictions of Ωarag from historical observations (1980-2009) in this region reveal that the saturation horizon (Ωarag=1) tended to be more stable in winter and spring and highly variable and occasionally shallow in summer and fall during and following the upwelling season. Undersaturation with respect to aragonite was more likely to occur at shallower depths over the shelf relative to adjacent offshore waters likely as a result of upwelling. The Ωarag saturation horizon tended to be more variable in depth on the shelf compared to offshore waters. The saturation horizon tended to occur at deeper depths over the Queen Charlotte Sound (QCS) shelf and be more stable with respect to the west coast of Vancouver island (WCVI). Thus, the WCVI may experience adverse effects of ocean acidification more acutely than QCS. The use of this approach may provide insight into natural variability and the key controls of Ωarag in future studies at a low cost. However, this predictive model cannot hind-cast data to evaluate the presence of the anthropogenic signal.
Graduate

Sedimentation rates and compositions of sinking particles were investigated at three sites on the Beaufort slope and one in Canada Basin during the period 1990-1994 using moored sequential sediment traps. A method was developed to identify the terrigenous and biogenic components of the fluxes. The physical context including ice cover, ocean currents, river inputs, winds, air temperature, incident light, and nutrient availability provide essential information to the interpretation of the particle fluxes and to the understanding of shelf-basin sediment transport in this area. Eddies, internal waves, upwelling and downwelling, and the state of the ice cover all played important and overlapping roles in the pattern of observed fluxes. A peak in the flux of highly terrigenous material under complete ice cover in mid-winter to the northwest of Mackenzie Trough was associated with predominantly downwelling conditions and the passage of a series of eddies and internal waves. A prolonged spring diatom bloom occurred in the mid-slope area and was clearly associated with an early opening of the ice on the east side of the shelf. Higher fluxes at the Canada Basin site were associated with a large eddy clearly identifiable from the current-T-S record and also from the composition of the suspended material carried with it. At the base of the slope (2700 m), the composition was highly terrigenous and remarkably consistent. Higher up the slope (700 m), biogenic peaks in the summer diluted the terrigenous material briefly, but it appears that there is a constant background of highly terrigenous material. There was a high degree of variability between sites and over the slope there was not enough data to asses the inter-annual variability. In Canada Basin, the inter-annual variability was closely linked to the extent of open water in the summer period. At all sites, lateral transport is clearly indicated by the increase in flux with depth. The data robustly demonstrate the need for detailed knowledge of physical processes for informed interpretation of particle fluxes and sediment transport in this area.