Tesi: "Physical oceanography"

1

Buffett, Grant George. "Seismic Oceanography: A New Tool to Characterize Physical Oceanographic Structures and Processes." Doctoral thesis, Universitat de Barcelona, 2011. http://hdl.handle.net/10803/1939.

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Large scale global oceanic circulation redistributes heat and freshwater and therefore affects global climate. One of its main forcing mechanisms is, in addition to surface heat and freshwater fluxes, the diapycnal (across lines of equal density) mixing in the ocean interior. The energy needed to drive the mixing processes is mainly provided by tides and wind [Wunsch, 2002]. It is transformed into internal wave energy, cascading through a range of smaller scales leading finally into turbulence and molecular dissipation. Water masses in the ocean are stratified and often separated by relatively thin layers with strong gradients in temperature and/or salinity across which heat and mass transfer occur in order to maintain global circulation and stratification. However, these processes are difficult to observe in practice. Below a few meters, the ocean is opaque to light, and thus to direct optical observations of deep processes [Thorpe, 2005]. Therefore, the development of scientific methodologies and instruments to directly or indirectly measure processes in the ocean interior are of high importance to understanding those processes and their implications. The motivation behind this research is two-tier: 1) broadly, and academically, it is the scientific curiosity of understanding the ocean in order to better comprehend its role in the context of Earth systems; 2) expressly, the motivation is to develop the methodological toolset necessary to observe the ocean on a spatial and temporal scale not possible with traditional oceanographic techniques, thus allowing the foundation of more accurate models of ocean circulation and thereby, ocean-climate interactions. The toolset is emerging as a robust technique of physical oceanography known as 'seismic oceanography'. By definition, seismic oceanography is the application of multichannel seismic (MCS) reflection profiling to physical oceanography. This definition, however, could be subject to future revision and refinement because the development of seismic oceanography observational tools will inevitably lead to newer perspectives. The Mediterranean Outflow Water (henceforth, MOW) is a natural laboratory for seismic oceanography. The MOW was chosen to test seismic reflection in oceanography for three main reasons: 1) The strong oceanographic signature of the MOW. Due to the penetration of the MOW into the North Atlantic through the Strait of Gibraltar, strong characteristic contrasts in temperature (1.5 °C) and salinity (0.3 psu) and thus, density (0.4 kg/m3) are observed between the MOW and the surrounding Atlantic waters [Baringer and Price, 1997]. These contrasts in density (along with sound speed) are the contributing factors to reflection coefficient, making the identification of structures and processes possible. 2) The large variety of oceanographic and topographic features, such as a continental slope, undulating seafloor (including seamounts and basins) and mesoscale Mediterranean salt lenses (meddies). These structures and processes are believed to play an important role in maintaining the temperature and salinity distribution in the north Atlantic [Bower et. al., 1997]. 3) Finally, extensive archived data sets of bothoceanographic and seismic data place interpretive constraints on the data collected. Part I of this thesis consists of two peer-reviewed papers published by the author and coauthors (Chapters 1 and 2), one manuscript submitted for publication (Chapter 3) and two published peer-reviewed research letters that the author played a lesser role developing (Chapter 4). Part II of the thesis addresses the seismological (Chapter 5) and oceanographic backgrounds (Chapter 6) in the context of some of the structures and processes that are amenable to seismic ensonification. Part III consists of general discussions and conclusions (Chapter 7) and potential future research and development (Chapter 8). La motivació que hi ha al darrera d'aquest treball es pot separar en dos nivells: 1) En termes generals, i acadèmicament, és la curiositat purament científica d'estudiar l'oceà per tal de comprendre millor el seu paper en el context de les Ciències de la Terra; 2) Concretament, la motivació és desenvolupar les eines necessàries per a observar l'oceà a una escala espaial i temporal que no és possible amb les tècniques tradicionals oceanogràfiques, permetent així generar models més precisos de circulació oceànica i, per tant, de les interaccions oceà-clima. L'objectiu a curt i mitjà termini d'aquesta tesi és el desenvolupament de noves eines d'oceanografia física que proporcionin noves perspectives sobre la dinàmica oceànica. Aquest conjunt d'eines està emergint com una metodologia sòlida dins de l'oceanografia física coneguda com 'oceanografia sísmica'. Per definició, l'oceanografia sísmica és l'aplicació de la sísmica de reflexió multicanal (MCS) a l'oceanografia física. Aquesta definició, però, podria estar subjecte a una futura revisió i perfeccionament, ja que el desenvolupament d'eines d'oceanografia sísmica inevitablement donarà lloc a noves perspectives. La part principal d'aquesta tesi la constitueixen quatre articles, publicats per l'autor i co-autors al llarg del seu període d'investigació (capítols 1, 2 i 4); així com un article sotmès (Capítol 3). En la segona part, com a suport per als lectors no familiaritzats, s'aborden els antecedents sismològics (Capítol 5) i oceanogràfics (Capítol 6) en el context d'algunes de les estructures i processos que són susceptibles de ser identificats mitjançant la sísmica. Les conclusions generals es presenten en el Capítol 7 i en el Capítol 8 es donen algunes recomanacions per a futures investigacions i desenvolupaments (Part III). La tesi es complementa amb quatre apèndixs, on a banda d'un ampli resum en català (Apèndix I), hi ha els diagrames de flux utilitzats per l'autor en el processament de les dades sísmiques (Apèndix II), un conjunt de set desplegables de les seccions sísmiques en gran format (Apèndix III) i finalment un glossari de termes útils per ajudar als lectors no iniciats en qualsevol de les branques de la sismologia o l'oceanografia (Apèndix IV).

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2

Veilleux, Lorraine. "Physical oceanography of northern estuaries." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59830.

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Within the context of oceanographic research on northern estuaries in James Bay and Hudson Bay, and in relation with hydroelectric developments and their impact on the physical environment, two studies were undertaken. Both concern the importance of bottom topography, tidal motion and fresh water input on the estuarine processes in these areas. The first one, in Rupert Bay (south-eastern corner of James Bay), describes tidal and local wind effects on circulation and mixing patterns for summer conditions. An estimate of terms in the lateral momentum equation shows that the centrifugal acceleration, the Coriolis force and the baroclinic pressure gradient are the most important forces at a mid-bay cross section transect. The second study is concerned with the freshwater plume of Great Whale River (south-eastern Hudson Bay). CTD measurements were used to examine the lift-off point of the plume for under-ice and increasing discharge conditions. Comparison with existing models shows them to be inappropriate for under-ice conditions. Finally, the presence of supercooled water masses in the region of the study is reported.

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3

Mondello, Nicholas. "Physical oceanography off the South Coast of Western Australia." Thesis, Mondello, Nicholas (2017) Physical oceanography off the South Coast of Western Australia. Honours thesis, Murdoch University, 2017. https://researchrepository.murdoch.edu.au/id/eprint/40163/.

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Compared to neighbouring regions of ocean, the south coast of Western Australia (WA) has received relatively little scientific attention despite a range of Australian Commonwealth marine protected areas having been established in the region as of 2012. The ocean off the south coast of WA is characterised by a canyon-dense continental shelf edge including the Bremer Canyon, a shelf edge canyon of approximately 8 km width. There are also two main currents in the region, the eastward flowing Leeuwin Current (LC) situated above the continental shelf edge, and the westward flowing Flinders Current (FC) situated south of the continental shelf. The Blue-link Reanalysis (BRAN) ocean forecasting model simulates the currents, temperature and salinity around Australia at daily intervals from 1994 – 2016 with 1/10th degree resolution. It has been speculated that these currents may interact with the canyons along the shelf edge to induce oceanographic conditions conducive to increased pelagic productivity and ecological diversity. This study was a two-part investigation of the physical oceanography off the south coast of WA with a focus on shelf edge dynamics near Bremer Canyon. It involved the use of the (BRAN) model and in situ data including conductivity, temperature and depth (CTD) profiles during January 2017 and temperature logger measurements from near Bremer Canyon between 2015 and 2017. The BRAN outputs were in close agreement with previous studies of the LC and FC and showed that the mixed layer depth (MLD) was shallowest (<50 m) in summer and deepest in winter (>200 m), in sync with seasonal heat flux. The CTD results were within one SD of the average BRAN profiles and MLD results for January. The volume transport of the LC and strong westerly wind events were dominant drivers of the temperature variation along the shelf edge during autumn and winter of 2015 as the warm LC water was forced downwards. In spring and summer, the volume transport of the LC was lowest (1.6 Sv) and other factors became dominating drivers of the shelf edge temperature variation including eddy kinetics and canyon-related processes. The BRAN outputs effectively simulated the mesoscale features examined in this study including the volume transport of the LC, westerly wind forced response and the influence of mesoscale eddies. These processes have the potential to influence the pelagic ecology through vertical mixing and upwelling.

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4

Jarvis, Marley. "Physical Oceanography, Larval Dispersal, and Settlement Across Nearshore Fronts." Thesis, University of Oregon, 2015. http://hdl.handle.net/1794/18711.

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The larvae of coastal species interact with nearshore currents that are complex and can alter dispersal. I investigated two sites in southern Oregon with different nearshore hydrodynamics: the first site, Sunset Bay, is a small cove with a topographic front that extends across the mouth during upwelling-favorable winds. Using holey sock drogues at 1.5 m and 5.5 m depths and surface drifters at 10 cm depth, I found that, when the front was present, water at 1.5 m was retained within the bay whereas water was exchanged across the front at a depth of 5.5 m. Surface drifters indicated a surface convergence. Surface plankton tows on either side and within the frontal convergence (a shore-parallel foam line) found significantly higher concentrations of barnacle cyprids, crab megalopae and zoea, polychaete larvae, platyhelminthes juveniles, isopods, amphipods, harpacticoid copepods, and fish eggs. Crustacean nauplii (barnacle, euphausiid, and copepod) and calanoid copepods were not concentrated in the convergence, and when the front and foam line were absent, no taxa were concentrated. Plankton tows taken within the foam line as it dissipated shoreward during a wind-reversal event found that concentrations of cyprids, megalopae, and gastropod veligers remained high as the foam line moved, suggesting that it acts as a moving convergence propagating competent larvae shoreward. I measured settlement of two taxa at Sunset Bay and Shore Acres, an open-coast site <2 km away. Barnacle settlement measured every other day from June-September 2013 was significantly cross-correlated with the maximum daily tidal height at lags of -2 days at Sunset Bay and +2 and +4 days at Shore Acres. Settlement was also significantly negatively cross-correlated with wave height at a lag of -4 days at Sunset Bay. Coralline algae settlement measured during eight 48-hr periods in July-August 2013 was significantly negatively correlated with wave height (n = 8, R2 = 0.76, P = 0.0049) at Shore Acres but not at Sunset Bay. Despite the close proximity of the Sunset Bay and Shore Acres sites, settlement patterns differed between taxa, suggesting that differences in nearshore hydrodynamics might affect the supply of water and larvae to shore. This dissertation includes unpublished co-authored material.

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5

Bâcle, Julie. "The physical oceanography of waters under the North Water Polynya /." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ64314.pdf.

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6

Le, Quéré Corinne. "Physical oceanography of the Baie des Chaleurs, Gulf of St. Lawrence." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=56761.

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Time series of temperature and salinity from current meters moored in 1988 and 1990 along the north shore of Baie des Chaleurs were analyzed to characterize the frequency of upwelling events. Upwelling was found to propagate cyclonically with speeds of 40 to 85 km per day. Moderate correlations between $ sigma sb{ rm t}$ and zonal wind stress were found. The interaction of buoyancy, topography, and oscillating wind stress simulated the upwelling in a reduced gravity model. The dominant frequencies of the upwelling events were approximately 4.5 to 10 days. Three water masses, one between the surface and the thermocline, one straddling the thermocline, and one at the bottom, were found to describe nicely the TS properties of the water column, as observed from the 1991 CTD data. The observed circulation, from August to October 1990, was cyclonic, with baroclinicity observed in the bottom two layers, and at two stations in the top layers.

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7

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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8

Addison, Victor G. "The physical oceanography of the northern Baffin Bay-Nares Strait region." Thesis, Monterey, California. Naval Postgraduate School, 1987. http://hdl.handle.net/10945/22417.

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Approved for public release; distribution is unlimited A dense network of conductivity-temperature-depth measurements was conducted from Baffin Bay northward to 82 deg 09 min N at the entrance to the Lincoln Sea, in the most comprehensive physical oceanographic survey ever performed in the northern Baffin Bay-Nares Strait region. These data indicate Nares Strait Atlantic Intermediate Water and Arctic Basin Polar Water to be derived from Arctic Basin waters via the Canadian Archipelago, whereas the West Greenland Current (WGC) is the source of the comparatively dilute West Greenland Current Atlantic Intermediate Water and West Greenland Current Polar Water fractions. Baffin Bay Surface Water is found seasonally throughout northern Baffin Bay. Recurvature of component branches of the WGC, which attains a maximum baroclinic transport of 0.7 Sv, occurs primarily in Melville Bay (0.2 Sv), south of the Carey Islands (0.1 Sv) and ultimately in Smith Sound (0.2 Sv). The Baffin Current originates as an ice-edge jet in Smith Sound and is augmented by net outflow from Smith, Jones and Lancaster Sounds at rates of 0.3 Sv, 0.3 Sv and 1.1 Sv, respectively. Circulation in Smith, Jones and Lancaster Sounds can be described in terms of the Geostrophic Estuarine Circulation Model. The North Water is caused by the combined influences of near-surface layer enthalpy and mechanical ice removal. KeywordsL Sea water temperature; Oceanographic data; Straits; Sounds(Waterways); Ocean currents

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9

Collins, Charine. "The dynamics and physical processes of the Comoros Basin." Doctoral thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/6467.

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Includes abstract. Includes bibliographical references. The main objective of this thesis was to investigate the circulation in the ComorosBasin using observed and model datasets. These data were used to establish whether or not a Comoros Gyre exists and to investigate the nature of the eddy variability in the basin.The water masses in the Comoros Basin emulate those found further south in the Mozambique Channel. The presence of AAIW north of Madagascar confirmed that this water mass enters the Comoros Basin from the east while the presence of North Atlantic Deep Water showed that this water mass is capable of spreading northward over the Davie Ridge. The main currents in the Comoros Basin, the westward flowing NEMC and a poleward current along the western boundary, are under the influence of the monsoon winds. The NEMC intensifies during the Southwest monsoon in response to a strong wind jet which develops off the northern tip of Madagascar, whereas the poleward current weakens due to the opposing force imposed by the southwesterlies. Additionally, the circulation in the basin consist of meso-scale eddies of both polarities. Anti-cyclonic eddies, with lifespans of

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10

Barnes, Brian Burnel. "The Combined Effects of Light and Temperature on Coral Bleaching| A Case Study of the Florida Reef Tract Using Satellite Data." Thesis, University of South Florida, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3604824.

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Coral reefs are greatly impacted by the physical characteristics of the water surrounding them. Incidence and severity of mass coral bleaching and mortality events are increasing worldwide due primarily to increased water temperature, but also in response to other stressors. This decline in reef health demands clearer understanding of the compounding effects of multiple stressors, as well as widespread assessment of coral reef health in near-real time. Satellites offer a means by which some of the physical stressors on coral reefs can be measured. The synoptic spatial coverage and high repeat sampling frequency of such instruments allow for a quantity of data unattainable by in situ measurements. Unfortunately, errors in cloudmasking algorithms contaminate satellite derived sea surface temperature (SST) measurements, especially during anomalously cold events. Similarly, benthic interference of satellite-derived reflectance signals has resulted in large errors in derivations of water quality or clarity in coral reef environments. This work provides solutions to these issues for the coral reef environments of the Florida Keys. Specifically, improved SST cloudmasking algorithms were developed for both Advanced Very High Resolution Radiometer (AVHRR; Appendix A) and Moderate Resolution Imaging Spectroradiometer (MODIS) data (Appendix B). Both of these improved algorithms were used to reveal the extent and severity of a January 2010 cold event that resulted in widespread mortality of Florida Keys corals. Applied to SST data from 2010, the improved MODIS cloudmasking algorithm also showed improved quantity of SST retrievals with minimal sacrifice in data quality. Two separate algorithms to derive water clarity from MODIS measurements of optically shallow waters were developed and validated, one focusing on the diffuse downwelling attenuation coefficient (Kd, m-1 ) in visible bands (Appendix C), the other on Kd in the ultraviolet (Appendix D). The former utilized a semi-analytical approach to remove bottom influence, modified from an existing algorithm. The latter relied on empirical relationships between an extensive in situ training dataset and variations in MODIS-derived spectral shape, determined using a stepwise principal components regression. Both of these algorithms showed satisfactory validation statistics, and were used to elucidate spatiotemporal patterns of water clarity in the Florida Keys. Finally, an approach was developed to use Landsat data to detect concurrent MODIS-derived reflectance anomalies with over 90% accuracy (Appendix E). Application of this approach to historical Landsat data allowed for long-term, synoptic assessment of the water environment of the Florida Keys ecosystem. Using this approach, shifts in seagrass density, turbidity increases, black water events, and phytoplankton blooms were detected using Landsat data and corroborated with known environmental events. Many of these satellite data products were combined with in situ reports of coral bleaching to determine the specific environmental parameters individually and synergistically contributing to coral bleaching. As such, SST and visible light penetration were found to be parsimoniously explaining variance in bleaching intensity, as were the interactions between SST, wind and UV penetration. These relationships were subsequently used to create a predictive model for coral bleaching via canonical analysis of principal coordinates. Leave-one-out-cross-validation indicated that this model predicted `severe bleaching' and `no bleaching' conditions with 64% and 60% classification success, respectively, nearly 3 times greater than that predicted by chance. This model also showed improvement over similar models created using only temperature data, further indicating that satellite assessment of coral bleaching based only on SST data can be improved with other environmental data. Future work should further supplement the environmental parameters considered in this research with databases of other coral stressors, as well as improved quantification of the temperature at the depth of corals, in order to gain a more complete understanding of coral bleaching in response to environmental stress. Overall, this dissertation presents five new algorithms to the field of satellite oceanography research. Although validated primarily in the Florida Keys region, most of these algorithms should be directly applicable for use in other coastal environments. Identification of the specific environmental factors contributing to coral bleaching enhances understanding of the interplay between multiple causes of reef decline, while the predictive model for coral bleaching may provide researchers and managers with widespread, near real-time assessments of coral reef health.

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11

Bardin, Ann Marie. "Novel Analysis Tools for Ocean Biogeochemical Models." Thesis, University of California, Irvine, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3646712.

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Ocean general circulation models of the IPCC class have biases even when simulating present-day conditions, which may bring into question their predictions of future conditions. This dissertation is about tools for, and results from assessing biases in the Community Earth System Model (CESM) ocean component, by itself and when combined with the Biological Ecosystem Cycling (BEC) model. Newly developed tools and their applications are listed. 1. An offline matrix tracer transport model for the ocean component of CESM. 2. A fast Newton-Krylov implicit tracer equilibrium solver for both the annually-averaged and the seasonally-varying circulation. 3. An effective preconditioner for the solver simulating radiocarbon. Application results: For a natural radiocarbon simulation, an equilibrium solution was obtained in 23 model-years, a dramatic decrease from the 4000 model-years reported for time-stepping. The modeled circulation in the deep Pacific Ocean produced radiocarbon ages twice those of observations. 4. A capability for computing the surface origin of water mass fractions as well as the age of the various water masses. Application results: The North Atlantic was the major supplier of ventilated water to not only the Atlantic, but also the Pacific and Indian Oceans. A lack of formation of bottom water in the Southern Ocean was discovered. 5. A capability for restricting the tracer simulation domain to a limited region of the ocean while retaining the effectiveness of advection and diffusion fields on the boundary. This reduces computational costs and allows separating local versus remote impacts of tracer sources on the biogeochemical tracer concentrations. This capability has the potential to provide a platform for further biogeochemical studies. Application results: The Indian Ocean region was isolated. Global versus regional circulation effects were determined using radiocarbon. Most of the bias within the region was eliminated by using observational, rather than globally calculated values, on the boundaries. Oxygen production and consumption from a CMIP5 BEC simulation were used to drive a regional oxygen model. Boundary values of oxygen from the CMIP5 BEC simulation were replaced with observations, resulting in less bias within the region. However, significant bias in the location of the Arabian Sea oxygen minimum zone remained.

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12

Kumar, Vijay. "Modelling the physico-biological processes of eastern Arabian sea." Thesis, IIT Delhi, 2016. http://localhost:8080/xmlui/handle/12345678/7093.

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13

Vianello, Patrick Angus. "A qualitative and physical analysis of processes around the Mascarene plateau." Doctoral thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/16940.

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Includes bibliographical references The Mascarene Plateau is a submerged volcanic plateau to the east of Madagascar which extends over 2200 km between the Seychelles and Mauritius. It is a complex feature, which is composed of 4 banks separated by 3 channels - namely the Seychelles, Saya de Malha, Nazareth and Cargados-Carajos Banks. The main objective of this thesis is to analyze cruise data obtained during the October/November 2008 ASCLME (Agulhas Somali Current Large Marine Ecosystem) cruise on board the Dr Fridtjof Nansen which surveyed the region around the Mascarene Plateau. Due to the paucity of data in the region, the cruise was a routine cruise with no specific scientific questions to be answered. A comparison is also made between sea surface temperature (SST) and Acoustic Doppler Current Profiler (ADCP) derived currents on board to satellite estimate to possibly extend cruise results in space and time. Although the resolution of satellite estimate is low compared to cruise measurements, satellite estimate of geostrophic velocities and sea surface temperatures compare well with cruise data and can therefore be used in the region with confidence. This is invaluable since the Mascarene Plateau is relatively poorly understood and it allows us to link cruise data with Rossby waves and currents impacting the region. This is the second cruise in the region as there was a research cruise on board the RRS Charles Darwin during June/July 2002. However, the June/July 2002 cruise did not sample the banks of the Mascarene Plateau.

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14

Navarro-Perez, Eleuteria. "Physical oceanography of the Canary current : short term, seasonal and interannual variability." Thesis, Bangor University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318561.

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15

Murton, Gary John. "Wave overtopping : a comparison of physical and numerical studies." Thesis, University of Plymouth, 1991. http://hdl.handle.net/10026.1/2361.

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The overtopping of low-crested breakwater is investigated by means of hydraulic and mathematical models. A conventional laboratory wavemaker with a wedge-type paddle is converted into an absorbing wavemaker so that it can be used to investigate accurately wave overtopping of reflective coastal structures. The absorption system is achieved by use of a feedback loop added to the control circuit. The design criteria and implementation of the circuit are presented in detail. Enhanced control software is used to generate different 'random' sea states with the same statistical properties. The absorption system is validated by an extensive series of tests made possible by the development of automated data acquisition and analysis software. Particular attention is given to the derivation of incident and reflected wave spectra. The results show over 90% success in reducing reflected waves. It is also possible to establish stable standing wave patterns over a wide frequency range. The results show significant improvement over similar existing wavemakers and in effect create an open-ended channel in the sense that the test structure hardly influences incident wave conditions. A closely controlled series of overtopping tests was carried out using the absorption system to prevent any re-reflections. Equipment and software were designed to quantify the overtopping rates for the structures used. The design and implementation of all aspects of the tests is fully described. Overtopping tests were carried out on breakwaters with smooth 1: 1 and 1: 2 seaward slopes. The results are tabulated and plotted in a dimensionless form which permits comparison with earlier work carried out at Hydraulics Research Ltd. The range of available data is extended and the new data for fully-developed sea states shown to be compatible with a linear extrapolation of the earlier results. It is believed that the earlier results were obtained using fully developed sea states but this is not known for certain. The importance of rigorously defining and publishing both test conditions and analysis techniques is highlighted. In the numerical study the 1-D mass and continuity equations were solved by a hybrid finite element/finite difference scheme. Whilst a good comparison is achieved between the physical and numerical tests for breakwater slopes of 1: 2 and less, realistic results are not achieved for steeper slopes. The reasons for this are discussed and the results presented. Both sets of model tests add valuable data to an area presently lacking detailed information.

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Qin, Qubin. "Impacts of Physical Transport on Estuarine Phytoplankton Dynamics and Harmful Algal Blooms." W&M ScholarWorks, 2019. https://scholarworks.wm.edu/etd/1550153910.

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The spatial and temporal variability of phytoplankton biomass in estuaries is determined by both local processes and transport processes. Local processes include biological processes (e.g., photosynthesis, respiration/excretion, and grazing) and settling, whereas transport processes include advective and diffusive transports. Transport processes have been demonstrated to regulate phytoplankton dynamics significantly by distributing both phytoplankton and other dissolved and particulate substances (e.g., nutrients, salts, sediments, and chromophoric dissolved organic matter). Yet, these transport properties lack a framework that unifies the pieced description of their various effects, and quantification of their importance under various environmental conditions. This dissertation highlights the role of horizontal transport processes on phytoplankton dynamics in estuaries, including the initiation of harmful algal blooms (HABs). in Chapter 2, the flushing effect of transport processes and its interaction with local processes are exclusively examined, and its relative importance on the variability of phytoplankton biomass is quantified and compared to that of the local processes over timescales from hours to years, using an introduced concept of transport rate that can be numerically computed. in Chapter 3, a simple yet inclusive mathematical model is developed to examine the temporal and spatial variabilities in phytoplankton biomass in response to the various effects of physical transport, under nutrient and light limiting conditions. For estuaries whose dominant nutrient loading is from river input, three basic patterns are revealed for the relationships between phytoplankton biomass and flushing time under various environmental conditions. in Chapters 4 and 5, the flushing effect of transport processes on the initiation of harmful algal blooms (HABs) in estuaries is investigated, which is then applied to examine the location and timing of the initiation of an annual Cochlodinium (recently renamed Margalefidinium) polykrikoides bloom in the lower James River. Theoretical analysis shows that the flushing is the key factor that affects HAB initiation in multiple interconnected systems, and a relatively long period of time (weeks) is required for a successful bloom. A HAB tends to be observed first in locations with relatively long residence time, such as tributaries or areas with large eddies. Multiple unconnected originating locations can co-exist within an estuary that highly depends on hydrodynamics and salinity. A numerical module for C. polykrikoides bloom is developed and built into a 3D numerical model - EFDC, which considers the competitive advantages of C. polykrikoides such as mixotrophic growth, swimming, grazing suppression, and resting cyst germination. Numerical model results show that the flushing effect determines the origins of C. polykrikoides blooms in the lower James River, and the sub-tributary of Lafayette River, which is characterized by relatively long residence time, is favorable for the first bloom to occur, regardless of the cyst distribution. A further investigation of various environmental conditions for the C. polykrikoides bloom reveals that temperature and physical transport control the interannual variability in the timing of its initiation, and individual perturbations by southerly wind, heavy rainfall, and spring tide can cause strong flushing capable of interrupting, or even terminating, initiation of a HAB event in the lower James River.

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17

Arfeuille, Gilles. "Modelling the interannual variability of the Arctic sea ice cover." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21505.

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A thermodynamic-dynamic sea ice model based on the granular material rheology of Tremblay and Mysak is used to study the interannual variability of the Arctic sea ice cover during the 41-year period 1958--1998. The sea ice model is coupled to both a mixed layer ocean model and a one-layer thermodynamic atmospheric model. The model is first run with monthly climatology for most of the thermodynamic and dynamic forcing components to obtain a stable periodic seasonal cycle. For the 41-year run, the monthly wind stress forcing is derived from analyzed sea level pressures from the National Centers for Environmental Prediction (NCEP Reanalysis) data. The atmospheric thermodynamic forcings are based on monthly climatology. In this thesis we explore the high-latitude sea ice circulation and thickness changes due to year-to-year variations in the wind field. We focus our study on the interannual variability of the sea ice. volume in the Arctic Basin, and the subsequent changes in the export of sea ice from the Arctic Basin into the northern North Atlantic via Fram Strait. (Abstract shortened by UMI.)

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18

Yi, Dingrong 1969. "Singular value decomposition of Arctic Sea ice cover and overlying atmospheric circulation fluctuations." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=20610.

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Abstract (sommario):

The relationship between the Arctic and sub-Arctic sea-ice concentration (SIC) anomalies, particularly those associated with the Greenland and Labrador Seas' "Ice and Salinity Anomalies (ISAs)" occurring during the 1960s/1970s, 1970s/1980s, and 1980s/1990s, and the overlying atmospheric circulation (SLP) fluctuations is investigated using the Empirical Orthogonal Function (EOF) and Singular Value Decomposition (SVD) analysis methods. The data used are monthly SIC and SLP anomalies, which cover the Northern Hemisphere north of 450 and extend over the 38-year period 1954--1991. One goal of the thesis is to describe the spatial and temporal variability of SIC and atmospheric circulation on interannual and decadal timescales. Another goal is to investigate the nature and strength of the air-ice interactions. The air-ice interactions are investigated in detail in the first SVD mode of the coupled variability, which is characterized by decadal-to-interdecadal timescales. Subsequently, the nature and strength of the air-ice interactions are studied in the second SVD mode, which shows a long-term trend. The interactions in the third SVD mode which has an interannual timescale are briefly mentioned. (Abstract shortened by UMI.)

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19

Tamsitt, Veronica. "Aspects of the Three-Dimensionality of the Southern Ocean Overturning Circulation." Thesis, University of California, San Diego, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10748784.

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Abstract (sommario):

The circulation of the Southern Ocean is unique due to the lack of meridional boundaries at the latitudes of Drake Passage. Westerly winds drive the Antarctic Circumpolar Current (ACC), linking the major ocean basins and facilitating inter-basin exchange of properties. Additionally, the steeply tilted isopycnals in the Southern Ocean allow interaction between the deep ocean and the atmosphere, and as a result the Southern Ocean has an outsized contribution to the global uptake and redistribution of heat, carbon and nutrients. Complex topography and eddies make this circulation fundamentally three-dimensional, but many features and associated mechanisms of this three-dimensional circulation are not well understood. The objective of this thesis is to use the 1/6°, data-assimilating Southern Ocean State Estimate (SOSE), along with other high-resolution ocean models and available observations, to describe aspects of the three-dimensional structure of the upper cell of the Southern Ocean overturning circulation. First, we diagnose the upper ocean heat budget in the Southern Ocean (Chapter 2), and determine that a strong zonal asymmetry in the air-sea heat flux over the Southern Ocean is associated with large-scale meander the ACC mean path and associated asymmetry in geostrophic heat advection. Second, we use Lagrangian particle release experiments to show, for the first time, the full three-dimensional upwelling pathways of deep water from 30°S to the surface of the Southern Ocean (Chapter 3). We find that deep water moves south in narrow paths along the western and eastern boundaries of each ocean basin, then within the ACC upwelling is concentrated at hotspots associated with high eddy activity at major topographic features. Next, we quantify the water mass transformation along the upwelling pathways from Chapter 3, and find that although the upwelling in the ocean interior is largely along isopycnals, there is significant transformation just below the mixed layer and homogenization of deep water mass properties due to isopycnal mixing (Chapter 4). Finally, we highlight a newly identified poleward pathway of deep water along the eastern boundary of the Indian Ocean and describe the structure and variability of this pathway (Chapter 5).

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20

Le, Roux Daniel Y. "A semi-Lagrangian finite element barotropic ocean model." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ44492.pdf.

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21

McCardell, Grant. "Physical Supplies of Oxygen to the Bottom Waters of Western Long Island Sound." Thesis, University of Connecticut, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=3569983.

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Abstract (sommario):

Western Long Island Sound (WLIS) bottom waters experience low dissolved oxygen (DO) levels in the summertime. The seasonal hypoxia in the WLIS motivated the development of a coupled biogeochemistry/hydrodynamic model named the System Wide Eutrophication Model (SWEM). A critical assessment of the SWEM model, however, reveals that vertical transport rates are grossly underestimated, indicating a need for data-based estimates of these rates. I present a novel approach to estimate vertical mixing coefficients from time-series of measurements made at two or more depths by measuring the attenuation and phase lag of scalar signals generated periodically at the surface as they propagate downwards and estimate mean summertime depth-averaged downward fluxes of DO and heat of 14±4 μM day–1 and 17±10 Wm–3, respectively. In order to assess the importance of horizontal transport in the bottom waters, I present an analysis of time-series of moored temperature, DO, and current observations in the hypoxic area of Long Island Sound and estimate mean near-bottom along-channel flux differences of DO and heat as 4±6 μM day–1 and –5±6 Wm–3, respectively. I conclude that vertical transport forms the bulk of the physical supply of both DO and heat to the hypoxic zone. When WLIS moored instrument records are examined, it is evident that near-bottom increases in DO and heat and a decrease in salt occur during the middle of the flood tide; an analysis of water mass signatures indicates that the transport involved is vertical and not horizontal. Temperature data from a thermistor string deployed in the WLIS for 16 days in August 2009 clearly shows internal waves and a pycnocline depression of approximately 25% of the water depth occurring at mid-flood. Near-bottom internal wave energy is correlated with near-bottom DO and temperature changes at both supertidal and subtidal scales, and I conclude that internal mechanisms are potentially important to vertical transport in the WLIS region.

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22

Holland, David M. "Numerical simulation of the Arctic Sea ice and ocean circulation." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41114.

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Abstract (sommario):

A numerical model study of the seasonal cycle of sea-ice cover and ocean circulation in the Arctic Ocean is presented. The investigation is carried out in four parts using the coupled sea ice-ocean model of Oberhuber (1993a). The Oberhuber model is the first global ocean general circulation model to use Lagrangian isopycnal coordinates. First, a sensitivity study is given of the sea-ice model, which is both dynamic and thermodynamic. The robustness of the sea-ice component in an uncoupled mode is demonstrated. Secondly, the addition of a snow model to the coupled sea ice-ocean model of Oberhuber (1993a) is described. The inclusion of snow is shown to be important for obtaining a good simulation of ice thickness in both the Arctic and Antarctic. Thirdly, the coupled ice-ocean model is used to investigate the general circulation of the Artic Ocean and its connection with the North Atlantic. The cyclonic motion of the Atlantic layer within the Arctic is correctly simulated. Fourthly, a sensitivity study of the Arctic mixed-layer circulation is presented.

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23

Reynaud, Thierry. "Propagation d'ondes côtières piégees sous la couverture de glace dans la Baie d'Hudson." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=59288.

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Abstract (sommario):

Since the beginning of the sixties, coastal trapped waves have been one of the most popular subjects in physical oceanography. Initially, we discuss their characteristics in the Southeast Hudson Bay, using the Brink and Chapman model. Then we compare the normal modes obtained with the observations made in Kuujjuarapik (Hudson Bay) in 1986 using the technique of Freeland et al (1986). This area is difficult to model because of rapid changes of stratification in the water column during the ice break-up period. The best fit was found for two topographic waves both having a period of three days with phase speeds of 70 cm/s and 13 cm/s. In this work it has been shown that the response function of the system due to atmospheric pressure gradients has a maximum at a period corresponding to the period of the topographic waves.

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24

Gan, Jianping 1962. "Internal hydraulics, solutions and associated mixing in a stratified sound." Thesis, McGill University, 1990. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60021.

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Abstract (sommario):

Observations of tidally forced flow in a constricted region of a highly stratified sound are examined as a problem of two-layer hydraulic exchange. It is shown that the narrowest section and the region downstream of the narrowest section were subject to internal hydraulic control. Bores moved upstream and evolved into packets of internal solitary waves with 3-6 minute period when the tide turned to ebb. Using results from different models of the solitary wave based on the KdV equation, it is shown that the second-order nonlinear term must be included in the two-layer model. The results from a first-order continuously stratified model gave similar good results. This implies that two-layer models may ignore some properties of the real fluid and that the internal solitons are also sensitive to the stratification characteristics of the water column. It is found that the mixing was related to both the vertical velocity shear, the hydraulic characteristics of the flow and the presence of solitary waves.

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25

Dupont, Frederic. "Comparison of numerical methods for modelling ocean circulation in basins with irregular coasts." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37886.

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Abstract (sommario):

Comprehension of global oceanic currents and, ultimately, of climate variability requires the use of computer modelling. Although much effort has been spent on the accuracy of traditional finite difference (FD) models used in ocean modelling, there are still concerns, especially since these models have a crude representation of the geometry of oceanic basins. Such a crude representation may influence the accuracy of modelling boundary currents, or unrealisticly represent the impinging of eddies or the propagation of Kelvin waves along the coastline. This motivated the use of alternative modelling techniques applied on completely irregular geometries such as finite element (FE) and spectral element (SE) methods. In this thesis, we want to investigate the accuracy and cost-effectiveness of these three numerical methods in irregular domains and to understand to which extent the unstructured grid FE and SE methods constitute an improvement over the more traditional FD methods. To accomplish this, we limit ourselves to modelling the shallow water equations in presence of irregular coastlines with no bottom topography. In the first part of the thesis, we compare the performances of FD methods on Cartesian grids with FE and SE methods in various geometries for linear and non-linear applications. We argue that the SE method is to a certain extent superior to FD methods. In a second part, we study the influence of step-like walls on vorticity budgets for wind-driven shallow water FD models. We show that vorticity budgets can be very sensitive to the FD formulation. This has certain implications for using vorticity budgets as a diagnostic tool in FD models. In the final part, we use a SE shallow water model for investigating the "inertial runaway problem" in irregular domains for the single-gyre Munk problem. Ideally, one would like the statistical equilibrium observed at large Reynolds number to be insensitive to model choices that are not well founded, e.g., the precise value of the viscous coefficient, and choice of dynamic boundary condition. Simple models of geophysical flows are indeed very sensitive to these choices. For example, flows typically converge to unrealisticly strong circulations, particularly under free-slip boundary conditions, even at rather modest Reynolds numbers. This is referred to as the "inertial runaway problem". We show that the addition of irregular coastlines to the canonical problem helps to slow considerably the circulation, but does not prevent runway.

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26

Gertz, Aaron Blake Rollinson. "2D-3D interactions in a thin rotating fluid : implications for the energetics of ocean circulation." Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99181.

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Abstract (sommario):

The general circulation of the ocean acts as an energy reservoir. This means that the external forcing (primarily by the wind field) is balanced by dissipation. However, the dissipation is not well understood because energy does not easily cascade forward to small scales where dissipation is active. Approximate geostrophic balance holds over much of the ocean because the advective timescale is typically long compared to the Coriolis timescale. The resulting geostrophic turbulence behaves similarly to 2D turbulence in the sense that energy is not cascaded forward to small scales. In fact, there is an inverse cascade of energy toward large scales for these "balanced" flows. One possible mechanism for dissipation of the balanced flow is nonlinear interactions with unbalanced flow. In this thesis we made an analogy between balanced flow and 2D flow for the unstratified case. We numerically integrated the hydrostatic, barotropic vorticity equation using a pseudo-spectral, triply-periodic model varying the rate of rotation and the level of 3D (corresponding to unbalanced) energy via a 3D forcing. We analysed the energetics of the 2D flow to determine the impact of rotation and the 3D energy level. We found that there is a critical Rossby number between 0.1 and 1 above which there is 2D energy drain and below which there is 2D energy gain. We found that the magnitude of the drain/gain at large scales increases with forcing up to a limiting value. A review of ocean energetics and turbulent 2D-3D interactions is also presented.

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27

Reynaud, Thierry H. "Dynamics of the Northwestern Atlantic Ocean : a diagnostic study." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28521.

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Abstract (sommario):

New high resolution density fields for the northwestern Atlantic Ocean are calculated from objectively analyzed temperature and salinity fields obtained from archived data. The original data set is the Marine Environment Data Service (MEDS) archived data and is supplemented by a subset of the National Oceanographic Data Centre (NODC) data from J. Reid and by the 1980s additional data of Fukumori and Wunsch (1991). The objective analysis scheme is a modification of that used by Levitus (1982) and uses 37 vertical levels. The scheme is used to calculate the climatological mean (1910-1989) temperature and salinity fields for the summer and the warm and cold seasons. Inverse methods are then applied to these new density fields in order to determine the transport and circulation during these periods. A study of the seasonal and interdecadal variations of the ocean transport and circulation is also presented. The interdecadal analysis is based on temperature and salinity fields analyzed for the warm season of the 1950-1964 and 1965-1981 periods.

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28

Li, Yongxiang 1962. "Intraseasonal and interannual variability of sea ice in the Gulf of St.Lawrence." Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36640.

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Abstract (sommario):

Intraseasonal and interannual variability of sea-ice cover (SIC) in the Gulf of St. Lawrence, including the time of first ice presence (TFIP), time of last ice presence (TLIP), and sea-ice duration (SID), were investigated, using weekly sea ice observations from 1963--1996. For the intraseasonal variations of sea ice, it was found that SIC in different sub-regions displays contrasting features. The largest intraseasonal variations of SIC occur in the Strait of Belle Isle region and in the southwestem Gulf, where the mean SIC is largest and SID is longest. For the interannual variability of sea ice, the largest variability of SIC occurs in the area off mid-Newfoundland, where the mean SIC is small. For the TFIP and TLIP, the largest interannual variability occurs in the area off western Newfoundland and along coasts in the northeast sector of the Gulf, respectively. In addition, sea ice appeared earlier in the coastal regions and disappeared later over the entire Gulf in severe ice years; while sea ice appeared later in the central and eastern Gulf and disappeared earlier over the entire Gulf in light ice years. Several of the forcing factors influencing sea ice variability in the Gulf of St. Lawrence were examined and mechanisms controlling this variability were discussed. It was found that surface air temperature (SAT), the eastward wind component (u-wind), sea surface temperature (SST), sea surface salinity (SSS), mixed layer depth (MLD), total river runoff, the ocean circulation pattern, and sea-ice advection from the Labrador Sea, all play important roles in explaining sea ice variability in the Gulf. However, the relative contributions of these factors to the observed sea ice variability differ in different subregions. Quantitative relationships between sea ice variability and various forcing factors were investigated using statistical analysis and a simplified Hibler's sea-ice model. Both approaches indicated that the December--April averaged SAT, u-wind, and November SST all contribute to the variability of December--June SIC in the Gulf, with SAT playing the most important role. The analysis also indicated that the dependence of SIC on various forcing factors varies with geographical location. For example, SAT influences sea ice variability mainly in the central Gulf, while the u-wind component effects SIC mainly in the eastern Gulf. In addition, statistical analyses also suggest that SSS values present in the previous November play an important role in determining SIC variability. The linear regression between SIC and three independent variables: December--April SAT, November SST and SSS, accounts for 81% of the total SIC variance. The statistical analysis and model study also indicated that December SAT, u-wind, November SST, and MLD control the time of first ice presence, with SAT and SST playing the dominant role. The linear regression between TFIP and three independent variables (u-wind, SST, and SSS) accounts for 76% of the total TFIP variance. For TLIP, both SAT and u-wind play an important role.

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29

Scott, Robert Bruce 1965. "Geostrophic energetics and the small viscosity behaviour of an idealized ocean circulation model." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=35669.

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Abstract (sommario):

The role of the mechanical energy budget is analyzed in relation to the small viscosity behaviour of an idealized model of the wind-driven circulation. This is addressed theoretically and numerically in part one. In part two the connection to the real ocean is made through an analysis of the energy source with real data. The theoretical arguments based on the QG energy equation show that, with the assumption that the maximum velocities occur at inertial length scales or smaller, a Sverdrup interior is consistent with the small Rossby number assumption only when the frictional parameters exceed critical values. For frictional parameters smaller than these values, valid solutions must decrease the energy source. This is possible for non-Sverdrup solutions since the energy source is dependent on the solution. The numerical study is focused on insensitivity to frictional parameters in the nonlinear Stommel-Munk model. Dependence of the multiple solutions of the steady state model on the boundary layer Reynolds number, Re, are investigated by varying the eddy viscosity for fixed wind forcing. An important finding is the tendency to decrease the energy source for solutions that are nonsymmetric about the centre latitude. Antisymmetric solutions display the opposite behaviour, and diverge more quickly with increasing Re. Also interesting is the tendency for the total energy and transport to become less sensitive to eddy viscosity with increasing Re. The robustness of the results to dynamic boundary condition, symmetry and strength of wind stress, time dependence and bottom friction are tested. A significant, though not surprising, result is that the no slip condition leads to high Rossby number in the boundary layer at much lower Re than for the free slip condition. It is demonstrated that recent advances in altimetry measurements allow for a reasonable estimate of the rate of mechanical energy transfer from the atmospheric winds to the surface geostrophic velocity integrated over large regions. (Local values are highly uncertain due to the very large uncertainty in the marine geoid undulation field.) The feasibility and methodology of a quantitative uncertainty estimate is also demonstrated. The estimate of the energy source term allows comparison of the theoretical and numerical results with the real ocean.

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30

Bourgault, Daniel. "Circulation and mixing in the St. Lawrence estuary." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=37871.

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Abstract (sommario):

Circulation and mixing processes in the St. Lawrence Estuary are examined using both newly acquired and historical observations, as well as numerical modeling. In the Summer of 1997 a field experiment was undertaken to verify the prediction of a three-dimensional numerical model on the occurrences of shear instabilities within the upper estuary. The instabilities were found as predicted and documented from acoustic imaging, current profiler and density measurements. The instabilities, as in the case of Kelvin-Helmholtz instabilities, first develop in the form of wavelike disturbances before they break. The unstable waves have wavelength of around 140--150 m and a vertical extent of between 10 and 25 m. It is shown that the modeled gradient Richardson numbers near the pycnocline are reasonably well reproduced and appear to be useful for the prediction of flow instabilities in such a complex environment. The seasonal variability of the general circulation and mixing is examined with a newly developed laterally averaged numerical model. The model takes into account tidal forcing and a realistic topography while forced with a large seasonal change in the river discharge. The model is able to reproduce important processes associated with the tidal forcing and mean conditions (density field, residual circulation). The numerical results show that mixing in the St. Lawrence Estuary is not evenly distributed. Mixing is found to be large near the sill at the head of the Laurentian Channel, as previously thought, as well our new results show that equivalent levels of mixing are also found near English Bank and near Ile-aux-Coudres. During the spring freshet, when the river discharge is 40% higher than normal, the limit of salt intrusion is moved seaward by approximately 12 km, the residual circulation is intensified by approximately 10%, and the turbulent vertical mass flux increases throughout owing to greater availability of freshwater. The results also suggest that during high runoff periods, the vertical stability of the water column increases in the upper estuary. The model is also used to assess the impacts of climate change on the estuarine dynamics. (Abstract shortened by UMI.)

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31

Robitaille, Daniel Y. "A box model study of the Greenland Sea, Norwegian Sea, and Arctic Ocean /." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69689.

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Abstract (sommario):

A simple box model of a a high-latitude two-layer ocean, first developed by Martinson et al., 1981, is applied to four Arctic regions connected together: the Greenland Sea, the Norwegian Sea, the Arctic Ocean, and the Greenland Gyre. The latter, in fact, is a small convective region embedded in the northwest corner of the Norwegian Sea region. The model for each region consists of a thermodynamic ice layer that covers two layers of salty water which can, under specific conditions, become statically unstable and hence create a state of active overturning. The system is forced by monthly mean atmospheric temperatures in the four regions, as well as by continental runoffs and by inflows from adjacent oceans. The model predicts the ice thickness, and the temperature and salinity of the water in the upper layer for the four regions. Also determined are the water temperature and salinity for the lower layer in the Arctic Ocean box. The convective state of any given region, i.e., whether it is in an active overturning mode or not, is also obtained continuously. The different output variables of the model, which are the response to climatological forcing conditions, compare favourably with observed data. In this control run, the Arctic Ocean region is characterized by continuous ice cover only during winter, and the Norwegian Sea region never forms an ice cover. Another feature of the model is the winter time occurrence of convective overturning in the upper 200 m in the Greenland Gyre region. (Abstract shortened by UMI.)

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32

Smith, Gregory C. "The Gulf of St. Lawrence in winter : tides, mixing and watermass transformation." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=86051.

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Abstract (sommario):

The winter watermass properties and circulation of the Gulf of St. Lawrence and St. Lawrence Estuary are examined using a combination of new wintertime observations and numerical modelling. Ten moorings were deployed over the winter 2002/3, providing the first continuous observations of the upper 200m of the water column in winter. A harmonic analysis of current data in the estuary confirms the existence of a semi-diurnal internal Poincare wave. The analysis also provides strong evidence of a neap-tide intensification of the estuarine circulation. The cold intermediate layer (CIL) in the estuary is seen to be renewed abruptly in late March, with the advection of a wedge of near-freezing water from the gulf. An eddy-permitting sea ice-ocean model is used with the observations to quantify the formation and circulation of the CIL. As a first step, a two-equation second moment turbulence closure parameterization is implemented to better account for vertical mixing processes. The model sensitivity to this parameterization is tested and differences of several salinity units are found in the surface layer throughout the southern half of the gulf. The model reproduces the strong spring renewal event of the CIL into the estuary, and helps to explain the role of local dynamics, including the coupled circulation in the northwest gulf, in controlling the exchange processes at depth. The model results suggest the existence of a separated Gaspe Current that persists for more than a month. A significant correlation is found between the inflow through the Strait of Belle Isle and outflow through Cabot Strait. In order to isolate the effects of this inflow on the CIL heat content, we examine a sensitivity experiment in which the Strait of Belle Isle is closed. This simulation shows that the inflow has a relatively small effect on the total CIL heat budget. With the Strait of Belle Isle closed, the outflow of CIL through Cabot Strait is reduced by 61%. It is estimated that only 64% of CIL inflow through the Strait of Belle Isle in fall and winter contributes directly to the heat content of CIL present in the gulf.

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33

Crevier, Louis-Philippe. "Dependence of the transport in channel models of the ACC on the Rossby radius of deformation." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21532.

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Abstract (sommario):

It has been suggested that the transport of the Antarctic Circumpolar Current is set, essentially, by the southward Sverdrup flux at latitudes just north of Drake Passage. Although this idea is consistent with observations, it has been critized in that Sverdrup dynamics fail at Drake Passage latitudes. Here, we think of the total transport as being comprised of two components: one associated with the basin-like dynamics to the north of Drake Passage and the other associated with the dynamics of the Drake Passage latitude band itself. The Drake Passage latitudes are often simulated using channel models with bottom topography. For a two-layer channel, large topography effectively blocks geostrophic contours at depth and allows zonally-reconnecting contours in the upper layer. This concentrates the through-channel transport in the model's upper layer. Furthermore, it is argued that the statistical steady state for wind-driven channel flow (that is not too viscous) should be baroclinically unstable. Assuming marginal instability then leads to an estimate of the through-channel transport. A two-layer primitive-equation channel model with bottom topography and wind forcing is used to test this relationship. Model integrations are made to obtain statistical steady states for a range of parameters. The Rossby radius and the wind strength are varied as the theory predicts that transport should go like the square of the former and be relatively insensitive to the latter. Integrations to test the robustness of these results to model resolution are also conducted.

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34

Laval, Bernard E. "Tidal flow modification by a small bay in the lower St. Lawrence estuary." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23281.

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Abstract (sommario):

The tidal flow characteristics around L'Anse du Petit Mitis were described using velocity data from six moored current metres. L'Anse du Petit Mitis is a shallow bay in the lee of the downstream slanting Pointe Mitis. The predominantly M$ sb2$ current showed the following signs of tide induced transient recirculation within the bay: the M$ sb2$ phase within the bay is 65$ sp circ$ ahead of that outside of the bay; the amplitude of the M$ sb4$ and Eulerian mean constituents are relatively large within the bay; and the M$ sb2$ tidal ellipse and the Eulerian mean are oriented towards the tip of Pointe Mitis. The effects of tide induced transient recirculation were not found to extend to the station furthest within the bay. Flow in the bay region was found to be an order of magnitude weaker than the free stream tidal flow.

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35

Doyon, Patrick. "Seasonal structure of the Gulf of St. Lawrence upper-layer thermohaline fields during the ice-free months." Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=23998.

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Abstract (sommario):

The interactions between the atmosphere and the oceans play a critical role in determining our climate. These generally consist of various exchanges of heat, mass and momentum between the two media through the air-sea interface. Therefore, the physical state of the upper few meters of the oceans influences the rate at which these exchanges take place. Furthermore, these surface waters are of importance in affecting the primary biological production of the seas. In this context, knowledge of the upper-layer monthly averaged thermohaline state, i.e. temperature (T) and salinity (S) as a function of latitude-longitude and depth, is necessary for further climatological/oceanographic studies in the Gulf of St. Lawrence (GSL). The primary goal of this research is to produce, using basic statistical analyses, monthly mean fields of T and S related quantities at various depths throughout the GSL. The historical hydrographic dataset covers the last 75 years. Objective fields of sea surface temperature (SST), salinity (SSS) and chlorophyll-a (Chl-a) were also computed and compared with other similar climatologies (when available). (Abstract shortened by UMI.)

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36

Wang, Jia 1957. "Interannual variability of sea-ice cover in Hudson Bay, Baffin Bay and the Labrador Sea, and numerical simulation of ocean circulation and sea-ice cover in Hudson Bay." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=39802.

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Abstract (sommario):

In part 1, the spatial and temporal relationships between subarctic Canadian sea-ice cover and atmospheric forcing are investigated by analyzing sea-ice concentration, sea-level pressure, and surface air temperature, as well as ice thickness, runoff, and sea surface temperature, from 1953-1988. The sea-ice anomalies in Hudson Bay, Baffin Bay and the Labrador Sea are found to be related to the North Atlantic Oscillation (NAO) and the Southern Oscillation (SO). From the application of a spatial Student's t-test and a Monte Carlo simulation, we found that sea ice responds significantly to the SO event only in summer, and to the NAO event only in winter. A spectral analysis shows that sea-ice cover in Baffin Bay and the Labrador Sea responds to the SO and SAT fluctuations at about 1.7 year, 3-5 year and about 8-10 year periods. In addition, a sea-ice signature associated with the so-called "climate jump" during the early 1960s was found. The ice thickness and ice-melt date data are also used to verify the above findings. In part 2, the three-dimensional ocean general circulation model of Blumberg and Mellor (1983, 87) was used to simulate the winter and summer ocean circulation in Hudson Bay under specified atmospheric forcing and runoff. This model uses vertical sigma coordinates and horizontal orthogonal curvilinear coordinates. The vertical viscosity and diffusivity are computed using the Mellor-Yamada (1982) second-order (2.5) turbulence closure, while the values for similar horizontal parameters are calculated using the Smagorinsky (1963) parameterization. The new version of this model uses the semi-implicit scheme for the shallow water equations (Casulli, 1990). A consistent, modified radiation boundary condition has been developed for the surface elevation and the normal barotropic velocity for the universal multi-level, baroclinic model with strong vertical stratification. The surface cyclonic circulation in summer and winter, due in part to the boundary inflow from Roes Welcome Sound to the northwest of the domain, has been well simulated. In part 3, a dynamic thermodynamic model of sea ice with viscous-plastic rheology (Hibler, 1979; 1980) is used to simulate the seasonal cycle of sea-ice motion, thickness, compactness, and growth rate in Hudson Bay under monthly climatological atmospheric forcing. The simulated results for ice cover in other seasons also compare favourably with the observed climatology and with measurements from satellites. In particular, the model gives complete sea-ice cover in winter and ice-free conditions in late summer. (Abstract shortened by UMI.)

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37

Myers, Paul Glen. "Seasonal forcing and low-frequency variability of the thermohaline circulation." Thesis, McGill University, 1992. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=60722.

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A series of numerical experiments are conducted using the Bryan-Cox Ocean General Circulation Model to investigate the potential existence of low-frequency variability of the thermohaline circulation under seasonal forcing. Experiments are performed with different combinations of a seasonal cycle being present or not on the restoring temperature, the surface freshwater flux fields (mixed boundary conditions) and the surface wind forcing. Despite the presence of the forcing on the dominant seasonal timescale, it is found that the system may oscillate at the decadal period or longer. The decadal variability is excited by changes in the net surface density flux which are due to the advection of temperature and salinity anomalies in the model domain. The magnitude of the seasonal cycle also plays an important role in determining the timescale of variability. Violent overturning events may occur on the century timescale under seasonal forcing. The magnitudes of the flushes are reduced compared to those found in similar experiments without the presence of a seasonal cycle.

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38

Zhang, Sheng 1956. "The formulation of a thermocline model and application[s] to ocean-climate studies." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=41214.

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In this thesis, we formulate a new 3-dimensional planetary geostrophic (PG) ocean general circulation model in spherical coordinates for use in ocean-climate studies. The model equations consist of full prognostic temperature and salinity equations and diagnostic momentum equations. The model is verified by comparison with results obtained by the well known Bryan-Cox model at coarse resolution. Extensive process studies are carried out to determine the roles played by various processes in determining the thermocline structure and the thermohaline circulation, especially the role of convective overturning. A secondary circulation theory which treats the thermohaline circulation as a geostrophic flow instead of frictional current is proposed, and the implications of the results to 2-dimensional latitude/depth models are discussed. The model is also used to examine the stability and variability of the thermohaline circulation, especially the role played by air-sea heat flux at the surface. We show that the large reduction in the surface heat flux under mixed boundary conditions (restoring on temperature and flux on salinity) is essential for the occurrence of the "polar halocline catastrophe" (F. Bryan. 1986). Replacing the infinite heat capacity atmosphere implied by mixed boundary conditions with an atmosphere that can adjust thermally to the ocean, the amount of the heat flux reduction is less and thus the polar halocline catastrophe is less likely to occur; when it does occur, it is less severe. This is demonstrated by coupling our model to a simple zero heat capacity atmosphere (Schopf, 1983). Instead of a total collapse of the thermohaline circulation, the results show a decaying oscillation of 20 years period. The ocean model is next coupled to a thermodynamic sea ice model to examine the effect of sea ice on the stability and variability of the thermohaline circulation. A robust 17-year period oscillation is obtained, and a new mechanism involving a feedback between ice cover and temperature is proposed. Conceptual models are formulated for further interpretation of the results, and to compare the thermal insulation and salinity rejection effects due to an anomalous ice cover, on the density of the surface water. The heat budget required for ice formation leads to a constraint on the convective overturning, and hence the transfer of heat and salt from the deep ocean to the bottom of the ice. As a result, the thermal insulation effect is dominant, at least for the case of annual mean surface forcing examined here.

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39

Hughes, Tertia M. C. "Uniqueness and variability of the ocean's thermohaline circulation." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28780.

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Abstract (sommario):

A numerical modelling approach is chosen to study equilibrium and time-dependent aspects of the ocean's thermohaline circulation. In the first part, the roles of basin geometry and surface buoyancy forcing in determining the asymmetry of the present-day thermohaline circulation are considered. An idealized flat-bottomed two-basin model of the Atlantic and Pacific is found to favour equilibria with sinking in the southern hemisphere only (Southern Sinking) or also in the North Atlantic (Conveyor), even under a freshwater flux forcing field with more precipitation over the North Atlantic than over the North Pacific. Another new result is the range of Conveyor equilibria found under mixed boundary conditions. Rare cases with North Pacific sinking are characterized by a very fresh halocline in the Southern Ocean and a reversed pole-to-pole surface density contrast. A more quantitative investigation leads to an approximately linear relationship between the Atlantic overturning and the meridional gradient of zonally-averaged depth-integrated steric height from the northern boundary of the ocean to the southern tip of Africa; on the other hand, the local linear relationships postulated in most two-dimensional plane models of the overturning circulation could not be validated. In the second part, the climatology of a global ocean model is presented, and the importance in the model of the warm water route of the Conveyor through the Indian Ocean relative to the cold water route through Drake Passage is noted. The implied ocean heat and freshwater transports from the Canadian Climate Centre second generation atmospheric general circulation model are then presented, and are shown to be incompatible with the present-day thermohaline circulation. Finally, in the third part, a simple new parameterization of the sea surface temperature-evaporation feedback is developed as an extension of the traditional mixed boundary conditions. The positive sign of the feedback for the thermohaline circulation is demonstrated, and three examples featuring decadal, century and millennial timescale variability in one-hemisphere idealized basins are discussed. No fundamental alterations of the mechanisms under mixed boundary conditions are found, although the timescale is altered or the variability interrupted sooner in some cases.

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40

Wang, Zhaomin 1963. "A simple coupled atmosphere-ocean-sea ice-land surface-ice sheet model for climate and paleoclimate studies /." Thesis, McGill University, 1999. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=36068.

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Abstract (sommario):

We develop a new coupled atmosphere-ocean-sea ice-land surface-ice sheet model for long-term climate change studies. This five-component model incorporates the seasonal cycle, and the three major ocean basins, the Antarctic Circumpolar Current region and the major continents are resolved. The model variables are sectorially averaged across the different ocean basins and continents. The above coupled model (less the ice sheet component) is first used to simulate the major features of the present day climate. In a global warming (cooling) experiment, the thermohaline circulation (THC) in the North Atlantic Ocean is weakened (intensified) due to the increased (reduced) moisture transport to, and warmer (cooler) sea surface temperatures at northern high latitudes. Secondly, the above four-component model is employed to investigate the initiation of glaciation, which is accomplished by reducing the solar radiation and increasing the planetary emissivity only in high northern latitudes. When land ice is growing, the THC in the North Atlantic Ocean is intensified, resulting in a warm subpolar North Atlantic Ocean. The intensified THC maintains a large land-ocean thermal contrast at high latitudes, which leads to enhanced land ice accumulation. We conclude that increased fresh water or massive iceberg discharge from land is responsible for a weak or collapsed THC. Lastly, a dynamic ice sheet model is coupled to the above four-component model. Sensitivity experiments show that a smaller lateral (east-west) ice discharge rate maintains a larger ice volume and extent in our model. Also, a reduced atmospheric CO2 concentration, which is parameterized as an increased planetary emissivity, may lead to the expansion of the ice sheets and hence a larger ice volume and extent. A simple iceberg calving scheme is next introduced to investigate ice sheet-THC interactions on the millennial timescale. We find that the longer the duration of iceberg calving, the longer the time that must elapse before the next calving event can occur. Also, it is shown that the strength of the THC in the North Atlantic Ocean is very sensitive to the discharge rate of the ice sheets. This makes the simulation of the interactions between ice sheets and the THC extremely challenging.

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41

DeTracey, Brendan. "Modelling interannual sea ice variability in the Gulf of St. Lawrence." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=68167.

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Abstract (sommario):

An uncoupled, modified Hibler ice model has been applied to the Gulf of St. Lawrence for three different winters of varying severity, in order to examine interannual sea ice variability. The simulation was initialized with observed November sea surface temperatures, and forced by weekly geostrophic winds, monthly averaged meteorological data and model geostrophic surface currents. Results showed a general correlation with observations, reproducing differences in the sea ice cover between the years chosen. Neglecting oceanic effects caused excessive ice formation in the northwest Gulf and produced discrepancies between the observed and modelled ice edge. Sensitivity studies revealed a high sensitivity to variations in both the forcing fields and the model free parameters. Further modelling studies must include a coupled ocean component, and force the ice component with weekly meteorological data to improve the accuracy of the prediction.

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42

Zanowski, Hannah Marietta. "The Influence of Antarctic Open-Ocean Polynyas on the Abyssal Ocean." Thesis, Princeton University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10248291.

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In the mid-1970s, an enormous open-ocean polynya developed in the Weddell Sea. Since the Weddell Polynya's occurrence, no polynya of similar size or duration has been observed in the region. A polynya of this magnitude could significantly affect global abyssal ocean properties via increased Antarctic Bottom Water (AABW) formation and large Weddell Sea water mass property perturbations. However, the scarcity of 1970s Weddell Sea observations, coupled with the sparseness of abyssal ocean observations, make it difficult to study this phenomenon's oceanic impact without models. This dissertation examines the influence of Weddell Polynyas on abyssal ocean water mass properties and circulation using the GFDL CM2G coupled climate model. Abyssal ocean temperature, salinity, and water mass changes resulting from Weddell Polynyas are quantified in CM2G and compared to observations. The model polynyas initially cool the abyssal Southern Ocean and South Atlantic, but 2-3 decades after polynya cessation the same regions warm as they relax toward their mean state. Composites of multiple, spontaneously-occurring polynyas in CM2G reveal that up to 10% of recently observed warming in the abyssal Southern Ocean could be the result of the 1970s Weddell Polynya recovery. Weddell Polynya transport mechanisms are also investigated. Polynya signal transport is governed by two processes acting on different timescales and spreading at different rates: 1) topographic and planetary waves that act on interannual-to-decadal timescales, and 2) advection that acts on decadal-to-centennial timescales. Both mechanisms generate property changes on isobaths. Despite different spreading rates, the advective and wave signals act contemporaneously in many Southern Hemisphere abyssal basins. The combined effect and relative magnitude of the two signals dictates the prevailing property changes. During Weddell Polynyas, vigorous exchange occurs between the surface and deep waters, resulting in increased abyssal ventilation. In climate models, ideal age tracer is often used to investigate oceanic ventilation. This tracer suffers from several flaws that detract from its suitability as a ventilation diagnostic. We develop a new tracer, ?-age, that rectifies some of ideal age's problematic aspects and examine its utility in an offline tracer model.

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43

Nhesvure, Belinda. "Impacts of ENSO on coastal South African sea surface temperatures." Master's thesis, Faculty of Science, 2021. http://hdl.handle.net/11427/32954.

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Abstract (sommario):

The impact of El Niño Southern Oscillation (ENSO) on the Southern African inland climate is well documented and provides skill in the seasonal forecast of rainfall but little is known of the impact of ENSO on the ocean surrounding South Africa. The aim of this study is to assess the impact of ENSO on sea surface temperatures around the coast of South Africa and to calculate SST trends around the coast. I start by updating the study of Rouault et al (2010) on the very topic with an additional 10 years of data and two additional newer datasets which allow sampling closer to the coast where wind-driven upwelling is more active. The new highresolution ERA 5 reanalyzed climate dataset is also used to look at the atmospheric forcing of sea surface temperatures by ENSO. As in Rouault et al. (2010), I study five similar threedegree-long coastal regions around South Africa, namely: West Coast, South Coast, Port Elizabeth/Port Alfred, Transkei, Kwazulu-Natal and a larger offshore Agulhas Current area domain. Three SST datasets are evaluated in this study: the 1 ̊x1 ̊Optimal Interpolation sea surface temperature (OI SST) used by Rouault et al (2010), the 0.25 ̊x 0.25 ̊ Optimal Interpolation SST and the 4 km x 4 km Advanced Very High-Resolution Radiometer (AVHRR) Pathfinder SST version 5.3. The 0.25 ̊x 0.25 ̊OI SST resolvesSST anomalies better in these coastal regions as compared to 1 ̊x1 ̊ OISST. The difference in results among the three products concerning trends and correlation with ENSO is a cause for concern. The 4 km x 4 km AVHRR Pathfinder allows for SST to be extracted even closer to the coast but missing values are numerous and hamper the use of this dataset for ENSO composites and trend analyses. Results show a significant positive correlation with El Niño in summer at the monthly scale, reaching a maximum correlation of 0.45 at 3 months lag. Correlation is the highest in late summer. There is a negative correlation in the Agulhas Current area, opposite to those with ENSO and West Coast. The impact of ENSO on the coast of South Africa, West Coast and South Coast is due to change in surface wind speed with weaker upwelling favorable during El Niño leading to warmer than normal coastal water SST and stronger than normal Southeasterly winds during la Niña leading to cooler than normal coastal water. The wind perturbation is part of largescale basin-wide perturbations in the tropical Atlantic, in the South Atlantic high-pressure atmospheric system and in the westerly wind pattern of the midlatitude to the south. Non-ENSO related impact can be as important as ENSO related SST perturbation and is also linked to large scale perturbations in the South Atlantic. There is no relation between the strength of ENSO and the strength of the perturbation, and some ENSO events do not lead to the expected canonical warming or cooling. The large-scale SST perturbations seem to be caused by anomalous surface turbulent flux of latent and sensible heat and abnormal wind speed and direction. This study opens the possibility of seasonal forecasting of SST in the South Benguela upwelling system because of the positive lag correlation between ENSO and SST with ENSO leading SST.

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44

Evers-King, Hayley Louise. "Phytoplankton community structure determined through remote sensing and in situ optical measurements." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13076.

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Abstract (sommario):

Includes bibliographical references. Linking variability in optical signals with phytoplankton community characteristics is important to extend the use of the vast resource that is the satellite ocean colour archive. Detection of species, functional types or size classes has been addressed through a spectrum of empirical to analytical approaches. A key step in developing these techniques is quantifying the sensitivity in reflectance, which can be attributed to phytoplankton characteristics (e.g cell size) under different optical regimes. Ultimately, highly spatially and temporally resolved information on phytoplankton characteristics can help the global scientific community to answer important questions relating to primary ecosystem variability. In the southern Benguela, Harmful Algal Blooms threaten public health and the economic viability of fishery and aquaculture industries in the region. Concurrently, the dominance of phytoplankton biomass amongst optically significant constituents in the southern Benguela makes the region ideal for assessing the extent to which phytoplankton characteristics beyond biomass can influence the ocean colour signal. A forward and inverse approach is presented. Phytoplankton absorption and back scattering are generated from a phytoplankton particle population model coupled to two radiative transfer approaches: a reflectance approximation and the radiative transfer model, EcoLight-S. Non-linear optimisation inversion schemes are then implemented. A simulated dataset is created to investigate how much variability in reflectance can be associated with changes in phytoplankton cell size in different bio-optical water types. This dataset is inverted to investigate the errors inherent in the inversion process as a result of ambiguity. Comparison of the two radiative transfer techniques allows for consideration of the suitability of approximations for bidirection-ality and subsurface propagation. The inversion algorithm is then applied to hyperspectral in situ radiometric data to provide validation and further assessment of errors from all sources. Results indicate that size related sensitivity in reflectance is highly dependent on phytoplank-ton biomass, as determined by the relative phytoplankton contribution to the Inherent Optical Property budget. The algorithm is finally applied to ten years of MERIS data covering the southern Benguela. A time series of biomass and cell size is presented and metrics developed to demonstrate the utility of this approach for identifying previously unobserved interannual variability in Harmful Algal Blooms.

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45

Joubert, Warren Ryan. "Primary productivity and its variability in the Atlantic Southern ocean." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13366.

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Abstract (sommario):

Includes bibliographical references. The two principal bottom-up drivers of the High Nutrient Low Chlorophyll (HNLC) characteristics of the Southern Ocean are light and nutrient (mainly dissolved iron) limitation ( Boyd , 2002; Mitchell et al., 1991), which have varying limiting roles over the growing season ( Boyd, 2002; Swart et al., 2014). This research commenced with an investigation of the meridional characteristics of primary productivity in the Atlantic Southern Ocean during austral summer 2008.

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46

Nhantumbo, Bernardino João. "Drivers of coastal sea level variability along the east and south of South Africa." Doctoral thesis, Faculty of Science, 2019. http://hdl.handle.net/11427/30348.

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Abstract (sommario):

Sea level rise and variability is of great concern in the coastal areas where a significant part of the global population is settled. Therefore, understanding regional and local long-term sea level variability as well as its trend is critical. On the other hand, quantifying how the sea level has varied on different timescales and why, is critical for understanding sea level changes, and crucial for improving future global, regional, and local projections. In this study, monthly mean sea level records of seven individual tide gauges, from the east and south coast of South Africa were used to analyse the embedded timescales of variability. These timescales were separated through the Empirical Mode Decomposition (EMD) method. This is the first time that the EMD method has been applied to southern African tide gauge records. The sensitivity of the EMD method when dealing with data gaps was tested on artificially created gaps in monthly mean synthetic altimetry sea level records, representing the seven individual tide gauges under consideration. The missing values were filled by linear interpolation, average value and linear trend value. The results suggested that whichever gap filling method is applied, the separated EMD timescales will display a distorted temporal structure of the continuous time series. As a consequence, monthly mean tide gauge sea level records were optimised by filling the gaps as best as possible using satellite altimetry data and the adjacent tide gauge records where possible, and then the oscillatory timescales of variability were separated using the EMD method with the intent to determine their physical drivers. However, identifying a single driver for each separated timescale is challenging due to our limited knowledge of how sea level is linked to the various forcing mechanisms. Therefore, the timescales of sea level variability extracted using the EMD were grouped into sub-annual and interannual timescales, and their relationship to possible driving mechanisms was investigated. The sub-annual timescale indicates how sea level responds to the mesoscale and synoptic weather systems in the annual cycle, including seasonal and annual large-scale wind and atmospheric pressure pattern changes. The interannual timescale indicates an association with the climate indices including El Niño-Southern Oscillation, Indian Ocean Dipole and Southern Annular Mode through large-scale sea surface temperature patterns and large-scale pressure and wind patterns. In addition, the results have suggested that the studied coastal sea level has an association with the Agulhas Current at both sub-annual and interannual timescale through absolute dynamic topography variations at the Agulhas Current core locations. However, due to limitations in Agulhas Current data, the study was limited to East London and Port Elizabeth and the results suggested that the Agulhas Current contribution is responsible for over 62% of the monthly sea level variability at East London. However, the results were not sufficiently consistent to suggest a firm conclusion at Port Elizabeth.

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47

Driver, Penny Meredith. "Rainfall variability over southern Africa." Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/12830.

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Abstract (sommario):

Includes bibliographical references. Southern Africa is subject to high inter annual rainfall variability and the factors influencing southern African rainfall are not fully understood. The variability has been linked with various sea surface temperature anomalies (SSTAs) in each of the three major ocean basins as well as variability in the strength and position of regional atmospheric features. One of the atmospheric factors that may play a substantial role in southern African rainfall variability is the Botswana high, a high pressure cell which exists at the 500hPa level and is centred over central Namibia and western Botswana during austral summer. 20th Century reanalysis data is used to further investigate this feature and analysis reveals an association between the strength of the Botswana high and ENSO. Further analysis indicates that a connection between the Botswana high and rainfall over southern Africa not only exists during ENSO years, but is also apparent during neutral years that display ENSO-like characteristics in the Botswana high. This result may assist in producing better rainfall forecasts for non-ENSO years. The frequency of dry days over southern Africa during austral summer is investigated using GPCP observational data. Correlation analysis is generally in agreement with previous studies and showed that dry day frequency(DDF) over the Limpopo and North East Zambia regions is correlated with ENSO, while DDF over coastal northern Angola and central South Africa is correlated with SSTs in the Indian and Atlantic Oceans. The possible role played by DDF during JFM 1998 and JFM 2010 is investigated and results indicate that the distribution of DDF over southern Africa was notably different during these two seasons and may have contributed to the unexpected rainfall experienced over southern Africa.

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48

Funke, Michael. "On the subtropical front in the South Atlantic Ocean." Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/6473.

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Abstract (sommario):

Includes abstract. Includes bibliographical references (leaves 64-72). The region surrounding the Tristan da Cunha Archipelago has received little attention to date due to its remote location. An extensive revision of previous literature covers the majority of oceanographic research undertaken in the region of interest. New satellite derived oceanographic data sets and the SODA Reanalysed model are used to overcome the sparse extent of in-situ data in this region. Using latitudinal temperature gradients to track the surface expression of the Subtropical Front from AMSR and OISST satellite derived sea surface temperature data reveals consistencies with previous literature.

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49

Hunter, I. T. "The Weather of the Agulhas bank and the Cape South Coast." Master's thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/21858.

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Abstract (sommario):

Until 1982, when the National Research Institute for Oceanology (NRIO) erected self-contained, automatic weather stations (AWS) on the Cape South Coast, no continuous coastal measurements were available. This Institute had erected an AWS on the drilling rig Sedco K in 1978, so that over 3 years of very valuable off- shore data was already available on the adjacent Agulhas Bank. Al though the weather offices at George and Port Elizabeth have made accurate meteorological observations for over 30 years, this data is shown here to differ significantly from actual coastal measurements. Thus the NRIO AWS network, which operated for just over a year, provided a detailed, short-term data set for the study of coastal weather processes. In order to acquire longer term data from coastal observations, five years of hourly wind observations from lighthouse keepers along the Cape South Coast were also utilised. Although these are estimates, it is shown that a coastal estimate may be more representative of marine conditions than an anemometer reading some distance inland. Voluntary Observing Ship's data (VOS) extracted from SADCO's Marine Climatology database, provided the long-term offshore information, whilst also supplying very useful 'present weather' (synoptic code ww) observations for case studies. Observations from synoptic stations for the period that the coastal AWS were deployed (February 1982 - March 1983), were provided by the South African Weather Bureau. With this unique and comprehensive data set, the various weather systems affecting the region are discussed. Twelve case studies form the main reference for this discussion, which includes relevant oceanographic parameters. The weather systems are considered firstly as individually propagating circulations with the AWS network providing details of propagation speeds and coastwise development. Secondly the combined 'weather producing' effects of these systems are discussed, with a strong emphasis being placed on man/weather interactions. It is shown that certain operations along the Cape South Coast and over the Agulhas Bank, are extremely weather sensitive, and would benefit considerably from an increased knowledge of weather processes. Recommendations aimed not only at those managing weather sensitive operations, but also at those involved in coastal meteorological measurement and research, complete the thesis.

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50

Dove, Veronica Fernando. "Seasonal and interannual variability of surface chlorophyll-a and sea surface temperature in the Delgoa Bight, southern Mozambique." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/19978.

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Abstract (sommario):

Multi satellite data for surface chlorophyll‐a (Chl‐a), sea surface temperature (SST), sea surface wind (SSW) and sea level anomalies (SLA) have been obtained and analysed over the Delagoa Bight (24‐28°S, 32‐36°E), southern Mozambique for the period 2003‐2012 at monthly time scales. Both descriptive and quantitative analysis using wavelets have been used to obtain a better understanding of the nature of the interannual, seasonal and intra- seasonal variability of the data. Strong seasonal structure and interannual modulation were observed in the area averaged Chl‐a concentration and SST. The lowest maximum in monthly Chl-a was in December (0.127 mg.m--‐3) and the highest in August (0.541 mg.m‐3). The lowest maximum in monthly SST was in August (21.8°C) and the maximum in February (27.9°C). The Chl‐a and SST were strongly anti-correlated and both exhibited a well- defined seasonal cycle, contrasting with the SSW and SLA. The daily observations of temperature at 17 meters depth, from the northern Delagoa Bight at Ponta Zavora (24.48°S- 35.24°E) for the period 2006‐2011, have confirmed a seasonal signal with amplitude of about 6.5°C. Cool coastal water events were found mostly in summer and spring, with maximum amplitude of 6°C. Further analysis of this daily data did not reveal the timing of such events to be regular.

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Tesi sul tema "Physical oceanography"

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