Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept. of Meteorology. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 320-325. / by Mark A. Cane. / Ph.D.

Thesis. 1977. Sc.D.--Massachusetts Institute of Technology. Dept. of Meteorology. / Microfiche copy available in Archives and Science. / Vita. / Bibliography : leaves 167-170. / Sc.D.

Thesis. 1977. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Vita. / Bibliography : leaves 198-204. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1980. / Microfiche copy available in Archives and Science. / Vita. / Bibliography : leaves 122-129. / by Dean Howard Roemmich. / Ph.D.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 126-138). Also available on the World Wide Web.

Channel constrictions in which strong currents are mainly driven by tidal processes represent sites with high potential for harvesting renewable and predictable tidal stream energy. Tidal Current Turbines (TCTs) deployed in arrays appear to be the most promising solution to efficiently capturing this carbon neutral energy resource. However to ensure the sustainable character of such projects, the balance between power extraction maximization and environmental impact minimization must be found so that device layout optimization takes into account environmental considerations. This is particularly appropriate since both resource and impact assessments go intrinsically hand in hand. The present method proposes the use and adaptation of ocean circulation models as an assessment tool framework for tidal current turbine (TCT) array-layout optimization. By adapting both momentum and turbulence transport equations of an existing model, the present TCT representation method is proposed to extend the actuator disc concept to 3-D large scale ocean circulation models. Through the reproduction of physical experiments to reasonable accuracy, grid and time dependency tests and an up-scaling exercise, this method has shown its numerical validity as well as its ability to simulate accurately both momentum and turbulent turbine-induced perturbations in the wake. These capabilities are demonstrated for standalone devices and device arrays, and are achieved with a relatively short period of computation time. Consequently the present TCT representation method is a very promising basis for the development of a TCT array layout optimization tool. By applying this TCT representation method to realistic cases, its capability is demonstrated for power capture assessment and prediction of hydrodynamic interactions as would be required during the layout deployment optimization process. Tidal energy has seen considerable development over the last decade and the first commercial deployments are likely to take place within the next 5 years. It is hoped that this new tool and the numerical approaches described herein will contribute to the development of TCT array power plants around the world.

Thorium-230 and protactinium-231 have been widely used as proxies of oceanic processes in both modern and past marine environment. Their application as such proxies is, however, limited by sparse data from the modern ocean with which to characterize their distribution and behavior. This thesis aims to provide such data and to assess their uses as oceanic proxies for ocean circulation, sediment dissolution, and modern dust input. Twelve profiles of dissolved ²³⁰Th, ²³¹Pa and ²³²Th obtained on a meridional GEOTRACES section in the Southwest Atlantic confirm the expected transport and fractionation of ²³¹Pa from ²³⁰Th by deep ocean circulation out of the modern Atlantic. There is however neither a water mass dependence nor progressive change as water masses age, which challenges the use of sedimentary ²³¹Pa/²³⁰Th to assess past flow in the South Atlantic. Decreases of ²³⁰Th and ²³¹Pa observed in near-bottom water indicate enhanced sea-floor removal in regions where nepheloid layers are present. In a second study of sedimentary nuclides concentration, high-resolution ²³⁰Th_xs profiles from sediment in Southeast Atlantic exhibit increasing ²³⁰Thxs concentrations from core-top to a depth of ∼3 cm followed by relatively constant values at greater depth, suggestive of sediment dissolution in the upper sediment core. This observation suggests the use of ²³⁰Thxs to quantify sediment dissolution. Combined with sediment composition measurements, ²³⁰Th_xs also provides an assessment of which constituents are dissolving from the sediment. (²³¹Pa/²³⁰Th)_xs ratios do not appear to be affected by sediment dissolution. A third study, in the tropical Atlantic Ocean, combines water-column measurements of ²³⁰Th, ²³²Th with coeval aerosol measurements, and allows assessment and improvement of the use of ²³²Th to quantify dust input to the surface ocean. ²³²Th-derived dust flux increases from 0.43 g/m²/yr at low latitude in the South Atlantic to 10.70 g/m²/yr at higher latitude in the North Atlantic, and broadly agree with a model of dust input. The data presented in this thesis have expanded the dataset of ²³⁰Th, ²³²Th and ²³¹Pa in the Atlantic Ocean, and provide an insight into future uses of these nuclides as oceanic proxies.

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

Bibliography: leaves 169-178.

Graduation date: 1997