During the fourth International Polar Year, an interdisciplinary study was conducted to examine the couplings between sea ice, ocean, atmosphere, and ecosystem in the southeastern Beaufort Sea. This thesis examines components of the system that control the air–sea exchange of carbon dioxide. Using eddy covariance measurements, we found enhanced CO2 exchange associated with new ice formation in winter flaw leads. This exchange was typically directed towards the surface, although we also measured one instance of outgassing. Sea surface dissolved CO2 measurements (pCO2sw) in Amundsen Gulf showed significant undersaturation with respect to the atmosphere at freeze–up, followed by a slow increase over the winter until spring phytoplankton blooms caused strong undersaturation at break–up. Over the summer, pCO2sw increased until becoming slightly supersaturated due to surface warming. Along the southern margins of Amundsen Gulf and on the Mackenzie Shelf we found pCO2sw supersaturations in the fall due to wind–driven coastal upwelling. In the spring, this upwelling occurred along the landfast ice edges of Amundsen Gulf. By combining observations of enhanced winter gas exchange with observations of pCO2sw in Amundsen Gulf, we derived an annual budget of air–sea CO2 exchange for the region. This exercise showed that uptake through the winter season was as important as the open water season, making the overall annual uptake of CO2 about double what had previously been calculated. Prior to this work, the prevailing paradigm of air–sea CO2 cycling in Arctic polynya regions posited that strong CO2 absorption occurs in the open water seasons, and that a potential outgassing during the winter is inhibited by the sea ice cover. As a new paradigm, we propose that the spatial and temporal variability of many processes – including phytoplankton blooms, sea surface temperature and salinity changes, upwelling, river input, continental shelf processes, and the potential for high rates of winter gas exchange – need to be considered in order to understand the carbon source/sink status of a given Arctic polynya region. A paradigm that considers such varied processes is useful in understanding how climate change in the Arctic can impact air–sea CO2 exchange.

During the fourth International Polar Year, an interdisciplinary study was conducted to examine the couplings between sea ice, ocean, atmosphere, and ecosystem in the southeastern Beaufort Sea. This thesis examines components of the system that control the air–sea exchange of carbon dioxide. Using eddy covariance measurements, we found enhanced CO2 exchange associated with new ice formation in winter flaw leads. This exchange was typically directed towards the surface, although we also measured one instance of outgassing. Sea surface dissolved CO2 measurements (pCO2sw) in Amundsen Gulf showed significant undersaturation with respect to the atmosphere at freeze–up, followed by a slow increase over the winter until spring phytoplankton blooms caused strong undersaturation at break–up. Over the summer, pCO2sw increased until becoming slightly supersaturated due to surface warming. Along the southern margins of Amundsen Gulf and on the Mackenzie Shelf we found pCO2sw supersaturations in the fall due to wind–driven coastal upwelling. In the spring, this upwelling occurred along the landfast ice edges of Amundsen Gulf. By combining observations of enhanced winter gas exchange with observations of pCO2sw in Amundsen Gulf, we derived an annual budget of air–sea CO2 exchange for the region. This exercise showed that uptake through the winter season was as important as the open water season, making the overall annual uptake of CO2 about double what had previously been calculated. Prior to this work, the prevailing paradigm of air–sea CO2 cycling in Arctic polynya regions posited that strong CO2 absorption occurs in the open water seasons, and that a potential outgassing during the winter is inhibited by the sea ice cover. As a new paradigm, we propose that the spatial and temporal variability of many processes – including phytoplankton blooms, sea surface temperature and salinity changes, upwelling, river input, continental shelf processes, and the potential for high rates of winter gas exchange – need to be considered in order to understand the carbon source/sink status of a given Arctic polynya region. A paradigm that considers such varied processes is useful in understanding how climate change in the Arctic can impact air–sea CO2 exchange.

A transferência de gases através da interface ar-água em escoamentos turbulentos é um processo importante para diferentes sistemas ambientais. Para avançar no entendimento dos princípios básicos envolvidos no fenômeno é necessária a utilização de técnicas e aparatos experimentais adequados. Neste estudo, foi realizada simulação numérica e experimentos em tanque de uma e duas grades oscilantes. Para a configuração de duas grades, dados experimentais foram comparados com soluções analíticas, obtendo-se boa concordância. Quatro quantidades foram analisadas: energia cinética turbulenta, taxa de dissipação de energia, viscosidade turbulenta e escala de comprimento. Na configuração de uma grade oscilante, foram realizadas medidas de concentração através da utilização de micro sonda de oxigênio. Adicionalmente, foram realizadas medidas concomitantes de velocidade e concentração, próximas à interface, utilizando, respectivamente, as técnicas particle image velocimetry (PIV) e laser induced fluorescence (LIF). O uso combinado das técnicas PIV e LIF permite a obtenção direta do fluxo de massa através da interface ar-água. Os resultados qualitativos e quantitativos devem servir de auxílio para direcionar futuros desenvolvimentos na área. / Gas transfer across the air-water interface in turbulent flows is an important process for many environmental systems. To improve the understanding of the basic principles involved in this phenomenon it is necessary to use suitable apparatus and experimental techniques. In this study, experiments and numerical simulation were conducted in a tank with one and two oscillating grids. In the two-grids configuration, experimental data were compared with analytical solutions, obtaining good agreement. Four quantities have been evaluated: turbulent kinetic energy, dissipation rate, eddy viscosity, and length scale. In the one-grid configuration, a microprobe has been used for measurements of oxygen concentration. In addition, the velocity and concentration fields near the interface were measured simultaneously using the combined particle image velocimetry (PIV) - laser induced fluorescence (LIF) technique. With the combined PIV-LIF technique, the total mass flux across the air-water interface could be obtained directly. The qualitative and quantitative results should help guide future work at the subject.

A transferência de gases através da interface ar-água em escoamentos turbulentos é um processo importante para diferentes sistemas ambientais. Para avançar no entendimento dos princípios básicos envolvidos no fenômeno é necessária a utilização de técnicas e aparatos experimentais adequados. Neste estudo, foi realizada simulação numérica e experimentos em tanque de uma e duas grades oscilantes. Para a configuração de duas grades, dados experimentais foram comparados com soluções analíticas, obtendo-se boa concordância. Quatro quantidades foram analisadas: energia cinética turbulenta, taxa de dissipação de energia, viscosidade turbulenta e escala de comprimento. Na configuração de uma grade oscilante, foram realizadas medidas de concentração através da utilização de micro sonda de oxigênio. Adicionalmente, foram realizadas medidas concomitantes de velocidade e concentração, próximas à interface, utilizando, respectivamente, as técnicas particle image velocimetry (PIV) e laser induced fluorescence (LIF). O uso combinado das técnicas PIV e LIF permite a obtenção direta do fluxo de massa através da interface ar-água. Os resultados qualitativos e quantitativos devem servir de auxílio para direcionar futuros desenvolvimentos na área. / Gas transfer across the air-water interface in turbulent flows is an important process for many environmental systems. To improve the understanding of the basic principles involved in this phenomenon it is necessary to use suitable apparatus and experimental techniques. In this study, experiments and numerical simulation were conducted in a tank with one and two oscillating grids. In the two-grids configuration, experimental data were compared with analytical solutions, obtaining good agreement. Four quantities have been evaluated: turbulent kinetic energy, dissipation rate, eddy viscosity, and length scale. In the one-grid configuration, a microprobe has been used for measurements of oxygen concentration. In addition, the velocity and concentration fields near the interface were measured simultaneously using the combined particle image velocimetry (PIV) - laser induced fluorescence (LIF) technique. With the combined PIV-LIF technique, the total mass flux across the air-water interface could be obtained directly. The qualitative and quantitative results should help guide future work at the subject.

<p> Using a single bubble suspended in a liquid flow regime, the effects of velocity, bubble size, and surfactant levels on the gas transfer process across the bubble interface were investigated. Mass transfer data reported in the literature for non-circulating carbon dioxide bubbles was verified. A mathematical model predicting the mass transfer process for the single bubble system used in this study was formulated and this model provided a reasonable fit for experimental data obtained for the dissolution of a carbon dioxide bubble into an aqueous solution of a second sparingly soluble gas. The fate of a hypothetical air bubble in an aerator was briefly considered.</p> / Thesis / Master of Engineering (MEngr)

No description available.

O trabalho apresenta uma investigação sobre a influência da umidade atmosférica no processo de absorção de oxigênio atmosférico por corpo de água através de sua superfície líquida livre. Os experimentos realizados em laboratório consistem na reoxigenação de uma massa de água, contida em um tanque cilíndrico, submetida à agitação mecânica. A atmosfera que reabastece de oxigênio a massa líquida é controlada e os ensaios são conduzidos com vários níveis de umidade do ar, o que provoca diferentes taxas de evaporação. Simultaneamente, determinam-se os coeficientes de reoxigenação, K2 (h-1), em cada experimento. Investiga-se neste trabalho a correlação entre esses dois parâmetros. O processo de reoxigenação é analisado inicialmente com o uso de metodologia clássica baseada em modelos matemáticos tradicionais (possivelmente inadequados). Propõe-se neste trabalho, um modelo original para essa mesma análise. / The influence of the atmospheric humidity on the process of absorption of oxygen by a water body through its free surface is presented herein. Laboratory experiments were run for the reoxygenation of a water mass kept in a cylindrical vessel under mechanical agitation. The quality of the atmospheric air transferring oxygen to water is controlled and the tests are run with several levels of air humidity, what renders different rates of evaporation. The corresponding coefficients of reaeration K2 (h-1) are determined for each experiment. The correlation between these two latter parameters is investigated. The process of reoxygenation is analyzed initially using a classical methodology based on traditional mathematical models (possibly inadequate). An original model for the same analysis is proposed in this work.

O parâmetro que determina o processo de transferência de oxigênio através da interface ar-água em escoamentos com superficie livre é o coeficiente de reaeração superficial, \'K IND.2\'. Existe um grande número de equações na literatura científica que realizam a previsão do coeficiente de reaeração, no entanto, a maioria dessas equações considera apenas algumas características hidráulicas do corpo de água como a velocidade e a profundidade, e ainda, como em sua maioria são de natureza empírica, acabam sendo adequadas para corpos de água específicos. Além destes dois parâmetros (velocidade e profundidade do escoamento), existem outros doze que são considerados importantes para estudos de reoxigenação em águas superficiais. É neste contexto que o objetivo deste trabalho foi estudar em condições de laboratório a influência da rugosidade do leito de um canal sobre o coeficiente de reaeração superficial. Além da rugosidade, foram variadas as condições de velocidade média do escoamento e profundidade da lâmina de água. A variação da rugosidade foi realizada através da implementação de obstáculos com geometria conhecida, dispostos transversalmente ao escoamento, e denominados como macro-rugosidades. Os resultados demonstraram evidências de que o coeficiente de reaeração superficial é controlado de forma significativa pela rugosidade do leito do canal. Foram desenvolvidos dois modelos matemáticos de natureza semi-empírica para a previsão do \'K IND.2\', os quais incorporam variáveis hidrodinâmicas e geométricas consideradas relevantes para o processo de transferência de massa na interface ar-água. / The parameter that determines the process of oxygen transfer through the air-water interface in flows with free surface is the superficial reaeration coefficient, \'K IND.2\'. There are a large quantity of equations in the cientific literature that perform the prevision of the reaeration coefficient; however, most of them consider only some of the hydraulic characteristics of water body; for example, the velocity and the depth. Most of these equations have empirical origin and are adequate just for a specific water body. In addition to these two parameters (velocity and depth of flow), there are another twelve important parameters in reoxygenation studies in superficial waters. In this context, the aim of this work was to study the influence of bed roughness of a channel on the superficial reaeration coefficient, under laboratory conditions. Besides the roughness, the conditions of mean velocity of the flow and depth of water were varied. The variation of roughness was done with implementation of obstacles with known geometry, arranged transversely to the flow direction, and called macro-roughness. The results have shown evidences that the surface reaeration coefficient is controlled significantly by the roughness of the channel bed. Two mathematical models of semi-empirical origin for the \'K IND.2\' prevision were developed, which incorporate hydrodynamic and geometric variables considered relevant in the process of mass transfer in air-water interface.

O trabalho apresenta uma investigação sobre a influência da umidade atmosférica no processo de absorção de oxigênio atmosférico por corpo de água através de sua superfície líquida livre. Os experimentos realizados em laboratório consistem na reoxigenação de uma massa de água, contida em um tanque cilíndrico, submetida à agitação mecânica. A atmosfera que reabastece de oxigênio a massa líquida é controlada e os ensaios são conduzidos com vários níveis de umidade do ar, o que provoca diferentes taxas de evaporação. Simultaneamente, determinam-se os coeficientes de reoxigenação, K2 (h-1), em cada experimento. Investiga-se neste trabalho a correlação entre esses dois parâmetros. O processo de reoxigenação é analisado inicialmente com o uso de metodologia clássica baseada em modelos matemáticos tradicionais (possivelmente inadequados). Propõe-se neste trabalho, um modelo original para essa mesma análise. / The influence of the atmospheric humidity on the process of absorption of oxygen by a water body through its free surface is presented herein. Laboratory experiments were run for the reoxygenation of a water mass kept in a cylindrical vessel under mechanical agitation. The quality of the atmospheric air transferring oxygen to water is controlled and the tests are run with several levels of air humidity, what renders different rates of evaporation. The corresponding coefficients of reaeration K2 (h-1) are determined for each experiment. The correlation between these two latter parameters is investigated. The process of reoxygenation is analyzed initially using a classical methodology based on traditional mathematical models (possibly inadequate). An original model for the same analysis is proposed in this work.

O parâmetro que determina o processo de transferência de oxigênio através da interface ar-água em escoamentos com superficie livre é o coeficiente de reaeração superficial, \'K IND.2\'. Existe um grande número de equações na literatura científica que realizam a previsão do coeficiente de reaeração, no entanto, a maioria dessas equações considera apenas algumas características hidráulicas do corpo de água como a velocidade e a profundidade, e ainda, como em sua maioria são de natureza empírica, acabam sendo adequadas para corpos de água específicos. Além destes dois parâmetros (velocidade e profundidade do escoamento), existem outros doze que são considerados importantes para estudos de reoxigenação em águas superficiais. É neste contexto que o objetivo deste trabalho foi estudar em condições de laboratório a influência da rugosidade do leito de um canal sobre o coeficiente de reaeração superficial. Além da rugosidade, foram variadas as condições de velocidade média do escoamento e profundidade da lâmina de água. A variação da rugosidade foi realizada através da implementação de obstáculos com geometria conhecida, dispostos transversalmente ao escoamento, e denominados como macro-rugosidades. Os resultados demonstraram evidências de que o coeficiente de reaeração superficial é controlado de forma significativa pela rugosidade do leito do canal. Foram desenvolvidos dois modelos matemáticos de natureza semi-empírica para a previsão do \'K IND.2\', os quais incorporam variáveis hidrodinâmicas e geométricas consideradas relevantes para o processo de transferência de massa na interface ar-água. / The parameter that determines the process of oxygen transfer through the air-water interface in flows with free surface is the superficial reaeration coefficient, \'K IND.2\'. There are a large quantity of equations in the cientific literature that perform the prevision of the reaeration coefficient; however, most of them consider only some of the hydraulic characteristics of water body; for example, the velocity and the depth. Most of these equations have empirical origin and are adequate just for a specific water body. In addition to these two parameters (velocity and depth of flow), there are another twelve important parameters in reoxygenation studies in superficial waters. In this context, the aim of this work was to study the influence of bed roughness of a channel on the superficial reaeration coefficient, under laboratory conditions. Besides the roughness, the conditions of mean velocity of the flow and depth of water were varied. The variation of roughness was done with implementation of obstacles with known geometry, arranged transversely to the flow direction, and called macro-roughness. The results have shown evidences that the surface reaeration coefficient is controlled significantly by the roughness of the channel bed. Two mathematical models of semi-empirical origin for the \'K IND.2\' prevision were developed, which incorporate hydrodynamic and geometric variables considered relevant in the process of mass transfer in air-water interface.