Thesis (S.M.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering; and the Woods Hole Oceanographic Institution), 2005. / Includes bibliographical references (leaves 78-79). / The initial water impact of a free-falling object is primarily related to the fluid forces on the wetted surface of the object. The shape-dependent added-mass coefficients express the fluid forces integrated over the body, and thus physically represent the additional inertia of water accelerated with the body. The field of hydrodynamic impact has been primarily concerned with estimating the added-mass coefficients of various types of bodies for different water impact types, such as seaplane landings, torpedo drops, and ship slamming. In this study, a numerical model has been constructed to estimate the hydrodynamic impact loads of a REMUS dropped in free-fall from a helicopter in a low hover. Developed by von Alt and associates at Woods Hole Oceanographic Institution, the REMUS (Remote Environmental Monitoring UnitS) is a small, man-portable, torpedo shaped Autonomous Underwater Vehicle (AUV) that is normally operated from small boats for a variety of scientific, industrial, and military applications. Finite-element method software and computer aided drafting tools were used to create a simplified model of REMUS without fins, propeller, or transducers. / (cont.) This axisymmetric REMUS model was cut by a flat free surface at various pitch angles and submergence values, and a panel mesh of the wetted surface of the vehicle was created using an automatic mesh generator. Surface boundary conditions are enforced for the free surface by reflecting the body panels using the method of images. Each panel mesh was evaluated for its added- mass characteristics using a source collocation panel method developed by Dr. Yonghwan Kim, formerly of the Vortical Flow Research Laboratory (VFRL) at the Massachusetts Institute of Technology. Experimental impact tests were conducted with a specially-instrumented test vehicle to verify the initial impact accelerations. / by Stephen Michael Roe. / S.M.

Thesis (Ph. D.)--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), 1997. / Includes bibliographical references (p. 411-422). / Pelagic sedimentation is the primary modifier of topography generated by ridge-associated volcanic and tectonic processes. This thesis represents an effort to understand the processes of, and the general distribution of, pelagic sedimentation on rough topography, particularly in the Atlantic Basin but with applications to the world ocean as a whole. This study utilizes a simple numerical model of sedimentation which, when applied to models of rough basement topography, allows us to study sedimentation effects in terms of commonly-measured stochastic parameters including seafloor RMS height, abyssal hill spacing, and slope distribution. We also address the effect of sediment compaction on seafloor morphology, and the impact of long-wavelength topography on stochastic measures of sedimented seafloor. Understanding gained allows the construction of inverse problems to obtain information about sediment distribution and basement morphology from multibeam bathymetric data in regimes where backscatter from rough, reflective basement highs obscures returns from wide-beam seismic systems. By using maximum likelihood estimation to compare slope distribution functions calculated from data to those from filtered model topographies, we estimate average sediment thickness L, basement RMS height H, and a measure of sediment mobility k. Using data from near-ridge surveys and off-axis transit lines, we invert for L, H, and K for 3-29 Ma seafloor from the western flank of the Mid-Atlantic Ridge (MAR) near 26* N, 2- 45 Ma seafloor from the western flank of the MAR near 260 S, 2-40 Ma seafloor from the eastern flank of the MAR near 25* S, and 1-38 Ma seafloor from the western flank of the MAR near 35* S. Variations in L with seafloor age allow us to constrain sediment rain rate and the corrosivity of bottom waters to calcite since the Oligocene. We hypothesize that sediment rain rates during much of the early and middle Miocene were only 10-50% of the average rate for the past -10 m.y. Variations in H suggest correlation between tectonic setting and topographic variability. A relatively narrow range of K is needed to describe intrahill sedimentation patterns. / by Helen Faith Webb. / Ph.D.

Thesis (Ph. D.)--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), 2005. / Includes bibliographical references. / Minor and trace element records of planktic and benthic foraminifera from Atlantic sediment cores, as well as output from a coupled OAGCM, were used to investigate the magnitude and distribution of the oceanic response to abrupt climate events of the past 20 kyr. The study addressed three major questions: 1) What is the magnitude of high-latitude sea surface temperature and salinity variability during abrupt climate events? 2) Does intermediate depth ventilation change in conjunction with high-latitude climate variability? 3) Are the paleoclimate data consistent with the response of a coupled OAGCM to a freshwater perturbation? To address these questions, analytical methods were implemented for the simultaneous measurement of Mg/Ca, Zn/Ca, Cd/Ca, Mn/Ca and Al/Ca in foraminiferal samples using inductively-coupled plasma mass spectrometry. Paired records of planktic foraminiferal [delta]¹⁸O and Mg/Ca from the subpolar North Atlantic reveal trends of increasing temperatures ([approx.] 3⁰C) and salinities over the course of the Holocene, which were punctuated by abrupt events. The variability does not appear to be periodic, but tends to recur within a broad millennial band. The records provide the first evidence of open-ocean cooling (nearly 2⁰C) and freshening during the 8.2 kyr event, and suggest similar conditions at 9.3 ka. / (cont.) However, the two largest temperature oscillations ([approx.] 2⁰C) occurred during the last 4,000 years, suggesting a recent increase in temperature variability relative to the mid-Holocene. Benthic foraminiferal Cd/Ca from an intermediate depth, western South Atlantic core provides insights into changes in the southward penetration of North Atlantic Intermediate Water (NAIW). Cd seawater estimates (Cdw) for the last glacial are consistent with the production of NAIW and its export into the South Atlantic. At [approx.] 14.5 ka, the NAIW contribution to the South Atlantic began to decrease, marking a transition from a glacial subsurface geometry to a Younger Dryas geometry, which occurred concurrently with the onset of the Bolling-Allerod to Younger Dryas cooling. High Cdw in both the deep North Atlantic and the intermediate South Atlantic imply reduced export of deep and intermediate water during the Younger Dryas, and a major decrease in northward heat transport. Modern subsurface geometry was established at [approx.] 9 ka, concurrently with the establishment of Holocene warmth in the North Atlantic region, further supporting a close linkage between subsurface circulation and North Atlantic climate. / (cont.) Paired benthic foraminiferal Mg/Ca and [delta]¹⁸O data from two intermediate depth low latitude western Atlantic sites - one from the Florida Current and one from the Little Bahama Bank- provide insights into the spatial distribution of intermediate depth temperature and salinity variability during the Younger Dryas. The Florida site lies within the deeper portion of the Florida Current; the Little Bahama Bank site lies within the deeper, unventilated portion of the North Atlantic subtropical gyre. During the Younger Dryas, temperatures increased at the Florida Current site and temperatures decreased at the Little Bahama Bank site. The temperature increase within the Florida Current is consistent with the reduced northward heat transport associated with a reduction in the Atlantic meridional overturning circulation (MOC); the temperature decrease at Little Bahama Bank is consistent with a cooling of high latitude surface waters. To test the possibility that a freshening of the surface North Atlantic caused the terrestrial and oceanographic changes during the Younger Dryas, the GFDL R30 coupled ocean-atmosphere general circulation model was forced using a North Atlantic freshwater perturbation of 0.1 Sv for a period of 100 years. The freshwater flux causes an overall reduction in the Atlantic overturning from 25 Sv to 13 Sv. / (cont.) However, at [approx.] 1,100 meters water depth, ventilation increases, causing decreases in both temperature and salinity throughout much of the intermediate depth North Atlantic. In the open North Atlantic, intermediate depth temperatures decrease by approximately 1⁰C; at the eastern side, intermediate depth temperatures decrease by less than 0.4⁰C. Intermediate depth temperatures at the western boundary, however, increase due to a reduction in northward heat transport, and also due to a shift in the location of the Intertropical Convergence Zone, which causes a reduction in surface salinity and a decrease in the upwelling of colder, deeper waters. Benthic foraminiferal Cd/Ca from an intermediate depth Florida Current core documents the history of the northward penetration of southern source waters within the return flow of the Atlantic meridional overturning circulation (MOC). Cd seawater estimates (Cdw) for the last glacial are consistent with the reduced influence of southern source waters at this location relative to the present. / (cont.) At [approx.] 18.5 ka, the southern source contribution to the Florida Current began to increase significantly, marking the onset of a transition from a glacial circulation pattern to a deglacial pattern, which lasted from [approx.] 17 ka to [approx.] 14 ka. At [approx.] 12.5 ka, following the onset of the Younger Dryas cooling in the North Atlantic and the reduction in North Atlantic Deep Water (NADW) production, the influence of southern source waters within the Florida Current decreased abruptly. A renewed influence of southern source waters occurred at [approx.] 9 ka, concurrent with the establishment of Holocene warmth in the North Atlantic region. / by Rosemarie Evangeline Came. / Ph.D.

Thesis (Ph.D.)--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), 2002. / Includes bibliographical references (leaves 169-187). / The marine geochemistry of the North Atlantic Ocean varies on decadal to centennial time scales, a consequence of natural and anthropogenic forcing. Surface corals provide a useful geochemical archive to quantify past mixed layer variability, and this study presents elemental and isotopic records from the tropical and subtropical North Atlantic. A consistent method for stable lead isotope analysis via multiple collector ICP-MS is first presented. This method is then applied to western North Atlantic surface corals and seawater, constraining historical elemental and isotopic lead variability. Six stable lead isotope profiles are developed from the western and eastern North Atlantic, demonstrating consistent mixed layer, thermocline, and deep water variability. Finally, coralline trace element records, including cadmium, barium, and lead, are presented from the Cariaco Basin. First, a reliable method is developed for stable lead isotope analysis by multiple collector ICP-MS. This study presents new observations of the large (0.7% amu-l), time-dependent mass fractionation determined by thallium normalization, including preferential light ion transmission induced by the acceleration potential and nebulizer conditions. These experiments show equivalent results for three empirical correction laws, and the previously proposed [beta]Pb/[beta]TI correction does not improve isotope ratio accuracy under these conditions. External secondary normalization to SRM-981 provides one simple alternative, and a rationale is provided for this correction. With current intensities less than 1.5x10-12 A, external isotope ratio precision less than 200 ppm is observed (2[sigma]). Matrix effects are significant with concomitant calcium in SRM-981 (-280 ppm at 257 [mu]M [Ca]). / (cont.) With the appropriate corrections and minimal concomitants, MC-ICP-MS can reliably determine 206Pb/207Pb and 208Pb/207Pb ratios of marine carbonates and seawater. Anthropogenic lead represents a promising transient oceanographic tracer, and its historical isotopic and elemental North Atlantic variability have been documented by proxy reconstructions and seawater observations. Two high-resolution surface coral and seawater time series from the western North Atlantic are presented, demonstrating past variability consistent with upper ocean observations. The elemental reconstruction suggests the primary lead transient was advected to the western North Atlantic from 1955 to 1968, with an inferred maximum lead concentration of 205 pmol kg-1 in 1971. The mean 1999 North Atlantic seawater concentration (38 pmol kg-1) is equivalent to 1905, several decades prior to the initial consumption of leaded gasoline in the United States. A 206Pb/207Pb transient from 1968 to 1990 is also observed, lagging the elemental transient by ten years. The provenance of this isotopic record is distinct from Arctic and European ice core observations and supports a 40% ... / by Matthew K. Reuer. / Ph.D.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), September 1998. / Includes bibliographical references (leaves 226-246). / The upper ocean crust contains a comprehensive record of the shallow geological processes active along the world's mid-ocean ridge system. This thesis examines the magnetic and seismic structure of the upper crust at two contrasting ridges-the fast spreading East Pacific Rise (EPR) and the slow spreading Mid-Atlantic Ridge (MAR)-to build a more complete understanding about the roles of volcanic emplacement, tectonic disruption and hydrothermal alteration in the near-ridge environment. A technique that inverts potential field measurements directly from an uneven observation track is developed and applied to near-bottom magnetic data from the spreading segments north of the Kane transform on the MAR. It is concluded that the central anomaly magnetization high marks the locus of focused volcanic emplacement. A cyclic faulting model is proposed to explain the oscillatory magnetization pattern associated with discrete blocks of crust being transported out of the rift valley between intensely altered fault zones. Seismic waveform and amplitude analyses of the magma sill along the EPR reveal it to be a thin (<100 m) body of partial melt. These characteristics have important implications for melt availability and transport within the cycle of eruption and replenishment. A genetic algorithm-based seismic waveform inversion technique is developed and applied to on- and near-axis multichannel data from 17'20'S on the EPR and the spreading segment south of the Oceanographer transform (MAR) to map and compare for the first time the detailed velocity structure of the upper crust at two different spreading rates. Combined with conventionally processed seismic profiles, our results show that, while final extrusive thickness is comparable at all spreading ridges (300-500 m), the style of thickening may vary. While a thin (<100 m) extrusive carapace quadruples in thickness within 1-4 km of the EPR crest, the extrusive section at the MAR achieves its final thickness within the inner valley. Both show evidence for a narrow zone of volcanic emplacement. Vigorous hydrothermalism at the EPR may produce a more rapid increase in basement velocities relative to the MAR. Rapid modification of the extrusive/dike transition at both ridges indicates that hydrothermalism is enhanced in this interval. Along-axis transport of lavas may thicken the extrusive pile at slow spreading segment ends, strengthening the magnetic highs generated by lava chemistry. / by Stefan Anthony Hussenoeder. / Ph.D.

Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), 2007. / Includes bibliographical references (p. 188-204). / Geochemical signatures in the otoliths of diadromous fishes may allow for retrospective analyses of natal origins. In an assessment of river-specific signatures in American shad (Alosa sapidissima), an anadromous clupeid native to the Atlantic coast of North America, stable isotope and elemental ratios in otoliths of juvenile American shad produced accurate natal tags from 12 rivers. Significant inter-annual variability in geochemical signatures from several rivers was detected, due largely to differences in 8180 values among years. The database was further expanded to include 20 rivers from Florida to Quebec, encompassing all major spawning populations. This task was accomplished by collecting juvenile otoliths along with water samples from rivers where juveniles were not sampled. Regressions between otolith and water chemistry for those rivers where both were collected showed significant relationships for Sr:Ca, Ba:Ca, 86180, and 87Sr:86Sr ratios but not for Mg:Ca or Mn:Ca. Despite reducing the combined signature to only four chemical ratios, cross-validated classification accuracies of known-origin juveniles averaged 93%. Ground-truthed signatures were used to classify migrants of unknown origins. Adults returning to spawn in the York River were classified according to their otolith composition. / (cont.) Only 6% of spawners originated from rivers other than the York, supporting the hypothesis that most American shad spawn in their natal river. Of remaining spawners, 79% originated from the Mattaponi River and 21% from the Pamunkey River. The results suggested that while most American shad home to their natal river there is less fidelity to individual tributaries, allowing subsidies to subpopulations with persistent recruitment failure. Otolith signatures were also used in mixed-stock analyses of immature migrants along the coast of Maine in the spring and Minas Basin in the summer. Mixed-stock compositions showed remarkably low diversity and were dominated by fish from the Shubenacadie and Hudson rivers, with an increasing proportion of Potomac River fish over time. In contrast to results from adult tagging studies, southern stocks were virtually absent. These data suggest ontogenetic shifts in migratory behavior. The thesis concludes with a report that water contributed 83% of Sr and 98% of Ba in the otoliths of a marine fish. / by Benjamin Walther. / Ph.D.

Includes bibliographical references (p. 211-216). / Thesis (Ph. D.)--Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and the Woods Hole Oceanographic Institution), 2008. / Inspired by the swimming abilities of marine animals, this thesis presents "Finnegan the RoboTurtle", an autonomous underwater vehicle (AUV) powered entirely by four flapping foils. Biomimetic actuation is shown to produce dramatic improvements in AUV maneuvering at cruising speeds, while simultaneously allowing for agility at low speeds. Using control algorithms linear in the modified Rodrigues parameters to support large angle maneuvers, the vehicle is successfully controlled in banked and twisting turns, exceeding the best reported AUV turning performance by more than a factor of two; a minimum turning radius of 0.7BL, and the ability to avoid walls detected > 1.8BL ahead, are found for cruising speeds of 0.75BL/s, with a maximum heading rate of 400/s recorded. Observations of "Myrtle", a 250kg Green sea turtle (Chelonia mydas) at the New England Aquarium, are detailed; along with steady swimming, Myrtle is observed performing 1800 level turns and rapidly actuating pitch to control depth and speed. Limb kinematics for the level turning maneuver are replicated by Finnegan, and turning rates comparable to those of the turtle are achieved. Foil kinematics which produce approximately sinusoidal nominal angle of attack trace are shown to improve turning performance by as much as 25%; the effect is achieved despite limited knowledge of the flow field. Finally, tests with a single foil are used to demonstrate that biomimetically inspired inline motion can allow oscillating foils utilizing a power/recovery style stroke to generate as much as 90% of the thrust from a power/power stroke style motion. / by Stephen Carl Licht. / Ph.D.

Thesis: Ph. D., Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2019 / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 137-153). / Each year, surface ocean ecosystems export sinking particles containing gigatons of carbon into the ocean's interior. This particle flux connects the entire ocean microbiome and constitutes a fundamental aspect of marine microbial ecology and biogeochemical cycles. Particle flux is also variable and intricately complex, impeding its mechanistic or quantitative description. In this thesis we pair compilations of available data with novel mathematical models to explore the relationships between particle flux and other key variables - temperature, net primary production, and depth. Particular use is made of (probability) distributional descriptions of quantities that are known to vary appreciably. First, using established thermodynamic dependencies for primary production and respiration, a simple mechanistic model is developed relating export efficiency (i.e. the fraction of primary production that is exported out of the surface ocean via particle flux) to temperature. / The model accounts for the observed variability in export efficiency due to temperature without idealizing out the remaining variability that evinces particle flux's complexity. This model is then used to estimate the metabolically-driven change in average export efficiency over the era of long-term global sea surface temperature records, and it is shown that the underlying mechanism may help explain glacial-interglacial atmospheric carbon dioxide drawdown. The relationship between particle flux and net primary production is then explored. Given that these are inextricable but highly variable and measured on different effective scales, it is hypothesized that a quantitative relationship emerges between collections of the two measurements - i.e. that they can be related not measurement-by-measurement but rather via their probability distributions. / It is shown that on large spatial or temporal scales both are consistent with lognormal distributions, as expected if each is considered as the collective result of many subprocesses. A relationship is then derived between the log-moments of their distributions and agreement is found between independent estimates of this relationship, suggesting that upper ocean particle flux is predictable from net primary production on large spatiotemporal scales. Finally, the attenuation of particle flux with depth is explored. It is shown that while several particle flux-versus-depth models capture observations equivalently, these carry very different implications mechanistically and for magnitudes of export out of the surface ocean. A model is then proposed for this relationship that accounts for measurements of both the flux profile and of the settling velocity distribution of particulate matter, and is thus more consistent with and constrained by empirical knowledge. / Possible future applications of these models are discussed, as well as how they could be tested and/or constrained observationally. / by Brendan Barry. / Ph. D. / Ph.D. Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)

Thesis (S.M. in Electrical Engineering)--Joint Program in Oceanography and Oceanographic Engineering (Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science; and the Woods Hole Oceanographic Institution), 2000. / Includes bibliographical references (leaves 64-65). / by James Willard Partan. / S.M.in Electrical Engineering

Thesis (S.M.)--Joint Program in Oceanographic Engineering (Massachusetts Institute of Technology, Dept. of Ocean Engineering, and the and Woods Hole Oceanographic Institution), 2000. / Includes bibliographical references (p. 100-101). / A finite difference computer model is developed to simulate the exposure statistics of a radio frequency buoyant antenna as it is towed in a three-dimensional random seaway. The model allows the user to prescribe antenna properties (length, diameter, density, etc.), sea conditions (significant wave height, development of sea), tow angle, and tow speed. The model then simulates the antenna-sea interaction for the desired duration to collect statistics relating to antenna performance. The model provides design engineers with a tool to predict antenna performance trends, and to conduct design tradeoff studies. The floating antenna envisioned is for use by a submarine operating at modest speed and depth. / by Sam R. Geiger. / S.M.