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The inner main asteroid belt is an important source of near-Earth objects and terrestrial planet impactors; however, the dynamics and history of this region are challenging to understand, due to its high population density and the presence of multiple orbital resonances. This dissertation explores the properties of two of the most populous inner main belt family groups - the Flora family and the Nysa-Polana complex - investigating their memberships, ages, spin properties, collision dynamics, and range in orbital and reflectance parameters. Though diffuse, the family associated with asteroid (8) Flora dominates the inner main belt in terms of the extent of its members in orbital parameter space, resulting in its significant overlap with multiple neighboring families. This dissertation introduces a new method for membership determination (the core sample method) which enables the distinction of the Flora family from the background, permitting its further analysis. The Flora family is shown to have a signature in plots of semimajor axis vs. size consistent with that expected for a collisional family dispersed as a result of the Yarkovsky radiation effect. The family's age is determined from the Yarkovsky dispersion to be 950 My. Furthermore, a survey of the spin sense of 21 Flora-region asteroids, accomplished via a time-efficient modification of the epoch method for spin sense determination, confirms the single-collision Yarkovsky-dispersed model for the family's origin. The neighboring Nysa-Polana complex is the likely source region for many of the carbonaceous near-Earth asteroids, several of which are important targets for spacecraft reconnaissance and sample return missions. Family identification in the Nysa-Polana complex via the core sample method reveals two families associated with asteroid (135) Hertha, both with distinct age and reflectance properties. The larger of these two families demonstrates a correlation in semimajor axis and eccentricity indicating that its family-forming collision occurred near the parent body's aphelion. In addition, the Eulalia family is connected with a possible second component, suggesting an anisotropic distribution of ejecta from its collision event.

Thesis: Ph. D. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, May, 2020 / Cataloged from the official PDF of thesis. / Includes bibliographical references (pages 235-273). / Interpretation of seismic wavespeed anomalies inferred from global and continental-scale tomographic models is complicated by the competing effects of temperature and chemical composition. Understanding the origin of a seismic anomaly requires constraining multiple seismic parameters and quantifying how they are influenced by thermal and geochemical variations. In this Thesis I jointly interpret inverse modeling of seismic data and forward modeling of chemical and thermodynamic data in order to investigate the origins of seismic heterogeneity within the cratonic lithosphere. I present a joint inversion of body and surface wave travel-times to determine independent but mutually-constrained variations in V[subscript p] and V[subscript s] within the continental United States. From this, the V[subscript p] /V[subscript s] ratio may be determined, which is sensitive to compositional changes such as Fe - Mg substitution and Si enrichment. / The seismically-inferred wavespeeds are compared to predictions of V[subscript p] and [subscript p] /V[subscript s] made from forward-modeling of mantle rock compositions at a range of temperature and pressure conditions. By combining both forms of modeling it is possible to identify where thermal or compositional factors dominate the seismic and density structure. The first-order seismic structure within the North American lithosphere may be attributed to variations in temperature, but in certain regions compositional anomalies must be invoked. Subsequently, this framework is applied to questions related to the cratonic lithosphere. Compared to younger orogenic belts, Archean cratons have a relatively Fedepleted composition and low temperatures, the latter of which is sustained by a thick lithosphere. Finally, I investigate two anomalies within the North American craton that have been affected by mantle plumes. / Plumes influence the lithosphere in several ways, including thermal perturbations as well as the emplacement of compositionally distinct plume material into the lithosphere. The structure of the lithosphere at the time of plume passage influences how these interactions are manifested. The ways that the continental lithosphere can be altered therefore depend on its initial properties as well as on its history, and both must be considered to make a full geologic interpretation. / by Eva Marie Golos. / Ph. D. in Geophysics / Ph.D.inGeophysics Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, May, 2020 / Cataloged from the official PDF of thesis. / Includes bibliographical references (pages 169-187). / When the Earth experiences a perturbation in its radiative budget, the global ocean can buffer climate change, while sea ice may amplify its effects via a positive albedo feedback. It is therefore of interest to consider the role of the ocean in the climate's response to changes in external forcing, such as volcanic eruptions, Snowball Earth initiation and rearrangements of the carbon cycle. The first part of this thesis isolates the impact of the deep ocean in the surface response to volcanic cooling. Relaxation of the surface temperature follows a two-timescale decay, due to ocean heat exchange being significantly stronger than climatic feedbacks. Deep ocean cooling sequestration helps explain long periods of cold climate that occurred, for example, during the Little Ice Age. The second part explores the volcanic forcing required to initiate state transitions in a GCM with multiple climate equilibria. Snowball transitions require cooling on the order of -100Wm⁻² for several decades. These transition timescales are a consequence of the whole water column needing to be cooled to the freezing point before sea ice develops at the surface. The third part investigates biogeochemical interactions between oceans and sea ice around Antarctica. During the glacial cycles of the Pleistocene, sea ice may have helped trap carbon in the ocean by inhibiting CO₂ outgassing. This work shows that flux capping may be weakened by the effect of sea ice on reducing the light available for biological productivity. Consequently, a large sea ice fraction is required to effectively cap the flux of carbon to the atmosphere. / by Mukund Gupta. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences

Thesis: Ph. D. in Climate Science, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, May, 2020 / Cataloged from the official PDF of thesis. / Includes bibliographical references (pages 159-172). / The characterization of climate change depends on the location and rate of change while its impacts on nature and society also depend on vulnerabilities. This thesis contributes to the quantification of uncertainties, drivers, the spatial variability, and impacts of the climate change trajectory. Results of this work have evolved using a range of data science techniques that combine observations and Earth models aimed at informing adaptation and mitigation policies. In the first chapter, the drivers, timing, and impacts of aridity change over the 21st century are assessed using an ensemble of general circulation models (GCMs) together with population statistics. Results indicate that drier regions are projected to dry earlier, more severely and to a greater extent than humid regions, a result driven by differential changes in precipitation across aridity zones. / Impacts are exacerbated as arid regions (such as the Mediterranean etc.) are more populated and experiencing much higher population growth than humid regions (which includes the Arctic). Under an unconstrained emissions scenario, GCMs project that most of humanity will live in a more arid climate by the end of the 21st century. For the second chapter, the southern African rainfall (SAR) response to sea surface temperature (SST) anomalies in the Indian Ocean, Atlantic Ocean and Niño 3.4 region is examined. This is done using observations and three large ensembles of GCMs run over the 20th and 21st century. Some previous studies suggested that the Indian Ocean dominated changes in SAR. In this chapter, Niño 3.4 SSTs are found to be most strongly correlated with SAR, while correlations between SAR and the Indian Ocean are dominated by their respective responses to Niño 3.4. GCMs project that this relationship persists under a warming background state. / In the third chapter, the end of rapid warming is examined by considering emissions trajectories where atmospheric greenhouse gas concentrations ([GHG]) are stabilized. Under such scenarios, the rate of global temperature increases eventually steady at a rate significantly lower than those of the 21st century. I present a framework for defining the beginning of this 'Time of Steady Change' (TSC) and, with the use of GCM ensembles, evaluate the spatial variability of TSC. Results indicate that TSC occurs latest in low latitudes and in the Arctic, despite these areas steadying at very different absolute warming rates. These broad patterns are robust across multiple GCM ensembles and alternative definitions of TSC. The fourth chapter contributes to the measurement and analysis of sea level change. As an ice sheet rapidly melts, it produces a unique geometry of sea level change driven by perturbations in the height of the sea and crustal surfaces. / While satellite altimeters only measure changes in the sea surface height (SSH), local impacts from changes in sea level depend on both changes in SSH and changes in the solid surface. The literature commonly conflates the two estimates by directly comparing them. Here I quantify the error incurred by conflating changes in SSH with changes in sea level for various ice mass flux scenarios. Results indicate that using satellite altimetry records to estimate global ocean volume changes can lead to biases that can exceed 15% and that the level of bias will depend on the relative contributions to sea level changes from the Antarctic and Greenland Ice Sheets. The final chapter of this thesis provides a probabilistic quantification of chlorofluorocarbons (CFCs) that were banked in old equipment and continue to be released, contributing to global CFC emissions. / A Bayesian probabilistic model is developed to quantify banks and emissions of CFC-11, 12, and 113, incorporating the broadest range of constraints to date. Implied bank sizes of CFC-11 and CFC-12 are larger than recent international scientific assessments suggest, and can account for much of current estimated CFC-11 and 12 emissions (with the exception of increased CFC-11 emissions after 2012). If current banks are left unrecovered, their future emissions could delay polar ozone hole recovery by about six years and contribute 9 billion metric tonnes of equivalent CO₂ emission. While observationally-derived CFC-113 emissions are subject to uncertainty, they are too large to explain from banks, raising questions about sources of this gas as well. / by Megan Jeramaz Lickley. / Ph. D. in Climate Science / Ph.D.inClimateScience Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, May, 2020 / Cataloged from the official PDF of thesis. / Includes bibliographical references. / Our understanding of the biosphere prior to the rise of complex life is built largely upon microbial mat structures and some exceptionally well-preserved microbial fossils from the Proterozoic (2500 to 540 million years ago). Some of these exceptional fossils are identifiable as cyanobacteria that were preserved by pyrite, amorphous silica (SiO₂) and other minerals. Although a record exists of these organisms, the sparse nature of fossil assemblages and simplicity of many Proterozoic fossil morphologies makes it difficult to identify specific taxa or create a complete picture of the ancient biosphere and how it interacted with the early Earth. Cyanobacteria are thought to have evolved early in Earth history and played a large part in shaping the ancient biosphere and geosphere, but questions remain about their evolution and the ways in which cyanobacterial communities interacted with the Earth during the Proterozoic Eon. / In this thesis, I seek to build a more complete understanding the record of Proterozoic cyanobacteria, their responses to environmental perturbations and the chemical conditions and microbe-mineral interactions that characterized the Proterozoic marine realm. I begin by investigating the evolutionary relationships between different cyanobacterial lineages and their relationship to chloroplasts. I then analyze an assemblage of pyritized cyanobacteria that were preserved during the Cryogenian and provide a record of primary productivity in the oceans following a global glaciation. Finally, I investigate factors that enabled the fossilization of some exceptionally preserved cyanobacteria and implications of these mechanisms for cyanobacterial biochemistry, chemical conditions, and interactions between microbes and Proterozoic tidal environments. / The combined molecular, fossil and experimental insights allow us to go beyond morphological interpretations of microbial fossils and build a more complete understanding of the evolutionary history of cyanobacteria, the types of cyanobacteria that were preserved during the Proterozoic, the responses of these cyanobacteria to environmental stresses and the interactions of those cyanobacteria with the evolving seawater chemistry. / by Kelsey R. Moore. / Ph. D. / Ph.D. Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences

Thesis: S.M. in Geophysics, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, May, 2020 / Cataloged from the official PDF of thesis. / Includes bibliographical references (pages 97-101). / A number of human activities associated with the petroleum industry are known to trigger or even induce anthropogenic earthquakes of varying magnitudes. Examples of the damages of the infrastructure in oil and gas fields due to production make clear the need to monitor processes in the field. Land surface deformation is one method that can yield insights into geodynamic processes. Knowledge of the processes can lead to mitigation approaches. This Master's thesis focuses on the application of geodetic techniques to study land-surface deformations associated with oil and gas production. In particular, it focuses on optimizing existing methodology based on the example of the data from one of the oilfields in the western part of Kazakhstan. The geodetic techniques used for this project include interferometric synthetic aperture radar (InSAR), continuous and campaign global positioning system (GPS) surveying, precise leveling surveying, and gravimetric measurements. The data set, spanning 11 years, was reprocessed to improve the results of the existing standard processing procedures using more sophisticated software packages and reducing uncertainties and/or noise. The thesis also suggests the field-work protocols that may increase the accuracy of the measurements. The results of the project will allow the application of the developed methodology to the monitoring of oil-production-induced subsidence and uplift in the Republic of Kazakhstan and elsewhere. / by Anuar Zhanybekovich Togaibekov. / S.M. in Geophysics / S.M.inGeophysics Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, May, 2020 / Cataloged from the official PDF of thesis. / Includes bibliographical references (pages 55-58). / This thesis investigates the Salar del Huasco (northern Chile) as a potential site for palaeohydrological reconstructions of precipitation over the South American Altiplano, and presents a preliminary lake level chronology for the last deglaciation. Resolving the timings of past lake level highstands in the South American Altiplano will ultimately provide better understanding of what climate events force the South American Summer Monsoon (SASM) further south. Better insight into the forcing mechanisms of the SASM will improve our understanding of monsoon systems, and can be applied to refine global climate models of the region. To create this lake level chronology, tufa samples deposited at different elevations within the Salar del Huasco were dated using U/Th disequilibrium dating, and stable isotope measurements were applied to examine the past hydrology of the basin. The Salar del Huasco was found to have remained a hydrologically closed basin during highstand events, meaning lake level variations within the basin are purely driven by local precipitation-evaporation balances. Furthermore, the preliminary lake level chronology broadly agrees with the timings suggested by other palaeohydrological studies from the region, and provides support for a currently controversial lake level highstand between 120-100 ka. These results imply that the Salar del Huasco accurately reflects SASM-forced lake level histories, and should be studied further. / by Ruth Rosegrant Tweedy. / S.B. / S.B. Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences