WHOAS : Browsing WHOI Theses by Issue Date

Thesis

Experimental studies of turbulence in liquid-solid flows

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1969-08) Bohlen, Walter Franklin

A series of laboratory experiments were performed to ascertain the extent and manner of turbulence modification induced by low concentration suspended loads of near neutral buoyancy. Hot-wire measurements of the fluid velocity field of free surface flows were obtained in a specially designed flume recirculating a dielectric liquid and 0.5 mm" diameter spherical plastic particles. In the fixed Reynolds number flow (16,800) the data obtained at six different concentration levels, ranging from 0 to 3.5% by volume, indicate that the presence of particles produces substantial turbulence changes. Even at this low level the mean velocity profile shows an increasing gradient near the bed and sharp deviation from a logarithmic profile. The rms level of each of the velocity components u', v' and w' increases, indicating a general rise in turbulence intensity. The Reynolds stress ρ u'v' increases, and its maximum value shifts away from the bed. The overall scale of turbulence appears to remain unchanged. The data indicate that offhand neglect of suspended particle presence is an oversimplification. There is a similarity between these data and those obtained under adverse pressure gradients. Some effort is made to clarify the altered turbulence production meechanism, and some future experimental work is proposed.

Thesis

A study of certain trace metals in sea water using anodic stripping voltammetry

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1970-01) Fitzgerald, William F.

Anodic stripping voltammetry utilizing a thin film mercury composite graphite electrode has been evaluated and applied for the direct analysis of the metals, Zn, Cu, Pb, and Cd in sea water. The electrode was observed to follow theoretical behavior for thin film electrodes and the technique was found not to be adversely affected by dissolved organic material in sea water. Good precision (ca., 5%) was obtained in both coastal and open ocean waters at the in situ concentrations of Zn, Cu, Pb, and Cd. It was shown that this method is at present most suitable for measurements of Cu, Pb, and Cd in sea water. Evidence is given suggesting that Ni may interfere with the determination of Zn through formation of an intermetallic compound, and further studies are indicated to understand this phenomenon. The anodic stripping apparatus was adapted and used conveniently on shipboard. It was demonstrated that stripping analysis could be combined with a method for the destruction of dissolved organic matter (photo-oxidation with ultra-violet radiation), and with an addification procedure to obtain measurements of trace metal speciation in sea water. An argument for the existence of Cu-aspartic acid chelates in sea water has been described theoretically and demonstrated empirically; suggesting that a significant fraction of Cu and other trace metals may be expected to be organically sequestered in sea water. A study of coastal waters employing the total method (anodic stripping-photo-oxidation-acidification) indicated the presence of a significant group of organic ligands that complex Cu (ca., 60%). It was also shown that the waters subject to gross pollution contain about 30% of the total Cu in very stable organic complexes that release Cu only when the dissolved organic matter is destroyed, and not when the pH of this sea water is adjusted to 3. An open ocean trace metal study of a thermal-front zone in the western Sargasso Sea gave data for Cu, Zn, Pb, and Cd that compared favorably with other relevant investigations. Higher free metal concentrations were observed south of the front than to the north, providing further evidence that these fronts may mark a change between southern and northern conditions in the Sargasso Sea. Data obtained from shipboard analyses using the total analytical method indicates the presence of weak organic complexes with Cu and Pb in open ocean waters.

Thesis

Inertial oscillations in the Mediterranean

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1970-06) Perkins, Henry T.

Measurements of ocean currents were made by the author in the Western Mediterranean Sea at five depths for two months during early 1969. In terms of the dominant and persistent presence of inertial oscillations, circularly polarized currents having periods of a half pendulum day, the data are among the most striking ever collected. Two contemporary theories have been adapted for interpretation of this data. On the basis of a ray or short-wave-length theory, energy arriving at the observing site is found to fall into two categories, that making direct arrival from the, surface where it is assumed to have been generated, and that which undergoes one or more reflections. To the extent that the former dominates, it is found that the Algerian Coast about 130 km. to the south would cast a shadow to the north, the precise shape of which would be highly dependent on small variations in frequency. The nature of this frequency dependence implies a gradual increase in frequency with depth at the observing latitude. Although the data show a measurable shift (about 3%) towards higher frequencies, which is roughly the required amount, the lack of progressive frequency change with depth does not support the shadow hypothesis. In addition, the data is interpreted in terms of normal mode theory, where the nearby coast is seen to force a discrete modal structure to the solutions. The observed variation of current phase with depth indicates that a single internal mode dominates over a large portion of the data, while variations of both current amplitude and phase with depth are consistent this being the third internal vertical mode. Existence of a normal mode is also consistent with the long time, on the order of three weeks, for which the oscillations were observed to persist and with the dimensions of the Mediterranean Basin.

Thesis

Experimental study of internal gravity waves over a slope

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1970-09) Cacchione, David A.

A series of laboratory experiments were conducted in a glass wave tank to investigate the propagation of internal gravity waves up a sloping bottom in a fluid with constant Brunt-Vaisala frequency. Measurements of the wave motion in the fluid interior were primarily taken with electrical conductivity probes; measurements in the boundary layer were made with dye streaks and neutrally buoyant particles. The results indicate that, outside of the breaking zone, the amplitude and horizontal wave number of the high-frequency waves increase lineariy with decreasing depth; this is shown to agree with existing linear, inviscid solutions. A zone of breaking or runup is induced by these high-frequency waves well upslope. Shadowgraph observations show that, if the wave characteristics are coincident, or nearly so, with the bottom slope, the upslope propagation of the low-frequency waves causes a line of regularly spaced vortices to form along the slope. Subsequent mixing in the vortex cells creates thin horizontal laminae that are more homogeneous than the adjacent layers. These laminae slowly penetrate the fluid interior, creating a step-like vertical density structure. Available linear theoretical solutions for the velocity in the viscous boundary layer, determined to be valid for certain experimental conditions, are used to develop a criterion for incipient motion of bottom sediment induced by shoaling internal waves. The maximum sediment sizes that can be placed into motion, according to this criterion, are larger than certain mean sediment sizes on the continental margin off New England. This suggests that internal waves might induce initial sediment movement. Speculation about the geological effects of breaking and vortex instabilities is also given. These processes, not definitely measured in the field as yet, might also be conducive to sediment movement.

Thesis

Shear of small vertical scale observed in the permanent oceanic thermocline

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1971-01) Van Leer, John Cloud

Two shear experiments performed in the permanent thermocline are described and analyzed in this thesis. The first employed dye streak techniques to gain fractional meter vertical resolution. Shears with small vertical scales with frequent reversals in direction and changes of magnitude were observed in every experiment between 160 and 900 meters depth. The ratio of the standard deviation of shear magnitude to the mean shear magnitude was computed at the depth of each dye experiment. These ratios decreased exponentially with depth suggesting a decay of surface supplied energy. The vertical wave number of the shear is not inconsistent with high mode inertio-gravitational internal waves or interleaving layers or salt-driven convection. The second experiment used sensor pairs to measure shear, temperature gradient, and salinity gradient with three meter vertical spacing. A weak but significant negative correlation between shear magnitude and density gradient magnitude was found in most of the records whether density gradient was computed from temperature and salinity or estimated from temperature alone. This result disagrees with a simple linear internal wave model developed for a layered medium. The expected positive correlation is strong enough to cause shear instability to occur first in regions of strongest static stability. This prediction again disagrees with observed shear density data in which the smallest Richardson numbers occur in weakly stratified regions. This negative correlation was observed to be strongest in regions of weak static stability. Perhaps we are observing the results of mixing processes in the main thermocline which cannot be described by the simple linear equations of motion. Two likely sources for the energy of mixing are suggested. Inertial motions are shown to have sufficient energy at thermocline depth and are known to have high enough vertical wave number to have shears comparable to those observed. Salt fingers are known to be able to release enough energy from an unstable salt buoyancy field to form convective layers under laboratory conditions. Since the temperature and salinity in the main thermocline near Bermuda both decrease with depth and have nearly equal and opposite buoyancy contributions, salt fingers must be considered likely. In the main oceanic thermocline no single mixing process seems likely to dominate everywhere or perhaps anywhere. The data collected in this thesis and elsewhere are not yet sufficient to define the statistics of these mixing processes or even to uniquely separate one from another at one location. A time series of experiments combining the two techniques developed in this thesis should be able to establish how shears vary in direction with time and vary with density gradient. These questions are at the heart of the thermocline mixing problem.

Thesis

The influence of topography on steady currents and internal waves

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1971-01) Hogg, Nelson G.

Observations of the ocean in the vicinity of Bermuda on two different occasions show systematic distortions of the isotherms close to the island and an area of intensive mixing on the northern coast. Two mechanisms are investigated and each produces some agreement with data from different flow regimes. Firstly, the island is modeled as a circularly symmetric obstacle with steep sides and a small aspect ratio. A steady, rotating, and stratified flow which, far from the island, is uniform in the horizontal and a linear function of the vertical coordinate is taken to be flowing past the island. Neglecting circulation effects, the problem is solved to first order in a small parameter, α, which measures the steepness of the island and a small Rossby number, ε. This allows a calculation of the depth contours of isotherms to 0(ε2,εα). For one set of data the flow is such that the slope effect of 0(εα) predominates while for another period of observation both slope and Rossby number influences are of the same magnitude. In both cases qualitative agreement between fact and theory is remarkably good. In addition, it is shown that the north slope (for a west-east current) is the most favored area for mixing as there the Richardson number is a minimum and the flow is most likely to separate from the boundary. A second means of producing isotherm distortion and mixing areas close to the island concerns the nonlinear effects of shoaling internal gravity waves. For normal incidence on a two-dimensional beach the Reynolds stresses produced by the fundamental wave motion are shown to force a mean Eulerian current which is equal hut opposite in sense to the Stokes drift. This causes the mean Lagrangian current to vanish so that the physical constraint that there be no net motion of fluid particles along isopycnals into the beach is satisfied. In addition, isotherms are distorted in a fashion analogous to the surface set-down produced by shoaling surface waves. The mean isopycnal shift can be as much as 10m where the theory has some validity. Distortions of the predicted form are observed in the data from a period when the mean currents were small. Consideration of the oblique incidence problem shows that this generalization has little effect on the expected magnitude of the shifts but that a significant longshore current can be forced by the breaking of the waves.

Thesis

On the flow induced in a thermally stratified fluid by a source of heat

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1971-06) Knox, Robert A.

The flow produced by an infinitely long horizontal heated strip in a thermally stratified fluid is examined theoretically. For strong stratification a long flat convection cell or tongue results. Profiles of velocity and temperature anomaly are displayed and contrasted with the profiles which would obtain if the temperature anomaly were only a passive tracer. The effects of small nonlineari ties are computed by perturbation methods and the profile alterations thus produced are discussed. A laboratory experiment set up to demonstrate the major features of this circulation is described. Qualitative agreement between theory and experiment is obtained, and certain of the predicted nonlinear effects are observed.

Thesis

Experiments in a rotating source-sink annulus

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1971-08) Ingram, Richard Grant

An experimental investigation of the different flow regimes in a rotating source-sink annulus is described. Both the steady and transient velocities are measured over a large range of Ekman Reynolds number and Rossby number. Differing probe configurations are used to investigate the corresponding motions in spatially separated regions of the annulus. The steady interior circulation field exhibits a strong dependence on the imposed flux values. The non-dimensional circulation increases with radius over a certain radial range for higher system Rossby number. The observed profile changes are related to the existence of an unstable Ekman layer at some inner radial position. The thickness of the observed Ekman layers is typically 85% of the theoretical scale height. For higher local Reynolds number (ReL), the thickness is generally much smaller. The width of the sidewall boundary layer adjacent to the sink increases with larger system Rossby number. Adjacent to the source, the radial boundary layer is wider than that at the sink wall. Observed oscillations are separable into three types. For ReL > 50, instability waves are observed in the Ekman layer flow. In the same Re range, inertial oscillations are detected in the interior region of the annulus. The observed inertial wave frequency at differing radial positions is explained by incorporating Doppler shift corrections and taking account of the steady circulation profiles. The radial wavelength of the inertial waves corresponds to the length of the Class A Ekman layer instabi1ity. For small values of Re and local Rossby number, an axisymmetric disturbance, with a characteristic frequency slightly greater than therotation rate, is observed at the outer radial positions.

Thesis

Drag coefficients of vibrating synthetic rope

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1971-09) Charnews, Daniel Paul

The drag, amplitude, frequency tension, diameter and length of synthetic ropes vibrating because of vortex-induced forces, and net vibrating at different tensions were measured. Photographs were taken of the vortices. Drag coefficients were calculated and plotted against Reynolds Number. The measured frequency is compared with data from other sources. The measured diameter is compared with that calculated from conservation of volume.

Thesis

The relationship between microscales and wind-wave spectral development

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1971-10) Dorman, Craig E.

The objective of this study was to describe the mechanics of wind wave generation and spectral development. Intermittency, high frequency microstructure in wind and wave fields, and strong nonlinear coupling involving a wide range of scales are shown to be crucial elements in the transfer of momentum to, from, and within the wave field. None of these elements are included in available theories. Measurements of wave height and of the turbulent atmospheric and subsurface boundary layers were made, from a small surface following platform and from a stable 38.5m spar buoy. The structure of moving gust patterns (cat's paws) is described and related to the generation of surface waves. Results from this and other background studies are then applied to a discussion of spectral growth during a two day period of active wave generation. Cat's paws contain 'bursts' of intense turbulent stress and buoyancy fluctuations separated by quiescent 'intervals'. There is a difference of over three orders of magnitude in fluctuation strength between these features. Rapid growth rate generation of high frequency surface waves and atmospheric turbulence occurs during the bursts. The resultant microscale components aid the growth of lower frequency instabilities by strong nonlinear coupling between scales of motion and by acting as drag or roughness elements. Evidence of strong coupling between frequency bands and of weakly resonant capillary-gravity wave interactions is presented. Thermal stratification has a strong influence on fluctuation magnitude and can delay the onset of surface wave generation. Major spectral growth is highly unsteady. Much of the momentum flux from air to sea occurs during intermittent events that are similar in nature to cat's paws, and goes directly into high frequency waves. The bursts occur predominantly over large groups of surface waves and involve strong nonlinear interactions between media and frequency bands. The long-term equilibrium balance between wind and water is disrupted by variations in surface currents. There are 'critical' wind speeds characterized by anomalous relationships between parameters of the predominantly logarithmic velocity profile.

Thesis

The gravity field and plate boundaries in Venezuela

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1972-01) Folinsbee, Robert Allin

Free-air and simple Bouguer anomaly maps of the Venezuelan continental margin (from 60°W to 72°W and from 7°N to 13°N) are presented. The major features of the free-air map are: the large lows associated with the deep sedimentary basins, -200 mgal in the Eastern Venezuela basin and -164 mgal in the Maracaibo basin; the high of greater than 300 mgal over the Venezuelan Andes; and a belt of highs associated with the offshore islands extending from Blanquilla to Curacao and then over the Guajira peninsula, where they terminate. The Bouguer anomaly map shows a large low (-196 mgal) over the Eastern Venezuela basin and relative minimums over the coastal mountains. A minimum associated with the Venezuelan Andes is shifted to the northwest of the topographic axis and lies over the flank of the Andes and part of the Maracaibo basin. Using the gravity data, structural sections were constructed for a series of profiles across the Venezuelan Andes and Caribbean mountains. They show that there is no light crustal root under the Andes, the relative mass excess is as much as 600 kg/cm2, and that there is an excess of low density material under the Maracaibo basin. This appears to be caused by a combination of a southeastward dipping shear zone in the lithosphere under the basin-mountain boundary and a component of compressive stress perpendicular to this zone, both of which have resulted in the uplift of the crust under the Andes, and downwarp under the basin. The apparent flexural rigidity of the lithosphere under the Maracaibo basin is 0.6 x 1023 newton-m, a normal value for lithosphere deformations of Miocene age. The Caribbean mountains have a light crustal root which has been formed by the sliding of blocks of crustal material from the north over the rocks to the south, and perhaps by the underthrusting of oceanic crust under the continental crust. This underthrusting may have been a result of the formation of a downgoing slab of lithosphere along the Venezuelan continental margin during the late Cretaceous. The downgoing slab may have existed until mid-Eocene time. The gravity minimum over the Eastern Venezuela basin is due to the downwarping of lighter crustal material into the higher density mantle. This may be a result of compression from the north along a north-south direction causing plastic downbuckling of the lithosphere. The present deformation along the northern boundary appears to be due to differences in relative motion between the North and South American plates. Because the Caribbean mountains are partially isostatically compensated, while the Venezuelan Andes are above isostatic equilibrium, this suggests that the relative motion of the Caribbean plate with respect to the South American plate is eastward. The compressive stress across the boundary in the region of the Venezuelan Andes is probably greater than the compressive stress across the Caribbean mountains.

Technical Report

On the calculation of wind stress curl over open ocean areas from synoptic meteorological data with application to time dependent ocean circulation

(Woods Hole Oceanographic Institution, 1972-02) Welch, Christopher Slocombe

The method used by N. P. Fofonoff for estimating wind stress curl from surface atmospheric pressure maps is developed for use with the National Meterological Center analysis grid. A formula is developed relating the wind stress curl directly to geometrically apparent features of the surface pressure analyses. The sensitivity of the formula to small deviations in the basic pressure field is estimated. Some statistical properties of the resulting formula as applied to actual pressure analyses are investigated. In particular, the geostrophic wind estimated for two finite difference grids is compared to observed winds from an independent anemometer located at W.H.O.L site "D". The statistical distribution of wind stress curl estimates is found to be non-Gaussian. The difficulty in estimating a mean value from such distributions is discussed. The root mean square values of wind stress curl are found to be approximately 10 times the mean values. Means are estimated and found to be inadequate to drive the mean transports in the Gulf Stream and Kuroshio. The formula is applied at Bermuda and the results compared to the record from the tide gauge located there. A significant relation between wind stress curl and sea level is found after tidal and inverted barometer effects are suppressed. The formula is applied to time dependent motions of the Labrador Current as evidenced by iceberg drifts for the 1959 ice season. Agreement is found between calculated and observed iceberg motions on the eastern slope of the Grand Banks using static Sverdrup dynamics.

Technical Report

Motion sensitivity of flame ionization detectors

(Woods Hole Oceanographic Institution, 1972-05) Gularte, Ronald Carl

A portable gas chromatograph, using a single flame ionization detector, was constructed. The unit was tested for response to surge, sway and heave accelerations up to 0.3g. Also the detector's response was studied for roll and pitch up to 25 degrees with periods ranging from 3 to 20 seconds. The effect on the detector's response of variation in hydrocarbon concentrations in the parts per million range was investigated and response increased with increasing concentration. Samples containing 1, 10, 100, 1000, and 10,000 parts per million dodecane were analyzed, and under the higher accelerations trace distortion was evident for concentrations below 10 parts per million. Stationary isothermal chromatograms of a normal alkane sample (nC6 - nC32) were compared with those obtained under the various test conditions and no detectable difference in peak area (which represented approximately 1 microgram of the particular hydrocarbon) or retention time was evident. The limits of detection for the Aerograph detector were found to be 21.8 x 10-6 mg/sec for a 30 degree roll, 29.1 x 10-6mg/sec for 20 degree pitching and 21.8 x 10-6 mg/sec for a 0.6g heave acceleration. For the range of translational and angular accelerations that might be expected on a platform at sea, it was found that medium resolution gas chromatography using a flame ionization detector can be conducted, but in the trace analysis region, trace distortion can be expected.

Thesis

Nonlinear interactions among standing surface and internal gravity waves

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1972-06) Joyce, Terrence M.

A laboratory study has been undertaken to measure the momentum transfer from surface to internal gravity waves in a nonlinear, resonant interaction. The interacting waves form triads for which σ1s - σ2s ± σI = 0 and κ1s - κ2s ± κI = 0; σj and κj being the frequency and wavenumber of the jth wave. In particular, the experiment is designed to model a generating mechanism for high frequency, oceanic internal waves. Unlike previously published results involving single triplets of interacting waves, all waves here considered are standing waves. The growth to steady state of a resonant internal wave is observed while two deep water surface eigen modes are simultaneously forced by a paddle. Results are compared to theoretical predictions which assume, ab initio, all waves to be standing. Inclusion of viscous side wall dissipation and slight detuning permit predictions of steady state amplitudes and phases as well as initial growth rates. Good agreement is found between predieted and measured amplitudes and phases. The experiments also suggest that the internal wave in a resonant triad can act as a catalyst, permitting appreciable energy transfer among surface waves.

Technical Report

An experimental analysis of the dynamics of a submerged tethered cradle in a seaway

(Woods Hole Oceanographic Institution, 1972-06) Cohen, Jay Martin

Submerged recovery of small submersibles by means of surface tethered platforms offers the possibility of operations in sea states higher than is now possible using surface recovery means. The Woods Hole Oceanographic Institution's submersible support catamaran LULU has such a tethered system. The system consisting of cradle, chains, and hoist is designed to recover DSRV ALVIN at a depth of 100 feet, and then lift the submersible rapidly through the air-sea interface. Scientific commitments as well as possible damage to the cradle and/or ALVIN, and danger to personnel have prevented full scale recovery experiments. A 1/40 scale model of the catamaran, chain and cradle was constructed to investigate cradle heave and pitch response in regular sinusoidal waves. Model tests were conducted at the Massachusetts Institute of Technology Tow Tank Facility and data was recorded electronically and photographically. Test runs were made at various ship speeds, cradle depths, wave heights, wave lengths, and cradle suspension modifications. Results indicate that for the existing system, cradle pitch and heave is only slightly attenuated over catamaran response at speeds less then 3 knots (full scale). By decreasing the number of cradle suspension points, and varying hoist resiliency and cradle added mass characteristics, cradle motion can be substantially reduced over catamaran motion.

Technical Report

Investigation into the feasibility of detecting salt fingers optically

(Woods Hole Oceanographic Institution, 1972-08) Albro, Carl S.

During the last decade there has been increasing interest in discovering the existance of salt fingering in the ocean. The purpose of this investigation was to determine the feasibility of optically detecting salt fingers. Theoretical calculations were conducted on the angular deviation and displacement of parallel light rays propagating through an ordered salt finger model. It is assumed that salt fingers are square cells (one centimeter) with a checkerboard pattern of cells having high and low indices of refraction. The amplitude of index of refraction, above and below the overall average, was assumed to be between 5 X 10-4 to 5 X 10-6. From the computer work it was concluded that an optical method that detects displacement or intensity would have more promise of finding salt fingers in the ocean than an optical method that detects angular deviations. From the computer results and experimental shadowgraph investigations conducted by others, it was concluded that a shadowgraph method is the most promising optical approach to use for detection of salt fingers. Depending on the strength of the salt fingers, the optimum distance between the fingers and the shadowgraph screen may be as far as one to three hundred meters to obtain a sharp image. To shorten this optical path a telescope-microscope lens system cal led a "shadowgraph shortener" was used. Salt finger detection experiments were conducted in a large tank of saltwater. An expanded laser beam (5 centimeters) was passed through the salt water and the "shadowgraph shortener" to fall on a ground glass screen which was photographed with a 16 mm movie camera. The weakest salt fingers detected had a salinity gradient of .02 parts per thousand per 6 centimeters. A survey was conducted on the salinity gradients in the Atlantic Ocean using Nansen bottle data from hydrographic stations. The larger salinity gradients found in parts per thousand per 50 meters were only one order of magnitude weaker than the experimental results. An optical salt finger detector was designed using the same basic set-up as used in the experiments.

Thesis

The design of an instrument to measure vertically averaged oceanic currents using geomagnetic electric fields

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1972-08) Poranski, Peter Frank

A bottom mounted electromagnetic current meter measures the vertically-averaged conductivity-weighted velocity. This measurement complements free-fall relative velocity profiles and is valuable for transport determination and dynamics studies. Such an instrument has been designed to measure the three components of the electric field, Ex, Ey, and Ez. Salt bridges used with switched electrodes permit the induced e1ectromotive forces to be measured with only a short baseline; eight foot arms are planned. The first part of this report covers the theory behind the bottom mounted electric field meter. The second part discusses the design of the instrument as well as a brief description of the prototype bottom mounted electric field meter.

Thesis

Structural framework of the Sunda Shelf and vicinity

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1973-01) Ben-Avraham, Zvi

The Sunda Shelf is one of the most extensive coherent shelves in the world. A geophysical survey was conducted over the southern Sunda Shelf (Java Sea). Water depth, sediment thickness, and the gravity and magnetic fields were continuously measured. Expendable radiosonobuoys were used for seismic refraction measurements. These geophysical data supplemented by earlier studies over the northern Sunda Shelf and geological data from land areas provide a comprehensive picture of the structural framework of the entire Sunda Shelf. In addition, structural studies over some of the deep-sea floors surrounding the Sunda Shelf are combined with those over the Sunda Shelf to develop an evolutionary scheme of the Sunda Shelf and adjacent deep seas. Seismic reflection profiles show that the Sunda Shelf consists of three major units: the northern Sunda Shelf basinal area, the Singapore Platform, and the Java Sea basinal area. In the northern Sunda Shelf are two large sedimentary basins, the Brunei and Gulf of Thailand basins, which are separated by the Natuna Ridge. In the Java Sea are several other basins separated by uplifts. The basins in the eastern Java Sea are narrow and long and seem to result from compressional forces, while those in the western Java Sea are more circular and seem to result from tensional forces. Radiosonobuoys revealed small basement features and resolved many strata having different velocities. Faults are abundant throughout the Sunda Shelf and clearly control the distribution and shapes of the basins. The faults strike north-south in the western Java Sea and northeast-southwest in the eastern Java Sea. A major discontinuity trending north-south (termed here the Natuna Rift in the northern Sunda Shelf and the Billiton Depression in the central Sunda Shelf) cuts the structures of the entire Sunda Shelf. The discontinuity continues south across Central Java to the deep ocean floor. Analysis of magnetic anomalies shows that the area can be divided into several distinct magnetic provinces that do not always follow the major structural units mapped by the seismic reflection data. These magnetic provinces coincide with corresponding provinces of lithic units. The gravity field over the central and southern Sunda Shelf averages around +30 mgal. Local gravity anomalies having relative amplitude of lO-25 mgal are superimposed on the regional background level. Although the local gravity anomalies were helpful in resolving the upper crustal structures, the cause for the relatively high regional gravity is unknown. The structural elements on the Sunda Shelf are interpreted as the result of past interaction between the Indian Ocean-Australian, Pacific, and Asian plates. The evolution of the Sunda Shelf during the Mesozoic resulted from horizontal differential movement in a north-south direction as both the Indian Ocean and Pacific plates were moving to the north. In Eocene time two major events affected the evolution of the Sunda Shelf: the direction of movement of the Pacific plate changed from north to west-northwest producing northeast- southwest trending structural elements in the eastern Java Sea, and a spreading ridge that previously existed in the deep sea south of the shelf (Wharton Basin) was subducted along the Java Trench.

Thesis

Oceanic microstructure observed near Bermuda using a towed sensor

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1973-06) Magnell, Bruce Arthur

Many hypotheses have been advanced to explain the formation of mixed layers in the ocean; the salt finger type of double-diffusive convection, in particular, has received much attention. Because of their uniquely ordered nature, salt fingers should be readily identifiable in the deep thermocline, if in fact they exist there. A relatively limited experiment could thus produce a definitive evaluation of the importance of salt finger convection in the ocean, at least in certain places and at certain times. Such an evaluation, which would help to direct future work on oceanic microstructure, was the primary objective of this thesis. A secondary and more general objective was to measure the intermittency of mixing events in the ocean; and also, by measuring the RMS gradients of temperature and salinity in such events, to evaluate directly the intensity of vertical mixing. Since a horizontally-towed sensor is essential if salt fingers are to be observed directly, a new instrument has been designed and built which can resolve fractional-centimeter structures of electrical conductivity while being towed at speeds of several knots. The design of this instrument is described in this report. The instrument has been towed in deep water near Bermuda. It is believed that salt fingers were observed in the main thermocline on several occasions; but they were so rare as to be negligible in the total vertical mixing. An analysis of one such possible salt finger event is presented. Numerous other small-scale fluctuations of electrical conductivity were observed, which can be reconciled only with a turbulent model. Intermittency statistics for these events are presented. The eddy diffusivity has been calculated from the data to be approxima tely 0.075 cm2/sec.

Thesis

Aspects of the biogeochemistry of carbohydrates in aquatic environments

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1973-06) Mopper, Kenneth

The goal of this thesis is to examine the distribution and diagenesis of carbohydrates in aquatic environments. The following questions are studied: what is the carbohydrate composition of sediment in different environments (e.g., deep-sea oxic; shallow-sea oxic; deep-sea anoxic; fresh-water anoxic; brackish-water anoxic, etc.)? How does the environment at the sediment-water interface affect the composition of the carbohydrate input? How do sedimentary carbohydrates compare to plankton carbohydrates? How do metal-carbohydrate interactions and biological degradation affect the diagenesis of carbohydrates in recent sediments? Can fossil carbohydrates be used as a means to elucidate paleo-environments? In order to investigate these questions in a quantitative manner, a liquid chromatographic sugar analyzer sensitive to 10-10 moles was constructed. Various extraction techniques, involving acid hydrolysis and EDTA treatment, were thoroughly examined to determine lability of sugars, sources of contamination, maximum yields, and reproducibility. Furthermore, several experiments were performed to show that sugars extracted from sediment by EDTA were originally associated with in situ metal ion organic complexes. Although the carbohydrate compositions of sediment from different aquatic environments are remarkably similar, the degree of metal binding of carbohydrates varies between oxidizing and reducing sediments and appears to be related to the degree of biological degradation at the sedimentwater interface. In an oxic environment, biological degradation produces a highly metal-bound carbohydrate residue. In a reducing environment, the degree of biological activity is low (relative to oxic environments) and hence the degree of metal binding of the resulting carbohydrate residue is low. There is no evidence for further abiotic, alteration after burial in either environment. Sewage material dumped into a shallow oxic environment is degraded rapidly despite the high content of potentially toxic metals; these metals are probably tied-up in the metal bound carbohydrate residue. Metal binding appears to fix potentially soluble carbohydrates in situ, thereby inhibiting diffusion. This finding undercuts the previous belief that chromatographic separation of organic molecules along mineral surfaces is a significant diagenetic process. The relative abundances of sugars in acid extracts of sediment and plankton from different aquatic environments are similar; this similarity suggests that plankton is the main source of sedimentar carbohydrates. Carbohydrates in sediment may be used to interpret paleo-environmental fluctuations. For example, the degree of metal binding is indicative of the Eh at the sediment-water interface. The glucose and ribose contents of sediment may be used to estimate relative terrigenous and marine organic inputs, respectively. Paleo-eutrophication conditions in the surface waters also may be discerned.

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