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  • Massachusetts Institute of Technology and Woods Hole Oceanographic Institution  (60)
  • American Chemical Society
  • MDPI Publishing
  • 2020-2023  (75)
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  • 1
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Aeronautics and Astronautics at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 2020.
    Description: Contemporary scientific exploration most often takes place in highly remote and dangerous environments, such as in the deep sea and on other planets. These environments are very hostile to humans, which makes robotic exploration the first and often the only option. However, they also impose restrictive limits on how much communication is possible, creating challenges in implementing remote command and control. We propose an approach to enable more efficient autonomous robot-based scientific exploration of remote environments despite these limits on human-robot communication. We find this requires the robot to have a spatial observation model that can predict where to find various phenomena, a reward model which can measure how relevant these phenomena are to the scientific mission objectives, and an adaptive path planner which can use this information to plan high scientific value paths. We identified and addressed two main gaps: the lack of a general-purpose means for spatial observation modelling, and the challenge in learning a reward model based on images online given the limited bandwidth constraints. Our first key contribution is enabling general-purpose spatial observation modelling through spatio-temporal topic models, which are well suited for unsupervised scientific exploration of novel environments. Our next key contribution is an active learning criterion which enables learning an image-based reward model during an exploration mission by communicating with the science team efficiently. We show that using these together can result in a robotic explorer collecting up to 230% more scientifically relevant observations in a single mission than when using lawnmower trajectories.
    Description: This work was partially supported by the National Science Foundation (NSF) Award #1734400, as well as by the Woods Hole Oceanographic Institution (WHOI). The author would like to thank both organizations for their support.
    Keywords: Robotics ; Autonomous ; Exploration
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 2
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Physical Oceanography at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2020.
    Description: A detailed understanding of the intensity and three-dimensional spatial distribution of diabatic abyssal turbulence is germane to understanding the abyssal branch of the global overturning circulation. This thesis addresses the issue through 1) an investigation of the dynamics of an abyssal boundary layer and through 2) the construction of a probabilistic finescale parameterization using mixture density networks (MDNs). A boundary layer, formed by the interaction of heaving isopycnals by the tide and viscous/adiabatic boundary conditions, is investigated through direct numerical simulations (DNS) and Floquet analysis. Turbulence is sustained throughout the tidal period in the DNS on extra-critical slopes characterized by small slope Burger numbers, leading to the formation of turbulent stratified Stokes-Ekman layers. Floquet analysis suggests that the boundary layers are unstable to disturbances to the vorticity component aligned with the across-isobath tidal velocity on extra-critical slopes. MDNs, trained on microstructure observations, are used to construct probabilistic finescale parameterization dependent on the finescale vertical kinetic energy (VKE), N2f2, , and both variables. The MDN model predictions are as accurate as conventional parameterizations, but also predict the underlying probability density function of the dissipation rate as a function of the dependent parameters.
    Description: My doctoral studies in the WHOI/MIT Joint Program were funded by the National Science Foundation (OCE-1657870) and the National Science Foundation Graduate Research Fellowship Program.
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 3
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-25
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution May 2020.
    Description: Developing accurate and computationally efficient models for ocean acoustics is inherently challenging due to several factors including the complex physical processes and the need to provide results on a large range of scales. Furthermore, the ocean itself is an inherently dynamic environment within the multiple scales. Even if we could measure the exact properties at a specific instant, the ocean will continue to change in the smallest temporal scales, ever increasing the uncertainty in the ocean prediction. In this work, we explore ocean acoustic prediction from the basics of the wave equation and its derivation. We then explain the deterministic implementations of the Parabolic Equation, Ray Theory, and Level Sets methods for ocean acoustic computation. We investigate methods for evolving stochastic fields using direct Monte Carlo, Empirical Orthogonal Functions, and adaptive Dynamically Orthogonal (DO) differential equations. As we evaluate the potential of Reduced-Order Models for stochastic ocean acoustics prediction, for the first time, we derive and implement the stochastic DO differential equations for Ray Tracing (DO-Ray), starting from the differential equations of Ray theory. With a stochastic DO-Ray implementation, we can start from non-Gaussian environmental uncertainties and compute the stochastic acoustic ray fields in a reduced order fashion, all while preserving the complex statistics of the ocean environment and the nonlinear relations with stochastic ray tracing. We outline a deterministic Ray-Tracing model, validate our implementation, and perform Monte Carlo stochastic computation as a basis for comparison. We then present the stochastic DO-Ray methodology with detailed derivations. We develop varied algorithms and discuss implementation challenges and solutions, using again direct Monte Carlo for comparison. We apply the stochastic DO-Ray methodology to three idealized cases of stochastic sound-speed profiles (SSPs): constant-gradients, uncertain deep-sound channel, and a varied sonic layer depth. Through this implementation with non-Gaussian examples, we observe the ability to represent the stochastic ray trace field in a reduced order fashion.
    Description: Office of Naval Research Grants N00014-19-1-2664 (Task Force Ocean: DEEP-AI) and N00014-19-1-2693 (INBDA)
    Keywords: Stochastic Processes ; Acoustic Wave Propagation ; Acoustic Rays
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 4
    Publication Date: 2022-01-07
    Description: Microplastic (MP) pollution has been found in the Southern Ocean surrounding Antarctica, but many local regions within this vast area remain uninvestigated. The remote Weddell Sea contributes to the global thermohaline circulation, and one of the two Antarctic gyres is located in that region. In the present study, we evaluate MP (〉300 μm) concentration and composition in surface (n = 34) and subsurface water samples (n = 79, ∼11.2 m depth) of the Weddell Sea. All putative MP were analyzed by attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. MP was found in 65% of surface and 11.4% of subsurface samples, with mean (±standard deviation (SD)) concentrations of 0.01 (±0.01 SD) MP m–3 and 0.04 (±0.1 SD) MP m–3, respectively, being within the range of previously reported values for regions south of the Polar Front. Additionally, we aimed to determine whether identified paint fragments (n = 394) derive from the research vessel. Environmentally sampled fragments (n = 101) with similar ATR-FTIR spectra to reference paints from the research vessel and fresh paint references generated in the laboratory were further subjected to micro-X-ray fluorescence spectroscopy (μXRF) to compare their elemental composition. This revealed that 45.5% of all recovered MP derived from vessel-induced contamination. However, 11% of the measured fragments could be distinguished from the reference paints via their elemental composition. This study demonstrates that differentiation based purely on visual characteristics and FTIR spectroscopy might not be sufficient for accurately determining sample contamination sources.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 5
    Publication Date: 2022-10-21
    Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Colson, B. C., & Michel, A. P. M. Flow-through quantification of microplastics using impedance spectroscopy. ACS Sensors, 6(1), (2021): 238–244, doi:10.1021/acssensors.0c02223.
    Description: Understanding the sources, impacts, and fate of microplastics in the environment is critical for assessing the potential risks of these anthropogenic particles. However, our ability to quantify and identify microplastics in aquatic ecosystems is limited by the lack of rapid techniques that do not require visual sorting or preprocessing. Here, we demonstrate the use of impedance spectroscopy for high-throughput flow-through microplastic quantification, with the goal of rapid measurement of microplastic concentration and size. Impedance spectroscopy characterizes the electrical properties of individual particles directly in the flow of water, allowing for simultaneous sizing and material identification. To demonstrate the technique, spike and recovery experiments were conducted in tap water with 212–1000 μm polyethylene beads in six size ranges and a variety of similarly sized biological materials. Microplastics were reliably detected, sized, and differentiated from biological materials via their electrical properties at an average flow rate of 103 ± 8 mL/min. The recovery rate was ≥90% for microplastics in the 300–1000 μm size range, and the false positive rate for the misidentification of the biological material as plastic was 1%. Impedance spectroscopy allowed for the identification of microplastics directly in water without visual sorting or filtration, demonstrating its use for flow-through sensing.
    Description: The authors thank the Richard Saltonstall Charitable Foundation and the National Academies Keck Futures Initiative (NAKFI DBS13) for their funding support.
    Keywords: Microplastics ; Plastics ; Impedance spectroscopy ; Dielectric properties ; Instrumentation ; Particle detection ; Flow-through ; Environmental sensing
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
    Publication Date: 2022-12-07
    Description: © The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in James, B., de Vos, A., Aluwihare, L., Youngs, S., Ward, C., Nelson, R., Michel, A., Hahn, M., & Reddy, C. Divergent forms of pyroplastic: lessons learned from the M/V X-Press Pearl ship fire. ACS Environmental Au, 2(5), (2022): 467–479, https://doi.org/10.1021/acsenvironau.2c00020.
    Description: In late May 2021, the M/V X-Press Pearl container ship caught fire while anchored 18 km off the coast of Colombo, Sri Lanka and spilled upward of 70 billion pieces of plastic or “nurdles” (∼1680 tons), littering the country’s coastline. Exposure to combustion, heat, chemicals, and petroleum products led to an apparent continuum of changes from no obvious effects to pieces consistent with previous reports of melted and burned plastic (pyroplastic) found on beaches. At the middle of this continuum, nurdles were discolored but appeared to retain their prefire morphology, resembling nurdles that had been weathered in the environment. We performed a detailed investigation of the physical and surface properties of discolored nurdles collected on a beach 5 days after the ship caught fire and within 24 h of their arrival onshore. The color was the most striking trait of the plastic: white for nurdles with minimal alteration from the accident, orange for nurdles containing antioxidant degradation products formed by exposure to heat, and gray for partially combusted nurdles. Our color analyses indicate that this fraction of the plastic released from the ship was not a continuum but instead diverged into distinct groups. Fire left the gray nurdles scorched, with entrained particles and pools of melted plastic, and covered in soot, representing partial pyroplastics, a new subtype of pyroplastic. Cross sections showed that the heat- and fire-induced changes were superficial, leaving the surfaces more hydrophilic but the interior relatively untouched. These results provide timely and actionable information to responders to reevaluate cleanup end points, monitor the recurrence of these spilled nurdles, gauge short- and long-term effects of the spilled nurdles to the local ecosystem, and manage the recovery of the spill. These findings underscore partially combusted plastic (pyroplastic) as a type of plastic pollution that has yet to be fully explored despite the frequency at which plastic is burned globally.
    Description: This work was supported by the Postdoctoral Scholar Program at the Woods Hole Oceanographic Institution (WHOI), with funding provided by the Weston Howland Jr. Postdoctoral Scholarship. Additional support was provided by the WHOI Marine Microplastics Catalyst Program, the WHOI Marine Microplastics Innovation Accelerator Program, the WHOI Investment in Science Fund, the March Marine Initiative (a program of March Limited, Bermuda), The Seaver Institute, Gerstner Philanthropies, the Wallace Research Foundation, the Richard Saltonstall Charitable Foundation, the Harrison Foundation, Hollis and Ermine Lovell Charitable Foundation, and the Richard Grand Foundation. AdV was supported by funding from the Schmidt Foundation.
    Keywords: Microplastic ; Resin pellets ; Pollution ; Additives ; Open burning ; Weathering ; Maritime accident
    Repository Name: Woods Hole Open Access Server
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  • 7
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Oceanography and Applied Ocean Science and Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2020.
    Description: The redox cycling of oxygen between O2, water, and intermediate redox states including hydrogen peroxide and superoxide, has profound impact on the availability and distribution of dissolved O2, the habitability of the marine biosphere, and cellular metabolic and physiological reactions that utilize O2. The sum total of processes that produce, consume, and exchange atoms with O2 in the atmosphere, oceans, and subsurface leave their isotopic fingerprints on the abundance of the three stable isotopes of O2 in the environment. In this thesis, I explore two aspects of the oxygen cycle in the past and present. First, I investigate the ability of manganese (Mn) oxide minerals to capture and retain the oxygen isotopic signature of dissolved O2 during the oxidation of aqueous Mn(II) to Mn-oxide minerals. I determine that approximately half of the oxygen atoms in Mn(III,IV) oxides are directly incorporated from dissolved oxygen, and use isotope labeling techniques to further constrain how the dissolved oxygen isotope signature may be determined from that of Mn oxides. I perform an in-depth characterization of a ferromanganese crust from the central Pacific and, using triple oxygen isotope measurements, demonstrate that Mn oxides in ferromanganese crusts from around the world retain signatures of dissolved oxygen for at least 30 million years. I next turn to a previously unconsidered aspect of the global oxygen cycle: dark, extracellular superoxide production by marine microbes. I measure extracellular superoxide production rates by some of the ocean’s most abundant organisms. I use these rates along with previous measurements to estimate that extracellular superoxide production yields a net sink of 5-19% of marine dissolved oxygen. Ultimately, the degree to which superoxide production is a sink of oxygen lies in the fate of its primary decay product, hydrogen peroxide. I determine the range of oxidative and reductive decay of hydrogen peroxide across a range of environmental conditions in a meromictic pond, thus validating several assumptions from our global estimate. Altogether, this thesis illuminates a path toward investigating the oxygen cycle on million-year timescales in Earth’s recent past and demonstrates the importance of microbial superoxide production in the biogeochemical cycling of O2.
    Description: This work was funded by the following grants and organizations: NASA Earth and Space Science Fellowship (NNX15AR62H), MIT Praecis Presidential Graduate Fellowship, NASA Exobiology (NNX15AM046), NSF-OCE grant 1355720, WHOI Ocean Ventures Fund, MIT Student Assistance Fund, WHOI Academic Programs Office, and the Stanford Synchrotron Radiation Lightsource. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DEAC02-76SF00515.
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 8
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Oceanography and Microbial Biogeochemistry at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2020.
    Description: Marine microbes play key roles in global biogeochemistry by mediating chemical transformations and linking nutrient cycles to one another. A major goal in oceanography is to predict the activity of marine microbes across disparate ocean ecosystems. Towards this end, molecular biomarkers are important tools in chemical oceanography because they allow for both the observation and interpretation of microbial behavior. In this thesis, I use molecular biomarkers to develop a holistic, systems biology approach to the study of marine microbes. I begin by identifying unique patterns in the biochemical sensory systems of marine bacteria and suggest that these represent a specific adaptation to the marine environment. Building from this, I focus on the prevalent marine nitrogen fixer Trichodesmium, whose activity affects global nitrogen, carbon, phosphorus, and trace metal cycles. A metaproteomic survey of Trichodesmium populations identified simultaneous iron and phosphate co-stress throughout the tropical and subtropical oceans, demonstrating that this is caused by the biophysical limits of membrane space and nutrient diffusion. Tackling the problem at a smaller scale, I investigated the metaproteomes of individual Trichodesmium colonies captured from a single field site, and identified significant variability related to iron acquisition from mineral particles. Next, I investigated diel proteomes of cultured Trichodesmium erythraeum sp. IMS101 to highlight its physiological complexity and understand how and why nitrogen fixation occurs in the day, despite the incompatibly of the nitrogenase enzyme with oxygen produced in photosynthesis. This thesis develops a fundamental understanding of how Trichodesmium and other organisms affect, and are affected by, their surroundings. It indicates that a reductionist approach in which environmental drivers are considered independently may not capture the full complexity of microbechemistry interactions. Future work can focus on benchmarking and calibration of the protein biomarkers identified here, as well as continued connection of systems biology frameworks to the study of ocean chemistry.
    Description: This work was supported by an MIT Walter A. Rosenblith Presidential Fellowship and a National Science Foundation Graduate Research Program Fellowship under grant number 1122274 [N.Held]. This work was also supported by the WHOI Ocean Ventures fund [N.Held], Gordon and Betty Moore Foundation grant number 3782 [M.Saito], National Science Foundation grant numbers OCE-1657766 [M.Saito], EarthCube-1639714 [M.Saito], OCE-1658030 [M.Saito], and OCE-1260233 [M.Saito], and funding from the UK Natural Environment Research Council (NERC) under grants awarded to C.M. (NE/N001079/1) and M.L. (NE/N001125/1). This thesis was completed during a writing residency at the Turkeyland Cove Foundation.
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 9
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2020.
    Description: The shallow marine ecosystems of coral atolls and the human communities they support are among the most vulnerable to anthropogenic climate change. Sea-level rise threatens to inundate low-lying reef islands, tropical cyclone intensification threatens islands with flooding and erosion, and ocean warming and acidification threaten the health of coral reefs. Unfortunately, the sediment dynamics that shape the morphology of coral reefs and atoll reef islands are poorly understood, hindering predictions of coral atoll responses to climate change forcing. Here, I apply an eclectic set of methods, including numerical modeling, physical lab experiments, and sedimentological analysis, to produce insights into the ways tropical cyclones and waves move sediment on fringing reefs. First, I use a numerical model of hydrodynamics to predict the influence of sea-level rise and wave climate change on sediment transport across a coral atoll fringing reef. I demonstrate that by the end of the century, sea-level rise will reduce sediment transport rates from the fore reef to the beach, but increase transport rates from the reef flat to the beach. Wave climate change will have relatively negligible influence on cross-reef sediment transport. Additionally, I use the weathering of foraminifera tests to produce a sediment proxy of transport duration and direction across atoll reef flats, but demonstrate that the proxy does not clearly identify storm deposits. Second, I execute a series of experiments in an oscillating flow tunnel to constrain the rate at which sediment erodes reef surfaces under waves. I find that the erosion rate increases as a power law of wave orbital velocity, and that amount of sediment has a second-order influence. Finally, I establish grain size in a sediment core retrieved from a blue hole in the Marshall Islands as a proxy for tropical cyclone genesis and, using the results from an ensemble of climate models, demonstrate that enhanced tropical cyclogenesis during the Little Ice Age may have been driven by an anomalously negative Pacific Meridional Mode. This thesis demonstrates the importance of sediment dynamics on the morphology of fringing reefs and atoll reef islands and the sensitivity of those dynamics to centennial climate variability.
    Description: Funding for this project was provided by the Strategic Environmental Research and Development Program (SERDP RC-2336).
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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  • 10
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    Massachusetts Institute of Technology and Woods Hole Oceanographic Institution
    Publication Date: 2022-05-26
    Description: Submitted in partial fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution September 2020.
    Description: Advances in the miniaturization of microelectronics has greatly contributed to the proliferation of small, low cost autonomous underwater vehicles (AUVs). These affordable vehicles offer organizations a flexible platform that can be adapted to support a multitude of research goals. The small size and low entry cost come with a trade off of simple navigation systems, typically dead reckoning (DR) using a speed determined via propeller counts and heading from a low cost micro-electromechanical system (MEMS) inertial measurement unit (IMU), whose error grows unbounded without the availability of a ground referenced fix source and is compounded by the bias present in the speed measurement due to the change in hydrodynamics from the addition of sensors to the hull form. Additionally, some capabilities such as water current velocity measurement traditionally requires the addition of equipment that is not only expensive, but also whose size and power consumption can adversely affect operating characteristics and deployment times. This thesis expands on previous research using one-way travel time inverted USBL (OWTT-iUSBL) to calculate the local current velocity without the addition of a Doppler velocity log (DVL) or acoustic Doppler current profiler (ADCP). A novel extended Kalman filter (EKF) is proposed that, in addition to calculating the current velocity, estimates and corrects for the bias present in the speed measurement as determined by the main vehicle computer. Using data collected on the Charles River at the Massachusetts Institute of Technology (MIT) Sailing Pavilion, it is shown that current velocities can be reasonably calculated using OWTT-iUSBL data as compared to the values calculated using long baseline (LBL) data.
    Description: Funding for this thesis research was provided the US Navy Civilian Institutions Office through the Massachusetts Institute of Technology/Woods Hole Oceanographic Institution Joint Program.
    Keywords: EKF ; low-cost ; AUV
    Repository Name: Woods Hole Open Access Server
    Type: Thesis
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