Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2002. / Includes bibliographical references (p. 31-33). / A method is developed for examining image frames containing Kuiper Belt objects and classifying those KBOs as binary candidate / not binary candidate. This method uses an elliptical point-spread function fitting technique, relying on the fact that a binary KBO system will appear in a.telescope image as an elongated source, with more or less elongation depending on the separation distance and the relative intensity of the two components. Mosaic images for forty-five Kuiper Belt objects from the Deep Ecliptic Survey were tested. Of these, four were binary candidates, twelve others were possible candidates, twenty one were circular within detection limits, and seven lacked the consistent set of field stars necessary for determination. Observations were planned for the nights of April 8-11, 2002 with the Magellan I telescope. However, due to unfavorable observing conditions during the three nights of the run, no good images of the ten candidate binaries and possible candidates visible at the time were able to be taken. This methodology of image analysis should continue to be applied to new KBO images, to identify additional binary candidates. Imaging of the candidates selected through this thesis work will be attempted during future Magellan observing runs, particularly in June 2002. / by Sarah J. Eddy. / S.M.

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 141-149). / In the mean, the Atlantic Ocean transports 1 to 1.5 PW of heat northward, and estimates suggest that 60% of this heat transport is associated with a circulation that reaches the cold waters of the abyss. Due to the role of the Atlantic Meridional Overturning Circulation (AMOC) in ocean heat transport, numerous studies have suggested that AMOC variability plays a role in climate variability on a wide range of timescales. My focus is AMOC and ocean buoyancy variability on decadal timescales. Decadal variability of sea surface temperature (SST) has been observed in the instrumental record and climate proxy data and is thought to be linked to variability in the AMOC. On the other hand, according to the thermal wind relation, buoyancy anomalies on the boundaries lead to anomalies in the AMOC, a fact that has been utilized in order to reconstruct the MOC at 26.5'N using data collected by the RAPID array. Here, I study decadal AMOC and buoyancy variability in a coupled and oceanonly GCMs run in idealized geometries. I focus on understanding the mechanisms of decadal variability of the AMOC, both the role of the AMOC in creating decadal buoyancy anomalies and the response of the AMOC to buoyancy anomalies. I find that decadal AMOC variability is driven by buoyancy anomalies near the western boundary of the subpolar gyre. When a buoyancy anomaly hits the western boundary, it is advected southward by the deep western boundary current. Via the thermal wind relation, buoyancy anomalies on the boundaries result in anomalies in the shear of the zonally integrated meridional velocity. Buoyancy anomalies on the eastern boundary are observed to be negligible, except in the subpolar gyre, indicating that negative (positive) buoyancy anomalies on the western boundary lead to a spin up (down) of the AMOC. The AMOC is observed to respond passively to buoyancy anomalies on the western boundary: although variability of the AMOC does lead to variability in the meridional transport of heat and salt, these transports are not responsible for creating the buoyancy anomalies on the western boundary that drive the AMOC variability. While the structure of the buoyancy anomalies is found to change with model bathymetry, in all the models studied the buoyancy variability is due to an oceanonly mode. In some cases, the mlode is weakly damped (large Q-factor), resulting in regular, predictable oscillations. In other cases, the ocean-only imode is highly damped (small Q-factor) and must be excited by stochastic atmospheric variability, resulting in irregular, less predictable variability. In nature, buoyancy anomalies along the western boundary might be created ill a number ways, including local baroclinic instability, baroclinic Rossby waves impinging on the western boundary, advection of anomalies from tropics, and advection/ propagation of convectively created anomalies from polar regions. In our models the dominant sources of buoyancy anomalies on the western boundary are local baroclinic instability and the propagation of baroclinic Rossby waves originating near the eastern boundary. However, we expect the response of the AMOC to decadal buoyancy anomalies on the western boundary to be similar regardless of the origin of these buoyancy anomalies. / by . / Sc.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012. / "February 2012." Cataloged from PDF version of thesis. / Includes bibliographical references (p. 43-45). / Combined field, microtextural, and geochemical observations are presented for pyroxenites in the Lanzo ultramafic massif in order to place chemical and petrological constraints both locally on the geologic history of the massif and more generally on the role of magmatic rifting and the rift-to-drift transition in ultraslow-spreading ridge environments. Two separate generations of pyroxenites have been distinguished. A young set of primitive Cr-diopside websterites of MORB affinity are related to melt infiltrations and melt-rock reactions during rifting and Jurassic exhumation, while a much older generation of websterites likely of subcontinental origin were inherited and pre-date continental rifting and exhumation of the massif. The regional compositional and textural variation observed in the latter group of pyroxenites is not due to primary heterogeneities but rather to differences in subsequent metamorphic histories. Pyroxenites from the northern domain experienced a colder exhumation history and physical isolation from the rest of the massif by means of a high temperature shear zone related to the rifting. These websterites preserve garnet pseudomorphs and elevated REE which are textural and geochemical evidence for the prior coexistence of clinopyroxene and garnet. The implications of this study are that the Lanzo massif was indeed subcontinental lithosphere prior its exhumation and existence as an Ocean Continent Transition Zone (OCTZ) and that high temperature shear zones do seem to serve as effective permeability barriers and melt-focusing zones in rifting systems. / by Kathryn A. Pesce. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 35-38). / Erosion of bedrock channels is frequently modeled with the stream power law, which relates erosion rates to drainage area, slope, and an erosional efficiency coefficient k. The value of k, however, varies with many physical factors and most of these relationships are not well quantified. This study uses a form of stream power dependent on mean annual precipitation. The island of Kauai in the Hawaiian island chain is used as a case study due to the island's steep precipitation gradient and relatively constant lithology. Erosion rates are calculated by constructing splines to approximate the island's shape at the end of the shield-building phase, and these data are used to calculate erosion rates. The precipitation-dependent stream power model is tested with a multiple regression analysis of the Kauai data. Erosion rates are positively correlated with precipitation rates and erosional efficiency is related to precipitation rate by a power of ~0.4. / by Michelle I. Slosberg. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2016. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 59-60). / This study investigates recent changes in the variability and seasonality of temperature and precipitation in the Northern Hemisphere. The mean and variance of daily temperature and precipitation anomalies are calculated for each year over a 35-year period and compared to a base period. For temperature in the Northern Hemisphere, a noticeable warming trend amplified in the higher latitudes was observed, as well as a significant decrease in variability in the mid and high latitudes. For precipitation in the Northern Hemisphere, a drying trend and decreasing trend in variability were observed in the mid latitudes during summer. The seasonal cycles of both temperature and precipitation were also analyzed. The trends in temperature seasonal amplitude and phase were studied and revealed some influence of Arctic sea ice loss that changes the seasonality of local temperature, and Arctic amplification that potentially influences temperature seasonality in the mid and high latitude land regions. To determine whether the changes in temperature seasonality may affect temperature variance, analyses were performed by removing the phase trends from the temperature data using two methods. The phase trend-removed temperatures were found to have no prominent trends in variance. This suggests that changes in the temperature variance may be related to changes in temperature seasonality. To study what affects precipitation variability, the coefficient of variation (ratio of standard deviation to mean), which determines the shape of the mixed gamma probability distribution function (PDF) of precipitation, was studied. It was found that the mean and variance of precipitation have a fixed ratio over time, suggesting that the shape of the precipitation PDF has not changed. Therefore changes in the precipitation variance in the midlatitudes could be simply explained by the change in the mean precipitation in the same region. / by Katrina L. Hui. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2008. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 50-52). / Increased pressure on fresh water reserves in southern New Hampshire requires new methods for monitoring exploitation. In a pilot study, surface water and groundwater samples from southern New Hampshire were analyzed for Sr, Pb, and U isotopes to test if they could be used to distinguish between different reservoirs (surface waters, bedrock wells, and sand and gravel wells). Detecting and monitoring communication between different aquifers is an essential part of water management, and mixing between the reservoirs due to overproduction of the wells could adversely impact drinking water quality. The results show that a mix of ²³⁴U/²³⁸U, ²⁰⁶Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb ratios was the most useful in distinguishing between the reservoirs. This method has great potential for the long-term monitoring of water wells to prevent overproduction. / by Lisa Song. / S.B.

Thesis: S.M., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 51-52). / Unsupervised k-Means clustering was implemented as a method for identifying anomalies in seismic time series. Sliding window approach was used for generating specific subsequences from the overall waveform. Dynamic Time Warping (DTW) was used as the method for comparing seismic subsequences. DTW barycenter averaging (DBA) was used as the method for averaging multiple subsequences within a group of similiar shapes. Clustering is able to discover anomalously shaped parts of a seismic time series in a completely unsupervised fashion, without requiring anyone to input actual times of the events, any predetermiend examples of events, or any other parameters about the signal. / by Elezhan Zhakiya. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 169-186). / NASA's New Horizons mission has provided a wealth of new data about the Pluto system, including detailed surface geology and volatile distribution maps revealing striking latitudinal and longitudinal variations. We begin by studying the methane distribution and surface colors using data from New Horizons' Ralph/MVIC instrument. From this study we find that Pluto's equatorial region shows a broader diversity of terrains and more stark longitudinal contrasts than the more homogeneous north polar region. Pluto's south polar region is currently in constant shadow and thus was not observed by New Horizons. We consider how this diversity formed and survived in the context of Pluto's extreme Milancovid cycles and resultant "super seasons". Over timescales of roughly 3 million years Pluto's obliquity varies by 23 degrees (between 103 degrees and 126 degrees) while its longitude of perihelion regresses. This pair of cycles create "super season" epochs where one pole experiences a short intense summer and long winter in constant darkness, while the other experiences a short winter and much longer, but less intense summer. Through thermal modeling and volatile sublimation and deposition modeling we determined that Pluto's high obliquity creates conditions at its equator that favor albedo contrast and can support them on million year timescales more effectively than Pluto's polar regions can. Finally, we look ahead to a possible next step in small body spacecraft exploration, a study of Apophis during its 2029 close approach to Earth. Since the earlier portion of this thesis focused on the encounter, data collection, and scientific analysis portion of a spacecraft mission (New Horizons), we go full circle by exploring the early stage of the / by Alissa M. Earle. / Ph. D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1997. / Includes bibliographical references (p. 105-108). / by Yijian Chen. / M.S.

Thesis: S.B., Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2007. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 39-41). / During nitrification there is an exchange of oxygen atoms between water and nitrite, causing the [delta]¹⁸O of nitrate produced by nitrification to be closer to the [delta]¹⁸O of water than expected. A series of lab and field experiments were set up in order to quantify the exchange, and then calculate the [delta]¹⁸O of nitrate with these values. The lab experiments tested the exchange in ammonia oxidation, using ammonia oxidizing bacteria, Nitrosomonas sp. C113a and Nitrococcus oceani, and nitrite oxidation using cultures of the nitrite oxidizing bacterium, Nitrosococcus mobilis. The exchange value in the ammonia oxidation experiments could not be calculated because of unexpected complications in the analysis in the [delta]¹⁸O of nitrite. Although we weren't able to obtain a confident value for the exchange we were able to find a way to correct the [delta]¹⁸O of nitrite, for blank and exchange that affects the sample [delta]¹⁸O value for nitrite measured by the mass spectrometer. The exchange in the nitrite oxidation experiment could not be measured because there was full abiotic exchange in the bottle preventing us from calculating biotic exchange. A control experiment was successful in eliminating this exchange by adjusting the pH to a value higher than 8 prior to inoculation of the media during the experiment. In a future nitrite oxidation experiment this change in experimental design would make it possible to measure the exchange during nitrite oxidation. The experiments were a good step toward developing the best way to measure microbially-catalyzed exchange, and hopefully this value can be quantified in future analysis. / by Carolyn Buchwald. / S.B.