The Southern Ocean is an important region for the sequestration of heat, carbon dioxide and other tracers. The Southern Ocean circulation is typically described in a circumpolarly averaged sense as a Meridional Overturning Circulation (MOC), but the detailed 3-D pathways that make up this circulation remain poorly understood. We use Lagrangian particle trajectories, obtained from eddy permitting numerical models, to map out and quantify different aspects of the 3-D circulation. We first introduce various definitions used to quantify efficient export from the Antarctic Circumpolar Current (ACC) to the subtropical gyres. Using these definitions, we show that the permanent northward export varies by water mass and occurs in localised regions; with 11 key pathways identified. We then examine the dynamics setting the location and efficiency of the identified pathways, which includes the investigation of the role of diapycnal mixing and the impact of short and long time variability in the flow. Although we show that the flow of particles in the 3-D model is predominantly isopycnal, we find that particles that are forced to remain on isopycnals lead to approx. 60% lower export (mainly via three pathways) than identical releases where the diapycnal component of advection is included. Enhanced upward mixing near rough topography, and downward mixing in the southeast Pacific, were shown to be mostly responsible for the export. In addition, we show that most of the export pathways are mainly influenced by timescales from 90 days to 20 years, which suggests that mesoscale eddies are not the leading-order importance in the northward export from the ACC to the subtropical gyres. However, we also find that mesoscale eddies and the mean-ACC flow play a significant role in setting the export from the ACC in some pathways. These results highlight the role of temporal variability and vertical transport in enhancing the northward flow from the ACC by allowing transport across barotropic streamlines and onto more efficiently exporting isopycnals. In addition, the asymmetrical response of the studied quantities emphasises the importance of the three dimensions in understanding the dynamics driving the overturning circulation. We also demonstrated that the annually repeating velocity fields, which are commonly used for trajectory calculations, increase the diapycnal transport of particles and as a consequence, increase the overall 20-year northward export from the ACC by approx. 10%. In the study of the meridional overturning circulation, we diagnose the geographical distribution of the streamwise averaged diffusivity calculated from meridional displacements of the Lagrangian particles. We examine streamwise averaging using both latitude and equivalent latitude and argue that the latter gives a more useful measure. Reconciling tracer and particle horizontal diffusivities, we show that in the ACC, the average diffusivity peaks between 1500m and 2500m with an average value of 1500 m$^{2}$/s and that it is highest near the topographic features. We compare the exact diffusivity and its approximation to show that an assumption of time homogeneity does not hold and therefore that standard expressions for diffusivity that assume time homogeneity are of limited usefulness. Finally, we use the calculated trajectories to provide a streamwise averaged 2-D advection-diffusion model of the Southern Ocean MOC and then examine the extent to which this 2-D model can capture the overall effect of the actual 3-D transport.

Abstract The purpose of this research is to investigate the ocean¡¦s sustainable uses and explore new development potentials for the Taiwanese fishing industry. In addition, several possible options are proposed, while the strategies for the operability and development of the Southern Ocean Park are discussed. Furthermore, analyses of the operations at the Little Ryukyu Demo Region, the preliminary demonstration site for the Southern Ocean Park, are performed and assessed. This research begins by analyzing the oceanic industries both in Taiwan and around the world, and then continues to examine ocean maricultures and aqua-farms. Legal regulations pertaining to the fishing industries are also investigated to assess the future and the potential of the Southern Ocean Park. The research draws the following key conclusions: 1. The ocean provides an important basis of development for Taiwan in its expansion of land use. 2. Current development of ocean use and relevant industries around the world are already showing progressive trends in a diversity of industries and fronts. 3. The Southern Ocean Park utilizes netted marine aqua-farms as a main developmental focus. However, opportunities to continue development in various oceanic industries in the future are greatly desired. 4. The netted marine aqua-farms are suitable for the growth of Taiwanese fishing industry, but are faced with the following issues: (1.) The degree of ocean pollution, although less than land-based mari-cultures and fisheries, are still an important and a necessary issue to address. Improvements to farming and feeding technologies will be required to reduce the environmental impact. (2.) The legal use of oceanic territories, especially pertaining to the regulation and security of netted marine aqua-farms, still await numerous bills to be passed. (3.) Faced with competition from other countries, a lack of immediate effort in Taiwan may result in losing the benefits and advantages of the netted marine aqua-farms. 5. The legal proceedings for the Southern Ocean Park have been categorized as part of the legislative group under the Ocean Administration Development Committee of the Executive Yuan. 6. The following presents key strategies in the development of the Southern Ocean Park: (1.) With the success of the Ryukyu Demo Region, the development can then be extended to other oceanic territories. The acquisition of such experience can serve to maximize the success rate of future, large-scale oceanic developments in other regions. (2.) Prime promoters of the Southern Ocean Park should persuade the higher-level government offices to draw attention and focus for the development of sustainable use of the environment and the bigger picture, rather than a singular development meant only for the fishing industries. This is the only way to acquire more resources and support from other offices and committees. (3.) After President Chen declared an increased effort to elevate oceanic industries in the south, the Southern Ocean Park has declined over time to its current status as an unimportant pending policy. Committed individuals must join forces with the legislative and scholar branches to apply continuous pressure on the Fishing Administration Department. This is the only way to successful stimulate proper development in the fishing industry. (4.) The Ryukyu Demo Region and other future regions should collect the local resources, especially those pertaining to tourism, and progress toward joint-industry developments. Consequently, the local communities will generate greater support, and bigger economic growth can then be expected.

This dissertation discusses a linkage between the Southern Ocean (SO) winds and the global ocean circulation in the framework of a coarse-resolution global ocean general circulation model coupled to a sea-ice model. In addition to reexamination of the conventional linkage that begins with northward Ekman transport and extends to the North Atlantic (NA) overturning, the author investigates a new linkage that begins with the Southern Hemisphere (SH) sea-ice – ocean interaction perturbed by the anomalous SO winds and extends to the SH overturning, the response of the NA overturning, and the long-term baroclinic adjustment of the Antarctic Circumpolar Current (ACC). How the above two linkages will interact with each other in a warming world is also investigated. An interactive momentum flux forcing, allowing for the strength of momentum flux between atmosphere and sea ice to vary in response to the simulated sea-ice conditions, enhances wind-driven ice divergence to increase the fraction of leads and polynyas, which increases dense water formation, and thus intensifies convection. Within three experimental frameworks, this increased dense water consistently increases the Antarctic Bottom Water formation, which directly intensifies the SH overturning and indirectly weakens the NA overturning. As a result of the hemispheric change in overturning circulations, the meridional density gradient across the ACC appears to increase, ultimately increasing the baroclinic part of the ACC via an enhanced thermal wind shear. Subsequently, impacts of the poleward shifted and intensified SH subpolar westerly winds (SWWs) on the global ocean circulation are investigated in phases. When the SWWs are only shifted poleward, the effect of the anomalous winds is transmitted to the northern NA, decreasing both the NA overturning and the North Atlantic Deep Water (NADW) outflow. However, when the SWWs are shifted poleward and intensified, this effect is cut off by the intensified Deacon cell overturning, and is not transmitted to the northern NA, and instead increases the NADW outflow substantially. To sum up, with respect to the SO winds perturbed by the global warming, the SH overturning cell and the NADW outflow increase, leading to an increase in the volume transport of the ACC.

Bacteria are mediators of biogeochemical cycles and are in this way vital for maintaining life on earth. Their distribution, abundance and functioning are driven by environmental heterogeneity and dynamic change in abiotic and biotic factors. Both, freshwater lakes and oceans play central roles in the global carbon cycle and bacteria in these systems perform many services for the ecosystems, such as the transfer of organic carbon from primary producers to higher trophic levels. With estimated relative abundances up to 50% of the total bacterioplankton, the Alphaproteobacteria lineage SAR11 is the most abundant group of aquatic bacteria. It is globally distributed and can be partitioned into multiple sub-clades, one of which is exclusive to freshwaters. Until recently, the distribution, abundance and ecological role of this freshwater SAR11 named LD12 was unknown. The aim of the thesis was to study the drivers and mechanisms that influence the dynamics of aquatic bacterial communities in general and the SAR11 and LD12 groups in particular. The thesis consists of environmental surveys of a mesotrophic Lake Erken and the western Southern Ocean, an experiment and a data-mining exercise to reveal the phylogenetic structure of the SAR11 lineage on various temporal and spatial scales. The analysis of a long-term bacterioplankton community survey in lake Erken provided insights about the dynamics of the entire bacterial community and the LD12 population over an annual cycle. The results demonstrate that LD12 can be an equally abundant member of freshwater communities as marine SAR11 in oceans. LD12 featured strong seasonality and was positively coupled to environmental conditions indicative for an oligotrophic lifestyle. LD12 as well as other dominant lake bacterioplankton also maintained stable populations throughout spatial and temporal varying environments, but at high phylogenetic resolution, habitat preferences were revealed, particularly in response to oxygen concentrations. The later was not the case in LD12 as a single ribotype dominated. This is in stark contrast to the habitat partitioning with light availability, depth and water masses observed for marine SAR11 subclades in the Southern Ocean. The global data-mining corroborated that LD12 as a group was much less diverse than SAR11 furthermore, suggesting that the marine-freshwater barrier acted as a population bottleneck. My work shows that bacterial populations can respond in very different ways to environmental drivers, highlight the importance of highly resolved temporal and spatial scales as well as the need for high phylogenetic resolutions to target ecologically coherent populations.

The ocean is the largest sink of anthropogenic carbon from the atmosphere and therefore the magnitude of ocean carbon uptake largely determines the airborne fraction of emissions and the ultimate severity of surface climate change. However, climate-feedbacks on ocean carbon uptake over the historical period and in the future are uncertain. In particular, much uncertainty in the ocean carbon response hinges on the influence of wind-driven changes in the Southern Ocean, which is the most significant region of anthropogenic carbon uptake. Here I show that the Southern Hemisphere westerly winds simulated by the Coupled Model Intercomparison Project Phase 3 (CMIP3) and CMIP5 climate models have significant biases in their pre-industrial and satellite era-climatologies, relative to observationally based estimates. I also show that the models project the westerlies to intensify and shift poleward under anthropogenic forcing over the 20th and 21st centuries, but that they significantly underestimate the trends over the satellite era. I then use a novel experimental design, wherein I isolate the influence of the models pre-industrial wind bias on simulations of ocean carbon uptake and climate. I do this by using the UVic Earth System Climate Model (ESCM) with an ensemble of members, each forced by the winds from an individual CMIP model. I show here that the climate model pre-industrial wind bias can significantly increase ocean carbon uptake in transient climate change simulations, reducing the airborne fraction and projected climate change. By contrast, the simulated wind-changes over the 20th and 21st centuries reduce ocean carbon uptake, largely through an increase in outgassing from the Southern Ocean. However, I show that this transient- wind effect is i) smaller than the pre-industrial bias effect and ii) does not occur when using a variable formulation for the Gent-McWilliams coefficient of eddy diffusivity in the coarse resolution model, under simulated or observed wind-changes. I then go on to demonstrate that the simulated transient wind-changes significantly reduce the Antarctic sea-ice area simulated by the UVic ESCM. I also test the influence of fresh water input to the Southern Ocean from dynamic Antarctic Ice Sheet mass loss, which is a forcing absent from the CMIP5 models. The magnitude of the fresh water effect is small and has little influence on the sea-ice area trends simulated by the CMIP5 models over the historical era. These results have significant implications for previous model-based studies of the ocean carbon cycle, as well as for the quantification of the wind-induced uncertainty in future climate projections by current Earth System Models. / Graduate / 0725 / 0425 / 0415

The ocean is the largest sink of anthropogenic carbon from the atmosphere and therefore the magnitude of ocean carbon uptake largely determines the airborne fraction of emissions and the ultimate severity of surface climate change. However, climate-feedbacks on ocean carbon uptake over the historical period and in the future are uncertain. In particular, much uncertainty in the ocean carbon response hinges on the influence of wind-driven changes in the Southern Ocean, which is the most significant region of anthropogenic carbon uptake. Here I show that the Southern Hemisphere westerly winds simulated by the Coupled Model Intercomparison Project Phase 3 (CMIP3) and CMIP5 climate models have significant biases in their pre-industrial and satellite era-climatologies, relative to observationally based estimates. I also show that the models project the westerlies to intensify and shift poleward under anthropogenic forcing over the 20th and 21st centuries, but that they significantly underestimate the trends over the satellite era. I then use a novel experimental design, wherein I isolate the influence of the model’s pre-industrial wind bias on simulations of ocean carbon uptake and climate. I do this by using the UVic Earth System Climate Model (ESCM) with an ensemble of members, each forced by the winds from an individual CMIP model. I show here that the climate model pre-industrial wind bias can significantly increase ocean carbon uptake in transient climate change simulations, reducing the airborne fraction and projected climate change. By contrast, the simulated wind-changes over the 20th and 21st centuries reduce ocean carbon uptake, largely through an increase in outgassing from the Southern Ocean. However, I show that this transient- wind effect is i) smaller than the pre-industrial bias effect and ii) does not occur when using a variable formulation for the Gent-McWilliams coefficient of eddy diffusivity in the coarse resolution model, under simulated or observed wind-changes. I then go on to demonstrate that the simulated transient wind-changes significantly reduce the Antarctic sea-ice area simulated by the UVic ESCM. I also test the influence of fresh water input to the Southern Ocean from dynamic Antarctic Ice Sheet mass loss, which is a forcing absent from the CMIP5 models. The magnitude of the fresh water effect is small and has little influence on the sea-ice area trends simulated by the CMIP5 models over the historical era. These results have significant implications for previous model-based studies of the ocean carbon cycle, as well as for the quantification of the wind-induced uncertainty in future climate projections by current Earth System Models. / Graduate / 0725 / 0425 / 0415

The Southern Ocean holds a unique place in our planet. It is home to the world’s longest and strongest ocean current, the Antarctic Circumpolar Current (or ACC), which is formed of jets (alternating velocity structures), thought to be significant surface transport barriers. The dynamical processes (particularly mixing processes) in the Southern Ocean are crucial to driving the global overturning circulation, which is in turn responsible for the global transport of heat, CO2, and nutrients. Despite the evident importance of the Southern Ocean to current and future climate, the important dynamical processes that occur there are poorly understood. This thesis attempts to contribute towards the understanding of some of the open questions in Southern Ocean dynamics. In particular, we investigate the effect that topography might have on the jets that form the ACC, with regards to their formation and in particular, their transport properties. Through a quasi-geostrophic model we investigate the properties of jets that form over a zonal slope in bottom topography, and find that the jets become tilted, aligning perpendicular to the large-scale barotropic potential vorticity gradient. As the jets tilt more, they become significantly more energetic, corresponding with an increase in across-jet transport. We compare various theories regarding the formation of such jets, involving linear analysis of the system. It is found that the analytical form of the Rossby wave frequencies correctly predicts the anisotropy of the energy spectra of simulations, and so the jet direction. Additionally, there is a need to characterise accurately the isopycnal mixing occurring throughout the Southern Ocean. We utilise satellite measurements to estimate isopycnal diffusivities in the Southern Ocean in two different studies. Using an effective diffusivity diagnostic to extend a previous study, we find reduced surface horizontal mixing at the latitudes of the ACC core. By comparing a tracer advection simulation with measurements from an experiment in the Southern Ocean, we find that simulations with a vertically averaged horizontal diffusivity of 20m2s−1 best match observations in the Pacific sector of the ACC.

The annual advance and retreat of sea ice in the Southern Ocean is recognised as one of the largest seasonal events on Earth. Such considerable physical changes have profound effects on the vertical structure of the water column, and hence controls the availability of both light and nutrients to phytoplankton. This means that in the region seasonally covered by sea ice (the SSIZ), the timing of the growth and decline (phenology) of phytoplankton is determined to a large degree by the dynamic interactions between ice, ocean and atmosphere. However, this region is simultaneously one of the most poorly observed in the global ocean, and one of the most complex. This has led to significant gaps in our understanding of how sea ice modulates the exchanges of heat and momentum between atmosphere and ocean, as well as the implications this has for phytoplankton phenology in the SSIZ. This study seeks to address these gaps by combining both model and observationallybased methods. The lack of observational data are directly tackled through an analysis of BGC-Argo float data sampling under ice. Such data reveal high growth rates in the presence of near full ice cover and deep mixed layers, conditions previously thought to prevent growth. These results suggest a revision of our current understanding of the drivers of under ice phytoplankton phenology, which should take into account the unique character of Antarctic sea ice and its effect on the under ice light environment. In addition, results obtained from several numerical process studies indicates that phytoplankton may have a higher affinity for low light conditions than previously thought. From a modelling perspective, an analysis and intercomparison of 11 Earth System Models (ESMs) and their representation of vertical mixing and phenology is presented. This revealed that misrepresentations in phenology where driven by model biases in sea ice cover and vertical mixing. That is, only models with either too much or too little ice cover were able to simulate phenology close to observations. Furthermore, a strong correlation between the location of the ice edge and the extent of vertical mixing suggested that ESMs overly dampen ocean-atmosphere fluxes as mediated by sea ice. This led to the development of a regional ocean-sea ice model of the Atlantic sector of the Southern Ocean, from which experiments enhancing both heat and momentum fluxes could be conducted. It was found that the model responded more uniformly to enhanced heat flux, generally deepening the mixed layer closer to observations in winter. On the other hand, the effects of enhanced momentum flux (implemented by increased air-ice drag) where more complex and spatially heterogeneous, with contrasting responses depending on the initial vertical density structure of the water column. Overall, the argument is made that the unique features of Antarctic sea ice should be included in models if we are to improve the representation of the SSIZ mixed layer, and hence phenology

Knowledge of iceberg location and size is important for safety reasons as well as for understanding many geophysical and biological processes. This dissertation analyzes large tabular icebergs in the Southern Ocean using the SeaWinds scatterometer. SeaWinds is a spaceborne radar designed to measure the microwave backscatter from the Earth's surface. Using resolution-enhancement techniques, backscatter measurements are processed into backscatter images in which icebergs can be observed. An iceberg detection methodology is formalized using daily scatterometer images. Radar profiles from common Antarctic scatterers are quantified and an iceberg detection methodology is formalized using daily scatterometer images. Iceberg positions are determined in real-time and a time-series of iceberg positions is maintained in an Antarctic iceberg database. Using the Antarctic iceberg database, characteristic iceberg motion trends are identified. Iceberg detection and tracking is demonstrated through real-time operational support of the 2005, 2008, and 2009 National Science Foundation Antarctic cruises. To supplement iceberg position reports, I develop multiple algorithms to estimate iceberg size and rotational orientation from backscatter images and from raw backscatter measurements. Estimates derived from SeaWinds images are found to be more accurate. Using iceberg size parameters in conjunction with Newton's equations of motion and forcing profiles (e.g., ocean and air currents), I also develop an iceberg motion model to predict the translational and rotational motion of large tabular icebergs. To improve model results, a Kalman filter is used to incorporate actual iceberg measurements into the motion model, and statistics from the Kalman filter are used to evaluate model performance. Simulated iceberg motion is found to best coincide with observed iceberg motion in regions where slower iceberg drift speeds are observed. The model is less accurate at high speeds. The iceberg motion model is inverted to produce estimates of ocean currents given observations of iceberg size and motion. Multiple ocean current estimates are combined using reconstruction techniques and compared with numerically-derived ocean currents from the Ocean Circulation and Climate Advanced Modeling (OCCAM) project. It is found that reconstructed ocean currents coincide with OCCAM currents in regions where observed iceberg motion is not extreme. Also, reconstructed ocean currents coincide more with OCCAM currents that have been averaged over multiple years than with monthly-reported values.

Neste trabalho a variabilidade climatica do oceano Austral e a ocorrencia da Onda Circumpolar Antartica (OCA) sao investigadas. Foram usados os dados de uma simulaçao do modelo numerico acoplado do Nacional Centre for Atmospheric Research/ Community System Model - NCAR CCSM de 150 anos, e um conjunto de dados climatologicos como base de comparaçao dos dados do modelo. estes foram obtidos da Re-analise do NCEP/NCAR (National Center for Envirommental Prediction) para o periodo de janeiro de 1948 a julho de 2002. Com o intuito de analisar o comportamento sazonal e anual foram analisadas as climatologias e utilizada a tecnica de analise harmonica das variaveis de temperatura da superficie do mar (TSM), pressao ao nivel do mar (PNM), componentes meridional (Vy) e zonal (Vx) do vento. Para analisar o comportamento interanual dessas variaveis sao utilizados diagramas Hovmoeller, espectros de potencia, alem de tecnicas estatisticas como Empirical Ortogonal Functions (EOF) e singular Value Decomposition (SVD). / In this study the climatic variability of the Southern ocean and the Antarctic Circumpolar Wave (ACW) are investigated. The National Center for Atmospheric Research/ Community System Model _ NCAR CCSM coupled model 150 years simulation data is compered with the climatology data from the Nacional Center for Envirommental Prediction - NCEP/NCAR Re-analysis, for a period from january/1948 until july/2002. Annual and seasonal climatology and harmonic analysis are used for the following variables: sea surface temperature (SST), sea level pressure (SLP), meridional and zonal wind. Hovmoeller diagrams, potencial spectra and statistics methods such as Empirical Ortogonal Functions (EOF) and Singular Value Decomposition (SVD) are used to analyze changes in interannual behavior of this variables.