ALBERT

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.

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.

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)

Description: The aim of this study is to improve our knowledge of the attenuation structure in the Southern Apennines using a new amplitude ratio tomography method (Phillips et al., Geophys Res Lett 32(21): L21301, 2005) applied on both direct and coda envelope measurements derived from 150 events recorded by 47 stations of the Istituto Nazionale di Geofisica e Vulcanologia National Seismic Network (Rete Sismica Nazionale Centralizzata). The twodimensional (2-D) analysis allows us to take into account lateral crustal variations and heterogeneities of this region. Using the same event and station distribution, we also applied a simple 1-D methodology, and the performance of the 1-D and 2-D path assumptions is tested by comparing the average interstation variance for the path-corrected amplitudes using coda and direct waves. In general, coda measurement results are more stable than using direct waves when the same methodology is applied. Using the 2-D approach, we observe more stable results for both waves. However, the improvement is quite small, probably because the crustal heterogeneity is weak. This means that, for this region, the 1-D path assumption is a good approximation of the attenuation characteristics of the region. A comparison between Q tomography images obtained using direct and coda amplitudes shows similar results, consistent with the geology of the region. In fact, we observe low Q along the Apennine chain toward the Tyrrhenian Sea and higher values to the east, in correspondence with the Gargano zone that is related to the Apulia Carbonate Platform. Finally, we compared our results with the coda Q values proposed by Bianco et al. (Geophys J Int 150:10–22, 2002) for the same region. The good agreement validates our results as the authors used a completely independent methodology.

Description: Published

Description: 355–365

Description: 1T. Struttura della Terra

Description: JCR Journal

Description: Poás is a complex stratovolcano with an altitude of 2,708 m asl, located in the Cordillera Volcánica Central of Costa Rica. Prior to 2017, the last three historical eruptions occurred on 7 February 1834, between January and May 1910 and during the period 1953-1955. Very few literature exists on the 1834 eruption. The only references state that it was an important event, that ash reached 〉53 km W-SW of Poás, and that it harmed the grasslands around the volcano. Related deposits of this eruption suggest phreatic activity, which launched bombs and blocks. Moreover, there is evidence of pyroclastic flow deposits near the crater. The 1910 eruption is better described. Despite the fact that ash fall is only reported near the volcano, a volume of the deposit of 1.6 x 107 m3 is estimated. Deposits of the eruption are white in color with many hydrothermally altered, and minor presence of juvenile fragments (vesicular lapilli). The eruption is classified as vulcanian, with deposits of ash fall and pyroclastic flows close to the crater. A Volcano Explosivity Index 3 (VEI 3) is estimated. The eruption affected agriculture. The 1953-1955 eruptions had a longer duration. Various ash fall deposits at several sites are reported. Deposits of this eruption, easily distinguished in the field, are black scoria lapilli, bombs with, sometimes fusiform, bread crust textures. In the eastern sector of the crater bombs can reach meters in size; such large bombs near the eruption centre at one side suggest the inclination of the eruptive conduct, or an asymmetrical vent-crater system. Inside the crater a 40 m-high dome and a lava flow were extruded during the eruption. Towards the east side of the current Laguna Caliente crater lake, relicts of a 8.5 m thick lava pool are found. During the entire eruptive episode, the acid lake presumably lacked. The eruption is described to be of a mixed type: strombolian, phreatomagmatic, vulcanian and dome extrusion eruptions. Considering the characteristics of this eruption, the height of the eruption column, ejected volume (2.1 x 107  m3), and its presumed duration, a VEI 3 is estimated. The eruptions damaged agricultural activity (including cattle), and forced the spontaneous evacuation of some people. In April 2017 magmatic eruptions followed a decade-long period of intense phreatic activity. These eruptions destroyed the 1953-1955 Dome and led to the complete dry out of Laguna Caliente. Pyroclastic cones and sulphur volcanism manifested at the bottom of the former crater lake bottom. The 2017 eruption severely affected touristic activities at and near Poás, with an estimated economic loss of 20 million dollars. By May-August 2018 Laguna Caliente reappeared. The volcanic hazards related to the three studied historical eruptions are: pyroclastic flows (at least 1 km from the eruptive centre, including reaching the current mirador sector), ballistics (bomb ejections up to 2 km from the emission centre), dispersion and fall of pyroclasts (tens of kms), gas emission and acid rain, dispersed by WSW dominant winds, and lahars in most of the river canyons SW of the volcano.  

Description: Published

Description: 261-299

Description: 1V. Storia eruttiva

Description: Between 2003-2016, the Greenland ice sheet (GrIS) was one of the largest contributors to sea level rise, as it lost about 255 Gt of ice per year. This mass loss slowed in 2017 and 2018 to about 100 Gt yr−1. Here we examine further changes in rate of GrIS mass loss, by analyzing data from the GRACE-FO (Gravity Recovery and Climate Experiment – Follow On) satellite mission, launched in May 2018. Using simulations with regional climate models we show that the mass losses observed in 2017 and 2018 by the GRACE and GRACE-FO missions are lower than in any other two year period between 2003 and 2019, the combined period of the two missions. We find that this reduced ice loss results from two anomalous cold summers in western Greenland, compounded by snow-rich autumn and winter conditions in the east. For 2019, GRACE-FO reveals a return to high melt rates leading to a mass loss of 223 ± 12 Gt month−1 during the month of July alone, and a record annual mass loss of 532 ± 58 Gt yr−1.

Description: We present an interdisciplinary review of the observed and projected variations in atmospheric and oceanic circulation within the southwestern South Atlantic focused on basin-scale processes driven by climate change, and their potential impact on the regional fisheries. The observed patterns of atmospheric circulation anomalies are consistent with anthropogenic climate change. There is strong scientific evidence suggesting that the Brazil Current is intensifying and shifting southwards during the past decades in response to changes in near-surface wind patterns, leading to intense ocean warming along the path of the Brazil Current, the South Brazil Bight, and in the Río de la Plata. These changes are presumably responsible for the poleward shift of commercially important pelagic species in the region and the long-term shift from cold-water to warm-water species in industrial fisheries of Uruguay. Scientific and traditional knowledge shows that climate change is also affecting small-scale fisheries. Long-term records suggest that mass mortalities decimated harvested clam populations along coastal ecosystems of the region, leading to prolonged shellfishery closures. More frequent and intense harmful algal blooms together with unfavorable environmental conditions driven by climate change stressors affect coastal shellfisheries, impact economic revenues, and damage the livelihood of local communities. We identify future modelling needs to reduce uncertainty in the expected effects of climate change on marine fisheries. However, the paucity of fisheries data prevents a more effective assessment of the impact of climate change on fisheries and hampers the ability of governments and communities to adapt to these changes.

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.

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.

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).