Thesis--Frankfurt a.M. / Vita. Includes bibliographical references (p. [6-21]).

Graduation date: 1978

A free-falling instrument was used in coastal waters to measure turbulent velocity fluctuations, temperature, conductivity and pressure from the near surface to 15 cm above the bottom. A probe guard system has been developed that protects the delicate temperature and shear sensors from bottom sediments and minimizes instrument vibrations that would otherwise contaminate the shear signal. From the shear signal the viscous dissipation rate of turbulent kinetic energy is calculated. A new technique is presented for the analysis of shear spectra for dissipation rate calculations. The identification and elimination of noise, both at low and high frequencies, is accomplished by a positive feedback loop during analysis and insures more accurate estimates of the microstructure shear variance, [formula omitted]. The technique improves the confidence in the dissipation rate estimates and results in a noise level of 3.0 X 10⁻⁷ W m⁻³. This noise level is low, considering the structural modifications made to the profiler for near-bottom sampling. The microstructure instrument was used for 670 profiles over the continental shelf west of Vancouver Island in June, 1985. From the dissipation rates near the bottom, within the constant stress layer, values of the bottom stress are calculated. Variations in the bottom stress and the height of the turbulent bottom boundary layer correlate with the diurnal tidal currents that dominate the flow near the bottom. The height of the bottom well mixed layer was found to be nearly independent of the height of the turbulent bottom boundary layer. Over most of the shelf, vertical density variations are attributable to advection rather than local mixing. Near shore, in depths less than 100 m, the tidally driven turbulent bottom boundary layer extends throughout most of the water column during periods of maximum tidal current. Seaward of the 100 m depth contour the current and density measurements above the bottom boundary layer, 40 to 50 m above the bottom, reveal the mean structure of the Tully eddy. Contours of constant density show that the structure is an upwelling centre confined to a region over part of the Juan de Fuca Canyon system. Turbulent mixing within the core of the eddy was found to be weak. Oxygen samples indicate that the wind-induced upwelling brings slope water up the canyons to the shallow (<100 m) banks near shore. Nutrients in the slope water are mixed vertically by the tidally driven bottom boundary layer over these banks. Flux rates for NO₃ of 387 mmole s⁻¹ per metre of coastline are estimated during the strong upwelling conditions in June, 1985. From the turbulent dissipation rate measurements within the bottom boundary layer an estimated lower limit to the decay scale for the K₁ period shelf wave is roughly put at 1100 km. This is in good agreement with the model of Brink (1982a). From the dissipation rate measurements above the bottom boundary layer, a friction decay time scale for the Tully eddy is estimated to be 231 hours. This is supported by the observations of Freeland and Mcintosh (1987, personal communication) that show large, frequent fluctuations in the circulation at periods of ~ 20 to 330 hours. A global dissipation of 4.8 x 10¹⁰ W is estimated for the tides over all continental shelf regions, only 2.5% of the total tidal kinetic energy dissipated by friction in all the oceans and seas. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Recently obtained airgun-sonobuoy wide-angle refraction and reflection profiles provide data to study crustal velocities and structures along the continental margin of northern California and Southern Oregon. In the thick sedimentary wedge at the base of the continental slope, as many as five distinct layers can be seismically observed, which range in velocity from 2.13 to 3.32 km/sec. The basement layers beneath the wedge are disrupted. The profile which crosses the southeasternmost portion of the Gorda Basin near Cape Mendocino shows evidence of compression at the base of the slope. Velocities of 3.14 to 5.15 km/sec were obtained for this line. Off the central Oregon margin on the abyssal plain near the base of the slope, oceanic layers and 3 overlie a shallow mantle of velocity 7.65 km/sec. Basement velocities average 4.75 km/sec and sediment velocities varied from 1.60 to 2.78 km/sec. The lower slope of the northern California-southern Oregon margin is characterized by rough, folded structures which trend north-south. Little recent sediment cover is seen. A velocity of 2.25 km/sec was obtained for a 520 m-thick surface layer underlain by material with a refraction velocity of 2.68 km/sec. The abyssal plain sediments near Cape Mendocino appear to be in the process of being uplifted and folded into the lower slope, while near Cape Blanco the lower slope displays sediments which abut against the base of the slope below a prominent lower shelf bench. The upper slope shows large anticlinal folds which form the basement of the upper slope basins, particularly beneath the Klamath Plateau off Northern California. Velocities obtained from the sediments of the Klamath Plateau vary from 1.73 to 2.63 km/sec. The inner shelf region is formed by a synclinal basin controlled by an outer continental high which parallels the shelf break. Velocities were studied mainly from refraction arrivals with an assumed surface sediment velocity of 1.66 km/sec. The underlying sediment velocities range from 2.07 to 2.75 km/sec. Evidence of uplift, basement deformation, sediment deformation within structurally controlled basins, compression features, and the north-south trending folds all support an imbricate thrust model for this continental margin. / Graduation date: 1979

Previous experiments to record seismic data at wide angle on the continental shelf have generally been unsuccessful in determining velocity structure in the lower crust; either the lines were too short or shot-receiver density too sparse to identify lower crustal arrivals. In contrast, deep normal incidence profiles show good structural resolution in the crust and uppermost mantle. This dissertation describes a new sea-bottom multichannel instrument which was developed to record datasets containing closely spaced traces to improve the resolution of reversed wide-angle experiments on the continental shelf. The Pull-Up Multichannel Array (PUMA) is a 1200 m, 12 channel, hydrophone array for remotely recording seismic data on the sea-bed. It consists of 12 short hydrophone sections linked by 100 m long passive sections. A pressure case is attached at one end in which recording electronics, cassette tape recorders and a battery power supply are housed. The PUMA is deployed in less than 200 m of water from a research ship and moored to buoys for recovery. The instrument, which was successfully used in an experiment west of Lewis, Outer Hebrides, U.K., was specifically designed to determine a well constrained velocity structure for the crust and uppermost mantle over part of the BIRPS WINCH deep, normal incidence profile. Data recorded by the PUMA show a high signal to noise ratio and it is easy to correlate phases across the record section and to monitor changes in amplitude because traces are closely spaced. A velocity structure for the continental crust and uppermost mantle has been devised using amplitude modelling. The model is interpreted to show that: the upper crust consists of Lewisian gneiss metamorphosed in the amphibolite facies, and contains a low velocity zone which is probably granitic in composition; the middle crustal layer has virtually no velocity gradient; and the lower crust, represented by second arrivals, contains a high velocity gradient and probably consists of granulites. The Moho is at 27.0 ± 0.5 km depth. This is shown to be a layered boundary and it is suggested that this layering is caused by crustal underplating. There is little velocity gradient in the uppermost mantle. This model shows good agreement with the BIRPS WINCH section, although the Moho appears to coincide with the top rather than the base of a band of reflections at 8.3 s two-way travel time on unmigrated WINCH data.

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Natural radionuclides may be indicators for dense mineral placers along marine shorelines. Relict beach and river deposits occur in continental shelf sediments. These deposits result from the reworking of beach sands by wave action during the Holocene Transgression. Some dense, resistant minerals associated with placer deposits are known to contain ²³⁸U and ²³²Th activities. Shelf sediments, enriched in heavy minerals, might be expected to be high in these natural radioactivities. The usefulness of natural radioactivity to locate and to map dense mineral deposits was therefore explored and relations between natural radioactivity in marine sediments and dense mineral content were established. High ⁴⁰K activity in sediments was positively correlated significantly with high mud content. High ²³⁰Th and ²³²Th activities were associated with fine, well-sorted sands and correlated very highly with the weight percent total heavy mineral sands in the sediment. These relations distinguish depositional environments as high in ⁴⁰K content and erosional environments as high in ²³⁰Th and ²³²Th content. Two areas of enrichment were found by radiometric mapping and by mineral analyses. Off Destruction Island, Washington, maximum ²³⁰Th and ²³²Th activities were found in 30 m water depth. Activity distribution and mineral enrichment were consistent with general northward transport of nearshore sediment. In 33 m water depth off Clatsop Spit, Oregon, the second enrichment area was found. The ²³²Th/²³⁰Th activity ratios are different for these two areas. Probably the heavy minerals in these two areas are from different sources. / Graduation date: 1975

Thesis (M.S. in Physical Oceanography)--Naval Postgraduate School, December 2003. / Thesis advisor(s): Thomas H.C. Herbers, Edward B. Thornton. Includes bibliographical references (p. 71-73). Also available online.

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