Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1999. / Includes bibliographical references (leaves 84-88). / Atmospheric studies of halogenated organics have centered on long lived halocarbons due to their effect on stratospheric ozone. Now that controls have been put in place to curb emissions of longer lived halocarbons through the Montreal Protocol, and speculation about the safety of many short-lived chlorinated organic molecules has been raised, there has been more consideration given to the efforts aimed at determining the levels of human exposure to all types of halogenated organics. Most previous studies of reactive chlorine compounds have focused solely on quantifying their ambient levels in urban and rural regions. However, for many of these organo-chlorine molecules a detailed knowledge of emissions levels, transport, and final environmental disposition still does not exist. The present work was designed to aid in understanding the emissions patterns for several reactive halogenated organic compounds including trichloromethane (chloroform, CHCl3), trichloroethene (TCE, CHClCCl2), and tetrachloroethene (perchloroethylene, CCl2CCl2). A high temporal frequency (hourly) measurement campaign in Nahant, Massachusetts (approximately 10 km. northeast of Boston) provided automated gas-chromatographic measurements for these species as well as the somewhat more stable 1,1,1 trichloroethane (methyl chloroform, CH3CCl3). Cryogenic preconcentrations, daily calibrations, and weekly linearity tests insure high precision (</= 5%) measurements using electron capture detection. Calibration gases used for these tests, initially manufactured at MIT, have been corrected by intercomparison with gas standards used by the AGAGE program (produced at Scripps Institution of Oceanography) as well as those used at the National Center for Atmospheric Research. The absolute accuracy of our corrected MIT standard is estimated to be 10%. Over 12,000 measurements of the selected species were made between March, 1998 and January, 1999. These data show wide variability for the shortest lived species ranging from our detection limits (4.5 ppt for trichloroethene, 4.2 ppt for tetrachloroethene, and 7.8 ppt for trichloromethane) up to several hundred ppt during periods of local pollution. Data analysis combines the measurements with back trajectory information obtained from the HYSPLIT4 model (HYbrid Single-Particle Lagrangian Integrated Trajectory model, NOAA Air Resources Laboratory, Silver Springs, Maryland). Using a Kalman filter inverse method and an analytical solution of the continuity equation to estimate the effect of diffusion, we calculate the surface emissions for the selected species necessary to optimally match the observations. These emissions are compared with the estimates determined by the Reactive Chlorine Emissions Inventory (RCEI) working group of the IGAC (International Global Atmospheric Chemistry Program) Global Emissions Inventory Activity (GEIA). RCEI estimates are primarily derived from point source emissions in the US Toxic Release Inventory (TRI) and population-based distribution of residual national consumption from sales records. The new emissions scenarios computed here provide an observation-based assessment for comparison with the emissions inventories produced by RCEI for the northeastern United States and southeastern Canada. Results are statistically consistent with the RCEI estimates given the currently rough accuracy (±47-67%) achievable through this observation-based technique. We note, however, that the best estimate of corrections factors for land-based grid cells presented here indicate that the RCEI emissions for trichloroethene and tetrachloroethene need to be increased by a factor of ~2 to explain the observations. Only anthropogenic sources of trichloromethane were gridded in the initial (RCEI) inventory representing roughly 11% of estimated global emissions. We find that these emissions are, as expected, too low to explain the observations and that a land-based correction factor ~12 is required to produce emissions estimates that are consistent with natural sources (e.g. soil emissions). We also note that very large correction factors are calculated over the oceanic grid cells resulting in revised emissions estimates of the same order of magnitude as many land-based grid cells, consistent with a large oceanic source for this compound inferred from oceanic observations. The 47-67% uncertainty in the estimates of emissions correction factors increases with distance from the observation site due to both the increase in trajectory error as a function of total trajectory length and the decrease in the number of trajectories which have passed through a particular grid cell as one moves further from the observation site. These and other sources of uncertainty can be reduced by providing a realistic weighting of each trajectory's accuracy thus minimizing the impact of the trajectories which are likely to be most inaccurate, increasing the total number of measurements so that all grid cells have greater trajectory coverage, and improving estimates of the effective mixed layer height. / by Gary Kleiman. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1990. / Includes bibliographical references. / by Paula G. Coble. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2000. / Includes bibliographical references (leaves 43-44). / The changing configurations of continents due to plate tectonics is thought to be responsible for some of the variation in climate over the last 600 Ma. Different topological constraints on the oceans may affect their ability to transport heat poleward and change the equilibrium pole-equator temperature of Earth. An ocean model was run for three simple continental geometries to determine the effect of land distribution on the heat transport capacity and pole-equator temperature gradient of the ocean. The first configuration, a circle of land centered over the south pole, meant to resemble Earth at 600 Ma, produces a haline mode of convection in which water sinks in the subtropics. The ocean in this mode has a high pole-equator temperature gradient and low levels of heat transport. The second configuration, a strip of land extending between the north and south poles, resembles the land of the Permian 250 Ma. This configuration with the same atmospheric forcing produces a thermal mode of circulation, similar to the modern North Atlantic, in which surface water sinks at the poles. The ocean in this mode has a lower pole-equator temperature gradient and higher levels of poleward ocean heat transport. A third configuration, similar to the second but with an equatorial ocean passageway, resembles the mid-Cretaceous. This configuration also produces a thermal mode and has slightly higher levels of heat transport than the second model. This research suggests that continental geometry could have played an important role in determining the pole-equator temperature gradient and the levels of ocean heat transport in the past. / by Lorraine Lisiecki. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2007. / Includes bibliographical references. / The main objective of the research presented in this thesis is to improve our understanding for the evolution of the upper mantle beneath East Asia and the Tibetan Plateau through high resolution P-wave tomography. The approach to high resolution tomography is based on (i) the combined use of a large range of different types of seismic data, (ii) the use of approximate finite frequency sensitivity kernels to account for difference in measurement technique and frequency content of the data, (iii) the use of an irregular grid with cell-size adapted to sampling density, and (iv) the use of a priori information, e.g., on crustal structure from receiver function analysis. I construct a multi-scale and high resolution seismic tomography model of the upper mantle structure beneath East Asia and the Tibetan Plateau. The new model reveals that the mantle structure associated with the Indian subduction varies considerably along the strike of the collision zone. From west to east, the dip angle of Indian subduction increases and the distance over which the plate underthrusts the Tibetan Plateau decreases. Oblique subduction and changes of dip angle in the central part of the collision zone may cause and determine the location of the north-south trending normal faults in central Tibet. The eastward retreating slabs of western Pacific and Philippine plates are deflected in the transition zone beneath the Korea, Japan Sea, and East China. Some of Mesozoic subducted slabs have reached as far west as 1100E longitude under the Yangtze Craton, which might have resulted from the Eocene subduction at the South China and Japan trenches. / (cont.) Precambrian continental roots under Ordos block and Sichuan Basin, which extend to 250-300 km depth, may form a boundary of transition in tectonic regimes from the India-Eurasia collision control in the southwest to Pacific, Philippine Sea, and Java-Sumatra subductions control in the east and southeast. I conclude that the (direct) influence of the India-Eurasia collision on the tectonic evolution of East Asia may be confined to the Tibetan plateau and vicinity, whereas the tectonic development of a large area east and southeast of Ordos, Sichuan and Burma is driven by the stress field and 3-D upper mantle processes associated with subductions of Pacific, Philippine Sea, and Indo-Australia plates. / by Chang Li. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2009. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (leaves 227-234). / The thesis consists of five studies relating impact processes to the evolution of planetary interiors as well as impact structures on planetary surfaces. Chapter 2 is concerned with developing methods for estimating the amount of heat deposited deep in terrestrial mantles by large impacts. Chapter 3 makes use of these results to compute the consequences of impact-related thermal buoyancy perturbations in numerical models of subsolidus convection. Among the important results of this work is a relation for the time-scale on which a buoyancy anomaly flattens and spreads before it is halted by convective downflows, as well as a condition that indicates for what perturbation magnitudes and Rayleigh numbers the flow is significantly slowed at a global scale. Chapter 4 describes a structural model of Endurance Crater in Meridiani Planum on Mars, which is constrained by observations gathered by the MER-B Opportunity rover. These results reveal new insights about the planform shape of the crater excavation flow, as well as the connection between crater shape and pre-existing structures in target materials. The study presented in chapter 5 relates the planimetric shape of simple impact craters on Mars (D < 5 km) to the geological targets in which they form, as well as rim diameter. Planform crater shape is characterized by a suite of morphometric parameters, including Fourier harmonic amplitudes and phase angles, as well as measures of deviation from radial symmetry and convexity. / (cont.) In addition to finding the morphometric dependence on target properties, this work has illuminated prominent transitions between different cratering regimes, and contains a measure of the global distribution of planform elongation azimuths - which may relate to impact azimuth and provide an estimate of Mars' past obliquity variations. Finally, Chapter 6 describes a stochastic-kinematic model of the interaction between the excavation front and fractures in the target, which replicates many of the observations obtained in Chapter 5. / by Wesley Andrés Watters. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1985. / Microfiche copy available in Archives and Science. / Folded map in pocket at back of thesis. / Bibliography: leaves 369-388. / by David Christian Gerlach. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2005. / Includes bibliographical references. / The central Nepalese Himalaya are characterized by a sharp transition in physiography that does not correlate with previously mapped faults. Rates of rock uplift, erosion, and exhumation for rocks surrounding this physiographic transition are investigated using digital topographic data, ⁴⁰Ar/³⁹Ar thermochronology, cosmogenic radionuclides, and thermal modeling, to determine whether this break in landscape morphology reflects active tectonic displacements at the foot of the Himalaya. The goals of the thesis are 1) to understand the degree to which landscape morphology can be used to delineate breaks in rock uplift in active orogens; 2) to characterize the neotectonics of central Nepal using data representing varied temporal and spatial scales of inquiry; and 3) to move closer to understanding the dynamic interactions among climate, erosion and tectonics in a field setting. Analysis of digital topographic data from Nepal and other tectonically active settings demonstrates how breaks in the simple scaling characterizing river systems can be used to identify tectonic boundaries. / (cont.) Limitations to these methods are illustrated by way of an example from the Eastern Central Range of Taiwan, but changes in landscape morphology become the foundation upon which further investigations are built for central Nepal. These investigations include data from detrital ⁴⁰Ar/³⁹Ar thermochronology to characterize changes in exhumation rates at million-year timescales; cosmogenic ¹⁰Be to characterize changes in erosion rates at millennial timescales; and simple thermal modeling to evaluate a range of alternative tectonic geometries for central Nepal. The data point to the existence of a tectonically significant, thrust- sense shear zone at the base of the high Himalaya in central Nepal, nearly 100 km north of the active thrust front. The existence of this fault zone in a location where the Indian summer monsoon is concentrated is consistent with the predictions of numerical and analytical models of orogenic growth, which suggest a direct feedback between focused erosion and tectonic displacements in active orogens. / (cont.) Future work is warranted to evaluate the persistence of climatic and tectonic signals over a variety of time and space scales in central Nepal, and to determine whether correlations between climate and tectonics exist in other field settings. / by Cameron W. Wobus. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1996. / Includes bibliographical references (p. 135-143). / by Einat Aharonov. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 53-57). / Difficulties encountered in reproducing Mercury's compositional attributes through modeling of formational processes have bolstered support for the hypothesis that one or more giant impacts stripped away a significant proportion of proto-Mercury's silicate mantle. Previous investigations demonstrate sufficient removal of mantle material to account for the planets unusually high mean density, but do not consider the effects of multiple silicate and oxide phases. In this study, we extend the present theory by investigating the consequences of a more realistic chemical model on the evolution of the ejected material. We suggest that the majority of condensation within the expanding vapor plume can be modeled as an equilibrium process following homogeneous nucleation of refractory phases leading to larger particle sizes than previously estimated. We use a thermodynamic model focused on major element composition of ejected material to analyze the effect of differential condensation on the expansion and final state of ejecta. We also adapt pre-existing models for chemistry of condensation and impact shock compression to address additional problems associated with the process. For ejecta of sufficiently high specific entropy, our simplified chemical models indicate that energy released during condensation of MgO-rich phases buffers the temperature, delaying or preventing onset of FeO condensation. If sufficient spatial separation between condensates and vapor arises or if significant amounts of uncondensed FeO vapor remain uncondensed, reaccumulated ejecta would be enriched in MgO and refractory phases. This is compatible with an FeO depletion of Mercury's surface relative to other terrestrial bodies as some spectroscopic data suggests. The proposed process leads to a greater depletion in FeO and a lesser depletion in refractory, incompatible elements (Al2 O3, CaO, TiO2 ), than models assuming uniform removal of material from a differentiated proto-Mercury. / by Sean M. Wahl. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2006. / Includes bibliographical references (leaves 49-50). / A state estimate produced by ECCO-GODAE from a global one-degree model and data spanning the years 1992-2005 is analyzed in terms of transports of volume, temperature, and freshwater. The estimate is assessed to be sufficiently close to observations to merit analysis. The methods of analysis are similar to those of Stammer et al. (2003). The longer time period allows trends to be measured with greater confidence. Time mean flow characteristics demonstrate agreement with previous estimates. The strength of the ACC (146±5Sv) is larger than in the Stammer et al. (2003) state estimate, but is within the range of other estimates. A twelve-year decreasing trend is observed in the strength of the ACC of approximately 0.88Sv/year. The Indonesian throughflow transport of 1 l±2Sv is within the expected range. There is also a decreasing twelve year trend in the strength of the ITF of 0.065Sv/year. The ITF is stronger in boreal summer than boreal winter by approximately 4Sv. A strong annual cycle is present in the transport record on most sections, but higher frequency variability is also present. Most temperature transport variability results from velocity fluctuations, except in the Southern Ocean where temperature fluctuations are more important. Recommended further work includes a more detailed analysis of variability in this state estimate. / by Elise Olson. / S.M.