Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1987. / Includes bibliographical references (leaves 181-186). / Several problems connected by the theme of thermal forcing are addressed herein. The main topic is the stratification and flow field resulting from imposing a specified heat flux on a fluid that is otherwise confined to a rigid insulating basin. In addition to the traditional eddy viscosity and diffusivity, turbulent processes are also included by a convective overturning adjustment at locations where the local density field is unstable. Two classes of problems are treated. The first is the large scale meridional pattern of a fluid in an annulus. The detailed treatment is carried out in two steps. In the beginning (chapter 2) it is assumed that the fluid is very diffusive, hence, to first approximation no flow field is present. It is found that the convective overturning adjustment changes the character of the stratification in all the regions that are cooled from the top, resulting in a temperature field that is nearly depth independent in the northernmost latitudes. The response to a seasonal cycle in the forcing, and the differences between averaging the results from the end of each season compared to driving the fluid by a mean forcing are analyzed. In particular, the resulting sea surface temperature is warmer in the former procedure. This observation is important in models where the heat flux is sensitive to the gradient of air to sea surface temperatures. The analysis of the problem continues in chapter 5 where the contribution of the flow field is included in the same configuration. The dimensionless parameter controlling the circulation is now the Rayleigh number, which is a measure of the relative importance of gravitational and viscous forces. The effects of the convective overturning adjustment is investigated at different Rayleigh numbers. It is shown that not only is the stratification now always stable, but also that the vigorous vertical mixing reduces the effective Rayleigh number; thereby the flow field is more moderate, the thermocline deepens, and the horizontal surface temperature gradients are weaker. The interior of the fluid is colder compared to cases without convective overturning, and, because the amount of heat in the system is assumed to be fixed, the surface temperature is warmer. The fluid is not only forced by a mean heat flux, or a seasonally varying one, but its behavior under permanent winter and summer conditions is also investigated. A steady state for the experiments where the net heat flux does not vanish is defined as that state where the flow field and temperature structure are not changing with time except for an almost uniform temperature decrease or increase everywhere. It is found that when winter conditions prevail the circulation is very strong, while it is rather weak for continuous summer forcing. In contrast to those results, if a yearly cycle is imposed, the circulation tends to reach a minimum in the winter time and a maximum in the summer. This suggests that, depending on the Rayleigh number, there is a phase leg of several months between the response of the ocean and the imposed forcing. Differences between the two averaging procedures mentioned before are also observed when the flow field is present, especially for large Rayleigh numbers. The circulation is found to be weaker and the sea surface temperature colder in the mean of the seasonal realizations compared to the steady state derived by the mean forcing. As an extension to the numerical results, an analytic model is presented in chapter 4 for a similar annular configuration. / by Haim Nelken. / Ph.D.

Thesis: S.M., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2020 / Cataloged from student-submitted PDF of thesis. / Includes bibliographical references. / Arctic marine and lacustrine systems are experiencing rapid warming due to climate change. These changes are especially important at the interface between sediments and surface waters because they are hotspots for biogeochemical transformations such as redox reactions, nutrient consumption and regeneration, organic matter leaching and degradation, and mineral weathering. Radium isotopes (²²³Ra, ²²⁴Ra, ²²⁶Ra, ²²⁸Ra) and radon-222, naturally occurring radioactive isotopes produced in sediments, are well-suited as tracers of nutrients, trace metals, and organic matter cycling processes at the sediment-water interface. In this thesis, I have applied radon-222 and the quartet of radium isotopes to study fundamental processes in subarctic lakes and on the Arctic continental shelf. First, radon-222 is used to quantify groundwater discharge into a shallow, tundra lake on the Yukon-Kuskokwim Delta in Alaska in summer of 2017. / Radon-derived groundwater fluxes were then paired with methane (CH₄) measurements to determine delivery rates of methane into the lake via groundwater. Groundwater CH₄ fluxes significantly exceeded diffusive air-water fluxes from the lake to the atmosphere, suggesting that groundwater is an important source of CH₄ to Arctic lakes and may drive observed CH₄ emissions. Higher CH₄ emissions were observed compared to those reported previously in high latitude lakes, like due to higher CH₄ concentrations in groundwater. These findings indicate that deltaic lakes across warmer permafrost regions may act as important hotspots for methane release across Arctic landscapes. Then, the quartet of radium isotopes is used to study the impacts of storms and sea ice formation as drivers of sediment-water interaction on the Alaskan Beaufort shelf. / The timeseries presented in this study is among the first to document the combined physical and chemical signals of winter water formation in the Beaufort Sea, made possible by repeat occupations of the central Beaufort shelf. Radium measurements are combined with inorganic nitrogen and hydrographic measurements to elucidate the episodic behavior of winter water formation and its ability to drive exchange with bottom sediments during freeze-up. / by Jessica Stephanie Dabrowski. / S.M. / S.M. Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)

Thesis (Sc. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences and the Dept. of Meteorology; and the Woods Hole Oceanographic Institution), 1979. / Vita. Also issued in leaves. / Includes bibliographical references (p. [191]-197). / Concern with the impact of human activities on the coastal region of the world's oceans has elicited interest in the so-called "coastal boundary layer"-that band of water adjacent to the coast where ocean currents adjust to the presence of a boundary. Within this zone, roughly 10 km wide, several physical processes appear to be important. One of these, the tides, is of particular interest because their deterministic nature allows unusually thorough analysis from short time series, and because they tend to obscure the other processes. The Coastal Boundary Layer Transect (COBOLT) experiment was conducted within 12 km of the south shore of Long Island, New York to elucidate the characteristics of the coastal boundary layer in the Middle Atlantic Bight. Analysis of data from this experiment shows that 35% of the kinetic energy of currents averaged over the 30 m depth are due to the semidiurnal and diurnal tides. The tidal ellipses, show considerable vertical structure. Near-surface tidal ellipses rotate in the clockwise direction for semidiurnal and diurnal tides, while near-bottom ellipses rotate in the counterclockwise direction for the semidiurnal tide. The angle between the major axis of the ellipse and the local coastline decreases downward for semidiurnal and increases downward for diurnal tides. The major axis of the tidal ellipse formed from the depth averaged semidiurnal currents is not parallel to the local shoreline but is oriented at an angle of -15 degrees. This orientation "tilt" is a consequence of the onshore flux of energy which is computed to be about 800 watts/m. A constant eddy viscosity model with a slippery bottom boundary condition reproduces the main features observed in the vertical structure of both semidiurnal and diurnal tidal ellipses. Another model employing long, rotational, gravity waves (Sverdrup waves) and an absorbing coastline explains the ellipse orientations and onshore energy flux as a consequence of energy dissipation in shallow water. Finally, an analytical model with realistic topography suggests that tidal dissipation may occur very close (2-3 km) to the shore. Internal tidal oscillations primarily occur at diurnal frequencies in the COBOLT data. Analysis suggests that this energy may be Doppler-shifted to higher frequencies by the mean currents of the coastal region. These motions are trapped to the shore and are almost exclusively first baroclinic mode internal waves. / by Paul W. May. / Sc.D.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences and the Dept. of Meteorology; and the Woods Hole Oceanographic Institution), 1972. / Includes bibliographical references (p. 153-159). / 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 10 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 under thrusting of oceanic crust under the continental crust. This under thrusting 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 down warping 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 down buckling buckling 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. / by Robert Allin Folinsbee. / Ph.D.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences; and the Woods Hole Oceanographic Institution), 1982. / "November 1981." Vita. / Includes bibliographical references. / Radiolarians which settle through the oceanic water column were recovered from three stations (western Tropical Atlantic-Station E, central Tropical Pacific-P1 and Panama Basin-PB) using PARFLUX sediment traps in moored arrays at several depths. The taxonomic diversities of the radiolarian assemblages in the sediment traps were very high. A total of 420 taxa, including 23 newly identified taxa, were found at the three stations; of these, 208 taxa were found at station E. The polycystine radiolarians generally reach the sea floor with little change in abundance or species composition, although slight skeletal dissolution occurs throughout their descent. The phaeodarian radiolarians, on the other hand, are largely dissolved within the water column; only a few species reach the sea-floor and these dissolve rapidly at the sediment-water interface. Most radiolarian skeletons sink as individuals through deep water columns without being incorporated into large biogenic aggregates. Because significant numbers of nassellarian and phaeodarian species are deep-water dwelling forms the diversity index of radiolarians increases with increasing depth in the mesopelagic zone. The vertical flux of the total radiolarians arriving at the trap depths (in x 103 individuals/m2/day) ranged from 16-24 (E), 0.6-17 (Pl), and 29-53 (PB). Of these on the average 25 % and 69 % of the total radiolarian flux is transported by Spumellaria and Nassellaria, respectively, while 5 % is carried by Phaeodaria. The measured SiO2 content of the skeletons averaged 91, 98 and 71 % of measured weight for Spumellaria, Nassellaria and Phaeodaria, respectively. The supply of radiolarian silica (mg SiO 2 /m 2/day) to each trap depth ranged from 2.5-4.0 (E), 0.9-3.2 (P ), and 5.7-10.4 (PB). The Radiolaria appear to be a significantly large portion of the SiO2 flux in >63 pm size fraction and thus play an important role in the silica cycle. When the radiolarian fluxes at the three Stations are compared with Holocene radiolarian accumulation rates in the same areas it became apparent that several percent or less of the fluxes are preserved in the sediments in all cases and the rest is dissolved on the sea-floor. Estimated excess Si which is derived from SiO2 dissolution on the sea-floor is fairly small relative to advective Si in the western North Atlantic and thus it appears to be insignificant to show any deviation in a simple mixing curve of deep water masses. Weight, length, width, projected area and volume of 58 radiolarian taxa were measured. The density contrast of radiolarians, relative to seawater, generally falls between 0.01 and 0.5 g/cm33. The sinking speed of 55 radiolarian taxa, measured in the laboratory at 3*C, ranged from 13 to 416 m/day. Despite the wide variety of morphology between the species, sinking speeds were best correlated with weight/shell among all the possible combinations of the examined variables. The estimated residence times of these taxa in the 5 km pelagic water column ranged from 2 weeks to 14 months. Large phaeodarians reached the water-sediment interface relatively quickly and ultimately dissolved on the sea floor. Small-sized taxa dissolved en route during sinking. The standing stock of 26 examined abundant taxa is on the order of 1 to 100 shells/m3 . Total radiolarian standing stock ranges from about 450 shells/m3 at Stations P1 and E to 1200 shells/m 3 at Station PB. The rate of production of total Radiolaria is calculated to be 77 to 225 shells/m 3 /day. The turnover time for these species ranges from several days to one month depending on the species and the assumption of the depth interval used for the estimation. / by Kozo Takahashi. / Ph.D.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences; and the Woods Hole Oceanographic Institution), February 1970. / "January 1970." / Includes bibliographical references (p. 173-177). / Anodic stripping voltammetry utilizing a thin film mercury composite graphite electrode has been evaluated and applied for the direct analysis of the metals, Zn,J 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 acidification procedure to obtain measurements of trace metal speciation in sea water. / (cont.) 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. / by William F. Fitzgerald. / Ph.D.

Thesis: Ph. D., Joint Program in Marine Geology and Geophysics (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), February, 2021 / Cataloged from the official PDF of thesis. / Includes bibliographical references (pages 175-198). / Subduction zones host the greatest earthquakes on earth and pose great threat to human society. The largest slip in megathrust earthquakes often occurs in the 10-50 km depth range, yet seismic imaging of the material properties in this region has proven difficult. This thesis focuses on developing methods to utilize high frequency (2-12 Hz) seismic waves scattered from the megathrust plate interface to constrain its fine-scale velocity structures and to investigate the relationship between velocity structures and megathrust slip behaviors. Chapter 2 investigates the locking condition of the subducted Gorda plate by simulating afterslip that would be expected as a result of the stress changes from offshore strike-slip earthquakes. Chapter 3 develops array analysis methods to identify P-to-S and S-to-P seismic converted phases that convert at the subducted Gorda plate interface from local earthquakes and uses them to constrain the geometry and material properties of the plate boundary fault of the subducted Gorda plate between 5-20 km depth. Chapters 4 and 5 use a dense nodal array and numerical modeling methods to study the seismic guided waves that propagate along the thin low velocity layer at the boundary of the subducted Gorda plate. Taken together, our results indicate that material properties of the subduction plateboundary fault is highly heterogeneous and the plate-boundary fault is potentially contained in a low velocity layer with significant porosity and fluid content at seismogenic depths. / by Jianhua Gong. / Ph. D. / Ph.D. Joint Program in Marine Geology and Geophysics (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references. / The structure of the oceanic lithosphere results from magmatic and extensional processes taking place at mid-ocean ridges (MORs). The temporal and spatial scales of the variability of these two processes control the degree of heterogeneity of the oceanic lithosphere, represented by two end-member models: the classical Penrose Model exemplified by layered magmatic crust formed along fast-spreading MORs, e.g., East Pacific Rise (EPR); and the recently defined Chapman Model describing heterogeneous mafic and ultramafic lithosphere formed in settings of oceanic detachment faulting common along slow-spreading MORs, e.g., Mid-Atlantic Ridge (MAR). This thesis is using advanced marine geophysical methods (including finite-difference wave propagation modeling, 3D multi-channel seismic reflection imaging, waveform inversion, streamer tomography, and near-bottom magnetics) to study lithospheric accretion processes in MORs characterized by contrasting tectono-magmatic settings: the magmatically dominated EPR axis between 9°30'-10°00°N, and the Kane Oceanic Core Complex (KOCC), a section of MAR lithosphere (23°20°-23°38°N) formed by detachment faulting. At the EPR study area, I found that the axial magma chamber (AMC) melt sill is segmented into four prominent 2-4-km-long sections spaced every -5- 10 km along the ridge axis characterized by high melt content (>95%). In contrast, within the intervening sections, the AMC sill has a lower melt content (41-46%). The total magma volume extracted from the AMC sill was estimated of ~46 x 106 M3, with ~24 x 106 M3 left unerupted in the upper crust as dikes after 2005-06 eruption. At the KOCC, I used streamer tomography to constrain the shallow seismic velocity structure. Lithological interpretation of the seismic tomographic models provides insights into the temporal and spatial evolution of the melt supply at the spreading axis as the KOCC formed and evolved. Investigation of a magnetic polarity reversal boundary in crosssection at the northern boundary of KOCC suggests that the boundary (representing both a frozen isotherm and an isochron) dips away from the ridge axis along the Kane transform fault scarp, with a west-dipping angle of ~45° in the shallow (<1 km) crust and <20° in the deeper crust. / by Min Xu. / Ph.D.

Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006. / Includes bibliographical references (p. 64-68). / Salt pond is a meromictic system with an outlet to the sea allowing denser seawater to occupy the monimolimnion while the mixolimnion has relatively low salinity and is the site of greater mixing and microbial activity. The density contrast between the two layers allows for a unique geochemical environment characterized by steep redox gradients at the interface. This chemocline is a habitat for magnetotactic bacteria (MB), and the spatial and temporal distribution of MB in the system along with geochemical (Fe2+, H2S, pH, 02 (aq), etc.) profiles have been analyzed from 2002 - 2005. It has been previously observed that magnetite-producing cocci occupy the top of the chemocline and greigite-producing MB occur at the base of the chemocline and in the sulfidic hypolimnion. This distribution may be attributed to analyte profiles within the pond; depth profiles show a sudden drop of dissolved oxygen (DO) at the chemocline associated with an increase in dissolved Fe (II) concentrations that peak where both 02 and H2S are low. In the sulfidic hypolimnion, Fe (II) concentrations decrease, suggesting buffering of Fe(II) by sulfide phases. / (cont.) Maximum concentrations of iron (II) and sulfide are 3 1 gM and 3 mM, respectively. Stability diagrams of magnetite and greigite within EH/pH space and measured voltammetric data verify fields of incomplete oxidation resulting in the production of elemental sulfur, thiosulfate and polysulfides. Calculations of the Gibbs free energy in the Salt Pond chemocline for potential microbial redox reaction involving iron and sulfur species indicate abundent potential energy available for metabolic growth. Oxidation of ferrous iron to ferrihydrite in the upper region of the chemocline consistantly has a yield of over -250 kJ/mol 02 (aq), - 12.5 times the proposed 20 kJ/mol minimum proposed by Schink (1997) necessary to sustain metabolic growth. This translates into biomass yields of ~ 0.056 mg dry mass per liter of upper chemocline water. If these numbers are applied to the dominant bacteria of the chemocline (MB that are 3% dry weight iron) then there could be up to ~ 1.68 mg of iron per liter of upper chemocline water just in the MB. / (cont.) This iron can be permanently sequestered by MB into the sediments after death because the organelles containing the iron phases are resistant to degredation. Geochemical and microbial processes relating to the cycling of iron heavily impact this system and perhaps others containing a chemocline that divides the water column into oxic and anoxic zones. / by Peter A. Canovas, III. / S.M.

The primary objective of this research is the development a wind and solar-powered autonomous surface vehicle (WASP) for oceanographic measurements. This thesis presents the general design scheme, detailed aerodynamic and hydrodynamic aspects, sailing performance theory, and dynamic performance validation measurements obtained from a series of experiments. The WASP consists of a 4.2 meter long sailboat hull, a low-Reynolds number composite wing, a 2000 Watt-hour battery reservoir, a system of control actuators, a control system running on an embedded microprocessor, a suite of oceanographic sensors, and power regeneration from solar energy. The vehicle has a maximum speed of five knots and weighs approximately 350 kilograms. Results from four oceanographic missions that were conducted in the Port Everglades Intracoastal Waterway in Dania Beach [sic] Florida are presented. Water temperature, salinity and oxidation-reduction measurements recorded during these missions are also discussed. The combination of a mono-hull and solid wing in an autonomous system is a viable design for a long-range ocean observation platform. The results of four near-shore ocean observation missions illustrate the initial capabilities of the design. Future work aimed to further reduce both the mass of the wing design and the power requirements of the system will increase performance in all operating conditions and should be considered. Furthermore, the progression of the legal framework related to ocean vehicles must be pursued with respect to unmanned autonomous systems. / by Patrick Forde Rynne. / Thesis (M.S.C.S.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2008. Mode of access: World Wide Web.